Catherine Rouby, Benoist Schaal, Danièle Dubois, Rémi Gervais, A. Holley - Olfaction, Taste, and Cognition-Cambridge University Press (2002)

OLFACTION, TASTE, AND COGNITION
The human organs of perception are continually being bombarded with chemi-
cals from the environment. Our bodies have in turn developed complex process-
ing systems that manifest themselves in our emotions, memory, and language.
Yet the available data on the high-order cognitive implications of taste and smell
are scattered among journals in many fields, with no single source synthesizing
the large body of knowledge, much of which has appeared in the past decade.
This book presents the first multidisciplinary synthesis of the literature in olfac-
tory and gustatory cognition. The book is conveniently divided into sections,
including linguistic representations, emotion, memory, neural bases, and indi-
vidual variation. Leading experts have written chapters on many facets of taste
and smell, including odor memory, cortical representations, psychophysics and
functional imaging studies, genetic variation in taste, and the hedonistic di-
mensions of odors. The approach is integrative, combining perspectives from
neuroscience, psychology, anthropology, philosophy, and linguistics, and is
appropriate for students and researchers in all these areas who seek the author-
itative reference on olfaction, taste, and cognition.
Catherine Rouby is an associate professor of neuroscience at Université Claude

Bernard.
Benoist Schaal is a research director at the CNRS, Centre Européen des Sciences
du Goût.
Danièle Dubois is a research director at the CNRS, Institut National de la Langue

Française.
Rémi Gervais is a research director at the CNRS, Institut des Sciences Cogni-
tives, Lyon.
A. Holley is a professor of neuroscience at Université Claude Bernard and

director of the Centre Européen des Sciences du Goût.
OLFACTION, TASTE,
AND COGNITION
Edited by
CATHERINE ROUBY
Université Claude Bernard, Lyon
BENOIST SCHAAL
Centre National de la Recherche Scientifique
DANI È LE DUBOIS
R ÉMI GERVAIS
A. HOLLEY
Centre Européen des Sciences du Goût
  
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo
Cambridge University Press

The Edinburgh Building, Cambridge  , United Kingdom
Published in the United States of America by Cambridge University Press, New York
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without the written permission of Cambridge University Press.
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guarantee that any content on such websites is, or will remain, accurate or appropriate.
Contents
Contributors page ix
Preface xv
Acknowledgments xvii
A Tribute to Edmond Roudnitska xix
Section 1: A Specific Type of Cognition 1

1 Olfaction and Cognition: A Philosophical and
Psychoanalytic View 3
annick le guérer
2 Cognitive Aspects of Olfaction in Perfumer Practice 16
andré holley
3 The Specific Characteristics of the Sense of Smell 27
egon peter k öster
Section 2: Knowledge and Languages 45

4 Names and Categories for Odors: The Veridical Label 47
danièle dubois and catherine rouby
5 Nose-wise: Olfactory Metaphors in Mind 67
david howes
6 Linguistic Expressions for Odors in French 82
sophie david
7 Classification of Odors and Structure–Odor Relationships 100
maurice chastrette
v
vi Contents
Section 3: Emotion 117

8 Acquisition and Activation of Odor Hedonics in Everyday
Situations: Conditioning and Priming Studies 119
dirk hermans and frank baeyens
9 Is There a Hedonic Dimension to Odors? 140
catherine rouby and moustafa bensafi
10 Influences of Odors on Mood and Affective Cognition 160
rachel s. herz
11 Assessing Putative Human Pheromones 178
suma jacob, bethanne zelano, davinder j. s. hayreh,
and martha k. mCclintock
12 Neural Correlates of Emotion Perception: From Faces to Taste 196
mary l. phillips and maike heining
Section 4: Memory 209

13 Testing Odor Memory: Incidental versus Intentional Learning,
Implicit versus Explicit Memory 211
sylvie issanchou, dominique valentin, claire sulmont,
joachim degel, and egon peter k öster
14 Odor Memory: A Memory Systems Approach 231
maria larsson
15 Repetition Priming in Odor Memory 246
mats j. olsson, maria faxbrink, and fredrik u. j önsson
16 Odor Memory in Alzheimer’s Disease 261
steven nordin and claire murphy
17 Development of Odor Naming and Odor Memory from
Childhood to Young Adulthood 278
johannes lehrner and peter walla
Section 5: Neural Bases 291

18 Odor Coding at the Periphery of the Olfactory System 293
gilles sicard
19 Human Brain Activity during the First Second after
Odor Presentation 309
bettina m. pause
Contents vii
20 Processing of Olfactory Affective Information: Contribution

of Functional Imaging Studies 324
robert j. zatorre
21 Experience-induced Changes Reveal Functional Dissociation
within Olfactory Pathways 335
nadine ravel, anne-marie mouly, pascal chabaud,
and rémi gervais
22 Increased Taste Sensitivity by Familiarization to Novel
Stimuli: Psychophysics, f MRI, and Electrophysiological
Techniques Suggest Modulations at Peripheral and
Central Levels 350
annick faurion, barbara cerf, anne-marie pillias,
and nathalie boireau
23 The Cortical Representation of Taste and Smell 367
edmund t. rolls
Section 6: Individual Variations 389

24 New Psychophysical Insights in Evaluating Genetic
Variation in Taste 391
katharine fast, valerie b. duffy, and linda m.
bartoshuk
25 The Individuality of Odor Perception 408
robyn hudson and hans distel
26 Olfactory Cognition at the Start of Life: The Perinatal Shaping
of Selective Odor Responsiveness 421
benoist schaal, robert soussignan, and luc marlier
27 Age-related Changes in Chemosensory Functions 441
thomas hummel, stefan heilmann, and claire murphy
Index 457
Contributors
Baeyens, Frank, Department of Psychology, University of Leuven, Tiensest-

raat 102, 3000 Leuven, Belgium, Tel: +32-(0)16/.32.59.63, Fax: +32-(0)16/.32.
59.24, e-mail: Frank.Baeyens@psy.kuleuven.ac.be
Bartoshuk, Linda M., Department of Surgery (Otolaryngology), Yale Uni-
versity School of Medicine, 333 Cedar Street, New Haven, CT 06520-
8041, USA, Tel: +1-203-785-2587, Fax: +1-203-785-3290, e-mail: linda
bartoshuk@quickmail.yale.edu
Bensafi, Moustafa, Laboratoire de Neurosciences et Systèmes Sensoriels,
Université Claude Bernard, Lyon 1, 50 avenue Tony Garnier, 69366 Lyon, Cedex
07, France; CNRS, 69622 Villeurbanne, France, Tel: +33 4 37 28 74 97, Fax:
+33 4 37 28 76 01, e-mail: bensafi@olfac.univ-lyon1.fr
Boireau, Nathalie, Laboratoire de Neurobiologie Sensorielle, École Pratique
des Hautes Études, rue des Olympiades, Massy, France, and Laboratoire
de Physiologie de la Manducation, Université Paris VII, Paris, France, Tel:
+1 69 20 63 39, Fax: +1 60 11 61 94, e-mail: boireau@ccr.jussieu.fr
Cerf, Barbara, Laboratoire de Neurobiologie Sensorielle, École Pratique des
Hautes Études, rue des Olympiades, Massy, France, and Laboratoire de Physio-
logie de la Manducation, Université Paris VII, Paris, France, Tel: +1 69 20 63 39,
Fax: +1 60 11 61 94, e-mail: cerf@ccr.jussieu.fr
Chabaud, Pascal, Institut des Sciences Cognitives, CNRS/Université Claude
Bernard, Lyon 1, 69675, Bron, France, Tel: +33 4 37 91 12 33, Fax: +33 4 37
91 12 10, e-mail: chabaud@isc.cnrs.fr
Chastrette, Maurice, Laboratoire de Neurosciences et Systèmes Sensoriels,
Université Claude Bernard, Lyon 1, 50 avenue Tony Garnier, 69366 Lyon, Cedex
ix
x Contributors
07, France; CNRS, 69622 Villeurbanne, France, Tel: +33 4 37 28 74 91,

Fax: +33 4 37 28 76 01, e-mail: chastret@olfac.univ-lyon1.fr
David, Sophie, Modèles, Dynamiques, Corpus, CNRS, Université Paris X –

Nanterre, Bâtiment L, 200 avenue de la République, 92001 Nanterre Cedex, Tel:
01 40 97 47 33, e-mail: sophie.david@u-paris10.fr
Degel, Joachim, Allmendring 12, 75203 K önigsbach-Stein, Germany, Tel:

0171-31 98 275, Fax: 0171-31 42 968, e-mail: jde@itm-research.de
Distel, Hans, Institut für Medizinische Psychologie, Ludwig-Maximilians-

Universität München, Goethestrasse 31, D-80336 München, Germany, Tel:
+49-89-5996-240, Fax: +49-89-5996-615, e-mail: hdistel@imp.med.uni-
muenchen.de
Dubois, Danièle, Laboratoire Languages, Cognitions, Pratiques, Ergonomie,

CNRS, Institut National de la Langue Française, 44, rue de l’Amiral Mouchez,
75014 Paris, France, Tel: +33 1 43 13 56 50, Fax: +33 1 43 13 56 60, e-mail:
danièle.dubois@inalf.cnrs.fr
Duffy, Valerie B., Department of Surgery (Otolaryngology), Yale University

School of Medicine, 333 Cedar Street, New Haven, CT 06520-8041, USA, and
School of Allied Health Sciences, University of Connecticut, Tel: +1-860-486-
1997, Fax: +1-203-785-3290, e-mail: vduffy@uconnvm.uconn.edu
Fast, Katharine, Department of Surgery (Otolaryngology), Yale University

School of Medicine, 333 Cedar Street, New Haven, CT 06520-8041, USA, Tel:
+1-510-845-3668, Fax: +1-203-785-3290, e-mail: kf37@pantheon.yale.edu
Faurion, Annick, Laboratoire de Neurobiologie Sensorielle, École Pratique

des Hautes Études, rue des Olympiades, Massy, France, and Laboratoire
de Physiologie de la Manducation, Université Paris VII, Paris, France, Tel:
+1 69 20 63 39, Fax: +1 60 11 61 94, e-mail: faurion@ccr.jussieu.fr
Faxbrink, Maria, Department of Psychology, Uppsala University, Box 1225,

751 45 Uppsala, Sweden, Tel: +46 18 18 21 50, Fax: +46 18 471 2123, e-mail:
mariafaxbrink@hotmail.com
Gervais, Rémi, Institut des Sciences Cognitives, CNRS/Université Claude

Bernard, Lyon 1, 69675, Bron, France, Tel: +33 4 37 91 12 33, Fax: +33 4
37 91 12 10, e-mail: gervais@isc.cnrs.fr
Hayreh, Davinder J. S., Department of Psychology, University of Chicago,

5730 Woodlawn Avenue, Chicago, IL 60637, USA, Tel: +1(773) 702-6016,
Fax: +1(773) 702-0320, e-mail: djhayreh@midway.uchicago.edu
Contributors xi
Heilmann, Stefan, Department of Otorhinolaryngology, University of Dresden

Medical School, Fetscherstrasse 74, 01307 Dresden, Germany, e-mail: stefan-
heilmann@hotmail.com
Heining, Maike, Ph.D. student, Department of Psychology, Institute of
Psychiatry, DeCrespigny Park, London, SE5 8AF, U.K., Tel: +44 020 7848
0365, Fax: +44 020 7848 0379, e-mail: m.heining@iop.kcl.ac.uk
Hermans, Dirk, Department of Psychology, University of Leuven, Tiens-
estraat 102, 3000 Leuven, Belgium, Tel: +32-(0)16/.32.59.63, Fax: +32-
(0)16/.32.59.24, e-mail: Dirk.Hermans@psy.kuleuven.ac.be
Herz, Rachel S., Department of Psychology, Box 1853, Brown University, Prov-
idence, RI 02912, USA, Tel: +1-401-863-9576, Fax: +401-863-1300, e-mail:
Rachel Herz@Brown.edu
Holley, André, Laboratoire de Neurosciences et Systèmes Sensoriels, Université
Claude Bernard, Lyon 1/CNRS, 69366 Lyon, France; Centre Européen des Sci-
ences du Goût, CNRS, and Université de Bourgogne, F-21000 Dijon, France,
Tel: +33 3 80 68 16 20, Fax: +33 3 80 68 16 21, e-mail: holley@cesg. cnrs.fr
Howes, David, Department of Sociology and Anthropology, Concordia
University, 1455 de Maisonneuve Ouest, Montréal, Québec, Canada H3G
1M8, Tel: +1(514) 848-2148, Fax: +1(514) 848-4539, e-mail: howesd@vax2.
concordia.ca
Hudson, Robyn, Instituto de Investigaciones Biomédicas, Universidad Nacional
Autónoma de México, Apartado Postal 70228, Ciudad Universitaria, 04510
México D.F., Mexico, Tel: +52-5-622-3828, Fax: +52-5-550-0048, e-mail:
rhudson@servidor.unam.mx
Hummel, Thomas, Department of Otorhinolaryngology, University of Dresden
Medical School, Fetscherstrasse 74, 01307 Dresden, Germany, Tel: +49-351-
458-4189, Fax: +49-351-458-4326, e-mail: thummel@rcs.urz.tu-dresden.de
Issanchou, Sylvie, Laboratoire de Recherches sur les Arômes, Institut National
de la Recherche Agrnomiques, 17 rue Sully, BP 86510, 21065 Dijon, France, Tel:
+33 3 80 69 30 76, Fax: +33 3 80 63 32 27, e-mail: issan@arome.dijon.inra.fr
Jacob, Suma, Department of Psychology, University of Chicago, 5730 Wood-
lawn Avenue, Chicago, IL 60637, USA, Tel: +1(773) 702-6015, Fax: +1(773)
702-0320, e-mail: sj11@midway.uchicago.edu
J önsson, Fredrik U., Department of Psychology, Uppsala University, Box 1225,
fredrik.jonsson@psyk.uu.se
xii Contributors
K öster, Egon Peter, ASAP Gesellschaft für Sensorische Analyse und Pro-
duktentwicklung, Drachenseestrasse 1, 81373 München, Germany, and The
Royal Veterinary and Agricultural University, Rølighedsvej 30, DK1958
Frederiksberg C, Denmark, Tel: +31 30 2510387, Fax: +31 30 2546071,
e-mail: ep.koster@wxs.nl
Larsson, Maria, Department of Psychology, Stockholm University, S-106 91
Stockholm, Sweden, Tel: +46 816 39 37, Fax: +46 8 15 93 42, e-mail:
maria.larsson@psychology.su.se
Le Guérer, Annick, 1, chemin Es Pots, Agey, 21410 Pont-de-Pany, France,
Tel/Fax: +33 3 80 23 61 88, e-mail: annick.le.guerer@wanadoo.fr
Lehrner, Johannes, Neurologische Universitätsklinik, Allgemeines Krank-
enhaus, Universität Wien, Währingergürtel 18-20, A-1097 Wien, Austria,
Tel: +43-1-40400-3443 or 3433, Fax: +43-1-40400-3141, e-mail: Hannes.
Lehrner@AKH-WIEN.AC.AT
Marlier, Luc, Centre Européen des Sciences du Goût, CNRS, Université
de Bourgogne, 15 rue Hugues Picardet, 21000 Dijon, France, Tel: +33
3.80.68.16.10, Fax: +33 3.80.68.16.26, e-mail: marlier@cesg.cnrs.fr
McClintock, Martha K., Department of Psychology, University of Chicago,
Fax: +1(773) 702-0320, e-mail: mkm1@midway.uchicago.edu
Mouly, Anne-Marie, Institut des Sciences Cognitives, CNRS/Université Claude
Bernard, Lyon 1, 69675, Bron, France, Tel: +33 4 37 91 12 41, Fax: +33 4 37
91 12 10, e-mail: mouly@isc.cnrs.fr
Murphy, Claire, University of California, San Diego, School of Medicine,
and Department of Psychology, San Diego State University, San Diego,
CA 92129, USA, Tel: +1-619-594-4559, Fax: +1-619-594-3773, e-mail:
cmurphy@sunstroke.sdsu.edu
Nordin, Steven, Department of Psychology, Umeå University, Sweden,
and Department of Psychology, San Diego State University, San Diego,
CA 92129, USA, Tel: +46-90-7866006, Fax: +46-90-7866695, e-mail:
steven.nordin@psy.umu.se
Olsson, Mats J., Department of Psychology, Uppsala University, Box 1225,
mats.olsson@psyk.uu.se
Contributors xiii
Pause, Bettina M., Institute of Psychology, Christian-Albrechts-Universität zu

Kiel, Olshausenstrasse 62, 24098 Kiel, Germany, Tel: +49-431-880-3675, Fax:
+49-431-880-1559, e-mail: bmpause@psychologie.uni-kiel.de
Phillips, Mary L., Department of Psychological Medicine, Institute of
Psychiatry, 103, Denmark Hill, London SE5 8AZ, England, Tel: +44-171-740-
5096/5089, Fax: +44-171-740-5129, e-mail: spmamlp@iop.kcl.ac.uk
Pillias, Anne-Marie, Laboratoire de Neurobiologie Sensorielle, École Pratique
des Hautes Études, rue des Olympiades, Massy, France, and Laboratoire de
Physiologie de la Manducation, Université Paris VII, Paris, France, Tel: +1 69
20 63 39, Fax: +1 60 11 61 94, e-mail: pillias@ccr. jussieu.fr
Ravel, Nadine, Institut des Sciences Cognitives, CNRS/Université Claude
Bernard, Lyon 1, 69675, Bron, France, Tel: +33 4 37 91 12 42, Fax: +33 4
37 91 12 10, e-mail: ravel@isc.cnrs.fr
Rolls, Edmund T., Department of Experimental Psychology, University of
Oxford, South Parks Road, Oxford OX1 3UD, England, Tel: +44-1865-271348,
Fax: +44-1865-310447, e-mail: Edmund.Rolls@psy.ox.ac.uk
Rouby, Catherine, Laboratoire de Neurosciences et Systèmes Sensoriels,
Université Claude Bernard, Lyon 1, 69 366 Lyon, France, Tel: +33 4 37 28
74 97, Fax: +33 4 37 28 76 01, e-mail: rouby@olfac.univ-lyon1.fr
Schaal, Benoist, Centre Européen des Sciences du Goût, CNRS, Univer-
sité de Bourgogne, 15 rue Hugues Picardet, 21000 Dijon, France, Tel: +33
3.80.68.16.10, Fax: +33 3.80.68.16.26, e-mail: schaal@cesg.cnrs.fr
Sicard, Gilles, Laboratoire de Neurosciences et Systèmes Sensoriels, Université
Claude Bernard, Lyon 1/CNRS, 69366 Lyon, France, Tel: +33 4 37 28 74 91,
Fax: +33 4 37 28 76 01, e-mail: sicard@olfac.univ-lyon1.fr
Soussignan, Robert, Laboratoire Personnalité et Conduites Adaptatives, CNRS,
and CHU Pitié-Sapêtrière, Pavillon Clérambault, 47 boulevard de l’Hôpital,
Paris, France, Tel: +33 1 42 16 16 51, Fax: +33 1 53 79 07 70, e-mail: soussig-
nan@wanadoo.fr
Sulmont, Claire, Laboratoire de Recherches sur les Arômes, Institut National
de la Recherche Agrnomiques, 17 rue Sully, BP 86510, 21065 Dijon, France,
Tel: +33 3 80 69 30 76, Fax: +33 3 80 63 32 27, e-mail: sulmont@arome.
dijon.inra.fr
xiv Contributors
Valentin, Dominique, École Nationale Supérieure de Biologie Appliquée à la

Nutrition et à l’Alimentation, Université de Bourgogne, 1 esplanade Erasme,
21000 Dijon, France, Tel: +33 3 80 39 66 43, Fax: +33 3 80 39 66 11, e-mail:
valentin@u-bourgogne.fr
Walla, Peter, Neurologische Universitätsklinik, Allgemeines Krankenhaus,
Universität Wien, Währingergürtel 18-20, A-1097 Wien, Austria, Tel: +43-
1-40400-3443 or 3433, Fax: +43-1-40400-3141, e-mail: Peter.Walla@akh-
wien.ac.at
Zatorre, Robert J., Montréal Neurological Institute, McGill University, 3801
University Street, Montréal, QC Canada H3A 2B4, Tel: +1-514-398-8903,
Fax: +1-514-398-1338, e-mail: robert.zatorre@mcgill.ca
Zelano, Bethanne, Department of Psychology, University of Chicago,
Fax: +1(773) 702-0320, e-mail: bzelano@dura.spc.uchicago.edu
Preface
This book arises from an acknowledgment: the lack, as far as we know, of a book
dedicated to the cognition of chemical senses.
Although recent discoveries in the field of molecular biology raise the hope
of a future understanding of the transduction and peripheral coding of odors
and tastes, it seems to us that they imply a risk: to make us forget that in the
other extreme of knowledge, that of maximal complexity, the evolution of cogni-
tive sciences allows an epistemologically fruitful reformulation of information-
processing problems.
Unlike the other senses, olfaction and taste do not have a learned discourse
dealing with elementary aspects, that is, sensory processing, as well as the most
abstract aspects, that is, symbolic processing. The purpose of cognitive science
is to orient these processings into a continuity, and particularly to try to find out
to what extent higher-order processes interact with the sensory level in order
to produce sufficiently reliable representations of the world. We are still quite
unaware of the nature of gustatory and olfactory representations, as compared
with what we know about vision and audition, for example.
Faced with this relative ignorance, our prejudice was the following: If odors
and tastes are ill-identified cognitive objects, then none of the available potential
resources should be neglected: Expert and naive people, as well as “savage”
and “civilized” ones, conscious knowledge and emotions, biology and social
sciences – all of those can contribute first to an assessment of our knowledge,
and then to confrontation of its inadequacies. This inter-disciplinary point of
view first gave rise to a meeting held in Lyon, in June 1999: the European
Symposium on Olfaction and Cognition, which tried to coordinate knowledge
from several scientific disciplines with that from perfumery professionals. The
other aim of that meeting was to publish a book, conceived not as a handbook
gathering all the validated knowledge but as a book reflecting the questions
xv
xvi Preface
and the divergences running through this field of knowledge, whose complexity
biology and chemistry still cannot explore thoroughly.
This book is meant for all those studying taste and olfaction. We hope that it
will foster other debates and other novel collaborations between neuroscience
and social science.
Acknowledgments
We acknowledge the support of a number of people without whom this book

would have gone no further than the stage of the outline. We are grateful to
all the authors for taking time and putting effort into contributing to this col-
lection. Apart from the editors, a number of people kindly refereed the chap-
ters herein, and we are very appreciative of their help. These are the following
doctors: Christiane Ayer-Lelièvre (Limoges), Olivier Bertrand (Lyon), Claude
Bonnet (Strasbourg), Driss Boussaoud (Lyon), Pierre Cadiot (Paris), Paul Castle
(Southampton), Bernard Croisille (Lyon), Philippe Descola (Paris), Hans-Jürgen
Distel (Munich), Marie-Hélène Giard (Lyon), Avery N. Gilbert (Montclair,
CA), James Hampton (London), Dirk Hermans (Leuven), Joseph Hossenlopp
(Clermont-Ferrand), David Howes (Montréal), Robyn Hudson (Mexico City),
Thomas Hummel (Dresden), Sylvie Issanchou (Dijon), Marilyn Jones-Gotman
(Montréal), Egon P. Köster (Utrecht), Jan Kroeze (Utrecht), Serge Larochelle
(Montréal), Annick Le Guérer (Agey), Johannes Lehrner (Vienna), Jean Marie
Marandin (Paris), Julie Mennella (Philadelphia), Mats J. Olsson (Uppsala),
Pierre Perruchet (Dijon), Paul Rozin (Philadelphia), Margret Schleidt (Andechs),
Gilles Sicard (Lyon), Dana Small (Chicago), Guy Tiberghien (Grenoble), Rémy
Versace (Lyon), Daniel Widlocher (Paris), and Don A. Wilson (Oklahoma City).
From the beginning, Michel Vigouroux was in charge of the different stages
of the book preparation, especially the task of repeatedly formatting texts and
editing illustrative material. Agnès Magron contributed to clear references and
to the elaboration of the index.
Finally, Michael Penn and Ellen Carlin, our editors at Cambridge Univer-
sity Press, advised and supported us through time. To all of these persons, our
wholehearted appreciation.
C. Rouby, B. Schaal, D. Dubois, R. Gervais, A. Holley
xvii
A Tribute to Edmond Roudnitska
This book is dedicated to Edmond Roudnitska, who was an artist, a creator of

perfumes, and a writer. The organizers of the symposium from which this book
originated feel that his work is one of the best illustrations of the relationship
between olfaction and cognition.
Through his olfactory creations, which constitute landmarks in the relatively
short history of the perfume industry, he was among the handful of people who
helped elevate olfactory composition to the rank of an art. Beyond sheer senso-
rial pleasure, his great perfumes1 convey to enlightened perfume lovers purely
aesthetic emotions fueled by reference to the history of perfumes, leaving con-
noisseurs marveling at the balanced combinations of olfactory elements similar
to a bold architectural construction, and finally bringing to the emotions this
cognitive component without which no art is possible.
Another aspect of Roudnitska’s work is of particular interest to scientists
researching the cognitive component of olfactory perception: It consists in
writings,2 in which he expresses his views regarding perfume creation. Perfume
creators, in accordance with a tradition of secrecy, rarely communicate about
their work. Roudnitska, however, communicated about his art with remarkable
freedom and pertinence. Throughout his books and articles, which clearly re-
veal pedagogical intent, he presents the results of a rigorous thought process
going well beyond practical applications and leading to perceptive examination
of the components of creation. One does not need to extrapolate or translate his
thoughts to recognize many of the themes of modern cognitive research. The
acuity of his analysis, combined with well-thought-out practice, finds its direct
reflection in the fields of perception, learning and memory, attention, mental
imagery, and the relationship between emotion and cognition.
This tribute to Edmond Roudnitska is an acknowledgment of our indebtedness.
This profoundly rational spirit, who was confident that scientific research could
enlighten any endeavor and someday facilitate the art of perfume creation, was
xix
xx A Tribute to Edmond Roudnitska
also a generous man. Through creation of the Fondation Roudnitska he enabled

many young researchers to progress in their knowledge of olfaction, and we
thank him for this.
André Holley
Notes
1. Among E. Roudnitska’s creations, let us mention “Femme” for Rochas (1944),
“Diorama” for Dior (1948), “L’Eau” for Hermès (1951/1987), “Diorissimo” (1956)
for Dior, “Eau sauvage” (1966) for Dior, and “Diorella” (1972) for Dior.
2. L’Esthétique en question, Presses Universitaires de France, Paris, 1977; Le parfum,
Presses Universitaires de France, Paris, 1990; Une vie au service du parfum, Thérèse
Vian, Paris, 1991.
OLFACTION, TASTE, AND COGNITION
Section One
A Specific Type of Cognition
Olfactory experience is difficult to define: From ineffable to unmentionable, it

seems to remain in the limbo of cognition. More than any artist’s work, the
competence of the perfumer is a challenge for explication. The few artists who
are able to communicate in writing about their creative processes are mainly
plasticians (painters and sculptors), musicians, and, of course, writers. As regards
chemical senses, the writings are extremely rare, and the very status of “artist” is
not easily conferred. As an example, Edmond Roudnitska faced a difficult task
in his effort to have olfaction accepted into the realm of aesthetics.
In Chapter 1, Annick Le Guérer proposes an explanation for that misappreci-
ation that has to do with the history of Western philosophy: Our philosophical
heritage denies any nobility to olfaction and taste, as compared with the other
senses, and depreciates them almost systematically. Psychoanalysis has cited
that fact as evidence that civilization can be built only if there is repression of
smell. However, as Le Guérer points out, the history of psychoanalysis itself
is marked by fantastic representations of the nose and its functions within the
relationship linking Freud and Fliess – their unconscious montre son nez in the
learned conception of smell.
Moving away from the neurophysiology of smell, André Holley, in Chapter 2,
looks into the perfumer’s knowledge, which remains largely secret and intuitive.
What is the difference between expert and novice, artist and amateur in the
cognitive treatment of odors? How does plain emotion become an aesthetic
feeling, and which departure from the common meaning of “odors” does this
imply? These questions require an understanding of how the composer perceives,
recalls, and imagines odors and whether abstract representations and rules are
superimposed on ordinary perception or replace it. Whereas audition research
has revealed differences between musicians and non-musicians, similar research
on expertise for smell has yet to be done: Is there an absolute sense of smell, as
there is an absolute sense of pitch?
2 Section 1: A Specific Type of Cognition
Egon Peter Köster has had long practical experience in research on preferences
and olfactory memory in various industrial applications of the chemical senses.
His research has been characterized by this pragmatic point of view, orienting him
toward the implicit, emotional, and infra-attentional functioning of this modality.
In Chapter 3 he examines here the differences between the chemical senses and
the “far senses” and questions the relevance of many marketing surveys: “People
will eat what they like, but do not know what they like, and certainly not why
they like it.”
1
Olfaction and Cognition: A Philosophical and
Psychoanalytic View1
Annick Le Guérer
“Are you not ashamed to believe that the nose is a means to find God?” wrote
Saint Augustine (1873) in his refutation of the Manichaeans in 389 C.E. Fifteen
centuries later, Sigmund Freud, addressing the members of the Vienna Psycho-
analytical Society, stated that “the organic sublimation of the sense of smell is a
factor of civilisation” (Freud, 1978, p. 318).
These peremptory opinions expressed by the Christian philosopher and by
the founder of psychoanalysis offer little support for any investigation into the
sense of smell as a tool for knowledge. Furthermore, they are typical of an
attitude widely held by both philosophers (Le Guérer, 1987) and psychoanalysts
(Le Guérer, 1996). There are many possible explanations for the mistrust –
indeed, the rejection – with which both groups have treated this sense, but all of
them converge on its animal nature.
Philosophers have often slighted and underestimated the sense of smell. Plato
(1961) and Aristotle (1959) maintained that the pleasures it provided were less
pure, less noble, than those offered by sight and hearing. Aristotle also found it
lacking in finesse and discernment. Descartes (1953) regarded it as vulgar, and
Kant (1978) thought it a coarse sense and one best left undeveloped, leading as
it did to more unpleasant experiences than pleasant ones. Schopenhauer (1966)
considered it an inferior sense; Hegel (1979) eliminated it from his aesthetics.
And at the beginning of the twentieth century, the German philosopher Georg
Simmel (1912) went so far as to term it the antisocial sense par excellence.
Animal, primitive, instinctive, lust-provoking, erotic, selfish, irrelevant, asocial,
dictatorial, imposing upon us willy-nilly the most painful of sensations, mak-
ing us unable to escape its subjective solipsism, incapable of abstraction or
of leading to any artistic ends, not to mention thought – the philosophical
reasons for denigrating the sense of smell are numerous (Le Guérer, 1988,
pp. 225–93).
3
4 Annick Le Guérer
Why Such Negativity?

If we approach the question analytically, we find two basic approaches. The
first derives from the hierarchy often established between the distanced, noble
“intellectual” senses (sight and hearing), which require some external medium
(e.g., the air), and the proximity senses, which are more physical, animal, and
sensual (taste and touch) and which have as their medium the body itself, the
flesh. Smell exists at the junction between these two groups and is regarded as
an intermediate sensorial faculty. We find this basic belief in the works of many
thinkers, from Aristotle to Jean Jaurès (1891), including Saint Thomas Aquinas,
Hegel, and Cournot, who variously described the sense of smell as ambiguous,
bastard, vague, and nonautonomous.
The second approach concerns the paucity of the olfactory vocabulary. In his
Timaeus, Plato dealt with the difficulty of arriving at any precise description
of odors. In his view, the only distinctions that can be made with any validity
are affective, that is, based on the pleasure or displeasure to which they give
rise. The list of subsequent philosophers making similar distinctions is a lengthy
one. The sense of smell was regarded as a dead end, incapable of abstraction.
Henning (1916, p. 66) noted that “olfactory abstraction is impossible. We can
easily abstract the common, shared color – i.e., white – of jasmine, lily-of-the-
valley, camphor and milk, but no man can similarly abstract a common odor
by attending to what they have in common and setting aside their differences.”
Simmel (1912, p. 3) noted: “ The difficulty of translating smell impressions into
words is far different from that of translating the impressions of sight and hearing.
They cannot be projected on an abstract level.” Dan Sperber (1974, p. 128) wrote
that the only possible way to classify smells was in relation to their sources
(the smell of roses, or coffee with milk). In saying that, he was in agreement with
many neurophysicists (Holley and MacLeod, 1977, p. 729): “Only the source of
an odor is truly apprehended as an entity, to the point that we are unable to give
a name to the latter save via the former. We lack the rigor of language required
for more precise description and are forced to fall back on metaphors.” 2
This perpetual problem of abstraction has meant that smell has come to be
viewed as a primitive, archaic, needed sense, one more important to sensory plea-
sure than to knowledge. Lacking in objectivity, and making us aware not of true
distinctions but rather of elements that are “complementary,” “congenerous,”
and “convenient” to us – making us aware, in a way, of ourselves – the sense
of smell therefore fails to afford us, in the words of the philosopher Maurice
Pradines (1958, p. 513), “any true knowledge, either of the world or of our-
selves.” Cournot (1851, p. 121) asserted that the sense of smell is too subjective
to provide any precise information about external objects: “A smell, like a taste, is
Olfaction and Cognition: Philosophical View 5
an affect of the feeling subject that affords no representation, that in and of itself
neither implies nor determines any knowledge of the thing sensed . . . . What is
incontrovertible is that the sense of smell alone can provide no notion of the outer
world and that, in a normal man, it adds no theoretical or scientific knowledge
of the outside world . . . scientific advances would in no way be hindered were
this sense to be done away with completely.”
Further, the sense of smell has been regarded as a hindrance to scientific
progress. Smells, because of their direct and intimate nature, their insinuating,
penetrating strength, and their permeability, are treated as active realities, as
the surest messengers from the real world. This view is buttressed by the belief
that smell contains the principle, the virtue, of any substance, a belief that the
philosopher Gaston Bachelard (1938, p. 115) has termed “substantialist” and
one that has often led scholars astray. Thus, for a long time, ozone failed to be
identified as a gas because it was believed to be the odor emitted by electricity.
Unlike sight and hearing, which are viewed as higher senses and are endowed
with a rich and specific vocabulary, the sense of smell has been regarded as
incapable of serving as the basis for any art form. That view can be attributed
to a long philosophical tradition wrought by many great thinkers – Plato, Kant,
Hegel, Schopenhauer, Bergson – whose opinions have weighed heavily on all
aestheticians.
However, there have been philosophers, though in fact very few, who have
taken exception to the categorization of olfaction as somehow disreputable.
The movement toward rehabilitation was begun by the eighteenth-century
Sensualists, who, in opposition to the intellectualizing Philosophes of the sev-
enteenth century, vaunted the importance of “feeling” as a part of knowledge
and maintained that the sense of smell had been unjustly disparaged in the past.
According to La Mettrie (1745), for example, all ideas derive from the senses,
and Helvétius (1774, p. 135) went so far as to state that “to judge is to feel.”
The famous example of the statue imagined by the Abbé de Condillac sym-
bolizes this program of reevaluation. To explain how perceptions are assimi-
lated to produce understanding, he imagined endowing a statue with each sense
separately, and he began with the sense of smell because it supposedly was the
one that made the least contribution to knowledge and understanding. Diderot
(1955) went even further and stated (without demonstration) that the sense of
smell was capable of abstraction. Rousseau (1969) considered it to be the sense
of the imagination and of love; pity the man, he wrote, so insensitive as to be
unmoved by his mistress’s odor.
In the nineteenth century, the sense of smell found defenders among philoso-
phers who set out to rehabilitate the role of the body in the search for knowledge.
The German philosopher Ludwig Feuerbach (1960) was an advocate for the
importance of the sense of smell. He declared that it was as capable as the sense
of sight of rising above animal needs and that it could make spiritual and scientific
contributions to both knowledge and art. Feuerbach condemned those thinkers
who found it necessary to reject the importance of the sense of smell in order
to improve their thinking: Without a “nose,” their theories were condemned to
emptiness.
It was Nietzsche, however, who spoke out most strongly against those who
denigrated the sense of smell. Whereas Feuerbach attempted to revalorize the
sense of smell by making it more spiritual, more intellectual, Nietzsche, on the
contrary, lauded its animal nature: The refusal of the majority to acknowledge
the sense of smell as a means for attaining knowledge was rooted in an absurd
rejection of man’s animal nature, in addition to revealing an exaggerated esteem
for logic and reason. The utility of the sense of smell resides in this animality,
obviating the need to employ language in order to advance thought and under-
standing. It is, in fact, the most delicate instrument available to us. Nietzsche’s
apologia took the shape of a metaphor. “Flair,” for him, was a real tool for psy-
chological and moral investigation. Its links to instinct, judgment, and mental
perception would make it a tool for the psychologist, who is guided by intuition
and whose art consists not in reasoning but in “scenting out.”
An accomplished psychologist, Nietzsche (1971, p. 333) claimed to have an
especially remarkable flair that enabled him to read people’s hearts and souls
and to sniff out falsity and illusion. “I am the first to have discovered the truth
by virtue of the fact that I am the first to have sensed, to have had the flair to
scent out, falsehood as falsehood.” As the sense most attuned to truth, smell, in
its search for veracity, overturns the cold logic that is the product of the struggle
against the instinctual and draws on the sure sources of the animal instincts that
endow the body with such great wisdom. Above and beyond its basic function,
therefore, the sense of smell assumes the function of a “sixth sense,” the sense of
intuitive awareness. All of the cognitive importance with which Nietzsche (1971,
p. 333) endows this unjustly despised sense is expressed in this statement: “All
my genius is in my nostrils.”
However, Nietzsche’s defense of the sense of smell did not have any lasting
effect, and the few subsequent attempts to plead on its behalf have not been note-
worthy. The most effective damper on such efforts came from psychoanalysis,
which has played an important role in the cognitive devaluation of the sense of
smell.
One might have expected the psychoanalysts, given their awareness of their
patients’ sexuality, to have undertaken a closer examination of this sense, which is
so intimately bound up with a person’s sensual side. Such, however, has not been
the case, and the situation may perhaps be explained as follows: The story of the
sense of smell with regard to psychoanalysis itself bears the mark of repression.
Freud’s olfactory investigations, which were undertaken at a time when hygiene
and an odor-free environment were becoming increasingly important and during
a period in which the scholarly discourse on the sense of smell tended to devalue
it, were conducted within the framework of his transferential relationship with
Fliess, in which the nose (frequently purulent) and the repression of concerns
about certain olfactory events each played a considerable role (Le Guérer, 1996).
Freud had met the Berlin otorhinolaryngologist Wilhelm Fliess in 1887 at
Vienna and had become fascinated by the wide-ranging scientific views ex-
pressed by that brilliant and original thinker, views in which the nose played
a major role (Freud, 1985). Indeed, Fliess (1893, 1977) believed that he had
discovered the existence of a neurosis linked to the nasal passages. He also be-
lieved that edemas of the nasal mucous membrane and infections of the sinuses
and nasal turbinate cartilage were at the root of a whole group of symptoms:
migraine headaches, neuralgias, and functional disorders of the heart and of
the respiratory, digestive, and sexual systems. According to Fliess, all of these
ills, notwithstanding the marked differences between them, shared one common
characteristic: They could momentarily disappear when the appropriate nasal ar-
eas were anesthetized with cocaine. Both men suffered from serious rhinological
problems, which further increased their interest in that organ. Fliess managed
to persuade Freud that Freud’s nasal problems were the root causes of his heart
condition. In an attempt to correct that, Freud allowed Fliess to operate on him
on several occasions. Indeed, they were joined by the nose, so to speak, and
that connection was strengthened by their use of cocaine. Present throughout the
course of their intellectual exchanges and a part of their daily lives, their fixation
on the nose was to become even more pronounced as the result of an unfortunate
surgical procedure.
In February 1895, Freud asked Fliess to perform an operation on one of his
patients, a hysterical young widow named Emma Eckstein. Fliess came from
Berlin to Vienna and performed the procedure. During the same visit, he cau-
terized Freud’s nasal turbinate bones (Freud was suffering from acute rhinitis).
After Fliess’s departure, however, the young woman’s nose remained extremely
painful and began to give off a foul odor. Freud summoned another special-
ist to Emma’s bedside, and the new doctor saw what appeared to be a string
in the young woman’s nasal cavity. He pulled on it and drew out what – to
everyone’s surprise – turned out to be a piece of surgical gauze nearly 50 cm long
(∼19.5 inches). The girl, streaming blood, promptly lost consciousness. The
hemorrhage was finally stemmed, but Freud was so shocked at Fliess’s profes-
sional negligence and his patient’s alarming state that he became sick and was
forced to leave the room and revive himself with a shot of brandy.
That failed operation was to play a fundamental role in psychoanalytic theory,

for it was the source for the well-known dream known as “Irma’s injection,” in
which the sense of smell is of prime importance, and it became the paradigm
for Freud’s theory of the dream as wish fulfillment. At the time, Freud greatly
needed Fliess’s friendship and support, and he did everything in his power to
retain his admiration for Fliess and repress his doubts. That process of repres-
sion is especially clear in the dream, in which the Fliess character appears to
be esteemed and guiltless. It is also much concerned with the noses of the three
protagonists involved in the minor tragedy that had occurred at Vienna a few
months earlier. In my view, it was within this transferential relationship with
Fliess – an otorhinolaryngologist, the author of a work on the relationship be-
tween the nose and sexuality, and a man deeply involved in an incident featuring
an evil-smelling nose – that Freud came to conceive his theory of smell, which
is centered around the notion of repression (Le Guérer, 2001, p. 460). Indeed,
on 14 November 1897 Freud wrote to Fliess as follows: “Memory now comes
up with the same stench as an actual object. Just as we turn away in disgust from
evil-smelling objects, so too do the preconscious and our conscious awareness
turn away from the memory. This is what we call repression.”
At the turn of the twentieth century, the olfactory observations cited in med-
ical and scientific discourse tended, for the most part, to have a negative tone.
Indeed, the great naturalist Charles Darwin (1971) considered that the sense
of smell, so important to most mammals, was, in humans, merely a weakened
and rudimentary function, a holdover from the distant ancestors for whom it had
been extremely useful. Subsequently, the majority of contemporary psychiatrists
and sexologists would connect the sense of smell not only to animality but also
to psychopathologic conditions. The famous Austrian psychiatrist Richard von
Krafft-Ebing (1931) and the German sexologist Albert Moll, as well as Charles
Féré (1974) in France, all felt that the sense of smell had little to do with any
normal sexuality. On the other hand, certain mental illnesses seemed to reveal a
close connection between the sense of smell and sexuality.
Freud’s theories were influenced by all of those ideas, but he was to go deeper
into the question by explicitly positing an indissoluble link between repression
and the almost universal contempt for the olfactory sense.
According to the founder of psychoanalysis, both our sense of smell and our
sexuality were altered profoundly when our distant ancestors abandoned walking
on all fours and adopted an upright position. When the nose was elevated higher
above ground level, the once-dominant sense of smell weakened, the sense of
sight moved to the fore, and hitherto-exciting olfactory sensations gradually
came to be considered disgusting. That virtual obliteration of the sense of smell
led to a broad-based repression of sexuality, though it facilitated the founding of
families and the development of civilization. In short, when humans broke away
from their animal nature, that entailed a dual abandonment: withdrawal from
the sense of smell and from sexuality. The virtual disappearance of the sense
of smell during phylogeny is a model of what occurs during ontogeny (Freud,
1961).
As a result, acute olfactory sensitivity came to be viewed as an archaic and
even pernicious trait, revealing a fixation on anal sexuality. According to Freud,
it persisted only in animals, in savages, and in very young children, who were
not disgusted by excremental odors: Education teaches the child to shun such
smells. The result held repression of the sense of smell and of anal sexuality. To
have a keen sense of smell was seen as a symptom of latent animality, a failure
of the socializing process.
Freud, in proposing a direct relationship between the development of civiliza-
tion and the virtual eradication of the sense of smell, was implicitly suggesting
that the olfactory sense was a hindrance to knowledge and aesthetics. Follow-
ing in his footsteps, many psychoanalysts came to view it as an archaic, animal
faculty that would have to be repressed if people were to function in society.
Such was the view of Lacan (1973, pp. 61–2) when he noted that repression
of the sense of smell in humans “has a great deal to do with [their] access to
the dimension of the Other.” It was also the view of Françoise Dolto (1980,
p. 342), who agreed with the philosophical tradition that deemed the sense of
smell inferior because it was incapable of abstraction. “Culture,” she stated, “is
speech and obviously not smell.”
Nevertheless, some psychoanalysts, like Nietzsche before them, have at-
tempted to rehabilitate the sense of smell by demonstrating that it is capable
of leading to intuitive knowledge. For example, the Hungarian psychoanalyst
Sandor Ferenczi (1974) sought for hidden links between the sense of smell and
thought processes. Like animals, some humans may have a gift for “sniffing out”
repressed feelings and tendencies. An extraordinarily subtle sense of smell
and a powerful olfactory imagination may underlie the performances of spirit
mediums, who may be sensitive to the odors emanating from certain people.
Ferenczi (1985, p. 142) went so far as to state that “a large part of what has
hitherto been regarded as an outré, occult or metaphysical performance may
have some psycho-physiological explanation.”
Owing to its ability to enable people to “sniff things out,” the sense of smell
plays a large role in transferral and countertransferral. Instances of sick persons
who gave off extremely unpleasant odors when experiencing attacks of repressed
rage made Ferenczi aware of the semiotic importance of odors: They could
replace speech and reveal affects that might be hidden in social communication.
The psychoanalyst went on to discuss the case of a patient who, when in a state
of repressed anger, emitted highly unpleasant odors, “as though, lacking other
weapons, she was attempting, like certain animals, to keep people away from
her body by frightening them with these emanations of hatred” (Ferenczi, 1985,
p. 141).
More recently, Didier Anzieu had an experience with the cognitive value of
olfactory messages in psychoanalysis. His patient, whom he called Gethsemane
(in reference to the Mount of Olives, where Jesus sweated blood), suffered from
excessive and very malodorous sweating. The psychoanalyst, repelled and al-
most paralyzed by the stench, which was made even more unpleasant by the eau
de cologne his patient liberally applied, probably to mask it, was unable to cope
with this particularly intense sensory manifestation. He began by setting up an
early countertransferential resistance to the manifestation, not verbalized but yet
“the most pervasive factor in the session,” which he considered devoid of any
“apparent communicative validity” and as falling outside the purview of psycho-
analysis. Anzieu (1985, p. 182) thus despaired of interpreting the condition, the
treatment languished, and boredom set in. Gethsemane, continuing to exterior-
ize his anxiety and conflicted feelings in this unique manner, went on smelling
worse and worse.
One day a patient protested about the fetid atmosphere in Anzieu’s clinic.
Anzieu shook off his lethargy and realized that he had almost reached a point
at which he himself was no longer able to “sense” Gethsemane, “with all the
meanings that that word entails.” “Might it not be a transferral neurosis simulta-
neously concealing and expressing itself through these bad-smelling – and, in my
case, slyly aggressive – emanations?” he asked, now alerted. But how to discuss
such nauseating emanations without seeming inconsiderate or hurtful? Because
he could find no psychoanalytic theory to guide him in answering that question,
the analyst ventured to make “a compromise and fairly general interpretation”
centered on the senses that, after several sessions, finally uncovered a memory
from the past connected with smell.
Gethsemane had had a difficult birth, during the course of which his flesh had
been lacerated and there had been considerable bleeding. He had been kept alive
by the care of a slatternly wet nurse, who had taken him into her own bed. At the
same time, his mother, an extremely well-groomed woman, was liberal in her
use of eau de cologne. “Thus,” concluded Anzieu (1985, p. 184), “the two con-
tradictory odors with which he filled my consulting room represented a fantasy
attempt to recreate in his own flesh the flesh of his wet-nurse and his mother. Did
this mean that he had none of his own?” By becoming aware of his conflicted
feelings, rather than sublimating them in the form of perspiration, Gethsemane,
unconsciously and without suffering, began to show marked progress, and his
bad odor gradually became less noticeable. The importance of the sense of smell
in that case and the actual odors noted by Anzieu during that treatment led him,
in a footnote, to venture a hypothesis rich in potential and in keeping with certain
of Ferenczi’s intuitions: “It may be that the analyst’s intuition and empathy both
rest on an olfactory basis that is difficult to study.”
Gisèle Harrus-Révidi (1987, p. 62) deplored the total negation of the impor-
tance of the sense of smell in analysis, for that sense plays a most basic role
in human communication. Citing the English psychoanalyst Donald Winnicott,
she viewed any smell that entered into the “intermediate area of illusion” of the
analytical space as a “transitional object” that called for interpretation: “When
making resumés of sessions, little attention is paid [to] the stomach rumblings,
hiccoughs or physical noises made by the patient’s body (and we piously omit
to mention those of the analyst as well!), all those things by which the patient
makes us aware that he has a body. The patient may be attempting to fill the
transitional space with his own odors in order to make it his own. ‘Regression’
may lead him to try to revive the odorous aura, basically of feces, surrounding his
relationship with his mother.” And the effluvia of the analyst are as meaningful
as those of the analysand. His odors, like those of his apartment, the smells of
the food prepared therein, the flowers that he has bought, can all play a part
in the process of transferral. The sense of smell, which was studied by Freud’s
earliest heirs, essentially with regard to anal sexuality, has gradually been shown
to have relationships to every libidinal stage, but it remains tainted with negative
references. The notion of it as a decadent sense, but especially the linkage of the
sense of smell to animality and anal eroticism, has contributed to this situation.
The few analysts who have concerned themselves with this sensorial mode have
often commented on the paucity of psychoanalytic documentation in this field.
Conclusion
The rare attempts by philosophers and psychoanalysts to provide a cognitive
reevaluation of the sense of smell have led to the idea of a “non-rational” intelli-
gence, a “flair” that cannot be expressed in words. Must we, then, with Aristotle,
conclude that the sense of smell is not of intellectual benefit? Frequently deni-
grated as a tool for rational knowledge because of its resistance to abstraction,
and because of its close links to sexuality, the sense of smell is nevertheless indis-
pensable in grasping some extremely subtle, pre-rational factors, the indefinable
“something” that emanates from a person, an object, a place, a situation. As the
sense most closely linked with affect and contact, a sense that helps to establish
a fusional relationship with the world, revelatory not only of substances but also
of ambiences, climates, and even existential states, the sense of smell is a subtle
tool for knowledge that allows for an intuitive and prelinguistic understanding.
Its links to respiration enable us to have a profound relationship with our envi-
ronment and give the sense of smell a very special vocation, one that Tellenbach
(1968) describes as “atmospheric flair.” Thus, in the past it played an important
role in medical diagnosis and had an essential function in communication.
Indeed, at a very early date, medical men knew that smells were one way of
identifying diseases. Hippocrates recommended that a doctor be a “man with an
open nose,” capable of recognizing diseases by their smells. Doctors have long
paid close attention to smells, and in the eighteenth and nineteenth centuries
there were specialists, known as osphresiologists, who drew up highly detailed
olfactory classifications for every sort of disease. Thus the patient suffering from
smallpox would smell of onions, a person with ringworm would smell of cat,
and a madman would emit the odor of a wild animal or of mouse urine. Monin
(1885, p. 16), an osphresiologist, stated that “smell is the subtle soul of the clin-
ical apparatus. Its language rings a faint bell in the practitioner’s mind, recalling
primal diagnostic ideas. It is a semiotic method in use from the earliest times.”
Recent surveys in medical circles have shown that, notwithstanding the decline
in the teaching of olfactory diagnosis, the sense of smell continues to play a
part in the acquisition of professional competence. Health-care personnel are
expected to identify certain pathologic conditions by their odors and to know,
solely on the basis of smell, whether or not they are serious (Candau, 1999,
p. 185). Present-day research using an “electronic nose” to analyze morbid
effluvia is in line with that age-old tradition.
Psychiatric phenomenology (Tellenbach, 1983) has demonstrated the impor-
tance of olfactory experiences in understanding the changes in one’s relation-
ships to one’s self and to the world. Thus, when patients suffering from olfactory
delirium complain that they are emitting obnoxious odors, their lives must be
dominated by feelings of guilt and corruption. The vile thing conveyed by the
evil smell can totally upset one’s relationship with reality. Such patients are con-
stantly humiliated at having to impose their supposed stench on those around
them. In a world in which there is a growing tendency toward deodorization,
those suffering from olfactory paranoia, trapped in their own stench, are contin-
ually fearful of being caught in the act of creating an unpleasant smell. Such a
person, experiencing himself as an object of disgust, comes to think that people
are laughing at his smell and even holding their noses when he goes by. Here,
smell is the symbol of the judgment such sufferers believe the world is leveling
against them: arrogant rejection, contempt, discrimination.
In The Brothers Karamazov, Dostoyevsky analyzes the critical changes that
an odor can trigger. When, instead of the expected odor of sanctity, the corpse
of Father Zosima exudes a stench of putrefaction, those in attendance interpret
it as the odor of doubt and hatred. The atmosphere of purity and freshness, trust
and idealism, that emanated from the monk when he was alive gives way to a
pestilence that confuses, dismays, and causes profound spiritual unease among
his followers.
Odors, more sheltered from intellectual analysis than the other sense impres-
sions, are the tools for intuitive and emotional knowledge of the world, as is
reflected in everyday language and in many colloquial expressions (we “sniff
out” wrongdoing, a person is said to “have a nose for” news or something else,
we say that we “smell a rat” or that someone is “in bad odor,” or that something
just plain “smells” – sometimes “to high heaven”).
It is also from this special locus “between experience and representation, affect
and percept” (Holley, 1999, p. 243), that odors derive their ability to evoke the
past in all its freshness, a power that so often benefits writers of all kinds. Like
individual, private signals, odors are the keys to hidden memories that often we
no longer know we have retained. We thus see that smell, as the philosopher
Gaston Bachelard (1960, p. 123) has written, “in a childhood, in a life, is . . . a
vast detail.”
Notes
1. Translated from the French by Richard Miller.
2. Research is under way into the hypothesis that odors, like colors, may have some
“universal qualities” (Schaal et al., 1998, p. 146). See also the investigations into
African languages in an attempt to discover terms employed exclusively to describe
odors (Mouélé, 1997, pp. 209–22).
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2
Cognitive Aspects of Olfaction
in Perfumer Practice
André Holley
1. Introduction
For their survival, human beings are less dependent than many other mammals
on the use of their olfactory systems. One of the reasons for this decreased bi-
ological role for smell in humans is that information about the world needed
for everyday life is available to humans through a wide variety of channels,
including language as a vehicle for scientific and technical knowledge. The cog-
nitive content of olfactory cues, which is of vital importance to many vertebrate
species, enabling them to behave efficiently in their physical and biological en-
vironments, is comparatively of very modest importance for humans, who have
come to rely on more sophisticated and more accurate sources of information.
This is especially manifest in advanced societies.
In contrast to the relative regression in the ways humans use the informative-
cognitive content of odors, odors still exert a powerful affective dimension.
Odors are pleasant or unpleasant. This emotional component presumably orig-
inated in an evolutionary strategy associating sensory pleasure with beneficial
consequences of approaching various odor sources, and displeasure with dan-
gerous consequences of such an approach. Although the link between the actual
emotional effect of an odor and its potential behavioral meaning was not clear
in most cases, there evolved a general attitude that consisted in attempts to avoid
unpleasant odors and increase one’s exposure to pleasant ones.
The art of concocting perfumes can be seen as a specifically human activity that
leads a biological mechanism out of its natural domain of expression in order to
make it serve a cultural purpose. In ecological conditions of olfactory perception,
odors diffusing from objects (fruits, flowers, congeners, potential prey) indicate
the presence of these objects, even though they may not be immediately percep-
tible through other sensory modalities. By contrast, in the realm of perfumes, the
odors of the synthetic and natural compounds present in these complex mixtures
16
Cognitive Aspects of Olfaction in Perfumery 17
are not attributable to identifiable objects. Odors are in some way separated from
their primary referents and therefore lose their informative-cognitive potential.
They become pure sensory qualities and positive affect inducers.
The reduction in the informative content of odors to the benefit of their af-
fective content in perfume compositions might suggest that composing pleasant
mixtures of odors is an activity that deals essentially with the emotional dimen-
sion of olfactory perception. However, it will be argued here that the reality is
more complex: The art of perfumes actually is a privileged domain for investi-
gating the involvement of cognitive processes in olfaction and, in addition, is a
promising area in which to explore the links between emotion and cognition.
Perception, categorization, attention, memory, learning, mental imagery, lan-
guage, innovation, and creation – all these traditional fields of cognitive studies
are represented in the complex processes leading to the creation and appreciation
of perfumes. The purpose of this essay is to identify specific lines of investigation
that might lead to a better understanding of the process of perfume creation in
particular, and thereby to a better appreciation of the cognitive involvements of
olfaction in general. There will be several references to the writings of the French
perfume composer Edmond Roudnitska, to whom the European Symposium on
Olfaction and Cognition was dedicated.
2. Perception
Regarding perception, one may first ask if perfumers adopt behavioral or mental
procedures different from those used by naive subjects when seeking to achieve
maximum efficacy from their olfactory systems in assessing complex mixtures.
Edmond Roudnitska instructed his students to use precise smelling procedures
that were intended primarily to minimize sensory adaptation and increase at-
tention and mental concentration. One can easily see that a full exploration of
olfactory perception requires optimization of odor inhalation. It is less clear,
however, whether or not trained practitioners develop procedures significantly
different from those spontaneously adopted by naive subjects. Studies by Laing
(1982, 1983) can be interpreted as giving a negative reply. Spontaneously, hu-
man subjects seem to adopt a sniffing technique that optimizes odor perception,
and it is difficult to improve on the efficiency of this technique. A new finding
could be relevant to this issue: Recently, Sobel et al. (1999) reported that alter-
nate fluctuations in the resistance in the nostrils to the inhaled airflow resulted
in concomitant variations in the analytical capacity of the nostrils for detecting
the physical properties of various odorants. It could be interesting to investi-
gate whether or not perfumers take advantage of this apparent cyclic functional
differentiation of the nostrils in order to improve their perception.
18 André Holley
It is currently recognized that odor attributes can be grouped in three main

classes: quality, intensity, and hedonic valence. However, perfumers are inclined
to avoid any reference to hedonism and instead insist on an additional dimen-
sion called “duration.” For example, Roudnitska (unpublished notes) said that
“for the perfumer, odors are classified with respect to quality, to intensity and
duration. The latter must be distinguished from intensity, even though duration
is expressed as intensity along time.” Regarding this surprising lack of reference
to the affective valence, one must understand that perfumers are more interested
in the “behavior” of a compound introduced in a composition than in its intrin-
sic value in terms of pleasantness. An odor is classified primarily with regard
to its potential utilization in compositions. Professionals need not consider the
pleasant–unpleasant polarity as a criterion in designing perfumes; in general,
they use a subset of odorants that all lie close to one pole of the hedonic dimen-
sion, the pleasant one. In addition, those odorants in their “palette” that have
negative hedonic value when smelled individually can reveal positive properties
when added to an odorant mixture in minute quantities.
Regarding the attribute called “duration,” this term refers to purely physical
characteristics of perfumes and, more precisely, to complex interactions taking
place between the perfume and its support vehicle across time. In other cases,
however, physical terms are used to designate perfume properties that can be
said to include a sensorial, qualitative component. For example, “volatility” is
used to describe a property that gives one the feeling that the odorous compound
is propelled out from its support. At first examination, “volatility” would seem
to designate physical properties having to do with the evaporation rates of the
components. Nevertheless, one may wonder if that impression is really related
to those physical properties or alternatively could be viewed as an aspect of
the olfactory quality. Such was suggested by Roudnitska (unpublished notes):
“I think that for a limited number of products, there is a particular phenomenon
[volatility] distinct from evaporation.” Along the same line, the term “volume,”
sometimes used to qualify a perfume, could refer more to the impression of
harmony and plenitude of sensation induced by the perfume than to physical
parameters such as evaporation.
3. Perceptual Analysis and Description of Perfumes

When attempting to describe the quality of sensations evoked by a fragrance,
perfumers use notions such as “notes,” “faces,” and “sub-tones,” terms whose
meanings are not always immediately clear. One might think that these terms refer
to odor qualities imparted to the mixture by individual components or subsets
of components. However, it must be noted that the same kinds of descriptors
are used to describe pure chemicals, as, for example, in the handbook published
by Arctander (1986). It is no longer possible to identify these “notes” as being
some primary odors that would be combined to produce the particular odor of
any product, according to the principle popularized by Amoore (1967). A more
reasonable interpretation would be that notes represent perceived similarities
between a given odor (the odor of a pure compound or of a complex mixture)
and several other odor qualities taken as references.
It should be noted that describing odor qualities as independent entities is
not an ecologically founded activity. Odors are essentially attributes of objects
and substances whose natural function is to reveal the presence of those ob-
jects and substances in the environment. As a consequence, odor naming turns
out to be odor-source naming (see Chapters 4 and 6 in this volume for recent
discussions). In some cultural practices, such as those exemplified by perfumery,
odors become dissociated from their sources insofar as their qualities rather than
their referents are brought into focus. However, the linguistic tools available to
a speaker remain those relevant to source naming, and because a vocabulary to
describe pure qualities is almost nonexistent (at least in French and English),
qualities must therefore be designated by the names of their most representative
sources.
Several factors can enter into the choice of which odor source will be seen as
representative of a quality perceived in a complex fragrance. Obviously, one of
these factors is the sensory similarity between the detected note and the quality of
the referent. In addition, the referent must be readily available and be familiar to
those who engage in linguistic exchange about odors. Meeting these requirements
is not an easy task. Long sessions of “linguistic negotiation” among panels of
professionals are needed to reach a consensus on the best term to describe a
note. Still much more difficult would be selection of a closed set of descriptors
intended to describe all fragrances. Because there is no theoretical reason to think
that there is a finite number of odor qualities, attempting to reduce the list of
reference terms to a few dozen items, as has sometimes been attempted, would be
a project that necessarily would involve considerable arbitrariness, even though
its usefulness would be indisputable.
In a successful composition whose odor components are adequately balanced,
these components lose part of their perceptual individuality and fade away, to the
benefit of the whole fragrance. Some professionals designate such a composition
an “olfactory form.” In this context a “form” is a Gestalt, a complex perceptual
structure undergoing a spatiotemporal development that yields more than the sum
of its components, just as a melody is not reducible to a sum of notes and can
keep its individuality through several transpositions. Roudnitska (1983b) wrote:
“A British specialist in perfumes asked me to describe as simply as possible,
20 André Holley
for a magazine, what I understand by the expression olfactory form. Here is my

reply: When you hear a very well-known musical tune, even if you have never
learned simple scales or an instrument, even if you are completely uninitiated in
music, you nevertheless recognize immediately the tune in question, even without
hearing a single word that goes with this tune. How is it that you recognize this
familiar tune? Quite simply by its musical form.”
If one accepts this musical metaphor, clearly borrowed from Gestalt theory,
it follows that a given olfactory form may keep its personality even though
there may be substitutions for several of the individual odors that compose it.
There is a practical consequence of adopting this view. For example, in terms
of patent rights, the perfumer may want to protect his creation from copying or
imitation, basing his ownership claim not on a list of the products included in
his perfume but on its “olfactory form.” However, whereas there are objective
means to compare two melodies, there is no objective criterion for determining
if two fragrances have similar forms.
4. Learning and Memory

Learning and memory are essential components of the perfumer’s expertise. It
is well known that becoming a perfumer requires very long training. In the ab-
sence of any possible generalizations regarding the sensory behaviors of odorants
entering into the composition of a complex mixture, perfumers must memorize
large amounts of empirical information acquired from experience. Predicting the
intensifying and qualitative effects of mixing several compounds is practically
impossible if one has no previous experience with these products. What are the
best conditions in which to encode odors? Can we draw interesting indications
from the training practices of perfumers?
Roudnitska (1983a) described an exercise he used for his students: “Exercise 1
consists in a very simple mixture of six products, all of them constituents of the
essence of Neroli, but intermingled in such a way as not to make it too easy.
The student will then be asked to reconstruct the composition, i.e., to identify –
by smell alone – the constituents and their proportions.” That initial part of the
training program was aimed at developing the analytical capacity of students by
providing them conditions that would favor their familiarization with odorants
perceived individually and in different combinations. It is interesting to note the
teacher’s concern “not to make it too easy,” emphasizing that the identifiability of
individual constituents would depend on their relative concentrations. Inciden-
tally, the exercise provides additional insight into the perfumer’s attitude when
he creates a composition (i.e., when he works on the synthetic side of his art).
Commenting on his exercise, Roudnitska wrote: “When preparing the Neroli
exercise, for example, what do I really do? I try to schematize the arrangement
worked out by Nature. . . . What then is my problem? It is precisely to try and

schematize, i.e., obtain by means of six products only the Neroli effect, which
Nature achieved with several hundred of constituents. And since it is more diffi-
cult to conceal the identity of six products than that of several hundreds well in-
tertwined, this requires a great effort in conciseness and rigorous harmonization.”
Another question related to odor and perfume memory is whether or not we
can reach a consensus regarding the role of odor naming in odor encoding and
recognition. As noted earlier, professionals wanting to exchange views about
fragrances use descriptors. Does the fact of knowing the name of an odor and its
semantic description have a positive influence on one’s long-term recognition of
this odor? There is an ongoing debate about the role of semantic processing in
the encoding of odors (Engen, Kuisma, and Eimas, 1973; Engen and Ross, 1973;
Lawless and Cain, 1975; Rabin and Cain, 1984; Walk and Johns, 1984; Lyman
and McDaniel, 1986; Jehl, Royet, and Holley, 1997). Whatever the conclusion
of this issue, there are conditions in which the perfumer’s performance neces-
sarily calls for the use of semantic knowledge. For example, one might well be
skeptical if a perfumer claimed that he could recognize all the compounds in a
complex fragrance made of 10 or 20 products. There have been controlled tests
indicating that humans have great difficulty in discriminating and identifying
more than three – exceptionally four – components in olfactory mixtures (Laing
and Francis, 1989; Livermore and Laing, 1998). What is more, training and ex-
perience seem to have little influence on discriminative performance (Livermore
and Laing, 1996). However, it must be supposed that the discriminative sensory
capacity of the expert will be strongly aided by the semantic dimension of his
expertise, insofar as the mixture to be analyzed will have been composed by an-
other perfumer. Professionals have learned, for example, that a neroli “accord”
can be made by combining six particular constituents. Recognizing a neroli note
in a perfume makes it possible to hypothesize that the mixture contains the main
constituents of neroli, thus somewhat orienting the sensory analysis. Because
perfume composition is an art based partly on traditional rules, knowledge of
these rules – the semantic knowledge – is synergistic with nonsemantic, purely
sensory expertise. By contrast, when confronted with a mixture prepared by
experimenters ignoring professional habits and traditions, perfumers must rely
solely on their detection and recognition capacities, and their performances are
more like those of naive subjects.
5. Attention
Olfactory perception is closely linked to attention. Whereas many studies have
explored the roles of different kinds of attentional processes in vision, very
few have investigated olfactory attention. When one’s attention is not directed
22 André Holley
toward olfactory stimuli, and especially when it is directed toward other sen-
sory modalities or non-olfactory tasks, stimuli of low and middle intensities,
even though ordinarily they would be readily detected, fail to be detected. In
one study, subjects presented with a fragrance while engaged in a demanding
cognitive task (playing an electronic game) were not aware of the olfactory
stimulation, whereas they readily detected the fragrance at the same concentra-
tion in a subsequent test when they were instructed to expect an odor (Bensafi
et al., 1998). There is no doubt that perfumers make use of such modality-specific
attention when exploring the quality of a fragrance.
Along the same line, it should be useful to further investigate the relationship
between attention and learning. One study found that subjects exposed to odors
without being aware of such exposure subsequently exhibited behaviors that
were influenced by their exposure to those odors (Degel and Köster, 1999). The
concept of “unconscious odor conditioning” was introduced in such a context
by Kirk-Smith, Van Toller, and Dodd (1983). In a review of the acquisition of
odor hedonics, Hermans and Baeyens (Chapter 8, this volume) discuss several
examples of such acquisition taking place even in subjects who were not aware
that they had been presented with an odor linked with a positive or negative event.
Another open question is whether or not attention can be focused on sub-modal
features. Perfumers seem to be able to focus their attention on different “notes”
or “sub-tones” of a complex fragrance. For example, one might concentrate on
a given note during a first sniff, then on another note during a second inhalation.
How can olfactory attention be directed toward particular components of a fra-
grance? Are attentional processes related to sniffing in humans, and if so, how
are they related? It is tempting to speculate that experts who want to analyze a
complex odor begin their analysis by assuming the presence of a certain note on
the basis of a quick first impression, then evoke a mental representation of that
note from memory, and confirm or abandon that initial assumption by comparing
the mental image with actual perceptions during subsequent inhalations. Could
this be systematically investigated? Laing and Glemarec (1993) reported that
subjects asked to identify the components of mixtures consisting of up to six
components performed at about the same level when they attempted to identify
all the components present as when they attempted to identify only one compo-
nent. In trials conducted under the latter condition, attempts at selective attention
did not significantly influence the identification process.
6. Olfactory Mental Imagery

Another interesting topic is conscious mental representation of odors. There
are divergent opinions on the possibility of achieving mental imagery in the
olfactory domain. However, perfumers claim that they can elaborate a schematic
for a perfume in the mind, sometimes for long periods, before formulating it.
Roudnitska (1983a) wrote that “a perfume, like a piece of music, can be composed
on paper without the help of any other sensorial references than those to be found
in the mind or the memory, the senses being used only afterwards as a mean
of checking up.” Would it be possible for a perfume composer to conceive an
“olfactory form” without representing it mentally in some way? One might argue
that professionals possess a vast store of semantic knowledge of their materials.
They know that a certain “accord” can be achieved by combining such and
such odors in adequate proportions. They have learned a number of rules that
must be followed in order to achieve a well-balanced composition. It is hardly
conceivable, however, that one would be able to create original combinations of
odors without being able to evoke a mental image of the Gestalt one wants to
elaborate.
When questioned about their ability to imagine odors, perfume composers
agree that they do have this capacity. Roudnitska (1983b) explicitly states that
olfactory mental images are postulated by perfumers: “If you have been in love
with a woman who used Arpège, and if, several years later, someone mentions in
your presence the name Arpège, won’t your mind call forth the particular form
of this perfume just as quickly as if you had the bottle right under your nose?”
Demonstrating experimentally that humans are able to evoke mental olfactory
images is difficult. Interesting attempts were those by Lyman (1988) and by
Carrasco and Ridout (1993), who compared the patterns of odor similarity rat-
ings for a set of odorants presented to subjects and the corresponding patterns
of similarity ratings for the same odorants simply evoked by their names. The
presented odors and the linguistically evoked odors showed quite similar group-
ing patterns. That was interpreted as indicating that subjects were able to evoke
from memory mental representations of odors and compare those representa-
tions. However, it has been objected that odor names could evoke a list of se-
mantic properties and that similarity evaluations could be based on previously
acquired knowledge, rather than on iconic mental evocation of odors. An exper-
imental strategy that should not incur that criticism has recently been suggested
(Sulmont, 2000). It was inspired by some research on visual mental imagery
conducted by Kosslyn and associates, who compared the imagined properties
of visual stimuli with their physical properties. According to Sulmont, similar-
ity judgments should be made in pairs between familiar odors evoked by their
names and unfamiliar odors physically presented to subjects. It is assumed that
subjects will evaluate the degress of separation between images of familiar odors
and perceptions of unfamiliar odors. This condition should reduce the possibility
that similarity judgments would be founded on purely conceptual properties, as
24 André Holley
unfamiliar odors would have minimal semantic properties. Finally, additional

evidence in favor of the possibility of mental olfactory imagery can be found in
functional magnetic-resonance imaging (MRI) studies of the human brain (Levy
et al., 1999): Subjects asked to imagine familiar odors show brain activation, and
the activation occurs in regions similar to those activated by real odors.
7. Creation
Artistic creation remains a very complex and mysterious process, whatever its do-
main of expression, whether music, painting, or olfactory composition. Creative
abilities are no more easily explained in olfaction than in any other artistic do-
main. However, the art of composing in perfumery encounters an unusual prob-
lem that arises from possible confusion between sensory emotion and aesthetic
emotion. When they want to practice art with odors, perfumers are challenged
by the apparent ease of their task. Most odors that are the raw materials of their
compositions are pleasant fragrances (even if perfumers claim that they do not
take pleasantness into consideration). Intrinsically, odors are endowed with he-
donic attributes, most often positive hedonic attributes, so that mixtures of such
odors can rather easily evoke pleasant feelings provided that they are combined
with at least a minimum of skillfulness. Nevertheless, aesthetic emotions, which
are expected to be generated in the art lover’s mind by fine pieces of art, must
be distinguished from purely sensory emotions.
A fine perfume is much more than a good-smelling mixture. In perfumery, the
innovative composition that is artistic creation involves cognitive components
similar to those involved in other varieties of art. Like any other artwork, a fine
perfume takes its place in our short artistic-cultural history made up of streams
of tradition. Some famous perfumes have played leading roles in that tradition. A
fine perfume achieves a delicate balance between tradition and novelty. It makes
reference to earlier works, often in addition to introducing innovative departures
in its construction, incorporating new notes or startling combinations of more
familiar notes. Connoisseurs obviously are not immune to the sensory pleasure
of a fine perfume. However, their sensory emotion is amplified and converted
into aesthetic emotion when they feel that they have access to the cognitive
dimension of the artwork.
8. Conclusion
The modern era of perfumery began more than a century ago with the discovery
of new synthetic compounds and their introduction into perfumes. Traditionally,
the relationship between perfumery and scientific knowledge has featured

a privileged connection with chemistry, whose syntheses have enriched the
palette of perfumers with original notes, stimulating the creative imagination.
This brief survey shows that perfume design is open to another kind of scientific
investigation. In the realm of perfumery the cognitive approach to olfactory
processes should find a rich collection of scientific problems, and, reciprocally,
cognitive investigations should provide perfumers with a better understanding of
their art.
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3
The Specific Characteristics of
the Sense of Smell
Egon Peter Köster
1. Introduction
In the nineteenth century, a distinction was commonly made between the “higher”
senses, vision and audition, and the “lower” senses, touch, taste, and smell. In
an age in which, at least in the Western world, faith in science and technological
progress was almost absolute and bodily pleasures were viewed with suspicion,
the senses of the intellect seemed to score a moral triumph over the senses of the
body. Or was there more to the distinction than that? Are the two types of senses
indeed different? And can they even today be grouped as they were then, but on
more objective grounds?
Vision and hearing are involved in such vital human activities as spatial ori-
entation (distance and depth perception, direction perception for sound sources,
equilibrium) and communication (hearing, speaking and reading language, per-
ception of body language, imitation of expressions and gestures). Furthermore,
vision plays a very important role in form perception and in gross and fine
manipulation of objects.
Finally, vision and hearing are the vehicles of the arts (painting, sculpture, ar-
chitecture, dance, music, theatre, cinema, and photography). Compared with that,
touch, kinesthesia, taste, and olfaction can show only lesser glories (perfumery
and cooking, and, to a certain extent and only in combination with vision, pottery,
sculpture, dance, and pantomime). They also seem rather subjective and less
universal – more related to feelings and emotions than to thoughts and deci-
sions. What, then, are the advantages of having these senses? And what are their
characteristics? They seem to be involved mainly in contributing to security,
well-being, and pleasure. In short, they tend to make us feel at home in our
world. In this chapter, some fundamental differences between one of the lower
senses, olfaction, and one of the higher senses, vision, will be discussed, and
the methodological consequences of these differences for cognitive olfactory
research and for sensory evaluation of foods and beverages will be shown.
27
28 Egon Peter Köster
2. Characteristics of the Sense of Smell

The sense of smell differs from vision and also from hearing in terms of a
number of factors. Most of these differences are not absolute, but, at least in
humans, the differences in those factors are spaced at rather large distances on
a continuum. In certain animals, some of these distances will be much smaller,
or even nonexistent. The main characteristics are discussed in the following
sections.
2.1. The Sense of Smell Is a “Nominal” Sense

Unlike vision and hearing, in which non-conscious assessments of relative in-
tensities, sizes, directions, hues, and tones play a major roles in informing us
about the structure of the world around us, the sense of smell primarily provides
us simple “nominal” data about the presence of qualitatively different odors
in our surroundings. In order to provide such nominal information, olfaction
combines good absolute sensitivity (for many odors, the nose is still the most
sensitive instrument we have) with excellent quality discrimination (Holley,
1999). The latter feature enables us to distinguish almost any two odorous com-
pounds presented to us. Even enantiomers like R-(−)-carvone (spearmint) and
S-(+)-carvone (caraway) or S-(−)-limonene and R-(+)-limonene [the R-(+)
being more orange-like than the other] can be distinguished (Laska and Teubner,
1999). The word “nominal” should not be taken too literally, however, for al-
though it is easy to distinguish many different odors, it is difficult to identify them
by name (Cain, 1979). In fact, it is much easier to detect that two successively
presented odors are not the same than to detect that they are identical (Köster
et al., 1997). This indicates that in olfaction, quality discrimination is much
more important than identification. In vision, the reverse is true, and matches are
always detected faster than non-matches in visual priming experiments (Posner,
1986).
At the same time, olfaction has rather poor intensity discrimination. When
starting from a given odor concentration, the concentration of that odor has to
be raised by about 20% in order for a difference to be perceived. In vision, an
increase of only 2% in brightness suffices for detection of a difference. Obviously
detection, discrimination, and recognition of odors as familiar or unfamiliar are
more important than assessments of intensity gradients or verbal identification of
the odor. All of this is in accordance with the function of olfaction as a warning
system against dangers in the immediate environment or in food taken into the
mouth. Changes in quality must be detected immediately, because we cannot
stop breathing, and we must not swallow toxic food.
Characteristics of Smell 29
2.2. The Sense of Smell Is a “Near” Sense

In vision and audition, information about distant objects is transmitted to the
eye and the ear by the mediation of light and sound waves, and the structural
properties of a distant object are reconstructed mentally with the help of inborn
rules. In olfaction and taste, all information about the quality of an object is
contained in the molecules that make direct contact with the receptors. The same
is true, to a certain degree, for the sense of touch when the textural properties
of food in the mouth are monitored, but during active manipulation of objects in
the mouth or outside of the body, touch and kinesthesia cooperate in a form of
object reconstruction over time. Clearly, in regard to touch, even with the same
degree of receptor stimulation, there is a distinction between the experience of
active intentional touching and the experience of the passive stimulation of being
touched (Gibson, 1968). In fact, such distinction is seen with all the senses, but
active intentional searching is a much more prominent feature in vision than
in any of the other senses. Olfaction and taste tend to be rather passive until
a stimulus arrives, and even then we rely mostly on vision to find its source.
When no head movements are made, an odor can offer no clue as to the direction
in which its source can be found, but merely serves as a cue for the visual
search. Kobal, Van Toller, and Hummel (1989) found that only when olfaction
was accompanied by pain sensations transmitted by the trigeminal nerve did it
give some directional information. However, recent findings by Boireau et al.
(2000) using vanillin as a non-trigeminal odor have raised some doubt about
that conclusion. Vision dominates, however. A well-hidden coffee cup will be
immediately detected in a visual display when the odor of coffee is presented to
a subject (Degel and Köster, 1998, 1999).
The fact that “far” senses like vision and hearing have such prominent roles
in our perceptions of the structural properties of the world, such as spatial orien-
tation, distance and form perception, whereas olfaction is truly a “near” sense,
suggests the basis for another major distinction between the two types of senses.
In regard to spatial orientation, inter-subjectivity (all subjects perceiving the
world in exactly the same way) has great survival value for most animals that
live in groups, including humans. Imagine having to deal with automobile traf-
fic without being sure that the other participants have the same perceptions of
distance, form, and size. Nobody would dare to cross a street. Also, we rely on
the precision of other people’s directional hearing many times each day. They
simply know where we are, even if they do not see us. It is therefore convenient
that the mechanisms for these perceptions are inborn, even if they still have to
be somewhat further developed in the first years of life, as in the case of size
constancy. This guarantees that we see the same things (forms, distances), even
though our interpretations of what we see may be different. A violin will look
the same (form, size) to us and to a man who has never seen one before, but he
may not interpret it as a musical instrument and thus may devote less attention to
the differences between the strings. In olfaction, which is not involved in spatial
orientation (but see Howes, Chapter 5, this volume), there is no necessity for
such strict inborn inter-subjectivity. Perhaps as a result, the only inborn feature
of olfaction and taste seems to be aversion to things that are decaying (the odor
of mushrooms, cadavers) or bitter, and even some of those smells and tastes we
can learn to appreciate (Limburger cheese, durian fruit, Campari). In fact, the
absence of inborn mechanisms in olfaction is an evolutionary advantage in an
omnivore (see Section 2.4). At the same time, however, that means that olfactory
variability among people is much greater than their variability for most other
senses. Threshold sensitivities for certain odorants (amyl acetate, pyridine) can
easily vary by a factor of 1,000 between individuals (Koelega and Köster, 1974),
and people who are very sensitive to one substance may be quite insensitive to
another (Punter, 1983). Specific anosmia, a strongly reduced sensitivity to one
particular odor in a person who shows normal sensitivity to other substances, is
the rule rather than the exception, although it seems to occur more often with
certain odorous substances than with others (Amoore, 1977). A large number of
such specific anosmias have been described, and they can be found in different
combinations. Even in its deficiencies, vision follows more general rules: The
number of receptor types is small, and as a consequence the number of forms
of color blindness is small. It is clear that people’s wide-ranging differences in
specific olfactory sensitivities also influence their perceptions of the very com-
plex odor mixtures to which they are exposed in everyday life. Thus it can be
concluded that people differ much more in the way in which they perceive odors
than in the way they perceive visual objects. These large inter-individual differ-
ences in olfaction have their origins not only in differences in interpretation, as
in vision, but also in the sensory basis of the perception itself. That such differ-
ences do not harm us is related to the fact that we do not use odor information
in orientation and movement and that we learn to attach (emotional) meaning
to odors. Even though a rose, with its mixture of flowery and fecal odors, may
smell different to each of us, we all have learned to like the smell and to connect
it with love and tenderness (and thorns).
2.3. The Sense of Smell Is a “Hidden” Sense

Unlike vision, olfaction is seldom the focus of attention. In vision, much informa-
tion is processed without explicit awareness (one can drive a car for many miles
while thinking about other things and without paying close attention to the sur-
rounding traffic), but in olfaction, awareness of odors is the exception rather than
the rule. We inhale all day, and smells can influence our moods (Ehrlichman and
Halpern, 1988; Knasko, Gilbert, and Sabini, 1990; Bastone and Ehrlichman,
1991; Kirk-Smith and Booth, 1992; Knasko, 1993; Gilbert, Knasko, and
Sabini, 1997), the time we spend in various locations (Teerling, Nixdorf, and
Köster, 1992), and our perceptions of other people (Teerling and Köster, 1988). In
some cases, odors can influence performance on vigilance tasks (Warm, Dember,
and Parasuraman, 1990) and mathematical tasks (Baron, 1990), even when the
subjects are unaware of the presence of the odor (Degel and Köster, 1999). The
latter research suggests that the presence of unnoticed and unidentifiable odors
may have a stronger effect than that of clearly perceptible odors or odors that can
be identified. In fact, the sense of smell seems to be trying to hide its presence.
Adaptation in olfaction, which is loss of sensitivity as a result of prolonged
stimulation, is very strong and often complete (no remaining awareness of the
stimulus). The same holds for habituation, which is a reduction of attention and
responsiveness to monotonous stimuli (see Dalton, 1999, who erroneously calls
it adaptation). Furthermore, suppression of odor intensities when odors are mixed
in uneven ratios is much more frequently seen than is mutual enhancement or
synergism (Köster, 1969; Köster and MacLeod, 1975). But even when olfactory
stimuli can no longer be consciously perceived or are no longer attended to,
they continue to exert influences on behavior and mood. It is in this way that
malodorous substances of animal origin – civet, for instance – are completely
hidden in perfumes that without them would not seem nearly so attractive.
The fact that humans are seldom aware of the odors that influence them is one
of the reasons for their difficulty in talking about and describing odors. We have
only a few abstract words to describe odors, like “fresh” or “musty,” and even
these words do not have the same meaning for everyone (see Howes, Chapter 5,
this volume). By far the majority of odors are described by the names of their
sources (strawberry, coffee, etc.). It is well known from sensory analysis and from
perfumery practice that lengthy training is required before people can reliably
describe olfactory experiences in detail. Furthermore, it has been demonstrated
(Degel and Köster, 1998, 1999; Degel, Piper, and Köster, 2001) that odors can
be implicitly remembered without any awareness of the learning event, and such
memories can be disturbed by explicit knowledge about the odor (see Section 2.5
and Issanchou et al., Chapter 13, this volume).
If olfaction is seen as a “hidden” sense, then in normal everyday life perhaps
odors are best not talked about, but simply experienced, with all the surprisingly
emotional reactions and memories they entail.
2.4. The Sense of Smell Is an “Associative” and “Emotional” Sense

As indicated earlier, in olfaction there seem to be few inborn features or mecha-
nisms: the aversive reactions to smells of decay and dead bodies, along with the
strong tendency for adaptation, mixture suppression, and habituation. In con-
trast to the situation with taste, where, apart from our aversion to bitter tastes,
at least our preference for sweet seems to be inborn, there are no inborn pref-
erences in olfaction, and all that we like, we probably have learned to like.
Because humans, like rats and pigs, are omnivores, not having inborn prefer-
ence restrictions in our food choices has been advantageous and has permitted
humans to live almost everywhere in the world. Very early in life, and perhaps
even prenatally (Schaal, 1988; Schaal, Marlier, and Soussignan, 1998, 2000),
we learn to distinguish between the edible and the nonedible. In this distinction,
olfaction and taste play the major role. Many of our first food perceptions are
related to motherly warmth and care and may remain with us for a good part
of our lives (Haller et al., 1999). In general, odors are easily linked to emotions
by association (Kirk-Smith and Booth, 1987; Robin et al., 1999), and olfactory
memories have been found to be more emotional than visual memories (Herz and
Cupchik, 1992, 1995). Many, if not most, of these links are created without any
intention to learn and result simply from contingent circumstances in which the
subject may be unaware of the presence of the odor. Thus the emotions evoked
by a given odor can be very different from one individual to another, depending
on the different emotional encounters with that odor in each person’s personal
history.
Dalton and colleagues (1999) have demonstrated that perceptual responses to
odors can easily be influenced by emotional suggestions. They exposed subjects
to clearly perceptible odors and asked them to rate the odor intensities regularly
during periods as long as 20 min. Before going into the odor room, different
groups of subjects were given the impression that the odors were “hazardous to
health,” “neutral,” or “relaxing.” As would be expected, that created rather strong
response biases that were expressed in differences in response habituation (not
“adaptation” as they stated). Those authors seemed to think that was typical
for olfactory perception, but they never compared their results with those from
similar experiments in other senses. If one went to do the same with a tone of
a certain frequency and were to suggest to the groups that prolonged exposure
to it might lead to “epileptic seizures” or to “healthier sleep,” one probably
would obtain similar results. If it could be shown that under circumstances less
unnatural than those used in these experiments olfaction was indeed less resistant
to suggestion than other senses, it would emphasize that odors are excellent
elicitors of emotions.
2.5. The Sense of Smell Has a “Special Memory”

From the foregoing it should be clear that learning and memory play important
roles in olfaction. Is this the same type of memory as the memory for words
and word associations that has been studied in psychology for about a century,
ever since Ebbinghaus wrote his book on memory in 1885? In a critical review,
Herz and Eich (1995) presented a number of arguments to support the view
that olfactory memory is different from verbal memory: Olfactory memory is
episodic and not semantic in nature. We can remember where and when we
encountered an odor before, but in most cases we cannot call up the name of the
odor, and if we do, often it is by deduction: “When I was small, I smelled this
odor in the attic of my grandparents’ house. They kept apples there during winter.
It is dried-apple odor!” Other differences between verbal memory and olfactory
memory have been reviewed by Herz and Engen (1996). Thus, forgetting seems
to follow a different time course for olfaction then for verbal memory. Most
odors that are presented to people in test sessions are more rapidly forgotten
than are words presented under the same conditions, but those few odors that
are remembered seem to linger on in memory almost forever, whereas words are
gradually forgotten completely. Furthermore, it is clear that olfactory memory, as
measured by nonverbal methods such as recognition, is better in women than in
men. Such differences are not found with verbal or visual memory. Because of the
episodic nature of olfactory memory and its longevity, odors play an important
role in making us feel at home in the world. Without any explicit awareness on
our part, we link emotionally meaningful situations to them and carry them with
us in an implicit memory that renders them up (usually involuntarily) when those
odors are encountered again.
Listening to people who have recently lost their olfactory sensitivity is perhaps
the best way to learn about the real meaning of the sense of smell and olfactory
memory in human life. Not only have such people lost the pleasure of eating
and drinking, but also they do not seem to come home by the same routers,
and they miss that sudden appearance of their most vivid memories. Generally,
they complain that their emotional lives have become less eventful and grayer in
tone. Some of them suffer to the point of depression (Van Toller, 2000), though
others clearly are less affected by the loss. It may well be that those in the latter
group have the capacity to imagine odors, a gift that seems to be found in only
part of the population (Köster et al., 1997). They probably can compensate for
the perceptual loss by imagining the odors they can no longer perceive. Visual
imagery is much more common than olfactory imagery.
In conclusion, it is clear that vision and olfaction differ in terms of a large
number of factors. Table 3.1 summarizes the differences and sketches a number
Table 3.1. Differences between vision and olfaction and their consequences
for future research
Consequences for olfactory

research and sensory
Vision Olfaction analysis
Relative perception: Absolute perception: More research on the
structural (intensity, nominal (qualities and processing of olfactory
direction, depth, size, discrimination); poor quality is needed
distance, movement, intensity discrimination
form, etc.); good
intensity discrimination
Strict inter-subjectivity No strict inter-subjectivity Large panels necessary;
(“far”) (inborn perception (“near”) (almost nothing analysis of smaller subsets
mechanisms); individual inborn); individual of perceiver (and
variations only in variations in both consumer) populations
interpretation sensitivity and interpretation
Usually at the center of Almost never at the center Explicit (conscious)
attention (“overt” sense); of attention (“hidden” methods may lead to
also subconscious sense); subconscious artifacts; implicit methods
information processing processing the rule rather (reaction time, authenticity)
than the exception needed
Prone to forming more Prone to forming more More indirect methods of
objective associations subjective and emotional investigation needed
associations
Semantic memory Episodic memory prominent; Situational analysis needed;
prominent; more explicit more implicit learning implicit memory methods
learning and memory and memory needed; questions about
actual behavior rather
than about feelings
and opinions
of the consequences those differences will have for the development of methods
and techniques for research in the fields of olfaction and sensory analysis. These
consequences will be discussed in the remainder of this chapter.
3. Methodological Consequences
Although many authors have pointed out differences between olfaction and other
senses, the methodological consequences of those differences have seldom been
drawn. Thus, in the area of fundamental research there is a vast literature on
olfactory intensity, but very little on odor quality and odor discrimination. Since
the odor classifications of Linnaeus (1764), Zwaardemaker (1895), and Henning
(1916), which were based on similarity judgments, there have been few attempts
to study qualitative relationships in the world of odors (Harper, Bate-Smith, and
Land, 1968). Besides the odor theories of Wright (1982) and Amoore (1962,
1963), who used certain examples of odor similarities to try to illustrate the valid-
ity of their models, and subsequently were shown other examples of similarities
that tended to discredit the generality of their theories, there have been some sys-
tematic efforts to classify pure odors using more quantitative methods. Amoore
(1967, 1977) based his effort on studies of specific anosmias, considering the
odorous stimuli for which specific anosmias occurred as primary odors and mea-
suring the relative hyposmias for other, but related, odors in specific anosmics
in order to assess the part played by the “primary receptor” in the perception of
these related odors. Woskow (1968) used similarity scaling and multidimensional
scaling techniques to assess qualitative distances among a group of 25 odors.
He found that the most important dimension in their three-dimensional solution
was strongly related to independent measures of odor liking, a variable that ob-
viously is highly culture-dependent. In an attempt to circumvent such culture
dependence, Köster (1971) tried to classify odors on the basis of their cross-
adaptational relationships. Although he was able to show a pecking order and
some general patterns in nonreciprocal cross-adaptations between substances,
which indicated that some odorous substances had access to more extensive
parts of the receptive system than did others, the method was too complicated
and time-consuming to lead to a realistic odor classification.
Since then, odor quality has seldom been investigated in fundamental re-
search. Even problems of odor mixing, in an area that would seem predestined
for qualitative research, have been studied almost exclusively with intensity mea-
sures (Köster, 1969; Köster and MacLeod, 1975; Laffort, 1989; Berglund and
Olsson, 1993; Olsson, 1994; Cain et al., 1995). Laffort and Olsson attempted
to study qualitative aspects, but only in binary mixtures. Meanwhile, in applied
odor research and in sensory analysis of foods and drinks, methods for descrip-
tion of the odorous qualities of the much more complex mixtures encountered
in real life have been developed. A large vocabulary of descriptive terms has
been developed, and data banks of odor descriptors for special products have
been compiled. Forced by the need to produce data that would have external
validity, those working in applied research went ahead and attacked the prob-
lems from which fundamental research had shied away. And even though some
of the methods they used can be criticized, they have contributed much more
to our knowledge of odor quality than have the sterile and intensity-dominated
methods of the psychophysicists. Furthermore, the attention paid to odor quality
in applied research made it clear that strict inter-subjectivity was not to be found
in olfaction: Different observers will have somewhat different perceptions of
a given stimulus. That led not only to the use of larger testing panels but also
to the development of new statistical methods allowing for analyses of various
subgroupings of observers and reanalysis of the data based on differences be-

tween them (Schlich, 1996; Dijksterhuis, 1997). Unfortunately, such methods
remain largely ignored in fundamental research, where averaging over subjects
(based on the false assumption that all observers are equivalent) is still the pre-
dominant way of dealing with data. Thus it becomes clear that what may be a
valid approach in the higher, “far” senses like vision and hearing, with their strict
inter-subjectivity, may not be appropriate for a lower, “near” sense like olfaction,
even if only simple sensory perception is involved. Such differences appear even
more pronounced when one considers the roles that attention plays in vision and
in olfaction. Whereas with an “overt” sense like vision the objects usually are at
the center of attention, that is not the case for odors, which most of the time are
not observed at all.
Nevertheless, odors influence our moods and our emotions, and they can
brighten our world with memories of places where we encountered them before,
without being aware of perceiving them. In the literature, it is often said that we
find it so difficult to name odors because, unlike the situation with colors, our
parents never taught us to name them. It is true that parents take great delight in
teaching children to name colors, but the proponents of that theory forget that
such learning usually is limited to about 10 words and that such a number is
ridiculously low if one considers the vast numbers of completely different odors
that surround us. There exist greenish blues and yellowish greens, but are there
tea-ish coffees or fruitish sweats and so on ad infinitum? To try to learn the names
of odors would be nonsensical for everyday life. But that it can be done is proved
daily by perfumers, flavorists, and people trained to work with descriptive panels.
But why should an ordinary person learn more than the handful that cannot be
avoided because they are encountered every day? And even if we did not know
the names of these, would that in any way change our lives? Usually we would
not notice that they were there, and if we did, they might just make us hungry
or thirsty or interested in the other sex. No identification is needed for that.
Gastronomy is an interesting pursuit, but it is highly questionable that analyzing
food and determining its components can add to the pleasure of eating it. Great
cooks need words to buy the materials they use, but their senses of smell and
taste to make the dish.
Degel and Köster (1999) and Degel, Piper, and Köster (2001) have shown
that knowing the name of an odor can block the encoding (or contribute to the
forgetting) of a new implicit episodic memory for it. Furthermore, it is well
known that after thorough training in odor identification, experts find odors
more interesting, but they no longer experience the natural emotional impact of
odors (Holley, Chapter 2, this volume). That is precisely why experts in sen-
sory evaluation cannot be used to predict consumer reactions to products and
why consumers should not be asked to make descriptive statements. In the lat-
ter case, one would force consumers to do something that they normally would
not do, thus changing their natural way of dealing with a product and defeating
one’s goal: insight into normal consumer behavior. The fact that olfaction is a
“hidden” sense, dealing mostly with non-conscious emotional associations, has
consequences for the types of questions that can be put to consumers. Unfortu-
nately, many investigators, both in fundamental research and in applied research,
grossly overestimate the capacity of people to answer their questions. One of the
most serious problems for psychology is that whenever one asks a question, one
almost always will get some kind of answer. Worse yet, the more unanswerable
the question is, the more uniform will be the responses of a group of respondents,
and the more rational the answers will seem.
In 1969, Weber and Bach instructed their experimental subjects to imagine
the letters of the alphabet; then they asked the subjects to indicate where in the
head the imagination had taken place. Without exception, all subjects pointed
to areas of their heads, and the vast majority pointed to the forehead. That sur-
prised the two psychologists, who were disappointed that the subjects did not
point to the back of the head, where visual signals are processed in the area
striata. They ascribed the uniform behavior of their subjects to “implicit cultural
stereotypes” and never realized that they had asked an absurd question. If such
a nonsensical and unanswerable question can be put by psychologists working
in the field of an overt sense like vision, it is not surprising that one finds many
more similar unanswerable questions in olfactory and flavor research. Here is
the strangest and most complex one that I have encountered: “How many just
noticeable differences [JNDs] is the whiteness of this coffee away from your
ideal whiteness?” All subjects had answered the question and given numbers.
Moreover, for all subjects those numbers became larger when the coffee white-
ness was nearer to the extremes (completely black or almost completely white).
The spurious conclusion was that people could use such a scale based on JNDs
very well to express their feelings about coffee whiteness. In fact, the subjects,
faced with this impossible question, must have resorted to a rationalization and
chosen numbers that were more extreme when the coffee seemed more extreme
to them. They did not use the intended scale units at all.
Whereas with such complex questions the absurdity of the questions is easy
to understand, many people find it more difficult to comprehend that a simple
question like “Why do you like this food?” is just as absurd. If one were looking
for the real sensory reasons for food choices, that would be the best question
to guarantee erroneous responses. People usually do not know what sensory
properties in a given food or drink really attract or repel them. The food may
be linked to implicit and non-conscious memories, or there may be sensory
sensations and feelings attached to it that are extremely difficult to describe.

Nevertheless, people feel that they have to give answers in order not to appear
stupid, and thus they come up with all sorts of notions as to what the attraction
is. Most of these notions are derived from advertisements for the type of food or
drink involved. In Germany, all coffee is advertised as being “mild.” Therefore,
if consumers like a particular coffee, they will say that it is mild. Unfortunately,
all research efforts to find out which sensory properties make a coffee mild
have been in vain. Certainly a very sour or bitter coffee is less mild than a less
sour or bitter one, but of two equally sour or bitter coffees, one may be judged
mild and the other not mild at all. Other notions often used by consumers to
answer “why” questions are rooted in their attitudes and their convictions about
healthfulness, vitamins, fat or fiber content, and the naturalness of foods. In
Europe, the importance of these convictions will vary from country to country,
but usually it is easy to show that such convictions lead to answers that are
contradicted by actual consumer behavior (Köster, Beckers, and Houben, 1987).
Unfortunately, in market research, “why” questions and questions requiring
descriptive answers are often asked, and belief in the answers that consumers
give to such questions probably is the reason for the many flops (8 out of 10
new products disappear from the market within a year) in the food industry.
Questions about actual consumer behavior and simple likes and dislikes are
much better predictors: “How many glasses of water do you drink from the
tap each day?” (Zoeteman et al., 1978; Köster et al., 1981) and “Do you serve
tap water when you have close friends over for dinner?” prove to be far better
questions to assess water quality than are evaluative questions like this: “How do
you like the drinking water from your tap?” For measurement of the implicit and
non-conscious feelings that are connected with odors and flavors, more indirect
methods have been developed. Thus, to estimate the liking of the odor of a
laundry powder, it is better to ask about the whiteness and softness of the clothes
washed with it. For foods also, special methods for evaluating hidden preferences
and changes in such preferences during repeated exposures have been developed
(Köster, 1998). Indirect ways of obtaining information often are even better than
questions about preferences for different specimens of the same type of product.
If people are told that there is a new way of making a traditional product, beer,
for instance, but that it is questionable that this new product has the right taste,
and these people are then asked to select the genuine old-fashioned beers in tests
in which four existing beers are presented a number of times, they discriminate
better between those beers than they do when they are asked which beer they
like best in a paired comparison experiment. This method has also been used to
find out how far one can reduce the alcohol content in beer before the beer is
judged to be no longer a “real” beer (Mojet and Köster, 1986).
The special memory for odors, with its strongly associative and episodic char-
acteristics, can lead to problems in both fundamental research and applied re-
search. Many people have taken home a few bottles of the inexpensive wine they
found so pleasing while on a holiday trip or a vacation, only to be disappointed
when they tasted the wine at home. Why is that? And why is that not the case with
the car they rented and also liked very much in that same country? Obviously,
appreciation of food and drink is highly dependent on situational factors, and a
given product can have quite different effects depending on the circumstances
in which it is consumed. If that is the case, it is strange that even in the best
research in sensory analysis all efforts are made to exclude situational factors:
People taste small portions of pasta at nine in the morning in a sterile cubicle
under “normalized” artificial daylight, or, even worse, we conduct so-called in-
home-use tests, in which a product is given to people and is to be tasted under
“normal” circumstances at home, with the result that instead of eating or drinking
it normally, the family members begin “analyzing” and discussing the product
in the most uncontrolled way, paying attention to aspects of the product that had
never before entered into their normal patterns of choosing. No wonder that 8
out of 10 new food products are flops. Situational analysis, in which people are
asked to imagine and helped to imagine the use of products in different eating sit-
uations, has been proposed (Köster, 1996) and can be used to test foods that will
be marketed in special circumstances, such as snacks in service stations, foods
to be eaten while watching television, and special foods for parties (fondues,
etc.). The best predictive results are obtained with indirect and implicit methods
in which the subjects have no idea that their opinions about the food are what
the investigation is all about. Observation of their behaviors (choices, quantities
consumed, eating speed and its variation over time during the meal) would seem
to provide much better indications of their likes and dislikes than could the direct
questions and scaling methods employed in market research and in traditional
sensory analysis. Situational analysis should be based on such methods and on
data about the frequencies of occurrence of specific situations in consumers’
daily lives. Such data could provide much better information for predictions of
real consumer choices and behaviors than can answers to questionnaires about
attitudes, convictions, and “values.”
4. Conclusion
In this chapter we have examined the differences between olfaction, as a rep-
resentative of the lower senses, and vision and audition, as the higher senses,
and a number of the methodological consequences of those differences for both
fundamental research and applied research have been mentioned. In many of the
examples given, flavor and food were used to illustrate the functioning of ol-
faction. Although olfaction plays an important part in the appreciation of foods,
it is by no means the only factor determining food choices and eating behav-
iors. Other factors, such as one’s internal physiologic state, the accompanying
intestinal feelings, the memory of such feelings, and well-studied phenomena
like sensory-specific satiety (Rolls, 1999, and Chapter 23, this volume), probably
are more important in determining food choices and eating behaviors. In fact,
there are indications that some of these factors modulate the electrical activity
of the olfactory bulb and probably the reactivity to food flavors (Pager, 1974).
This chapter has stressed the differences between olfaction and the other senses.
Obviously there are also many similarities in the ways the various senses are
used to interact with the outside world. Nevertheless, it is argued here that fail-
ure to properly take into account the obvious sensory differences has led many
a researcher to a dead end in the maze of scientific research and has hampered
progress in targeted marketing of food products. People eat what they like, but
do not know what they like, and certainly not why they like it.
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Section Two
Knowledge and Languages
The chapters in this section will clearly illustrate the multidisciplinary approach
of this volume, interweaving issues from different domains – chemistry, an-
thropology, psychology, and linguistics – to examine the complex relationships
between language for odors and knowledge of odors.
In Chapter 4, from a psycholinguistic point of view, Danièle Dubois and
Catherine Rouby’s analysis of verbal answers in laboratory identification tasks
for odors shows that scoring is not solely a technical issue, but also raises nu-
merous theoretical questions about cognitive representations and the naming of
odors. They first demonstrate that the “veridical label” is the name of the odorant
source rather than the name of an olfactory property. Therefore, because subjects
lack adequate labels for the olfactory properties of objects, they have to resort
to the use of a large diversity of linguistic devices to account for their olfactory
perceptions, and those must be interpreted by researchers as cues to subjects’
knowledge of odors.
In Chapter 5, David Howes examines a large body of data borrowed from
the history of Western culture and from distant cultures. Referring to Classen’s
“archeology of sense words” for intellect in the English language, he shows that
the sense of smell has been differently valued and interpreted in various cultures
and that, for example, intelligence was more “tactile” before the Enlightenment
than it is now. A cross-cultural study of sensory vocabularies from different
languages and a precise description of the Ongee people of Little Andaman
Island demonstrate that olfaction can serve as a medium for construction of an
elaborate cosmology and epistemology, according only a minor role to vision.
In Chapter 6, Sophie David presents a precise analysis of the diversity of lin-
guistic resources in the French language to account for olfactory experiences.
Her specific methodology (called lexical grammar) allows her to show that most
French olfactory terms do not refer to odors independently of their sources.
Furthermore, the contrasts between acceptable and unacceptable assertions
46 Section 2: Knowledge and Language
regarding odor naming allow her to argue that odors cannot be considered as
“objects,” as entities located in time and space (as in visually grounded experi-
ence), but rather as properties of objects experienced by subjects.
In Chapter 7, Maurice Chastrette presents the point of view of a chemist in
his overview of the various systems for classifying smells, ranging from em-
pirical classifications grounded in our taxonomic tradition for natural objects to
more recent systems based on semantic descriptions, odor profiles, similarity
data, and statistical methods. One conclusion is that even in expertise domains
such as perfumery, odor structures do not readily fit into the classical taxonomic
patterns used in the natural sciences. The complexity of the picture of knowl-
edge of odors raises interesting questions about relationships between chemical
structures and cognitive structures. A second finding is that the classification
systems are strongly associated with the descriptive systems that account for
odors as substances or as cognitive representations. Therefore it becomes im-
portant to pay closer attention to the relationships between knowledge of odors
and language for odors.
A common theme in all the chapters in this section is the contrast between
the language and body of knowledge that emerges from the olfactory sense
and the more widely used language and knowledge elaborated from the visual
modality. Because the visual realm has always been taken as the proper frame
of reference for interpreting olfactory knowledge and representation, odors have
not been conceptualized as effects experienced by a subject, but rather as entities
in the world. Thus their relationships to language and cognition need to be
reconsidered, emphasizing the contributions of linguistic devices available in
various languages to the construction of both individual and collective cognitive
representations.
4
Names and Categories for Odors:
The Veridical Label
Danièle Dubois and Catherine Rouby
The research presented here is aimed at clarifying the relationships between cog-
nitive categories and the naming of odors, our method being a close analysis of
the verbal answers given to odorants presented in various experiments.1 This is
part of a work in progress within a cognitive science research program on catego-
rization. By definition, such a program is multidisciplinary, involving chemistry,
neurophysiology, psychology, and, in this case, an emphasis on psycholinguistics
and linguistics. The concerns of these latter two disciplines led us to pay special
attention to the conceptualizations and wording chosen for odors. We shall focus
on the verbal answers given by subjects: On the one hand, they are considered
as direct and obvious, like any other outputs or responses from the cognitive
system in any experimental setting, like neural or behavioral responses; on the
other hand, they may be scored at the same time as “erroneous.” The questions
raised by this ambiguity when scoring verbal answers in olfactory research led to
examination of some theoretical issues regarding the conceptual representation
of “an odor” in human memory, as compared with the descriptions of odorants
in the natural sciences.
1. Odors and Their Names

When scoring the verbal performances of subjects in identification tasks and in
diagnostic tests, words such as “orange,” “apple,” and “vanilla” are considered
the “correct odor names” or the “veridical labels” (e.g., Engen, 1987; Doty, 1992).
However, little consideration has been given to what, precisely, a “word” is and
what it means to researchers and subjects. Even in cross-cultural studies, great
attention is paid to the choices of odorant samples to be used as stimuli, but little
or nothing is said about the choices of distractors in multiple-choice questions
(Doty et al., 1985). Thus, “words that may not be culture-free for the response
47
48 Danièle Dubois and Catherine Rouby
alternatives” are “ substituted” when translating tests from one culture to another:
“garlic” is changed for “pumpkin pie,” “dog” for “skunk,” and so forth (Doty,
Marcus, and Lee, 1996). Such scoring relies on the commonsense evidence that
the words simply refer to the things to be named. That may work quite well with
vision (Dubois, Resche-Rigon, and Tenin, 1997), but its applicability is not so
clear for olfaction.
Some authors have noted peculiarities of verbal behavior in olfactory research.
As a first contrast with the visual realm, where objects and their names are so
closely linked that they seem cognitively inseparable, “the linking of names and
odors is usually weak” (Engen, 1987, p. 498). A second contrast is that between
the vividness of odors in subjects’ memories and the poor performances in nam-
ing those odors. For example, “we can recognize odors virtually forever, though
we have difficulty conjuring up a particular smell and remembering its name,”
and “people are not good at naming even familiar odors” (Engen, 1987, p. 497).
Engen, like many other researchers, has suggested that such “poor” perfor-
mance may depend on some property of the stimulus: for example, the “real
thing” being a better stimulus than the “scratch-and-sniff” odorants, and some
odors simply being more easily identified than others. He has also suggested
that poor performance may be due to linguistic factors, such as “the nature of
the verbal response,” and psycholinguistic factors, such as “the subjects’ verbal
abilities.” For example, the better performances of women relative to men in
naming odors could be due to their greater verbal ability. In short, the theoretical
grounding for the relationship between odors and their names remains obscure
and appears to involve mainly problems in linguistics and psycholinguistics. An
understanding probably will also require input from psychologists involved in
basic empirical research into memory: Why should one score a verbal answer as
“correct” or “veridical”? For example, as asked by Engen (1987, p. 500), “What
is a correct answer for ‘musk’?”
We propose here that such difficulties in grasping the relationship between
odors and names (and therefore in scoring answers) are due mainly to an implicit
theory of lexical semantics rooted in the study of vision that fosters the illusion
that a veridical label should exist for anything in the world. If such a theory holds
for visual objects, why not for odors? Conversely, if such a theory of naming
is questionable for odors, it should lead us to reconsider the following implicit
assumptions:
(1) the linguistic conception of naming that exclusively determines word meanings
with reference to the “entities of the world,” a commonsense conception inher-
ited from a philosophical tradition, usually discussed in lexical semantics (e.g.,
Rastier, 1991; Wierzbicka, 1992; Lucy, 1992; Eco, 1997);
Veridical Names and Categories for Odors 49
« Odor »
mental representation
ss
Psycholinguistics
Pe
Psychology
ce
Re
rce
ac
co
pti
al
gn
Ide
on
xi c
itio
nti
Le
fic
n
ati
on
B A
Reference
Name « truth » Entity in the world
« odorant »
Linguistics
Figure 4.1. The semantic conception underlying the use of a veridical label.
(2) the corresponding psychological conception of “lexical access,” which supposes

that subjects can automatically access a mental lexicon that will provide the
correct label for the previously stored odor representation;
(3) the logical entailment of (1) and (2) implying that odors are cognitive repre-
sentations of entities in the world.
We shall therefore examine the conceptual frameworks that attempt to account

for the relationships among odorants, odors, and their names (Figure 4.1)
2. The Veridical Label: An Odor Name?

The notion of “veridical label” or “correct response,” when used in olfactory
research, implies that there are names that adequately (truthfully) refer to odors,
just as color terms adequately refer to colors. However, experimenters themselves
are not always sure how to name what is presented to the subjects, whether using
the names of the chemical substances (amyl acetate, phenylethyl alcohol) or the
names of the sources, that is, the names of the odorant objects (banana and rose,
respectively). To clarify the ambiguity, some explanations are needed: Strictly
speaking, and in contrast to the situation with colors, odors have no specific
names, at least not in English or in French (Dubois, Rouby, and Sicard, 1977).
The correct linguistic form for a veridical label would be of the form “the odor
of X,” X being the name of a source (e.g., the odor of rose), with the word
“rose” referring to the name of the odorant object (see David et al., 1997, for a
description of the linguistic ways of naming odors in French).
Such a lexical gap means that the distinction between the name of the odor-
ant (the substance) and the name of the odor (a subject’s verbal answers to a
stimulation) is not easy to express and therefore is not often made (see Hudson
and Distel, Chapter 25, this volume). Furthermore, as the instructions given
to the subjects often are not fully reported in the description of the experi-
mental procedure, we may not know whether the subjects were questioned by
“What is it?” or by “What do you feel?” when presented with an olfactory
stimulus. The former question concerns a subject’s identification of the objec-
tivity of the odorant, as an entity in the world (vertex A in Figure 4.1). The
latter is related to the subject’s experience of the odorant, the cognitive repre-
sentation of the odorant, which is commonly considered as odor (vertex C in
Figure 4.1). Whether or not and how these two entities (material and mental)
overlap remains one of the important questions (if not the question) for olfac-
tory research. We shall come back to this point later. In short, in psychological
research on olfaction, the so-called veridical label is actually the name that the
experimenter expects, as a relevant and obvious answer to the question within
the experimental setting, in other words, the noun for the commonly encountered
object that produces an odor quite similar to the one produced by the presented
odorant.
The complexity of this statement, as contrasted with the simple “veridical”
label, points to the need for further examination of the realities of the three entities
(odorant, odor, and name) and the mapping relationships among them. We shall
therefore reconsider what is represented at each vertex of the “semiotic triangle”
(Ogden and Richards, 1923; Eco, 1988; Rastier, 1991) as presented in Figure 4.1.
We shall also reexamine the criteria for determining that a verbal response to
an odorant is correct or incorrect, as well as why that question arises only for
verbal responses. Do we, in neurophysiology, talk about the “correct response”
of a receptor when it is firing, or of any type of central response (fMRI, PET, or
electrophysiological)? Why should verbal responses to experimental questions
be susceptible to being declared “erroneous,” whereas electrophysiological re-
sponses are always true?
2.1. The Stimuli

Olfactory research does not specify how similar a presented stimulus is to the
“real thing.” In other words, we do not know if the odorant presented as an
experimental stimulus is a good material (chemical) representation of the odor-
ant regularly and previously experienced by subjects. Consequently, we do not
know whether subjects are responding to “something that is considered similar
enough to a previously experienced odorant” or just to the “presented stimu-
lus,” something never experienced before, but to which they are asked to give
some “appropriate” name. As mentioned by Engen (1987), there are significant
C1 to C5 C’1 to C’2
Mental representations of
B1 to B5 A1, A2 previously encoded
C A’1, A’2 actually presented
Pe
r ce
p ti
on
Re
co
Physical representations
gn
it
ion
A’1. (rose petals, rose extract)
Linguistic resources B A’ Stimuli
A’2. Phenylethyl alcohol
B1. Source name («odor of rose»)
- source basic name « rose »
- category name « flower, soap » A Odorants
B2. Chemical name (phenylethyl alcohol) A1. Object-source (rose)
B3. Odor name («perfume») A2. Chemical substance
B4. Brand name
B5. Other wordings
Figure 4.2. Relationships among verbal (left side) and nonverbal (right side)
representations, linguistic resources, and percepts.
differences in odor-naming performances depending on the mode of presentation

or representation: The scratch-and-sniff odorants lead to poorer performances
than do the brand names (e.g., Crayola crayons, Johnson’s baby powder in opaque
bottles). In short, at vertex A, two classes of entities have to be explicitly dis-
tinguished: the commonly encountered odorants of the real world (A) and their
physical representations (A ) as stimuli within experimental settings (Figure 4.2).
Therefore, when subjects are asked to name an odorant, at least two processes
should be identified:
First, a psychological process of recognition of the stimulus as something iden-
tical with, close to, or different from something already experienced. (For an ex-
perimental exploration of just how representational visual stimuli are vis-à-vis
both the “real thing” and the subject’s previous experience, as well as the
influence of that variable, see Tenin, 1991.)
Second, a psycholinguistic process of giving a name to “something” quite
unspecified or at least implicit, the subject playing along with the experimenter
as if the presented stimulus were some “thing” they agree on.
2.2. The Names

The problem now is to decide which name (vertex B in Figure 4.1) is the genuine
veridical label: the chemical name or the name of the object that is the source
(the “object-source”), or a term or wording referring to the substance (vertex A,

and now A or A in Figure 4.2) or to the subject’s experience and memory for A
(a name for vertex C)? Of course, subjects are not expected to know the chemical
names, and therefore they have to rely on the specific resources of their language.
The resources in French and English for use in the olfactory domain are still
largely unexplored (see David, 1997, and Chapter 6, this volume), and recent
linguistic investigations have shown large variations in lexicality and naming
of smells across various languages (Classen, 1993; Boisson, 1997). Therefore,
vertex B in Figure 4.1 also has to be split into the different wordings available
in the different languages. We shall focus on this point in the next section.
2.3. The Mental Representations

Like a name, the mental representation (vertex C in Figure 4.1) cannot be reduced
to a unique entity. At least three types of mental representations should be taken
into account when subjects respond on experimental tests:
1. The sensory representations of the presented stimuli (C 1 or C 2 as a represen-

tation of A 1 or A 2 in Figure 4.2).
2. The representations of previously encountered odorant objects, stored in mem-
ory, that are similar enough to the actual stimuli to be activated; this type of
representation (C1 or C2 as a representation of A1 or A2 in Figure 4.2) is
investigated in recognition-memory experiments.
3. The representations of linguistic resources referring to olfactory experiences in
the subject’s linguistic community: names in the “mental lexicon” if there are
any, or any other device, including complex phrasing such as “the odor of an
object-source” commonly used in English or French, or any other idiosyncratic
wording available in the subject’s memory (C1 to C5 as mental representations
of B1 to B5 in Figure 4.2).
Besides the idea that naming as a psychological process has to do with the
perceived “thing to be named” (an idea that protects us from absolute rela-
tivism), and besides the ambiguity of what this “thing” is in olfaction (discussed
later), we would emphasize that naming also relies on an implicit contract of
communication between the experimenters and the subjects (Grossen, 1989).
The mapping of words onto things can therefore be considered as an illusion
grounded in the consensus between subjects and experimenters (the partners
in the transaction). However, this illusion can collapse, depending on the stim-
ulus qualities and on the subjects’ previous knowledge, expertise, familiarity
with the stimuli, and ability to “play the game” and to come up to the experi-
menters’ expectations. In tests of visual stimuli, Clark and Wilkes-Gibbs (1986)
showed that when presented with photographs of New York City buildings,
New Yorkers named them by proper names, referring to the precise buildings
(e.g., the Empire State Building), whereas non–New Yorkers described the pic-
ture itself, therefore referring to the representation of a specific type of building
(a skyscraper). Thus naming is not unique and depends not only on individual per-
ceptual processes but also on what the two partners in the transaction will accept
as the “correct response” within this specific communication setting. Inasmuch
as French and English lexicons do not have specific terms for odors, subjects do
“what they can with what is available” to communicate and give overt accounts
of their subjective, covert experiences in order to satisfy the experimenter’s
expectations (Dubois, 1996). Instead of a “true” reference (as represented in
Figure 4.1), a scoring of a “correct response” by the experimenter can therefore
be viewed as a référence heureuse (lucky reference) (Eco, 1997), the partners
agreeing on a name that is known to both. In the case of odors, we can come
back to the formulation proposed earlier: The correct and expected response is
the name of a commonly encountered source (odorant object) that produces a
sensation, an odor, quite similar to the one produced by the presented odorant
stimulus.
Considering the naming process within this frame of reference therefore leads
to reconsideration of the scoring of the answers. Instead of simply sorting out
correct versus incorrect responses, we shall reassess the verbal answers as one
way of getting at the knowledge that subjects want (or try) to communicate to
the experimenter about their olfactory experience, using the resources available
in their language itself (B1 to B5 in Figure 4.2) and in their individual linguistic
representations (C1 to C5 in Figure 4.2). This will lead us to reconsider the
validity of the triangle in Figure 4.1 and introduce new entities represented in
Figure 4.2.
3. Odors and Their Wording in Identification Tests

In sum, scoring verbal answers to odorants is not simply a technical question,
but involves the elaboration of theoretical knowledge in three domains:
1. an adequate semantic theory of lexical meaning (domain of linguistics), de-

scribing the entities at vertex B (Figure 4.2)
2. a theory of cognitive representations in memory (domain of psychology), repre-
senting entities at vertex C, specific to humans, as humans are the only primates
who can give linguistic answers to olfactory stimulations
3. a theory of the relationship between language and cognition (domains of lin-
guistics, psycholinguistics, and also philosophy)
The analysis here is a first attempt to employ this rationale in close coordina-
tion with work done in linguistics (point 1). It will involve explicit hypotheses
about the structural properties of categories in human memory (point 2), still
largely unknown for olfaction, and explored through other nonverbal paradigms,
such as pair comparisons and free-sorting tasks with odorants (see Rouby and
Sicard, 1997, for a review; Rouby et al., 1997). The psychological approach
differs from the linguistic approach, even though it may process the same data.
Whereas linguistics considers words only as parts of the linguistic system per
se and reasons about their structural properties (formal and/or semantic) inde-
pendently of any psychological functioning, psychology accounts for mental
processes that interact with the linguistic constraints involved in producing and
understanding language. Finally, the relationship between language and cogni-
tion (point 3) will be considered here only within psycholinguistics, by study-
ing the individual processes involved in verbal productions. Empirically, that
leads to a reanalysis of the “kinds of words or descriptions used by subjects
misidentifying odors” (Engen, 1987, p. 500). However, we shall no longer con-
sider that failure to produce a “correct response” is a misidentification of an
odor. Notwithstanding that there is no a priori veridical label available (neither
in language, nor consequently in subjects’ memories), we shall consider all
answers given by subjects as attempts by them to communicate to the experi-
menter “something” about their memories and identifications of the presented
odors.
This analysis has been carried out using the answers of 40 subjects in
a spontaneous identification task involving 16 familiar odorants (Rouby and
Dubois, 1995). The answers to only 3 of the 16 odorants (hereafter, lemon,
orange, and apple) will be presented here as examples of our rationale. We
also have relied on other sources of knowledge and psychological measure-
ments of memory for odors that were collected in rating tasks and in free-sorting
tasks.
Before proceeding, it must be emphasized that this analysis is partial and
is restricted to isolated lexical items, overlooking the context, the discourse,
within which the subjects produced these words. It has been shown else-
where (Mondada and Dubois, 1995; Mondada, 1997) that the discursive context
contributes to the construction of categories and also provides relevant infor-
mation on the personal involvement in cognitive representations in subjects’
memories.
In the cases of complex phrasing, we had to make choices in classifying the
answers.2 Our choices relied on psychological hypotheses about categorization,
not on linguistic motivations.
The resulting list of verbal answers is given in Table 4.1 and includes
the produced French words, English translations, and their frequencies of
occurrence (N ).
The verbal answers are presented along with explicit hypotheses about the re-
lationships between linguistic descriptions and cognitive structures. These latter
refer to conceptualizations of the categorical structures in memory for odors:
Seven major semantic types of answers (T.1–T.7) were identified, clustering 17
finer-grained categories (simply numbered 1–17). Table 4.1 shows the answers
categorized into these seven semantic types. Table 4.2 summarizes and quan-
tifies the occurrences of these different semantic types for the three odorants
considered here.
Type 1: The expected source
This first group of answers includes any answer (simple word, constructed, or
polylexical forms) that has some wording to describe the expected source (any
verbal form that includes the veridical label). This group includes the following
subtypes:
1. the simple name of the expected source (commonly called the veridical label):
lemon, orange, or apple. This canonical scoring was in accordance with the
olfactory literature: The frequency of this type of response ranged from 10%
(apple) to 24% (orange) up to 36% (lemon), with 22% as a mean value. [Such
a result is consistent with (even if lower than) the data of Engen (1987), who
found a mean value of 44% “correct” answers. The range was from 27% for rose
to 75% for bazooka bubble gum in the set of “odorants including the brand
names.” The set of scratch-and-sniff odorants ranged from 0% for musk, (“never
correctly identified,” according to such a strict scoring) to 83% for licorice.]
The robust conclusion is that some odors are regularly better identified than
others. However, it cannot yet be determined which factors most affected the
performances: That may have depended on the properties of the odorant, on the
type of odor, or on the link between the odor and some available name for some
potential source. The only provisional conclusions that can be drawn from tests
of these three odorants concern the level of categorization: Thus, “citrus fruits”
(clustering lemon and orange) would be at the same level of categorization as
“other fruits” (this latter including apple), with the better-identified lemon as a
prototype candidate within the first category (Rosch, 1978).
2. the name of the expected source plus an adjective that refers to a more spe-
cific level of categorization than the veridical label (citron sucré, sweet lemon;
pomme verte, green apple). This type of answer indicates that subjects are able
to discriminate odors below the preceding level, or that they can specify a
Table 4.1. Spontaneous responses to lemon, orange, and apple
Citron (Lemon) Orange (Orange) Pomme (Apple)

French words English words N French words English words N French words English words N
citron lemon 28 orange orange 20 pomme apple 10
citron sucré sweet lemon 1 peau d’orange orange peel 1 pomme verte green apple 3
citron acidulé sour lemon 1 zeste d’o. orange zest 1 shampoing p. a. shampoo 1
c. très doux very sweet l. 1 sirop d’o. orange syrup 1 T.1 14
citronnée lemon-like 2 sirop X d’o. o. brand syrup 1 fruit fruit 1
bonbon c. lemon candy 3 bonbon o. orange candy 4 fruité fruity 1
glace au c. l. ice cream 1 fleur d’oranger o. tree flo wer 1 fruit rouge red fruit 1
tarte au c. lemon pie 1 orang ée orange-like 1 fruit exotique exotic fruit 1
gélatine c. lemon jelly 1 T.1 30 fleur flower 3
liq. vaisselle c. l. detergent 1 agrume citrus 1 bonbon candy 4
citronnelle citronella 1 fruit fruit 3 bon à manger good to eat 1
T.1 41 fruit sucré sweet fruit 1 déodorant deodorant 1
fruitée fruity 1 fleur flower 1 chimique chemical 1
fleur flower 1 bonbon candy 1 T.2 14
nourriture food 1 agent nettoyant cleaning agent 1 orange orange 3
mangeable edible 1 T.2 8 mélange fruits mixed fruits 1
bonbon candy 2 citron lemon 18 fruit passion passion fruit 2
condiment spice 1 citron vert lime 2 fraise strawberry 20
T.2 7 citronnée lemon-like 2 fraise Tagada Tagada strawb. 3
fleur d’oranger o. tree flower 4 mandarine tangerine 2 pêche peach 5
orange orange 4 fruit passion passion fruit 1 abricot apricot 4
framboise raspberry 1 T.3 25 banane banana 1
fraise strawberry 1 citronnelle citronella 1 mûre blackberry 1
T.3 10 tilleul lime tree 1 framboise strawberry 1
bonbon sucré sweet candy 1 bonbon citron lemon drop 2 T.3 41
sucrée sweet 2 sucrée sweet 1 chewing gum f. fruit ch. gum. 1
caramel caramel 1 chewing gum c lemon c. g. 1 chg. fraise strawberry c. g. 2
chamallow chamallow 1 sucette lollipop 1 chg. menthe mint c. g. 1
gâteau kiwi kiwi cake 1 Pétrole Hahn Pétrole Hahn 1 yaourt aux f fruit yogurt 1
biscuit espagn. spanish cake 1 pansement bandage 1 bonbon Mentos Mentos candy 1
dans gâteau “in cake” 1 limonene limonene 1 bonbon fruité fruit candy 1
T.4 8 T.4 10 bonbon acidulé sour candy 1
agréable pleasant 2 fraı̂che fresh 1 b. chimique chemical candy 1
sent bon smells good 2 agréable pleasant 1 b. arome apricot flavor c. 1
abricot
T.5. 4 bon good 1 bonbon fraise strawberry c. 1
indéterminée undertermined 1 T.5 3 sur les bonbons “on candies” 1
connue known 1 indéterminé undertermined 1 sucrée sweet 1
inconnue unknown 1 familière familiar 1 acide sour 1
T.6 3 oubliée forgotten 1 vanille vanilla 1
parfum perfume 1 T.6 3 grenadine grenadine 1
odeur odor 4 senteur scent 4 rouge à lèvre lipstick 1
T.7 5 odeur odor 1 Tahiti douche T. shower gel 1
T.7 5 Tahiti douche T. s. fruit gel 1
fr.
shampoing shampoo 1
sh. parfumé perfumed sh. 1
sh. pêche peach sh. 1
T.4 22
agréable pleasant 1
T.5 1
connue known 1
T.6 1
odeur odor 3
parfum perfume 1
senteur scent 1
T.7 5
property of the “smell of X .” It is consistent with the hypothesis that odor

categories could be structured along typicality like other categories of objects
(Rosch, 1978; Dubois, 1991).
3. an adjectival form constructed on the source noun (citronné, lemony; orangé,
orange-like): Instead of giving a noun that would refer to an object, subjects
might suggest that odors are some property or quality of the object. Such word-
ing can be highly influenced by the linguistic resources of each language, and
that will require further investigation.3
4. the name of another source or artifact (e.g., candies) syntactically constructed
with the name of the expected source (as a compound noun: bonbon citron,
lemon drops; sirop d’orange, orange syrup; shampooing pomme, apple sham-
poo): This type of answer mainly occurs with food or drugs and cosmetics now
flavored with a wide variety of aromas. These answers can be considered as
relevant to a “genuine” source, inasmuch as they belong to subjects’ experi-
ences, following the same rationale that avocados and tomatoes are exemplars
of the category of vegetables (whereas they are “true” fruits), or that a whale
is a fish, as currently analyzed within the “ecological” approach for “natural”
categories (Neisser, 1987; Dubois and Resche-Rigon, 1995). This type occurs
for the three odors discussed here.
To sum up, the answers in this group reflect primarily the different levels of cat-
egorization that structure odors in subjects’ memories (vertex C in Figure 4.2),
worded in terms of the basic or derived names for known sources of the odors
(vertex B). It is still an open question whether that reflects a genuine basic level
for odors or a basic level for object-sources, an issue that cannot be settled be-
cause the same word is used for the odor and for the object. The cumulative
values for these four forms of “correct answers” (Type 1 in Table 4.2), referring
to the possible experienced sources of odors, range from 14% for apple to 36%
for orange and up to 53% for lemon, with an average of 33% for the three odor-
ants. These findings support data collected from other psychological indicators:
Memory for the odor of lemon seems to be most accurate and can be considered
as a candidate prototype within the category of “odors of citrus fruits,” the odor
of apple being also, but less frequently, categorized as a fruit odor. Therefore the
findings are consistent with the hypothesis that the different odors of fruits are
not structured at just a single level, isomorphic to the categorical organization
of the corresponding objects (sources), and therefore the categorization of odors
cannot be adequately represented by a taxonomic hierarchy like those used for
“natural” objects (cf. Chastrette, Chapter 7, this volume).
Type 2: Generic terms for sources

The second group of answers includes the generic terms for the sources specified
in the preceding group. Here we count as “correct answers” the generic terms
that are acceptable for the preceding specific Type-1 sources in Table 4.2:
Table 4.2. Semantic typology of the denominations of three odors in an identification task
Stimulus
lemon orange apple Total
Types of answers N % N % N % N % cumulated%
1. expected basic-level source (e.g., 28 36 20 24 10 10 58 22 22

veridical label)
2. expected source + adj. (specified) 3 0 3 6
3. adjectival form /expected source 2 1 0 3
4. other source + expected source 8 9 1 18
T.1 = expected source 41 52.6 30 35.7 14 14.3 85 32.7 32.7
5. fruit (or constructed on “fruit”) 1 5 4 10
6. fleur (flower) 1 1 3 5
7. aliment (food, including candy) 5 1 5 11
8. drugs and cleaning 0 1 2 3
T.2 = generic sources 7 9 8 9.5 14. 14.3 29 11.2 43.9
9. citron (lemon + derivation) 0 22 0 22
10. orange + der. derivation 4 0 3 7
11. pomme (apple) 0 0 0 0
12. other fruits 6 3 38 47
T.3 = co-hyponyms of fruits 10 12.8 25 29.8 41 41.8 76 29.2 73.1
13. co-hyponyms of foods 8 7 16 31
14. co-hyponyms of drugs & chemicals 0 3 6 9
T.4 = other co-hyponyms 8 10.3 10 11.9 22 22.4 40 15.4 88.5
15. -T.5 = hedonic judgment 4 5.1 3 3.6 1 1 8 3 91.5
16. T.6 = knowledge/familiarity 3 3.8 3 3.6 1 1 7 2.7 94.2
17. T.7 = generic olfactory term 5 6.4 5 5.9 5 5.2 15 5.8 100
Total 78 100 84 100 98 100 260 100 100

5. fruit, fruit; fruité, fruity [considered as a “related odor” (fruity) in Engen’s

“liberal scoring”], more frequent for orange and apple than for lemon
6. “flower,” mainly given for apple
7. generic names for foods (or any different wordings for different types of food,
e.g., bonbon)
8. drugs, cosmetics, and cleaning products, which are more and more frequently
being perfumed or flavored with “natural scents,” also given as Type-1 responses
using more specific wording.
These words also provide some relevant information about the categorical or-
ganization of odors, in the present case their superordinate level of knowledge
organization: orange is frequently considered as fruit, lemon is considered as
food (mainly candy), and apple is identified as fruit, flower, food, or cleaning
product. Such diversity of attributions of membership in multiple superordinate
categories is also encountered in the naming of “natural objects.” As previously
mentioned, the tendency to think that there is just one veridical category for
each exemplar relies on a logical conception of categories and concepts that has
been discussed in recent contributions to ecological cognition, the latter being
viewed as rather experiential than veridical (Lakoff, 1987; Varela, Thompson,
and Rosch, 1991). Within this framework, the diversity of attributions of mem-
bership in superordinate categories simply reflects the diversity of objects that
can now be flavored because of developments in food technology. Therefore,
we consider the scoring in terms of veridical labels for odors to reflect a belief
in an implicit theory of knowledge rather than an empirical result, because it
fails to account for a large proportion of the subjects’ answers. As far as the
organization of odor categories is concerned, it cannot be determined whether
such responses reflected the organization of the categories of odors per se or
the categories of objects whose representations would necessarily be “activated”
through the mediation of the source names (“lexical access” from vertex C to
vertex B in Figure 4.1), as was required by the task. The cumulative scorings
(Type 2) for these answers added to the previous ones (Type 1) now range from
29% (apple) to 45% (orange) up to 62% (lemon), with an average score of
44%.
Type 3: Co-hyponyms of the acceptable source names

Psychological hypotheses about categorization allow us to account for quite an
important set of answers that linguistically can be considered as co-hyponyms,
that is, as nouns referring to objects that belong to the same superordinate cate-
gories as the expected (acceptable) sources – for example, any specific name for a
fruit, except the expected one (lines 9–12, summarized under Type 3 in Table 4.2).
Such answers can be interpreted as reflecting some categorical knowledge that
subjects want to communicate about the odor. In the current case, if we take
into account that bit of knowledge, we find that orange was frequently given
as lemon (but not the reverse) and that apple was frequently named by various
fruit names (frequently as “strawberry”). Once more, we cannot determine solely
from the current data whether that result depended on the quality of the odorants
(A at vertex A) and their representativeness of the “real odor of X ” (A at ver-
tex A), on the accuracy of memory for the odors (vertex C), or on the structural
properties of the subject’s mental lexicon for fruits (vertex B). However, these
findings correlate with other nonverbal measures (such as similarity distances in
free-categorization tasks) and support the interpretation that the better score for
lemon reflects the fact that it is a more typical representation of the category
“citrus fruits” than is orange, whereas apple is an atypical exemplar of the
category “fruit” and was attributed to a diversity of categories.
Taking those answers into account in scoring leads to cumulative scores (Type
1 + Type 2 + Type 3) of 74%, 75%, and 70% for lemon, orange, and apple,
respectively, with an average score of 73%. That is, whereas there were qualitative
differences related to their categorical structuring in memory, the three odors
prompted quite similar quantitative scores as “extended acceptable answers.”
Type 4: Other co-hyponyms

The same rationale can be applied to the other categories listed in Table 4.2:
13. co-hyponyms for foods
14. co-hyponyms for chemicals, which could actually be flavored or odorized “real-
world objects” experienced by the subjects as smelling like the stimuli: As such,
these answers can also be taken into consideration in scoring. Such scoring
mainly concerns types of food and candies for lemon, orange, and apple, but
also soaps and cosmetics for orange and apple.
Scoring that information, the acceptable answers were 85%, 87%, and 93%
for lemon, orange, and apple, respectively (average: 88%). It will be noted
that apple got a higher score than lemon, a reversal of the order seen when
calculations were for the veridical label. That might be due to the fact that apple
is used to flavor a larger variety of objects.
Types 5–7
Finally, the last three types refer to the following:
15. hedonic judgments, which can be considered as relevant factors in knowledge
of odors, often being considered the main feature in olfactory classification.
The scoring of answers such as “agréable, pleasant” increased the acceptable
answers by 1% (apple) up to 5% (lemon).
16. elusive sensations: When subjects were able to state that they felt “something”
that was “known”, “unknown,” or “familiar,” being in the state of “tip of the
nose” (Engen, 1987), or “in lack of word,” as aphasic patients are, we counted
such responses as acceptable and gained 1% up to 4% in acceptable answers
(summed in T.6 of Table 4.1 and Table 4.2).
17. unidentifiable sensations: When subjects reported that they smelled “some-
thing,” instead of nothing, either using plain generic olfactory terms (odeur,
odor) or generic terms referring to the subclass of pleasant olfactory sensations
(senteur, smell; parfum, perfume), we gained answers to reach, in each case,
the 100% of answers that represent the bits of knowledge we have taken into
account.
In short, when verbal scoring incorporates hypotheses concerning both the possi-
ble lexicalizations for odors and their structural properties as cognitive categories,
we can count all the answers given by the subjects as acceptable. That is, even in
the absence of attested and negotiated names for odors, subjects managed to com-
municate their (even partial) knowledge about their cognitive representations of
odors.
4. Conclusion
The absence of specific names for odors forced us to confront fundamental
issues regarding the relationship between language and cognition and their con-
sequences for data scoring. Our analysis led us to question the validity of the
triangle in Figure 4.1 and to subdivide each vertex to a degree that has the dis-
advantage of preventing any simple geometric representation (Figure 4.2), but
also the advantage of helping to cope with the full range of verbal outputs ob-
tained in human olfactory research. Whereas numerous studies have postulated
a straightforward relationship between objects and words (mainly nouns), in our
study we faced the problem of how to consider that relationship in the absence
of “basic terms” for the categories of smells we were using. Our analysis is
therefore an attempt to base the scoring of the verbal answers on an explicit
theory of the psychological processes involved in naming. In other words, the
empirical issue of scoring a “correct” verbal response depends on progress in
understanding “whether these (as yet) unnamed categories share the same status
as labeled categories” (Waxman, 1999, p. 274).
The inherently weak link between odors and names should not divert us from
considering the contributions of the social sciences. Anthropological studies
(Howes, Chapter 5, this volume) and numerous linguistic and psycholinguistic
studies (Gentner, 1982; Markman, 1989; Taylor, 1995; Wierzbicka, 1992; Imai
and Gentner, 1993; Foley, 1997; Engen and Engen, 1997; Waxman, 1999) have
begun to indicate that the diversity of linguistic forms may constrain our on-
tological view of entities and lead to different distances between the “subject”
and the “objects” of the world, such diversity ranging from complex phrasing
expressing the effects of the world on the subject to simple “basic” names, which
suggests that things are “crying out to be named” (Berlin, 1973) and that words,
as labels, can be mapped onto things. Further experimental investigations will
have to account for the fact that our culture has diversely lexicalized the different
senses, and other cultures have also diversely lexicalized the different senses in
different ways than our culture, increasing diversity (Classen, 1993). If we al-
ways perceive “something” through the diversity of senses, language diversely
objectifies and “stabilizes” our cognitive representations of the world into a large
variety of linguistic forms. Concerning olfaction, the diversity of “entities” we
conceptualized at each vertex of the triangle leads us to reconsider the “mapping
hypothesis” that allows a simple scoring according to a “veridical” criterion.
Scoring has to take into account the different entities presented in Figure 4.2.
Ultimately there arises the question What is an odor? Is an odor (American) an
odour (British), as well as une odeur (French)? The issue is not trivial, because
dictionaries for these languages reveal interesting differences:
1. from the American Heritage Dictionary: “odor: the property of a thing per-
ceived by the sense of smell.”
2. from the Concise English Dictionary: “odour: any scent or smell, whether
pleasant or offensive.” Also: “scent: that which issuing from a body affects the
olfactory nerves of an animal.”
3. From the Robert (French common) Dictionary: “odeur: Emanation volatile,
caractéristique de certains corps et susceptible de provoquer chez l’Homme
ou chez un animal des sensations dues à l’excitation d’organes spécialisés”
(volatile emanation specific of some bodies and able to elicit in humans or in
animals some feelings provoked by the stimulation of specialized organs).
Odors or odorants?
These definitions indeed reflect diverse conceptualizations of odors. If an odor
is always defined as “something” (David, 2000), as stated in the first part of such
definitions, the expansions diverge from an objectivist description, ranging from
(in 1) where the word “odor” refers to some thing in the world (therefore almost
synonymous with “odorant”) to a more physiological response (as stated in 2) or
psychological object (as in 3), this latter being defined as a sensation related to
something from the world, an emergent result of different processes of eliciting,
provoking. Besides revealing different philosophical (ontological) assumptions,
this issue entails consequences for the design of experimental research and, as
discussed here, for scoring verbal answers. In contrast to experiments in vision
and audition, where the stimuli and the correlated psychological objects have the
same “name” (color, sound), olfactory research has to account for the fact that
the description of the stimulus is concerned with the odorant (the substance), not
with the odor it emits. Awareness that such questions are still open in olfactory
research (Dubois and Rouby, 1997; Hudson, 1999) should spare us general and
unproductive debates about past cognitive research, contrasting, for example,
universalist (biological) versus relativist (cultural) conceptions of cognition. The
challenge is rather to avoid opposing natural and therefore “veridical” sciences
to social sciences, and instead develop interdisciplinary research that specifies
how language articulates to categorization at every level of description within
the cognitive sciences.
Acknowledgments
This study was part of a research project funded by the cognitive science program
of the French Ministry of Education and by the CNRS (“Cognisciences”). We
are also indebted to recent linguistic work with S. David.
Notes
1. Such an analysis is required to understand how the different lexical forms and cognitive
representations can constrain one another. A first review of this general research
program is available (Dubois, 2000).
2. We had, for example, to decide whether to classify a polylexical form composed of
two source names, such as bonbon à l’orange, orange candy, as a “correct answer”
or as an “associated object” (Engen, 1987), or, within our scheme, to classify it with
the “expected source name” or with some “other possible source name.”
3. It is worth noting, once more, that all odors are not “equal” in their relationships
to word constructions and lexicalizations as in the current example (N + suffix é):
Thus citronné and orangé, as well as fruité, are possible in French, but ∗ pommé is not
acceptable, and there is no strict correspondence in English: One can have “fruity” or
“lemony,” but not “∗ orangy”. The consequences of such differences in lexicalization
for cognitive structures remain to be explored.
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5
Nose-wise: Olfactory Metaphors in Mind
David Howes
In Visual Thinking, the psychologist Rudolf Arnheim argued that there is no

division between seeing and thinking: “Visual perception is visual thinking”
(Arnheim, 1969, p. 14). As for smell and taste, “one can indulge in smells and
tastes, but one can hardly think in them” (Arnheim, 1969, p. 18). That dismissive
judgment as regards the cognitive potential of olfaction by such a prominent
psychologist does not bode well for a book that is dedicated to the theme of
olfaction and cognition.
Denigration of olfaction is a common theme among Western thinkers
(cf. Le Guérer, Chapter 1, this volume). The eighteenth-century philosopher
Condillac, for example, remarked that “of all the senses smell is the one that
seems to contribute the least to the operations of the human mind” (Condillac,
1930, p. xxxi). His contemporary, Immanuel Kant, similarly wrote: “To which
organic sense do we owe the least and which seems to be the most dispensible?
The sense of smell. It does not pay us to cultivate it or to refine it in order to
gain enjoyment; this sense can pick up more objects of aversion than of pleasure
(especially in crowded places) and, besides, the pleasure coming from the sense
of smell cannot be other than fleeting and transitory” (Kant, 1978, p. 46).
The Kantian line of thought continues to inform the way in which aesthetic
experience is conceptualized in the West. Aesthetic experience is defined as
the disinterested contemplation of some object in which beauty inheres. Such
experience is to be had in the context of the art museum, where art objects
are placed on display, and visitors are required to keep their distance. This
definition encodes an essentially visual relation to the art object, as Jim Drobnick
(1998) has observed, which is enforced by the basic sensual sterility of the
art gallery or “white cube.” The Kantian line of thought is also manifest in
the cognitive sciences. For example, in the literature of cognitive anthropology
there are numerous studies having to do with the categorization of sense data.
However, the vast majority of those studies pertain to the classification of visual
67
68 David Howes
stimuli – most notably color, following the lead of Berlin and Kay (1969) – and
only a few concern the categorization of olfactory stimuli (Classen, Howes, and
Synnott, 1994). Berlin and Kay drew a series of grand conclusions about the
evolution of language and the universals of human cognition on the basis of their
comparative study of color lexicons. Yet they never bothered to inquire whether
or not the same conclusions would follow from a comparative study of olfactory
or gustatory terminologies. That major oversight has gone largely unchallenged
in the literature, as if there were indeed nothing to be learned from study of the
language of gustation or olfaction, as if Condillac were right and smell and taste
do have little to contribute to the operations of the human mind.
This chapter poses a series of questions: Why the devaluation of olfaction by
cognitive psychologists such as Arnheim and philosophers such as Condillac
and Kant? What insights into the nature of cognition might be gleaned from
taking the so-called lower senses of olfaction, gustation, and touch, in place
of vision, as metaphors for cognition? What can anthropology teach us about
cognition in the context of societies that are more nose-minded than our own?
And, finally, what can a comparative study of olfactory terminologies tell us
that is different from what we have learned in cross-cultural study of color
terminologies?
1. The Rise of Visualism

In Western culture, sight is commonly held to be the most important of the senses
and the sense most closely allied with reason. This bias in favor of sight was
already present in ancient philosophy (cf. Le Guérer, Chapter 1, this volume).
Aristotle, for example, considered sight to be the most informative of the senses.
Although vision had been ranked first among the senses since antiquity, it had
remained “first among equals” and did not distance itself significantly from the
other senses in terms of cultural importance until the period of the Enlightenment.
Prior to the Enlightenment, the exalted position enjoyed by sight was tempered by
the conviction that whereas the senses existed in a hierarchy, all were “perfectly
formed in their own right,” as evidenced by the fact that “colours, sounds, smells,
tastes and touch can each be received by one and only one organ” (Sears, 1993,
pp. 33–5). Sight, therefore, had its limits. Full knowledge could be acquired only
if all the senses worked together.
The groundwork for the separation of sight from the other senses was laid in
the eighteenth century when, as Constance Classen informs us, “vision became
associated with the burgeoning field of science. The enquiring and penetrating
gaze of the scientist became the metaphor for the acquisition of knowledge at
this time. [Then, in the nineteenth century:] Evolutionary theories propounded by
Nose-wise: Olfactory Metaphors in Mind 69
prominent figures such as Charles Darwin [and, later, Sigmund Freud] supported
the elevation of sight by decreeing vision to be the sense of civilization. The
‘lower,’ ‘animal’ senses of smell, touch and taste, by contrast supposedly lost
importance as ‘man’ climbed up the evolutionary ladder. In the late nineteenth
and twentieth centuries, the role of sight in Western society was further enlarged
by the development of such highly influential visual technologies as photography
and cinema” (Classen, 1997, p. 402).
The cumulative effect of the developments described by Classen was that
vision came to usurp many of the roles previously played by the other senses as
means of cognizing reality. This process is apparent in the domain of medical
science, for example. Whereas in premodern medicine, touch was used to ascer-
tain the patient’s pulse and temperature, and taste and smell were used to test
the patient’s urine and other bodily emanations, in modern medicine there are
instruments and laboratory tests to perform these functions and generate graphic
results, which are destined for the physician’s eyes alone (Howes, 1995).
The Enlightenment thus marked the beginning of a fantastic mutation in the
Western hierarchy of sensing. The balance or ratio of the senses was tipped in
favor of vision, and the champions of sight have never looked back. The lower
senses (especially the sense of smell) were pushed beyond the pale of culture
and cognition and continue to languish in relative obscurity to this day. This pro-
cess was aided by the invention of numerous technologies for the extension of
sight (and hearing), from telescopes to television, which have no olfactory chan-
nel, thus effectively erasing olfactory stimuli from the modern consciousness.
However, the traces of a different consciousness remain embedded in the very
language we use to talk about intelligence, as will be shown in the next section.
2. Worlds of Sense
In Worlds of Sense, Constance Classen (1993) presents an in-depth study of the
sensory etymology of many current and some moribund English words for cog-
nitive operations. Her research shows that the senses that today are commonly
considered “lower” or “animalistic” senses were once associated with the intel-
lect. For example, “nose-wise,” a word now obsolete, could mean either “clever”
or “keen-scented.” In Latin, both the sense of taste and the sense of smell were
linked with wisdom, and that association is continued in some Latin words that
are retained in English. The English words “sagacious” and “sage,” both referring
to intelligence, are based on Latin words meaning to have a good sense of smell.
Similarly, the word “sapient,” meaning wise, is based on the Latin word for taste;
hence the term Homo sapiens means “tasting man” as well as “knowing man.”
In addition to the olfactory and gustatory links to cognition discussed earlier,
70 David Howes
Classen’s archeology of the sensory subconscious of the English language

reveals that many English terms for “thought” are, in fact, tactile or kines-
thetic in origin. These include “apprehend,” “brood,” “cogitate,” “comprehend,”
“conceive,” “grasp,” “mull,” “perceive,” “ponder,” “ruminate,” and “understand.”
The predominance of tactile imagery in words dealing with intellectual functions
indicates that thought is, or was, experienced primarily in terms of touch. Think-
ing was therefore less like looking than like weighing or grinding, and knowing
was less like seeing than like holding. What difference does this make? “The use
of tactile and kinaesthetic terms for thought expresses a more active involvement
with the subject matter than visual terms do. To understand is to stand under or
among, to be part of the picture, whereas to see is to view the picture from
without. In light of this it seems possible that an emphasis on visual metaphors
for intellectual functions, such as one finds in scholarly writing, for example,
has to do in part with a desire to have or convey a certain detachment from the
subject under consideration: to be ‘objective’ [see Jonas, 1970]. At the same
time, visual metaphors for thought convey an accessibility of meaning, which
tactile metaphors do not. There is a great deal more tension involved in grasping
or weighing a subject than in looking it over” (Classen, 1993, p. 58).
Classen’s examination of terms for intelligence further revealed that touch-
based words such as “acumen,” “acute,” “keen,” “sharp,” “smart,” “clever,” and
“penetrating” consistently outnumbered sight-based words such as “wise,”
“bright,” “brilliant,” and “lucid.” It appears that it was only during the Enlight-
enment that words with strongly visual associations began to be used to refer to
intelligence, perhaps as a consequence of the general rise of visualism at that
time. Prior to that period, intelligence “was conceived of not so much as sight
or light, as of sharpness. A knowledgeable person does not simply illuminate a
subject, but cuts into it. Likewise, difficult subject matter would be characterized
as ‘hard’ or ‘complicated’ (twisted together), resisting being cut or penetrated.
Intelligence itself, along with intellect, is a tactile-visual metaphor, as its basic
meaning is ‘to pick between’” (Classen, 1993, p. 58).
With Classen’s account of the sensory underpinnings of thought and intelli-
gence in mind, it becomes apparent that Rudolf Arnheim’s theorization of an
intrinsic link between vision and cognition in Visual Thinking represented but a
tiny fraction of the actual historical linkages between sensation and cognition.
Moreover, his denigration of the cognitive potential of olfaction and gustation
perpetrated a serious elision of the role these senses have played historically in
the construction of intelligence. It is understandable, given the hypervisualism
of contemporary Western culture, that Arnheim would choose to privilege the
connection between vision and cognition and overlook the contributions of the
other senses, but that does not make his position any more sound.
Of course, not every treatment of olfaction in the annals of Western thought

is marred by the visualist bias manifest in the work of psychologists such as
Arnheim and philosophers such as Kant. Think of the perfumer-philosopher
Edmond Roudnitska’s brilliant refutation of Kant and rehabilitation of the aes-
thetic power of smell in L’esthétique en question: Introduction à une esthétique
de l’odorat (Roudnitska, 1977). Or, in a more cognitivist vein, consider the fol-
lowing remarks of the naturalist Lewis Thomas: “The act of smelling something,
anything, is remarkably like the act of thinking itself. Immediately, at the very
moment of perception, you can feel the mind going to work, sending the odor
around from place to place, setting off complex repertoires throughout the brain,
polling one center after another for signs of recognition, old memories, connec-
tions. This is as it should be, I suppose, since the cells that do the smelling are
themselves proper brain cells” (Thomas, 1983, p. 42).
Earlier in the same essay, Thomas proclaims that “we might fairly gauge the
future of biological science, centuries ahead, by estimating the time it will take
to reach a complete, comprehensive understanding of odor” (Thomas, 1983,
p. 41). These are bracing words. However, it seems doubtful that biological
science will be able to accomplish this task on its own, unaided by the sorts of
examples that historical or anthropological research on the senses can yield by
way of models, for biological science remains preoccupied with issues of odor
detection and identification, if Thomas’s essay is any indication. Those issues
are important, but for us to arrive at a comprehensive understanding of odor
it will be necessary to explore how the medium of smell can, in some cases,
provide the conceptual framework for construction of an understanding of the
entire universe. Ongee cosmology offers a paradigm case of such “olfactory
thinking.”
3. A Nose-minded Society
Among the Ongee, a hunting and gathering people of Little Andaman Island
in the Bay of Bengal, smell is the primary sensory medium through which the
categories of time, space, and the person are conceptualized. Odor, according
to the Ongee, is the vital force that animates all living, organic beings. A new-
born is said to possess little scent. On growing up, people increase their ol-
factory strength. The odor that a person scatters about during the day is said
to be gathered up during sleep by an inner spirit and returned to the body,
making continued life possible. Death occurs when one loses one’s odor –
through illness or an accident or because it is absorbed by an odor-hunting
spirit. Once dead, a person becomes an odorless and inorganic spirit, devoted to
seeking out the odors of the living in order to be reborn. Thus the life cycle is
72 David Howes
conceptualized in terms of an olfactory progression. Indeed, the Ongee word for

growth, genekula, means “a process of smell” (Pandya, 1987, pp. xii, 19, 108,
111–12, 312).
Life for the Ongee is a constant game of olfactory hide-and-seek. They seek out
animals in order to kill them by releasing their odors, and at the same time they
try to hide their own odors, both from the animals they hunt and from the spirits
who hunt them. “To hunt” in the Ongee language is expressed by gitekwabe,
meaning “to release smell causing a flow of death.” The word for hunter, in turn,
is gayekwabe, “one who has his smell tied tightly” (Pandya, 1987, p. 102).
The Ongee employ different techniques to keep their smell “tied tightly.”
Living in community is believed to unite the odors of individuals and lessen
their chances of being smelled out by hungry spirits. When moving as a group
from place to place, for example, the Ongee are careful to step in the tracks
of the person in front, as this is thought to confuse personal odors and make it
difficult for a spirit to track down an individual. The Ongee also screen their odor
through the use of smoke. When traveling in single file, the person at the head
of the group carries burning wood so that the trail of smoke will cover the odors
of all those walking behind. For the same reason, the Ongee keep fires burning
at all times in their villages and have smoke-filled, unventilated homes. Indeed,
for the Ongee, a true fire is characterized not by the heat or light it produces, but
by its smoke. Even the sun has an olfactory identity, as it is believed to produce
an invisible smoke (Pandya, 1987).
The Ongee also limit their smell emission by painting themselves with clay.
Clay paints are believed to help bind smells to the body, while the different
designs used in painting alter the ways in which the body releases smell. An
Ongee whose body has been painted will declare: “The clay paint has been
good! I feel that my smell is going slowly and in a zig-zag manner like the snake
on the ground!” (Pandya, 1987, p. 137). The Ongee also dab clay paint on their
skin after eating meat in order to prevent the smell of the consumed meat from
warning living animals that one of their kind has been killed and eaten (Pandya,
1987).
Space is conceived of by the Ongee not as a static area within which things
happen but as a dynamic environmental flow. The olfactory space of an Ongee
village fluctuates: It can be more expansive or less, depending on the presence
of strong-smelling substances, such as pig’s meat, the strength of the wind, and
other factors. Given that smell is believed to guide both harmful and helpful
spirits to human sites, it is the olfactory ambience of the village that is of the
greatest concern to the Ongee, not its extension in physical space. The Ongee
“smellscape,” then, is not a fixed structure, but rather a highly fluid pattern that
can shift and change according to differing atmospheric and seasonal conditions.
This fluidity finds expression in the use of the same word, kwayaye, by the
Ongee for both the emission of odors and the ebb and flow of tides (Pandya,
1993).
A distinct succession of scents wafts through the jungle of the Andaman
Islands as one after another of the indigenous trees and climbing plants come
into flower throughout the year. The Ongee have constructed their calendar on
the basis of this cycle, naming the different periods of their year after the fragrant
flowers that are in bloom at different times. The Ongee year is a cycle of odors,
their calendar a “calendar of scents” (Radcliffe-Brown, 1964).
The Ongee seasonal cycle is further based on the winds that blow in from
different directions throughout the year, dispersing odors and bringing scent-
hungry spirits. The Ongee conduct their own migrations from the coast to the
forest according to this cycle: During the seasons when the spirits are believed
to be hunting at sea, the Ongee hunt in the forest, and during the seasons when
the spirits are believed to be hunting in the forest, the Ongee hunt along the
coast. The information the shaman brings from the spirit world helps the Ongee
plan their movements so as to continue to succeed in their game of olfactory
hide-and-seek with the spirits (Pandya, 1987).
Both time and space therefore acquire meaning for the Ongee in terms of the
movements of winds and spirits, humans and animals, and their odors. When
asked to draw a map, an Ongee will depict a line of movement from one place
to another, rather than the locations of the places themselves. The ethnographer
Vishvajit Pandya found that during his stay among the Ongee his official map
of the island was of little help in making sense of the routes his Ongee guides
took him along. When he complained to an Ongee friend that his experience
of the island did not coincide with the map of its geographical layout, the man
replied: “Why do you hope to see the same space while moving? One only hopes
to reach the place in the end. All the places in space are constantly changing.
The creek is never the same; it grows larger and smaller because the mangrove
forest keeps growing and changing the creek. The rise and fall of the tidewater
changes the coast and the creeks. . . . You cannot remember a place by what it
looks like. Your map tells lies. Places change. Does your map say that? Does
your map say when the stream is dry and gone or when it comes and overflows?
We remember how to come and go back, not the places which are on the way of
going and coming” (Pandya, 1991, pp. 792–3).
Here a static visual layout of space, such as is contained in a map, is op-
posed to a lived experience of movement through space, and of the movement
of space – swelling streams, shifting coastlines, expanding forests. Space is thus
as imprecise and changing as the odors that animate the world for the Ongee.
Time, in turn, is a cycle of olfactory production, loss and gain. It is impossible
74 David Howes
to adequately represent such an olfactory cosmology by means of a map or a

calendar: It can only be scented.
The Ongee may appear to constitute an exceptional or unusual case in terms
of the extent to which they use smell to order their world. However, from the
standpoint of the “anthropology of the senses” (Howes, 1991), the olfactory
cosmology of the Ongee is no more unusual than the thermal cosmology of
the Tzotzil of Mexico (Classen, 1993) or the gustatory cosmos of Hindu India
(Pinard, 1991) or the visual universe of the modern West. Different cultures attach
different meanings and uses to the different senses, and this affects the way in
which they imagine or represent the world. Each culture must be approached on
its own sensory terms if its perceptual world is to be apprehended and described
accurately by the anthropologist. We are fortunate that Vishvajit Pandya, the
principal ethnographer of the Ongee, had the presence of mind to follow his
nose in studying the Ongee life world.
Other students of cross-cultural psychology interested in issues of culture and
perception have not been so sensitive to the possible implications of variations
in the cultural construction of the sensorium. They often have opted instead to
repeat a little experiment involving Munsell color chips that was pioneered by
Brent Berlin and Paul Kay in the 1960s, not hesitating to draw grand conclusions
about “universals” of human cognition on the basis of the responses they received
(Brown, 1991). In the next section, a review and critique of the basic-color-terms
paradigm is presented, followed by a discussion of how to go about studying
olfactory classifications in their cultural contexts.
4. Sensory Vocabularies
In Basic Color Terms, Brent Berlin and Paul Kay make two claims, one of which
is empirical, and the other evolutionary. The empirical claim holds that there
exist certain universal “focal colors” that can be identified by test subjects when
presented to them in the form of Munsell color chips, independently of how
few or how many color terms their mother tongues possess. The evolutionary
claim holds that there is a progressive order to the sequence in which basic
color terms enter languages and that it is possible (in view of that order) to
plot the various languages of the world on a single evolutionary scale. In Berlin
and Kay’s own words, “the overall temporal order [to the encoding of percep-
tual categories into basic color terms] is properly considered an evolutionary
one; color lexicons with few terms tend to occur in association with relatively
simple cultures and simple technologies, while color lexicons with many terms
tend to occur in association with complex technologies” (Berlin and Kay, 1969,
p. 101).
In recent years, researchers interested in the study of nonvisual sensory vocab-

ularies have begun to raise serious questions about the universality and applica-
bility of Berlin and Kay’s conclusions. For example, as regards Berlin and Kay’s
empirical claim, Dubois and Rouby, in numerous publications (e.g., Dubois,
1997; Dubois and Rouby, 1997; Dubois, Rouby, and Sicard, 1997), have pointed
to some of the experimental difficulties involved in simply extending the basic-
color-terms paradigm to the study of odor terms. They note that there is no
determinate spectrum of smells in the way that there is for colors; moreover,
odors have no names in most Indo-European languages. Joel Kuipers (1991) ex-
pressed similar reservations about the applicability of Berlin and Kay’s methods
to the study of taste in his research on gustation among the Weyéwa of Sumba.
Dubois and Rouby, as well as Kuipers, have nevertheless gone on to study
odor and taste categorization. What is most interesting about the sorts of con-
siderations they advance in discussing their research findings is the importance
they attach to taking contexts – the diversity of human activities and practices –
into account because of the orienting effect contexts have on categorization.
This emphasis on customary activities and practices seriously contradicts the
abstractness of Berlin and Kay’s research design and results.
As regards Berlin and Kay’s evolutionary claim, even the briefest comparative
study of smell and taste lexicons reveals that there is no one-to-one correspon-
dence between the complexity of a given culture’s technology and the number
of terms in its taste or smell vocabulary. For example, the English language con-
tains four taste terms, and the Japanese language has five (Doty, 1986), but in the
language of the Weyéwa of Sumba there are seven taste terms (Kuipers, 1991),
even though Weyéwa culture and technology are ostensibly much “simpler” than
the culture and technology of the English- or Japanese-speaking world. The lan-
guage of the Sereer Ndut of Senegal contains only three taste terms; however, the
Sereer Ndut recognize five odor categories (Dupire, 1987). That is considerably
more than English (which contains two odor terms at best), but not as compre-
hensive as the language of the Bororo of Brazil, which counts eight odor terms
(Crocker, 1985), or the language of the Kapsiki of Cameroon, which boasts
14 odor categories (Classen et al., 1994)!
This brief survey shows that technological complexity is not a significant pre-
dictor of the encoding of smell or taste categories into language, however strongly
it may be associated with the encoding of so-called basic color terms. Berlin and
Kay were remiss not to repeat their study of color perception and categorization
for each of the other fields of sense before advancing their grand evolutionary
scheme. The apparent superiority of English-speaking cultures in their scheme
turns out to be an illusion based on the arbitrary selection of color terms and
technological sophistication as “universal” criteria for the ordering of cultures.
76 David Howes
What would a research design for the study of odor categorization that would
be sensitive to cultural context entail? Let me draw on my own experience in
studying the sensory order of the Kwoma of northwestern Papua New Guinea
by way of example. The Kwoma inhabit the Washkuk Hills, which are situated
about halfway up the Sepik River. They subsist on a diet of sago and yams, with
the cultivation of the latter being the focus of their annual ritual cycle.
During my stay in the Washkuk Hills, each time I visited a new Kwoma village
I would bring out my kit of odor samples. This kit contained over 30 plastic
cards, each one impregnated with a different scent and corresponding color: rose
is red, coconut is white, cinnamon is brown. The odor samples did not constitute
an exhaustive set, but rather a haphazard one, for they were supplied courtesy
of a major international flavor and fragrance manufacturer and consisted of the
sorts of scents found in typical North American bath, cleaning, cosmetic, and
confectionary products.
I used the odor samples as conversation-starters, rather than conversation-
stoppers or label elicitors (the way Berlin and Kay used their Munsell color
chips). That is, I was more interested in the associations the samples provoked
than in their identification, and the Kwoma did not disappoint. It often happened
that adults would send children off into the forest to bring back some tree bark or
other substance that would match the odor sample. Every one of the substances
they brought back had some practical, medicinal, magical, or gustatory virtue that
would be explained to me. My wintergreen sample, for instance, was matched
by the bark of a hardwood tree used for houseposts, known in the local language
as mijica. The cinnamon sample put many people in mind of their native ginger,
and because that plant (in its many varieties) was used in magic, it got me into
many discussion of magic and sorcery.
Not all of my samples were matched with natural products. For example,
the coconut sample was not identified with the coconuts that grew on trees, but
with the coconut-flavored cookies from the trade store; the lemon sample was
classified not as a fruit, but as soap, in keeping with the lemon-scented detergent
also available from the trade store. Thus, there were definite limits to the extent
to which the Kwoma were prepared to propose matches or analogies from the
natural world for my synthetic scents.
I was also interested in exploring Kwoma olfactory preferences. Interestingly,
at first my Kwoma friends consistently picked the rose sample as their favorite.
Could it be that humans are predisposed to prefer rose over all other odors, the
same way we are predisposed to prefer sugar over all other savors? As it turned
out, the redness of the rose sample must have been influencing responses – red
being the color associated with the pleasures of chewing betel, as well as sexual
arousal. Later, after I had learned to enclose the odor samples in envelopes so
that their color could not be seen, there was no longer the same consistency in
selecting rose as the favorite scent. The question whether or not there exist any
universal human olfactory preferences will therefore have to remain open.
Eliminating color as a variable might seem like a good procedure when in-
vestigating smell, but I was actually more interested in studying how the senses
interact than in separating them out, for it is only by analyzing the interplay of
the senses that one can arrive at a proper understanding of a culture’s sensory
order (Classen and Howes, 1991). The Kwoma language is interesting to study
from this perspective, particularly with the aid of Ross Bowden’s fine recent
dictionary (Bowden, 1997). For example, it appears that the Kwoma conceive
of visual attraction on the same model as olfactory attraction. This is evidenced
by the Kwoma word hirika, which means “smoke,” “steam,” “aroma” – as of
an object that has been rubbed with a strong-smelling magical substance – and
“aura,” or the aesthetic quality of people and sculptures when they have been
painted and decorated with shells and feathers in preparation for a ceremony that
will make them visually attractive.
Sight is definitely the dominant sense in the Kwoma sensory order, as sug-
gested by the importance the Kwoma attach to making visual representations
(paintings, sculptures) of the spirits that control their universe, the way they
privilege visual knowledge over aural knowledge in the context of male initia-
tion rituals, and other indicia (Howes, 1992). Smell complements sight, but it is
also frequently subversive or destructive of the visual order of society and the
cosmos. For example, in one Kowma myth, an old man who magically sloughs
off his aged skin and cavorts with two women in the forest is eventually found
out when his dog is brought along by the women and sniffs him out. This myth
suggests that olfactory identity transcends visual appearance.
In another myth explaining the origin of Ambon Gate, a particularly treach-
erous narrows in the Sepik River, it is told that there used to be a land bridge at
that point, but that a spirit destroyed it because a menstruating woman broke the
taboo on remaining isolated during her menses and her smell offended the spirit.
The Kwoma in fact have a special category to refer to the allegedly unpleasant
smell of a woman menstruating or one who has just given birth, maba gwonya.
It is the opposite of the category of mukuske gwonya, which refers to the smell
from the armpits and genitals of a pubescent girl, which Kwoma men claim to
find sexually attractive.
There is a significant gender dimension to the Kwoma sensory order. Men are
associated with the controlling power of sight, whereas women are associated
with the alternately seductive or debilitating and destructive power of smell.
Of course, men are also recognized to possess body odor among the Kwoma,
and like the women are very concerned to control it by washing and decorating
78 David Howes
themselves with leaves. But the body odor of males is unmarked compared with
the marked significance of female body odors, which stand for the opposed
poles of attraction and repulsion. The hierarchy of the senses, and within that
framework the hierarchy of smells, is thus a powerful means by which the hier-
archy of the sexes is conceptualized and enforced among the Kwoma. Olfactory
categorizations are rarely neutral discourses for describing the world.
5. Sensuous Intelligence
This chapter has shown that the hypervaluation of the visual sense in Western
science, beginning in the period of the Enlightenment, had the effect of dissociat-
ing the so-called lower senses of olfaction, gustation, and taste from the intellect.
However, the idea that the lower senses are devoid of cognitive potential can be
contradicted on the basis of Classen’s archeology of sense words for intellect in
the English language and a consideration of the nose-wise culture of the Ongee
of Little Andaman Island. The Ongee case, in particular, demonstrates that it is
possible for smell to serve as the medium for construction of a highly elaborate
cosmology and epistemology, with only a residual role played by vision. This
point is further confirmed by the cross-cultural study of sensory vocabularies,
which shows that cultures differ markedly in the intensity with which they attend
to each of the five senses and exploit them for classificatory purposes.
The preceding discussion illustrates the importance of conceptualizing intel-
ligence in a more sensuous manner than has been common in cognitive science
(Gardner, 1983; Johnson, 1987). Indeed, bearing the senses in mind appears fun-
damental to the future of cognitive science. In this respect, a highly stimulating
and suggestive sense-based model of cognitive (or, more accurately, brain) func-
tioning is provided by the Desana Indians of Colombia. Desana ideas about the
brain derive partly from their experience with hallucinogenic drugs. Such drugs
are used by shamans to manipulate brain functions. Desana ideas about the brain
are otherwise grounded in the knowledge they have gained from butchering game
and observing victims of head injury: “ The Desana imagine the brain to be di-
vided into many small compartments. In one image the brain is compared to a
huge rock crystal subdivided into many smaller hexagonal prisms, each contain-
ing a sparkling element of color energy. . . . In another image a brain consists of
layers of innumerable hexagonal honeycombs; the entire brain is one huge hum-
ming beehive. . . . Each tiny hexagonal container holds honey of a different color,
flavor, odor or texture, or it houses a different stage of insect larval development”
(Reichel-Dolmatoff, 1981, pp. 82–3).
Pointing to different compartments in a drawing he had made of the brain,
one Desana man explained: “Here it is prohibited to eat fish; here it is allowed;
here one learns to dance; here one has to show respectful behavior,” and so
on, demonstrating that each compartment is linked to social behavior (Reichel-
Dolmatoff, 1981).
The two cerebral hemispheres are said by the Desana to have complementary
functions. The left hemisphere is dominant and male and represents moral au-
thority, shamanic wisdom, and divine law. It is the seat of music, dreams, and
hallucinatory visions. The right hemisphere is female and subservient. It is con-
cerned with practical affairs, customary rules and rituals, physical nature, illness
and death. The left hemisphere presents the ideal, the right the potential to put
it into practice. The central role of the Desana shaman is to interpret all sensory
phenomena – from the song of a bird to the perfume of a flower – in terms of the
abstract social and cosmological ideals they represent and direct people to put
these ideals into practice.
Can the brain usefully be compared to a huge, humming beehive as the Desana
suggest? Needless to say, no Western-trained neuroscientist has ever asked this
question. True, the Desana understanding of the complementary functions of the
two cerebral hemispheres may not quite square with what Western neuroscience
teaches, but perhaps that is only because neuroscientists are more inclined to
conceive of the brain as a computer and have yet to ask the right questions.
It is time to start experimenting with the alternative models of perception and
cognition presented by the world’s indigenous cultures. For example, conceiving
of the belly – or, more precisely, the intestines – as the seat of the emotions and
the intellect the way the Kwoma (and many other indigenous peoples) do could
open up new possibilities for investigation. It is also instructive to ponder the
homology between hearing something and smelling something that the Kwoma
language posits by virtue of the fact that both of these perceptual processes are
designated by the same term, meeji. It appears that there are many possible ways
of combining the senses, which in turn create different patterns of consciousness.
The Ongee, with their notion of time as dispersion and their fluid conception of
space, represent a prime example of such a differently constituted consciousness.
In addition to mapping cross-cultural variations in the tone and shape of con-
sciousness in accordance with variations in cultural constructions of the senso-
rium, there is a need for further study of the sociological implications of divergent
sensory orientations. As was shown in the case of the Kwoma, sensory hierar-
chies and gender hierarchies reinforce each other, and there is also a hierarchy in
the ordination of smells that has important implications for relations between the
sexes. Olfactory categories may be contested by those who find themselves stig-
matized by virtue of their representation in the sensory and social order (Classen
et al., 1994). There exists, in other words, a cultural politics of olfaction that
needs to be studied in concert with the more cognitive dimensions of olfaction.
80 David Howes
Acknowledgments
Parts of the research on which this chapter is based were made possible by grants
from the Fonds pour la Formation de Chercheurs et l’Aide à la Recherche and
from the Olfactory Research Fund. I also wish to thank Catherine Rouby, Danièle
Dubois, and Benoist Schaal for their invitation to participate in the conference.
References
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6
Linguistic Expressions for Odors in French
Sophie David
Cette première pièce exhale une odeur

sans nom dans la langue, et qu’il
faudrait appeler l’odeur de pension.
– Balzac (1843, p. 53)
In this chapter I shall describe the grammar of a subset of French substantives

associated with olfaction, with two aims: (1) to identify, from a linguistic point
of view, the properties of these words and to examine the extent to which they
resemble or differ from others, especially those that are linked to other sensory
modes such as vision (colors) and hearing; (2) to evaluate some consequences of
the hypothesis that linguistic expressions contribute to the structuring of repre-
sentations in memory (Dubois, 1991, 1997, 2000). Indeed, the results of such an
analysis (i.e., an examination of the various properties of words) can have con-
sequences for the methods and analyses employed in experimental approaches
to olfactory cognition.
It is important to note that the French lexicon has few terms to refer to olfactory
entities. That paucity of terms is shared by many Indo-European languages, but
such is not the case in many other language groups.1 Basically, French speakers
are restricted to terms such as these:2
(1) odeur “odor” effluve “emanation” remugle “fustiness”

parfum “perfume” exhalaison “exhalation” miasme “miasma”
senteur “scent” puanteur “stench” fraı̂chin3
fragrance “fragrance” bouquet “bouquet”
Excepting the words remugle (“fustiness”), miasme (“miasma”), and fraı̂chin,

which name specific smells, the terms allow us to refer to olfactory entities only
generically. On a primary level, they appear to be “classified” according to the
criteria of pleasant and unpleasant.
82
Linguistic Expressions for Odors in French 83
Any sort of linguistic analysis necessarily involves, first, an ordered collection

of empirical data. This is why, in the context of this multidisciplinary volume,
I shall begin with a brief recapitulation of the aims of linguistics and of the manner
in which its facts are constructed, followed by a brief description of the theoretical
framework of lexical semantics I have adopted. Then I shall examine some of the
properties of the terms listed earlier in (1) and go on to draw some conclusions
about the various methodological consequences that could be of use for empirical
cognitive sciences.
1. Lexical Grammar: A Theoretical Framework

Linguistics is an empirical science that derives its data from descriptions and
analyses of real or potential verbal productions. Such data are given in the form
of examples (Milner, 1989; Kerleroux and Marandin, 1994). They are combined
by pairs to create a contrast: Two examples that differ by a single element are set
out in parallel, and we can then form a judgment concerning them. That judgment
is binary in nature, “well formed” versus “not well formed,” and hinges on
grammatical properties. Thus, we do not judge examples according to aesthetic,
moral, or cultural criteria,4 nor by the possible interpretations to which they may
give rise (Godard and Jayez, 1993). For example:
(2) (a) The dog is running
(b) *Dog the is running
(c) He fell asleep during the show
(d) *He fell asleep during the pavement
Examples (2b) and (2d) are not well formed; we shall henceforth identify such a
statement with an asterisk. The contrasts (2a) versus (2b) and (2c) versus (2d) are
considered as facts. The difference between (2a) and (2b) involves the position
of the determiner in English. The difference between (2c) and (2d) involves the
lexical relationship between the preposition “during” and the nouns “show” and
“pavement.”
My work involves lexical semantics, a particular sphere of linguistics that is
concerned with attempting to describe what is involved in the meaning of words. I
cannot here give a detailed account of the variety of earlier theoretical approaches
[i.e., the componential approach (Katz, 1972), the category and prototype ap-
proaches (Lakoff, 1987; Kleiber, 1990), the index approach (Cadiot and Nemo,
1997), the object-classes approach (Gross, 1994), etc.]. I work within a lexical
semantics framework initiated by Marandin (1984a,b) and recently formalized
by Godard and Jayez (1993, 1996) and Jayez and Godard (1995); but see also
Grimshaw (1990) and Pustejovsky (1995). My work focuses on the combinatorial
84 Sophie David
properties of lexical units, which are of two kinds: those based on argumental
properties and those based on sortal properties, which are the grammaticalized
correlates of referential properties (i.e., the properties of an “object in the world”).
Two types of properties will be examined: (I) syntactic/semantic properties
and (II) semantic properties:
(I) Syntactic/semantic properties can be observed from the complementation sys-
tem, in this instance a complement applied to a noun (the nature of the comple-
ment and its interpretation) (Grimshaw, 1990). For example:
(3) The destruction of the city
In example (3), the complement phrase “of the city” is interpreted as the object of
the noun phrase “the destruction”; in terms of thematic relations it is the theme
of “destruction.” These properties imply a judgment based on the structural
(syntactic) well-formedness of the expressions (preposition type, noun type,
the compulsory presence of a complement, the semantic interpretation of the
complement, etc.).
(II) Semantic properties can be observed in “selectional-restriction-based” con-
trasts. We use the term “selectional restriction” when the elements explaining
a particular possibility or impossibility are lexical in nature, as in the following
example:
(4) (a) * The boy may frighten sincerity (Chomsky, 1965, p. 109)
(b) The boy may frighten his sister
(c) Sincerity may frighten the boy
“Sincerity” cannot be the complement of “frighten,” because that verb requires

an object denoting an animate entity. Such properties imply a judgment based
on the semantic well-formedness of the expressions.
From these considerations, it follows that we separate the properties of mean-
ing from the properties of things. Although, from a conceptual viewpoint, some
words can share some properties, they may not share the same linguistic prop-
erties. They can belong to quite different linguistic classes. For example, plage
(“beach”) and désert (“desert”) can refer to entities that share properties on the
conceptual level (i.e., “place,” “sandy,” etc.), but we have the following contrast:
(5) (a) Je suis dans le désert (Berthonneau, 1998)
“I am in the desert”
(b) *Je suis dans la plage
“I am in the beach”
(c) Je suis dans la rue
“I am in the street”
In these examples, from a linguistic point of view, désert (“desert”) and rue
(“street”) have more in common than désert and plage do.
Thus, this approach does not a priori describe all of the semantic considerations
that can be associated with a word. Only the meaning properties that are based on
the analysis of contrast are taken into account, which ensures that the properties
underpinning word meaning are linguistic in nature.
2. Odor Lexicon: Syntactic and Semantic Properties

In this section, some of the syntactic and semantic properties of terms appearing
in list (1) will be presented. However, this review is neither exhaustive nor system-
atic. We shall focus primarily on odeur (“odor”) and parfum (“perfume”), indi-
cating some properties for the terms senteur (“scent”), fragrance (“fragrance”),
effluve (“emanation”), puanteur (“stench”), and exhalaison (“exhalation”).
A first focus will be on the linguistic heterogeneity of such terms. Then we
shall examine the nature of the relationship between a smell and its “source”
(as defined later) and consider whether or not the referent consists of parts,
especially if the “source” can be considered as a “part of” a smell. Lastly, we shall
consider whether or not these terms can have temporal properties. These issues
are related to questions concerning the typology of lexical units (here, nouns).
We adopt the hypothesis of Godard and Jayez (1996) to distinguish the following
types: material and informational objects, strong and weak events, property, and
activity, as shown in Figure 6.1.
Sections 2.1, 2.2, and 2.3 are concerned with different kinds of material objects,
or with the differences between material objects and properties. Section 2.4 deals
with temporal properties (a category that gathers events and activities).
For the sake of clarity, we shall henceforth employ the word “term” or
“expression” to denote a language unit (a word, a sentence); the word “referent”
stands for an entity in the world to which a given phrase points. For convenience,
we employ the locution “olfactory terms” in referring to terms in list (1).
Typology
event object property activity
weak strong material informational

Figure 6.1. A portion of the typology proposed by Godard and Jayez (1996).
86 Sophie David
2.1. Linguistic Heterogeneity of Olfactory Terms

Olfactory terms do not appear to constitute a homogeneous class. They do not
all have the same types of properties:
(I) We note simple names and also deverbal constructions such as puanteur and
exhalaison (i.e., constructions that are morphologically derived from verbs).
(II) Some of these terms can be linked to different fields of knowledge. Such is the
case with miasme in its more prevalent usage (naming a gas), or parfum, which is
also frequently associated with the sphere of taste (see note 3). In the remainder
of this presentation, we restrict our interest to the olfactory sphere alone.
(III) Constructions using odeur, parfum, senteur, fragrance, effluve, and exhalaison,
followed by the preposition de and a noun, are frequently employed in French
when a particular smell is being considered. Examples in which the second
noun (N2) names an odorous entity, corresponding to a “source” [from either a
psychological or a grammatical point of view (thematic role)], are our concern
here:5 For example: vanille (“vanilla”) or poisson (“fish”) in the phrases odeur
de vanille (“odor of vanilla”) [vanilla smell] and odeur de poisson (“odor of
fish”) [fish smell].
Odeur and parfum can both be in the N1 position: Il a senti une odeur de rose
(“He smelled an odor of rose”) [a rose smell]. Il a senti un parfum de rose
(“He smelled a perfume of rose”) [a rose perfume]. Parfum can also name a
source, as shown by the following contrast (6), where parfum is well formed in
the N2 position (6a), whereas odeur is not (6b):
(6) (a) J’aime l’odeur de parfum
“I like the odor of perfume”
[I like the perfume odor]
(b) *J’aime le parfum d’odeur
“I like the perfume of odor”
This is confirmed by the following examples:6

(7) (a) Ça (sent + pue) (le parfum + le poisson)
“It (smells + stinks) (the perfume + the fish)”
[It smells of (perfume + fish), it stinks of (perfume + fish)]
(b) *Ça sent (un parfum + un poisson)
“It smells like (a perfume + a fish)”
(c) Ça sent un parfum . . . je ne sais plus lequel . . . peut-être Chanel N˚5
“It smells a perfume . . .” [I cannot remember which one . . . maybe
Chanel No. 5]
(d) Ça sent un poisson . . . je ne sais plus lequel . . . peut-être le saumon
“It smells a fish . . .” [I cannot remember which one . . . maybe salmon]
In the context of ça sent/ça pue (“it smells/it stinks”), parfum behaves exactly
like any noun signifying an odorous source, examples (7a) and (7b). Example
(7c) is well formed, as is (7d), if the noun phrase un parfum (“a perfume”) refers
to an entity considered as “sort of,” as clarified by the sentences that follow.
Once again, odeur behaves differently: *Ça sent l’odeur (“It smells the odor”)
and *Ça sent une odeur (“It smells of an odor”). In the same way, parfum passes
the test of material-object type (8a) (Godard and Jayez, 1996), whereas the other
terms do not (8b):
(8) (a) Le parfum se trouve sur l’étagère

“The perfume is on the shelf”
(d) *(L’odeur + la senteur + la fragrance + l’effluve) se trouve sur l’étagère
“(The odor + the scent + the fragrance + the emanation) is on the shelf”
(IV) Parfum is the only term that allows for mass determination [(9a) versus (9b)
and (9c)]:
(9) (a) Il s’est mis

(du + un peu de + peu de + trop de + beaucoup de) parfum
“He has put
(some + a little bit of + little + too much + a lot of) perfume”
(b) *Dans cette pièce, il y a
(de l’ + un peu d’ + peu d’ + trop d’ + beaucoup d’)
(odeur + effluve)
“In this room, there is
(some + a little bit of + little + too much + a lot of )
(odor + emanation)”
(c) *Dans ce flacon, il y a
(de la + un peu de + peu de + trop de + beaucoup de)
(senteur + fragrance)
“In this bottle, there is
(some + a little bit of + little + too much + a lot of )
(scent + fragrance)”
In the following examples, parfum behaves as a “substance name” (according to

Van de Velde, 1995), like eau (“water”), fer (“iron”), or (“gold”), and so forth:
(10) (a) (Un flacon + une bouteille) de parfum

“(A flask + a bottle) of perfume”
[A perfume bottle, a perfume flask]
88 Sophie David
object property
material
parfum odeur
Figure 6.2. Linguistic types for parfum and odeur.
(b) (Deux litres + une goutte) de parfum

“(Two liters + a drop) of perfume”
(c) *Le parfum de deux litres
“The perfume of two liters”
(d) Il a acheté du parfum en bouteille
“He has bought some perfume in bottle”
These terms present distinct properties having to do with their (possible) mor-
phological constructions, the knowledge field to which they can be related, the
(possible) various entities to which they allow reference, and the question of
their determination. From these various tests, we can conclude that odeur has
only one type, the property type, whereas parfum has two types: the property
type and the material-object type, as shown in Figure 6.2.
2.2. Relationships between Olfactory Terms

and Their Source Names
In the construction “odeur + preposition + (det) + N2,” where “det” represents a
“determiner” and N2 is the name of a source, odeur is a characteristic, a property,
of the source, like couleur (“color”):
(11) (a) J’aime l’odeur de cette rose

“I like the odor of this rose”
(b) J’aime la couleur de cette chemise
“I like the color of this shirt”
And it is interesting to note that the preposition de is the only one possible and
that it is compulsory (David et al., 1997):
(12) (a) *Je déteste l’odeur gaz, les odeurs fumier

“I hate the odor gas, the odors manure”
(b) *Les odeurs fleur sont celles que je préfère

“The odors flower are those that I prefer”
(c) *La pièce sent une de ces odeurs produit d’entretien!
“The room smells one of these odors” [cleaning product!]
These examples show that this characteristic is not constructed independently of

the source [the compulsory presence of the preposition de; examples (12a), (12b),
and (12c) are not well formed]. However, one can at times note (exceptionally)
the absence of de, as in the following extract:7
(13) La méthylionone . . . permet de mettre en relief successivement ces facteurs

psychologiques. Ce produit, présentant simultanément ou successivement des
odeurs d’iris, de réglisse, de cuir, de bois, de vétyver, de violette, etc. . . . , il
est clair que plusieurs individus n’observeront pas forcément en même temps
la même face ou la même phase. Chacun suit son inclination naturelle et
s’accroche à un repère qui l’a spécialement frappé, l’odeur bois par exemple.
Si nous attirons son attention sur un autre repère, l’odeur cuir, il finira par
la remarquer à son tour. . . . De proche en proche . . . , nous lui ferons faire un
inventaire complet de l’ odorant. . . . (Roudnitska, 1980, p. 14)
[Methylionone . . . enables us to pinpoint these psychological factors succes-

sively. Since this product displays simultaneously or in succession odors of
iris, of liquorice, of leather, of wood, of vetiver, of violet and so on . . . , it
is clear that different people will not perceive the same aspect or the same
phase at the same time. Each person will follow his natural intuition and
will be responsive to the particular marker that has especially struck him,
for example the odor wood. If we draw his attention to another marker such as
the odor leather, he will then go on to notice it. . . . Little by little, therefore,
we shall bring him to make a complete inventory of the odorant.]
This is a quotation from an expert who deals with perfume synthesis, as shown
in particular by the use of the terms méthylionone (“methylionone”) (a perfume
component), odorant (“odorant”) (an odorous mixture), inventaire (“inventory”)
(a whole made up of parts), and repère (“marker”) (one of the components); in
this context, all of these terms add up to a material approach to odor. However, this
context is not one in current usage, and even so, we can employ the preposition,
as in odeurs d’iris, de réglisse (“odors of iris, of licorice”) [iris smells, licorice
smells].
In French, things are different in the realm of color. Couleur (“color”) can be
followed by a substantive, whether preceded by de or not (14a and 14b). The
ensuing nominal form is then interpreted like a color, even if it is a “discourse
color” (i.e., an expression of the speaker’s creativity that may not be lexicalized):
90 Sophie David
(14) (a) Un tapis couleur de feuille morte

“A carpet color of leaf dead”
[A dead-leaf carpet color]
(b) Un tapis couleur feuille morte
“A carpet color leaf dead”
[A dead-leaf carpet color]
These remarks are in line with the analyses of Corbin and Temple (1994, pp. 24–
5): “Neither eucalyptus nor musk nor thyme alone, for example, can serve to name
categories of objects [entities] having the smell characteristics of eucalyptus,
musk or thyme,” unlike such terms as poire (“pear”), which can name a fruit and
any pear-shaped entity (e.g., an “enema bag” in French). To corroborate this,
Corbin and Temple (1994) point out that no adjective associated with a smell can
be converted8 into a noun to name an entity having that smell as a characteristic,
unlike adjectives naming colors, as shown by the following examples:
(15) (a) fétide (“fetid”)

*un fétide (“a fetid”) (Corbin and Temple, 1994)
(b) bleu (“blue”)
un bleu de travail (“a blue of work”) [overalls]
une ecchymose (“a bruise”) (Corbin and Temple, 1994, p.13)
(c) noir (“black”)
une noire (“a black”) [a quarter note in music]
Parfum behaves like odeur (in the olfactory realm), but it can support a direct
construction in specific contexts, such as in advertisements, where parfum vanille
(“perfume vanilla”) [vanilla perfume] can be associated with a deodorant, or on
room-deodorant packaging, where parfum pin (“perfume pine”) [pine perfume]
may appear. However, we must emphasize the noncanonical character of this
usage (plays on words, diversions of the semantic properties of words, etc). For
senteur, I found only one example in Frantext, and the same for effluve, but none
for fragrance:9
(16) (a) Les odeurs lui reviennent: poussière de charbon, fumées, fond permanent,
mégot refroidi, fameux café-chicorée, gnole, pisse de chat, d’enfant, . . . vin
rouge, absinthe des comptoirs et sur chaque seuil l’ardente senteur savon
noir de la propreté ouvrière, de la pauvreté nickel. (Chabrol, 1977, p. 196)
[The smells return to his memory: coal-dust, smoke, permanent background,

stale cigarette butt, a coffee-chicory mix, cheap booze, cat’s and children’s piss,
red wine and absinthe, and on every doorstep the pungent scent soap black
[smell of strong black soap], the smell of shining working-class poverty.]
(b) [J]e regretterai sans doute la 208 . . . 480, la 512 . . . toutes les cellules de mes
prisons et leurs punaises, les effluves gogues, les gaffes et peut-être même le
mitard. (Boudard, 1963, p. 363)
[I’ll probably miss the 208 . . . the 480, the 512 . . . all my prison cells and their
bugs, the emanations shithole [shithole smells], the guards and maybe even
the solitary confinement.]
With the exception of these rare examples, which we always find in specific con-
texts (the speech of experts, advertisements, slang, etc.), French terms associated
with the olfactory field, and the term odeur in particular, refer to entities that
cannot be separated from their sources (Strawson, 1973). Moreover, the syntactic
contrast between color and olfactory terms (14) is congruent with the contrast
(15): A common noun denoting an object can be used as denoting the prototypi-
cal color of this object, whereas that is impossible with olfactory terms. In other
words, in French, the source name can never be the name of an odor.
2.3. Olfactory Terms and “Part of”

Using the tests designed by Van de Velde (1995) with regard to “substance
names” (which do not consist of identifiable parts), we first note that we cannot
use the formulation partie de (“part of ”) before the term odeur:
(17) (a) *Il a senti une partie de l’odeur
“He has smelled a part of the odor”
(b) Il a lu une partie du livre
“He has read a part of the book”
(c) *La partie de l’odeur que je préfère est la rose
“The part of the odor that I prefer is the rose”
Moreover, if the term under consideration consists of parts, it is possible to create

expressions like the following: “N1 + de + numeral + N2.” Thus, une maison de
trois pièces (“a house of three rooms”) [a three-room house]. Or “N1 + à + N.”
Thus, un verre à pied (“a glass with foot”) [a stem glass] (Cadiot, 1992; Van
deVelde, 1995), with N1 naming the entity containing the parts, and N2 naming
one of those parts. For the term odeur, there are no such names:
(18) (a) *Il a senti une odeur de trois ??
“He has smelled an odor of three ??”
(b) *Il a senti une odeur à ??
“He has smelled an odor with ??”
Nor can the source name be introduced by the preposition à, whether the name
is determined or not:
92 Sophie David
(19) (a) *Une odeur à vanille

“An odor with vanilla”
(b) *Une odeur à la vanille
“An odor with the vanilla”
Again, parfum behaves differently, for it can be followed by “à + det + noun”:
(20) (a) *Un parfum à vanille
“A perfume with vanilla”
(b) Un parfum à la vanille
“A perfume with the vanilla”
[A vanilla perfume]
(c) Il se promet d’acheter du parfum à l’iris (Bienne, 1990, p. 71).
“He promises himself to buy some ‘perfume with the iris’ [iris perfume]”
For Van de Velde (1995, p. 112), the sequence à la (“with the”) is possible if N1
denotes a man-made object and the complement expresses a means; for Cadiot
(1992, p. 203), N2 can be interpreted as an ingredient of N1. Thus, in French,
the “means” or “ingredient” relations are different from the “part of” relation.
Whatever the semantic relation may be, parfum can name an odorous mixture,
an artifact, the source of which cannot be interpreted as a part; compare Section
2.1, where (20a) is not well formed; moreover, test (17) is negative for parfum:
*Il a senti une partie du parfum (“He has smelled a part of the perfume”). Effluve,
fragrance, and senteur behave in the same way as odeur, although current usage
may be changing in the case of senteur, as in the use of phyto-senteur (“phyto-
scent”) on a cosmetics package (see note 3).
(21) (a) *Il a senti (une fragrance + un effluve) à la vanille
“He has smelled (a fragrance + an emanation) with the vanilla”
(b) ?Une senteur à la vanille
“A scent with the vanilla”
[A vanilla scent]
Finally, we note that we cannot have a phrase like (22a), whereas (22b) and (22c)
are well formed:
(22) (a) *La rose de l’odeur
“The rose of the odor”
(b) La plume du stylo
“The quill of the pen”
(c) Le guidon du vélo
“The handlebars of the bicycle”
Every phrase built as “N1 + de + det + N2” does not systematically mean “N1 =
part of N2” (Fradin, 1984a,b). However, if N1 is categorematic (i.e., N1 denotes
an “object in the world” and has a stable and non-processive meaning) (Fradin,
1984b), and if the two terms have a “part of” relationship, then it is possible to
create the types of phrases illustrated by (22b) and (22c). That is never the case
for the term odeur (22a). We do, however, find a few instances of pois de senteur
(“pea of scent”) [sweet peas], eau de parfum (“water of perfume”) [perfume],
foin d’odeur (“hay of odor”) (which names a plant).10 These are lexicalizations
that allow for reference to natural or man-made objects in which the second
term is taken as a distinct classificatory characteristic. The proof is that the
second term cannot have a determiner. Thus, we cannot have the following:
(23) (a) *Les pois de la senteur

“The peas of the scent”
(b) *L’eau du parfum
“The water of the perfume”
(c) *Le foin de l’odeur
“The hay of the odor”
The source associated with the term odeur is not a part or an ingredient of the
smell. Odeur cannot mean an odorous mixture, unlike parfum.
2.4. Olfactory Terms and Temporal Properties

In this section, I adopt the following tests or requirements devised by Godard
and Jayez (1996); both test (a) and test (b) must be passed for the term to have
temporal properties, and test (e) must be passed for the term to be a strong event:
(24) (a) *Il a dormi

(avant + après + pendant + durant + au cours de + lors de + depuis +
tout au long de + au moment de) l’odeur
“He has slept
(before + after + during/for + during + in the course of + at the time of +
since + throughout + at the time of) the odor”
(b) *Il a senti deux heures d’odeur
“He has smelled two hours of odor”
*Il a senti une odeur de deux heures
“He has smelled an odor of two hours”
(c) *L’odeur (a commencé à 8 h + a fini deux heures après + est interrompue +
s’est interrompue quelques minutes après + s’est achevée + est suspendue)
“The odor (began at 8 o’clock + finished two hours later + is interrupted +
broke off a few minutes later + ended + is suspended)”
(d) ?L’odeur a duré quelques minutes
“The odor lasted a few minutes”
94 Sophie David
(e) *Une odeur a eu lieu. Une odeur s’est produite

“An odor happened”
Example (24d) seems dubious, and with regard to the other verbs proposed by
Godard and Jayez (1996) – se prolonger pendant/jusqu’à (“to go on during/
until”), se continuer (“to continue”), s’étaler sur (“to spread over”), traı̂ner en
longueur (“to drag on”), n’en plus finir (“to take ages”), s’éterniser (“to drag on
interminably”) – the sentences are not well formed. Thus odeur has no temporal
properties, nor do parfum, effluve, fragrance, and senteur.11
These results stand in contrast to those in the auditory field, in which terms like
bruit (“noise”), vacarme (“din”), and brouhaha (“hubbub”), as well as many de-
verbal constructions such as grondement (“roaring”), aboiement (“barking”), and
so forth, pass several of these tests. Let us consider here the results for some of
them:
(25) (a) Il est parti (après + avant) ce (bruit + brouhaha + vacarme)

assourdissant12
“He has left (after + before) this (noise + hubbub + din) deafening”
(b1) Ils ont fait quelques minutes de bruit
“They have made a few minutes of noise”
Il y a eu un bruit de quelques minutes
“A noise of a few minutes happened”
(b2) Il a dû supporter deux heures (de brouhaha + de vacarme)
“He has had to suffer two hours (of hubbub + of din)”
?Il a dû supporter (un brouhaha + un vacarme) de deux heures
“He has had to suffer (a hubbub + a din) of two hours”
(c) Le (bruit + brouhaha + vacarme) (a commencé + a fini) à 8 h
“The (noise + hubbub + din) (began + finished) at 8 o’clock”
(d) Le (bruit + brouhaha + vacarme) a duré trois heures
“The (noise + hubbub + din) lasted three hours”
(e1) Un (bruit + clac) s’est produit
“A (noise + clac) happened”
(e2) *Un (bruit + clac) a eu lieu
“A (noise + clac) happened”
These terms function correctly in tests (a), (c), and (d). Test (e), using se produire
(“to happen”), is acceptable if it is “a fortuitous event” (Gross and Kiefer, 1995),
which is not the case, for example, with brouhaha (“hubbub”). Complemen-
tation (test b) shows different acceptabilities. Beyond these difficulties (which
call for further analysis of the terms associated with the auditory field), the
main point is to show that results for smells, expressed in the most current
olfactory terms, are clearly negative, and thus that these terms have no temporal
properties.
3. Conclusion
The various contrasts demonstrated here show that the terms linked with the
olfactory field do not make up a homogeneous class, that most of them do not
allow independent reference to their sources, nor do they allow for reference to
entities with identifiable parts, and, finally, that the most common among them
have no temporal properties. In linguistic terms, this means that the linguistic
type for words currently associated with the olfactory realm is one of property
and that parfum has two different types, property and material object. These
results can have important consequences for other fields, especially psychology.
The instructions issued for psychology experiments, as well as analyses of sub-
jects’ verbal replies, must take into account the fact that French is ill-suited for
testing the characteristics and properties of smells. The problems are of several
types: Instructions for identifying the various components of an odorous mixture
are difficult to formulate using the term odeur. Similarly, instructions dealing
with smell as a perceptive event are particularly difficult to formulate, for most
of the terms are not events. For example, it is difficult to express in words notions
about the origin or the cause of a smell, its location, the duration of the percep-
tion, and so forth (Gross and Kiefer, 1995). Lastly, the analysis of results derived
from the various tasks of categorization must always take into account the fact
that smells, which have no autonomy vis-à-vis their sources, tend to induce clas-
sifications based on resemblances with the characteristics of the source objects
(Dubois, 2000). In other words, analysis of the meanings of most olfactory terms,
and especially odeur, shows that the referent of a phrase built on that term is not
considered as an “object” independent of its source and of the person who per-
ceives it, which is clearly obvious through the widespread use of such deverbal
adjectives as agréable (“pleasant”), piquant (“pungent”), and so forth, to identify
types of smells (David et al., 1997). Thus, from a cognitive point of view, the
entities named by odeur do not have the concrete objectivity of visual or sound
entities (David, 1997) and must be considered as effects (i.e., as manifestations
of a sensation that cannot be dissociated from the subject sensing it).
Acknowledgments
I would like to thank Françoise Kerleroux and Rachel Panckhurst for their helpful
remarks and criticism.
96 Sophie David
Notes
1. That situation has been studied by Engen (1987), and some of its consequences have
been examined by Dubois and Rouby (Chapter 4, this volume) and David (2000). For
additional details about other lexicologic surveys, see the following: Boisson (1997),
who has studied the olfactory vocabularies of 60 languages from nine linguistic
families by analyzing various dictionaries; Mouélé (1997) and Traill (1994), who
have listed, respectively, the olfactory terms of Li Waanzi (a language of Gabon) and
of !xo@o) (a language of Botswana); and Classen (1993, pp. 60ff.). In a different
way, Camargo (1996) and Mennecier and Robbe (1996) described the properties
of evidentials operating, respectively, in Caxinaua (Pano family) and in Tunumiisut
(one of the Inuit languages).
2. French examples are given in italics, and they are followed by their literal translations
in English. If the literal translation in English is incorrect, it is followed by a translation
in square brackets reflecting the meaning of the French expression. To simplify
reading, the initial translation of a word into English will be maintained throughout
the text.
3. Miasme can name the particular smell associated with certain diseases, and fraı̂chin
names a fishy sea smell. It is a regional term in the west of France that does not
seem to have any equivalent in English. Some of these terms are not currently in
use. The Frantext data-base search I made concerned all literary genres, covered the
nineteenth and twentieth centuries, and referred to 2,012 different works. It produced
the following results (occurrences of the singular or plural forms): odeur, 11,047;
parfum, 5,664; bouquet, 3,999; senteur, 918; effluve, 389; puanteur, 355; exhalaison,
223; miasme, 213; remugle, 63; fragrance, 30; fraı̂chin, 0. We must note that, in
French, parfum can refer to both a perfume and a flavor, and bouquet can refer to
both a bunch and a smell, so there are numerous examples that have nothing to do
with smells (e.g., une glace au parfum vanille, “an ice cream with the flavor vanilla”
[a vanilla-flavored ice cream], or il avait apporté un bouquet de fleurs, “he brought a
bunch of flowers”). Senteur and fragrance are quite rarely used, although the former
seems to have been rejuvenated recently through the development of new odor-related
technologies (for masking smells but also for the eradication of unpleasant smells).
4. For example:
(1) Il a mangé les grenouilles, les cafards

“He has eaten the frogs, the cockroaches”
From a linguistic viewpoint, this example is not ungrammatical, because the only
reason for rejecting it would be based on cultural considerations.
5. This is not always the case, for the second term can name a time entity, as in odeur
d’autrefois (“odor of the past”), a state, as in odeur de pourri, de renfermé (“odor
of rotten, of fusty”) [rotten smell, fusty smell], a place, as in odeur d’hôpital (“odor
of hospital”) [hospital smell] or l’odeur de chez le coiffeur (“the odor of the hair-
dresser’s”) (Romains, 1932, p. 294).
6. By convention, a plus sign means the various possibilities of reading:
(1) (Une odeur + un parfum) de rose

“(An odor + a perfume) of rose”
Example (1) gathers two different examples, (2a) and (2b):

(2) (a) Une odeur de rose

“An odor of rose”
[A rose odor]
(b) Un parfum de rose
“A perfume of rose”
[A rose perfume]
7. In the longer quotations, only the words in boldface have been translated literally.
8. A “conversion” is a morphological operation of word construction (Corbin, 1987;
Kerleroux, 1996). We note a semantic and categorical change without any material
change (e.g., prefix or suffix) – for example, bleu (“blue”) (noun) constructed from
bleu (“blue”) (adjective).
9. The bibliographic references in literary extracts are those of Frantext.
10. I do not include expressions such as flacon de parfum (“flask / bottle of per-
fume”) [perfume bottle], bouteille de parfum (“bottle of perfume”) [perfume bottle],
and bouffée de parfum (“whiff of perfume”) [perfume whiff ], which are not
denominations.
11. That is not the case for puanteur and exhalaison, which are deverbal constructions
(Gross and Kiefer 1995):
(1) Alors, commençaient les puanteurs (Zola, 1873, p. 827).

“Then, began the stenches” [The stenches then began]
12. Considering the linguistic type of terms denoting noise, a complement is compulsory.
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7
Classification of Odors and Structure–Odor
Relationships
Maurice Chastrette
In spite of considerable recent progress in olfaction studies, the sense of smell

remains poorly understood, and the description of perceived odors is still a
difficult task. When our understanding of olfaction is compared with that for other
senses, such as vision, there are striking differences: In the field of vision, the
absorption spectra of electromagnetic radiation are easily measured and provide
information to predict the perceived colors of substances. As the molecular
features responsible for the characteristics of light absorption are well known,
the colors of substances, such as dyes, can be predicted with reasonable accuracy.
The situation is much more obscure for the olfactory properties of substances,
as in olfaction there is no equivalent for absorption spectra, and descriptions of
odors, which are absolutely necessary to establish structure–odor relationships,
have been far from rigorous.
To describe an odor, we generally search through our past experience to try
to make comparisons with similar chemical compounds encountered earlier, at-
tempting to find appropriate words. However, even if we decide that compound A
smells somewhat like compound B, but does not smell exactly the same, we nev-
ertheless feel justified in using the same words to describe both. Moreover, unless
we are carefully trained experts, there will be emotional, personal, and cultural
factors that will intervene in our perceptions and strongly influence our choices
of descriptors. Concern about such factors was long ago expressed by the Dutch
physiologist Zwaardemaker (1899), who called for a quantitative psychology of
olfaction. In the first part of this chapter, the point of view of a chemist regarding
classifications of odors will be presented. As classifications are strongly associ-
ated with description systems, these two aspects will be considered successively.
In the second part, problems associated with the determination of structure–odor
relationships will be briefly discussed.
100
Classification and Structure–Odor Relationships 101
1. Description of Odors
Usually, the description of an odor supposes that both its quality and inten-
sity characteristics can be precisely defined. Several description systems, based
on a thesaurus of words referring to pure substances or to complex mixtures,
have proved their utility in the various domains where olfactory descriptions
are necessary. Unfortunately, no general agreement has ever been reached, and
any compilation of a large data base would be difficult because of the many
differences between the various description systems.
1.1. Qualities of Odors

The qualities of odors usually are specified using specific words (descriptors), or
by detailing similarities between odors, or by using olfactory profiles. Whatever
the description system used, the distinction between olfactory and trigeminal
perceptions, as well as the factor of an odor’s concentration, must be considered.
For instance, the odors of thiols are known to be strongly dependent on their
concentrations: Thus p-menth-1-en-8-thiol has a grapefruit “note” at very low
concentrations, whereas the smell of the pure liquid is extremely powerful and
causes nausea (Demole, Enggist, and Ohloff, 1982). Contextual effects on odor
quality, frequently encountered in human perception, such as different sorts of
perceptual contrast, have been discussed by Lawless and associates. (Lawless,
1991; Lawless, Glatter, and Hohn, 1991)
1.2. Descriptions Using Word Descriptors

When naive subjects are used in testing odors, their descriptions of odors are
strongly influenced by emotional and subjective factors (Weyerstahl, 1994).
Olfactory descriptions are most often compiled, by panels of subjects trained to
use a given terminology in a more uniform and less personal way. However, even
perfumers sometimes use subjective descriptions, as shown by Ellena (1987),
who compiled a list of 122 descriptors used by perfumers that related to taste,
tactile sensations, affective responses, and so forth. Clearly, the various descrip-
tion systems are not equivalent, and a given word used in the various description
systems will not always have the same status, as shown by the results of linguistic
research (e.g., David, 1997).
Arctander (1969), in his reference work, cited about 260 different descriptors
and 88 classes of odors. A much shorter list of descriptors (32) has been used by
Swiss perfumers, and the international standard for training in the recognition of
102 Maurice Chastrette
odors features only 24 reference substances (ISO, 1992). Jaubert, Tapiero, and
Doré (1995) have described a system with 42 odor descriptors referring only to
pure substances.
It has been suggested (Dravnieks and Bock, 1978; Dravnieks, 1982) that se-
mantic descriptions are reproducible for many odorants. One would hope, and
expect, to find something close to a consensus among different experts sampling
a given odorant. However, when Brud (1986) asked 120 perfumers to associate
with each of 20 odor descriptions the name of only one substance, a total of 507
different substances were cited, nearly 400 of which were cited by only one per-
son. The consensus was good for odors like “musk” and very poor for odors like
“floral” and “fatty”. Harper (1975) asked seven experts to determine which pure
chemical substances were the best representatives for 44 particular odor quali-
ties and concluded that “the views of at least ten persons (i.e. their qualitative
descriptions) should normally be combined together to be reasonably sure that
all relevant qualities or notes have been identified.” It therefore seems important
in classifications to use homogeneous data sets originating from a single source
(e.g. a restricted group of experts using the same description system or at least
similar description systems).
1.3. Descriptions Using Profiles

Crocker and Henderson (1927) suggested that four odor “characters” (“fragrant,”
“acid,” “burnt,” and “caprylic”) “are the principal and perhaps the only units
which make up all the odors we perceive” and could perhaps explain all smells:
Any substance could be rated on the four character scales, with values from 0 to 8,
to generate a profile. That was the first description system based on profiles. The
simplicity of their approach seems attractive, although practicing perfumers no
doubt found their four dimensional description system too crude. A more com-
plex system was used by Wright and Michels (1964). Brud (1986) also used odor
profiles based on 10 descriptors (“green,” “fruity,” “floral,” “fatty-aldehydic,”
“herbal,” “animal-musky,” “amber-woody,” “spicy-balsamic,” “earthy-fungoid,”
and “chemical-unpleasant”), with values from 0 to 4. Dravnieks (1985) asked a
group of 120–140 panelists to rate, on a scale from 0 to 5, the applicability of each
of 146 descriptors or odor characteristics for 160 products, including 145 pure
substances and 15 mixtures. Statistical measures were derived from such data
and used in establishing profiles. In a study by Moskowitz and Gerbers (1974),
observers rated each of 15 odors on 17 attributes (14 descriptors of particular
qualities, such as “minty” or “burnt,” and three descriptors related to intensity,
pleasantness, and familiarity) using a method of magnitude estimation.
To obtain odor profiles without using such scales, Boelens and Haring (1981)
asked a panel of experienced perfumers to sample 309 compounds and assess
their similarities to 30 reference materials selected to represent different odor
aspects. The profiles derived by Boelens and Haring, on one hand, and Dravnieks,
on the other, are not always in agreement, and there are striking differences for an
odorant so frequently encountered as eugenol. A primary source of the divergence
between their systems may have been the very different numbers of reference
materials (30 compounds, against 146 descriptors) used in the two systems, a
second source being differences in the nature of their panels of testers.
1.4. Descriptions Using Similarities

Useful information that avoids language and semantic problems can be obtained
by measuring odor similarities. Polak (1983) has discussed the problems asso-
ciated with descriptions of odor qualities and measurements of odor similari-
ties and concluded that “odor quality as such is not yet definable in scientific
terms. . . . The result is at best quantifiable as an order of similarities on an ordinal
scale.” The principal description systems based on similarities will be discussed
later in Section 2.3.
2. Classification of Odors
The general problems of classification of odors have been discussed in depth by
Kastner (1973). A brief survey of attempts to produce general classifications of
odors, based on somewhat arbitrary distinctions among empirical, semiempirical,
and statistically based classifications, will be given. It must be remembered that
all these classifications were established with different aims in mind, and they
differ also in terms of their theoretical foundations, which often are implicit and
sometimes absent. Therefore, comparisons should be made cautiously.
2.1. Empirical Classifications

The first attempt to classify odors in a general system seems to have been that
of Aristotle, who divided odors into six classes, a number that remained stable
until Linnaeus (1756) proposed seven classes in his Odores medicamentorum.
He described two classes ( fragrantes and aromatici) as pleasant, two classes
(tetri and nauseosi) as fetid, and two classes (ambrosiaci and hircini) as pleasant
for some persons and unpleasant for others. The pleasantness of the last class
(alliacei) was not considered. That classification was then used to describe the
medicinal properties of substances according to class. Fourcroy (1798) proposed

a classification of odors in five classes (or genera), based on their olfactory char-
acteristics and as well as on their extraction techniques and chemical stability.
Rouby and Sicard (1997) have discussed old and recent research on categoriza-
tion and reported numerous examples of classification.
Classifications by and for perfumers have been much more numerous and use-
ful: Following the development of a fragrance industry at the end of the nineteenth
century, large numbers of empirical classifications were proposed. A few have
been based on physical or psychophysical properties such as volatility, intensity,
and odor threshold, and they are more or less convergent. Classifications based
on qualities or similarities of odors are strongly dependent on the description
system used, which sometimes constitutes in itself the core of the classification.
They are more numerous and are in only partial agreement, the number and
nature of the classes remaining highly variable and far from being stabilized.
The major examples of those classifications were briefly discussed by Wells and
Billot (1988). Several important classifications, mostly taken from their work,
will now be considered.
Rimmel (1895) proposed an 18-group classification in which only three classes
referred to pure substances, and Zwaardemaker (1895) designed a classifi-
cation based on nine groups (“fragrant,” “ethereal,” “aromatic,” “ambrosiac,”
“alliaceous,” “empyreumatic,” “hircine,” “foul,” and “nauseous”) with a total of
30 subclasses. Some of the reference substances were pure compounds possess-
ing strong primary notes and only weak secondary notes.
Another interesting classification was suggested by Billot (1948), who pro-
posed a system of nine classes, each containing 2 to 10 subclasses. Brud (1986)
described an odor ring with 12 sectors (“floral,” “aldehydic-ozone,” “woody,”
“conifer/evergreen,” “mossy,” “green-herbal,” “spicy,” “citrus,” “balsamic,”
“fruity,” “animal,” and “lavender like”) that attempted to serve both classifi-
cation and description purposes. Cerbelaud (1951) designed a more detailed
system with 45 classes and noted that each group could share some characteris-
tics with other groups (e.g., the group of “rose” odors has features common with
eight other groups). Arctander (1969) decided on 88 classes and also assumed
some cross references among classes.
In a classic paper on the art of perfumery, the famous designer of perfumes
Edmond Roudnitska (1991) offered some general recommendations for begin-
ners, based on a system of 15 classes covering the most important series of odors.
He wrote that “an odorant may have several ‘faces’ or several nuances. The
observer must remain objective and not linger on any one pleasant or unpleasant
characteristic as this could completely prevent him from discerning the other
faces.”
The latter three authors clearly recognized that their classes and subclasses
were not mutually exclusive, that a substance could belong, to different degrees,
in more than one category, thus suggesting that appropriate data processing
(e.g., fuzzy logic and neural networks) could be used productively in classifi-
cations and studies of structure–odor relationships. The numbers of subclasses
found in several recent systems are between 40 and 45, a seemingly acceptable
compromise between the desired generality and ease of use.
2.2. Classifications Based on Primary Odors

These classifications are based on a small number of reference odors and on a
more or less strong belief in some sort of primary odors. Henning (1915) proposed
his famous olfactory prism of six reference odors (“spicy,” “resinous,” “burnt,”
“floral,” “fruity,” and “foul”). Crocker and Henderson (1927) used a system in
which four characters (“fragrant,” “acid,” “burnt,” and “caprylic”) constitute, in
a way, primary odors. The idea of primary odors was developed on the basis of
studies of specific anosmia by Amoore (1967, 1977, 1982), who postulated, at
least during the first stages of development of his theory, the existence of seven
primary odors, a number that later was greatly increased. Because the idea of
primary odor is no longer as popular as it once was, the importance of those
classifications is declining.
2.3. Classifications Based on Statistical Methods

Several researchers have tried to avoid a priori decisions regarding the number
and nature of classes by using multidimensional statistical methods applied to
large sets of data. Essentially, three types of data have been used: classic semantic
descriptions, descriptions emphasizing similarities, and odor profiles featuring
estimation of the intensity of each feature.
Classifications Based on Semantic Descriptions. No doubt it has long

been tempting to use the large numbers of high-quality olfactory descriptions
accumulated by perfumers (although they were not compiled using a single
description system) to produce odor classifications. Descriptors (often called
“notes”) can be considered as variables that describe chemical compounds, and
they should be, at least to some extent, independent and discriminating. Correla-
tively, notes can be considered as “described” by the list of chemical compounds
that possess them.
In a large data set consisting of olfactory descriptions of pure compounds,
odor classification depends on correct estimation of the distances between notes,
seen as points in an unknown n-dimensional olfactory space. When no intensity

indication is given, distances between notes can be estimated on the basis of
their occurrences and co-occurrences in the descriptions of all the compounds
in the sample, and the usual multidimensional statistics can be applied, followed
by more or less complex statistical treatment of the data.
Jaubert, Gordon, and Doré (1987a,b) compiled, from books by Arctander
(1969) and Fenaroli (1971) and several other sources, a set of 1,396 pure sub-
stances with detailed olfactory descriptions. Culling of descriptors led to a list
of 64 descriptors, then to 41 “archetypes” represented by 41 pure substances.
Finally, the olfactory space was described using 45 descriptors structured into
six principal poles (“amine,” “citrus,” “terpene,” “sulfur,” “pyrogenated,” and
“sweet”). A very similar description system is currently used by Jaubert in the
training of future perfumers.
Chastrette, Elmouaffek, and Zakarya (1986) compiled a large data bank from
the book of Arctander (1969) only. They used a set of 2,467 pure substances, the
odors of which were described using 270 words, reduced to 233 after elimination
of descriptors such as “strong,” “cool,” “warm,” and so forth that did not provide
purely olfactory information. There was an average number of 2.8 notes per com-
pound, and the 34 most frequent notes accounted for 80% of the total number of
occurrences. In a preliminary study, similarity coefficients were calculated from
occurrences and co-occurrences of the 24 most frequently encountered notes,
and multidimensional methods were used to represent the olfactory space. It ap-
peared that those notes were largely independent and that the olfactory space was
not hierarchically organized. Some notes like “amber” and “anise” were rather
isolated, and others such as “minty/camphoraceous” constituted pairs of notes.
In a more detailed study of the same data set, Chastrette, Elmouaffek, and
Sauvegrain (1988) selected the 74 most frequently encountered notes and calcu-
lated the similarities between pairs of notes. They found generally low similarities
(no similarity for about 63% of the pairs) and strong associations for a few pairs
only, such as “pineapple” and “banana,” “camphor” and “minty,” “apricot” and
“peachy.” A cluster analysis resulted in a distribution of 60 notes into 27 groups,
and 14 other notes were not parts of groups. It was concluded that no primary
odors could be identified and that the olfactory space, as defined by a set of notes,
should be seen as a continuum, as proposed by Holley and MacLeod (1977). The
so-called isolated notes were considered as good candidates for future studies
of structure–odor relationships, in contrast to ill-defined notes such as “fruity”
and “floral.”
Chastrette, de Saint Laumer, and Sauvegrain (1991) analyzed a system of
description used by a group of perfumers at Firmenich S.A. in which olfactory
descriptions contained a maximum of four descriptors, chosen by consensus on
smelling a given compound, from a list of 32 words. A data matrix obtained for
628 pure compounds was analyzed by means of four multidimensional statistical
methods that gave results both convergent and in agreement with the practice of
perfumers.
Abe et al. (1990) used a data set of 1,573 compounds, also taken from the book
by Arctander, and selected 126 odor descriptors. A cluster analysis based on
occurrences and co-occurrences of descriptors resulted in 19 “obvious” clusters,
in good agreement with those found in previous studies. The four most frequent
descriptors (“fruity,” “floral, “herbaceous,” and “green”) were considered as
fundamental odor descriptors. It seems that those words would be used in the
first step of a description being drafted by an expert, who, for example, would
recognize first a fruity odor and later would specify which fruit. The descriptors
characterizing the clusters were compared to 38 odor descriptors chosen by
Jennings-White (1984) to represent the primary odors. In a cautious conclusion,
the authors considered that “semantic description is the only practical method
of representing odor quality, but it tends to be too emotional and subjective.”
In earlier studies, unfortunately not based on semantic descriptions, but also
using multidimensional statistics, Abe et al. (1987, 1988) sought to determine
if purely physicochemical results obtained from sensor data could be used to
classify and predict odors. They used cluster analysis on data obtained for 30
substances using eight gas-sensing semiconductor elements. A few obvious clus-
ters were observed and were found to correspond to “ethereal,” “ethereal-minty,”
“minty,” “ethereal-pungent,” and “pungent” substances (Abe et al., 1987). Those
authors suggest that their “semiconductor sensor system, though its sensing
mechanism is quite different from that of biosystems, makes it possible to iden-
tify the odors of chemical substances.” Their underlying hypothesis that “because
odor is an inherent property of substances, identification of substances should
correspond to identification of odors” might be seen with some suspicion by
physiologists and psychologists working in olfaction. Abe et al. (1988) extended
their studies to a set of data produced in response to vapors from 47 pure sub-
stances and applied three pattern-recognition techniques.
Classifications Based on Odor Profiles. Kastner (1973) has traced the

origins of the profile methods. The classification by Crocker and Henderson
(1927) was based on very simple odor profiles. As profile data are rather difficult
to obtain, only a few good data sets have been used in several studies using
different statistical treatments.
A first data set was produced by Wright and Michels (1964), who used nine
standards and asked members of a panel to rate the similarities of 45 com-
pounds or mixtures to each of those nine standards. From that set, Schiffman
(1974), using a nonlinear multidimensional scaling technique, obtained a two-

dimensional map of the nine-dimensional space defined by those similarities.
She found two large clusters (one more pleasant than the other, in agreement
with several studies showing the role of hedonic factors) and several subsets and
related them to physicochemical properties. She concluded that “there are no
clear psychological groups or classes of stimuli, merely trends.”
McGill and Kowalski (1977) used 43 physical properties to see how well
they could explain that nine-dimensional olfactory space. A factor analysis led
them to the representation of a two-dimensional continuum retaining 74% of the
total variance, with only two identifiable axes, reflecting electron distribution
and symmetry on the first axis, and the degree of electron delocalization on
the second axis. Coxon, Gregson, and Paddick (1978) used odor profiles for 18
compounds and 5 reference compounds, each rated on how it exemplified each
of the nine selected descriptors. Four- and five-dimensional classifications were
obtained (the first dimension, again, being related to hedonic aspects).
Yoshida (1975) selected 32 standard odors from several sources, including the
paper by Wright and Michels (1964), and asked 20 students to rate the similarities
of 40 essential oils to each of those standard stimuli, on a nine-point scale.
Statistical analyses (principal-component analysis, PCA, and multidimensional
scaling, MDS) were performed on the similarity-data matrix. PCA yielded seven
factors, and on factorial maps, stimuli were again clearly separated. The first axis
was linked to the kind of stimulus, the second axis discriminated unpleasant and
pleasant groups, and the third reflected the opposition between “resinous-spicy”
and “sweet.” The meaning of the other dimensions was unclear.
Another set was compiled by Boelens and Haring (1981), who defined profiles
for 309 compounds using 30 reference materials. A multivariate statistical treat-
ment led to the definition of 14 groups, without an attempt to obtain a graphic
representation. Ennis et al. (1982) analyzed the same set of data using several
methods of multivariate analysis and obtained 27 groups, some containing only
a few compounds.
In the descriptions proposed by Dravnieks (1985), each substance can be
seen as defined in an olfactory space with 146 dimensions. Correlation coef-
ficients calculated in our laboratory for all possible pairs of descriptors show
some expected correlations, positive (e.g., “lemon,” “grapefruit,” and “orange”)
and negative (“light” and “heavy”), but a surprising absence of a negative link
between the two opposite descriptors “cool” and “warm.”
Both linear and nonlinear multidimensional analyses have confirmed that no
clear hierarchical structure can be detected in the olfactory space defined by
descriptors, and they have shown the dominance of hedonic characteristics even
in experiments using carefully planned protocols. This brief survey shows that
profile ratings provide interesting data for classification studies. However, it

should not be forgotten that they are also expensive and time-consuming.
Classifications Based on Similarity Data. Similarity judgments for all

pairs of stimuli in a group of nine pyridyl ketones, provided by a panel of nine
subjects, were used by Southwick and Schiffman (1980) and Schiffman (1983)
to represent those compounds in a three-dimensional space and to investigate
relationships between odor quality and physicochemical parameters.
Jaubert et al. (1987b) selected 50 molecules to span the whole olfactory space,
as defined in a previous work (Jaubert et al., 1987a), and asked a panel of experts
to rate the similarities of all possible pairs. The 50 × 50 similarity matrix was
submitted to multidimensional statistical analyses, which resulted in an olfactory
space in which nine zones could be distinguished. Moskowitz and Gerbers (1974)
used similarity ratings among 15 odors and 17 descriptors, evaluated across four
days, to generate a two-dimensional representation of odorants and descriptors.
In a pilot study preceding some work mentioned earlier, Coxon et al. (1978)
asked subjects to estimate the similarities among nine pure substances. The
study showed consistency in responses between groups of subjects and between
replications a week apart, but was not otherwise exploited.
Lawless (1989) examined a more limited section of the olfactory space and
used simple sorting procedures to obtain similarity estimates for 18 chemicals
or essential oils that fell into three a priori categories: “woody,” “citrus,” and
“partially woody and citrus.” A multidimensional analysis (MDS) was performed
on the similarity estimates. The implications of that research and of several other
studies for the structure of the olfactory space were discussed, and the conclusion
was that “odor space may resemble an n-dimensional head of cauliflower more
than a simple Euclidean map.”
It seems fair to conclude from this survey of a large number of published
classifications of odors that all studies indicate a weak structure of the olfactory
space. The dimensionality of olfactory space, as defined by the data and methods
used to establish it, appears to be rather high, and the nature and significance of
these dimensions remain unclear. A hierarchical structure was never observed,
and, moreover, all multidimensional studies confirmed that classes of odors are
not sharply delineated.
2.4. Classification of Perfumes

Classification of perfumes is a difficult task, as they are complex mixtures that
can smell quite differently to customers and to perfumers. The most important
classification was proposed by the Société Française des Parfumeurs in 1988,
followed a decade later by a new version (SFP, 1998). Perfumes, without dis-
tinction as to masculine or feminine, are classified in seven families, with a total
of 45 subfamilies. Several other interesting classifications, such as the fragrance
octagons of Dragoco that have been proposed by some perfume companies, will
not be discussed here. Jellinek (1992) presented a critical study of existing classi-
fications showing that perfumers and consumers have different perceptions, and
proposed “a classification method that is more in line with consumer perceptions
and needs than the ones currently in use.”
3. Structure–Odor Relationships
Chemical structure is highly determinative of the quality and also the intensity
of an odor. It might seem at first sight that studies of quality would be almost the
sole interest of the perfume industry, as they offer ways to design new compounds
possessing interesting olfactory properties. In fact, intensity is also taken into
account, and compounds with high intensities are avidly sought. Nevertheless,
the vast majority of structure–odor relationships are concerned mainly with
quality.
3.1. Intensity Data

Intensity parameters of interest in various domains of olfaction are olfactory
thresholds and dose–response relationships linking the perceived intensity and
the stimulus concentration. Dose–response relationships are always difficult to
establish because of the often poor quality of intensity data. This discussion will
be restricted to olfactory thresholds, which have been more frequently studied.
Odor thresholds have been measured for more than a century (Cain, 1978),
and hundreds of compilations of threshold data have been published. Olfactory
thresholds show large person-to-person variability. They can differ by four and
even five orders of magnitude, and variations by a factor of a thousand are quite
common (Brown, McLean, and Robinette, 1968). As a result, even the published
thresholds, which are means obtained from panels of several persons, involve
enormous variability. The relatively large body of data available is very difficult
to use because of the intrinsic variability in the data and the variety of methods
used to obtain them. Devos et al. (1990) tried to circumvent those difficulties in
publishing a useful compilation of olfactory thresholds.
In a series of papers, Schnabel, Belitz, and Von Ranson (1988), Von Ranson
and Belitz (1992a,b), and Von Ranson, Schnabel, and Belitz 1992) reported
odor profiles and olfactory thresholds for a large number of oxygenated com-
pounds. Threshold values were measured in aqueous solutions and correlated
with structural parameters. In the first paper, Schnabel et al. (1988) reported
those values for a set of 281 compounds, including a subset of 99 aliphatic
alcohols (from C1 to C12 ) that later was used by several groups.
Anker, Jurs, and Edwards (1990) generated a set of 112 descriptors for 53
of those alcohols. From that set, four descriptors were found significant, and
attempts were made to understand their physical meaning. Zakarya (1992) also
used 53 alcohols from the Schnabel set and obtained good correlations using
different sets of variables, including autocorrelation vectors. Edwards, Anker,
and Jurs (1991), using a data set of 53 of those alcohols, obtained a good four-
parameter regression equation, after removal of four outliers. With a data set
including 60 pyrazines (Mihara and Masuda, 1988) and 14 other pyrazine deriva-
tives, they obtained a five-parameter regression equation, those five parameters
having been selected from a set of over 100 variables including various sorts of
descriptors as well as physical properties.
Chastrette, Crétin, and El Aidi (1996), thinking that the quality of odors might
be important even in a study of thresholds, selected a subset of 45 alcohols de-
scribed as “camphoraceous.” By means of a three-layer back-propagation neural
network, with input variables describing the sizes of substituents on a common
skeleton, they were able to correctly calculate 91% of the logarithms of concen-
trations at the threshold in the learning phase, but only 78% in the prediction
phase, probably as a result of a structural description that was too crude.
3.2. Quality Data

Lucretius probably was the first to suggest a theoretical basis for olfactory proper-
ties by relating them to the shape of atoms. Guillot (1948) discussed the problem
of structure–odor relationships (SORs) in relation to specific anosmia. More
ambitious SORs have been based on the large variety of so-called theories of
olfaction, which actually are theories of the molecule–receptor interaction. An
impressive number of SORs for a large variety of odors, generally of interest in
the perfume industry, have recently been published. For detailed descriptions of
many successful SORs, see the recent reviews by Rossiter (1996) and Chastrette
(1997). Only a brief description of the principal strategies used to establish SORs
will be presented here.
The first step in establishing an SOR is compilation of a data bank including
olfactory descriptions for a large number of molecules. Such descriptions must be
obtained from perfumers and flavorists because of the difficulty of such a task for
untrained persons. They should also be homogeneous (i.e., provided by the same
perfumers for all the substances in the sample). The substances in the sample
must be clearly distinguished chemical compounds, as pure as possible (minute
impurities can significantly modify odors). Isomers and even enantiomers must
be considered as distinct compounds, and consequently racemic mixtures should
be avoided. Molecules with low degrees of flexibility, for example, cyclic or
polycyclic molecules, are preferred to those that can assume many different
conformations.
The second step consists in the selection of variables to define the chemical
structure. This is not as simple as it might appear, for such a selection relies on
a more or less implicit theory of the interaction between molecules of odorant
and receptors. Recent progress in understanding the structures of receptors has
led to wider application of methods classically used in pharmacologic studies,
and researchers are continually searching for some aspect or part of a molecule
that reasonably could be expected to interact with proteins. They will be looking
for structural elements possibly involved in hydrogen bonding and dispersion
interactions, for example.
The third step is to establish a relationship between a set of variables describing
the chemical structure and a set of variables describing the odor. Researchers
in this field have used a vast array of statistical methods, including linear and
nonlinear procedures.
4. Conclusion
The description of an odor supposes that both its quality and intensity charac-
teristics can be precisely defined. Many different description systems, based
variously on profiles or on similarities or on a thesaurus of words referring not
only to pure substances but also to complex mixtures, have proved useful in the
domains where olfactory descriptions are necessary. Unfortunately, as no gen-
eral agreement has ever been reached, comparisons between any two systems
are not easy, and compiling large data bases remains a difficult task. Moreover,
olfactory perceptions are always more or less mixed with psychological aspects,
and consequently physiological data are not so pure as one would wish. When
intensity data are collected, huge inter-individual variations and the use of differ-
ent measurement techniques introduce enormous variability into published data.
However, some useful compilations have been achieved.
Notwithstanding the often poor quality of olfactory data, large numbers of
meaningful structure–odor relationships have been established in recent years,
in academic laboratories as well as in industrial research, by means of a vast
array of multidimensional statistical methods.
Numerous classifications based on different description systems and taxo-
nomic procedures have been published. These classifications can be quite dif-
ferent, as they reflect the different needs of their authors. As stated by Harper
(1966), “classifications can be carried out for a variety of purposes. . . . In the

widest possible context the aim is to develop a universal system, within which
all existing and all future odours could be placed.” We are still far from reaching
that goal, but researches generally agree that the olfactory space is a sort of
continuum, where the elements are not hierarchically organized.
In fact, classifications reflect complex cognitive processes and depend on the
needs and motivations of their authors, as well as on their choices of description
systems and statistical treatments.
Acknowledgments
I am grateful to the Fondation Roudnitska, which generously supported our
research on odor classification and structure–odor relationships.
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Section Three
Emotion
Going against the Cartesian tradition, Darwin considered emotions as behavioral

adaptations, “useful habits” inherited during phylogeny. Many authors think of
olfaction in much the same way: Like emotion, olfactory perception challenges
rational explanations of the world, and language itself. In the nineteenth cen-
tury, efforts were made to find links between such perceptions and knowledge,
which in turn implied a questioning of established knowledge. As psychologists,
Hermans and Baeyens (Chapter 8) are specialists in a form of learning: evalu-
ative conditioning, which supposes no awareness of the contingency between
conditioned and unconditioned stimuli and is resistant to extinction. They have
designed “ecologically valid” experiments, such as a bathroom study and a mas-
sage study, showing how emotional valuations of odors can be acquired and also
changed during adult life without awareness. Such experiments, if they confirm
that olfaction is an emotional sense, may also indicate that emotional processing
of odors does not differ from emotional processing in other modalities. This is
in contrast with memory processing, as will be discussed in Section 4.
In Chapter 9, Rouby and Bensafi question the concept of a hedonic dimension
as a continuous variation between pleasantness and unpleasantness. They gather
convergent cues from different disciplines indicating that hedonic judgment can
distinguish two main types of odors: those that may have meanings and possibly
attributes, and those that primarily have effects on the perceiver (see Section 2).
Moreover, they propose the hypothesis that faster and more automatic neural
networks subserve the processing of unpleasant odors.
What Herz, in Chapter 10, calls affective cognition is manifested as odor-
induced modulations of moods, attitudes, memories, performances, and even
perceptions of health: Odors can operate as conditioning stimuli, and later ex-
posure to the same odors may influence behavior in a covert way. Beliefs and
misinformation in turn are able to influence perceptual processes like adaptation.
Challenging the claim that odors are better cues to memory than pictures and
118 Section 3: Emotion
sounds, several experiments by Herz have shown that memories associated with
odors are more emotional, but not more efficient, than memories associated with
other sensory modalities.
The review by Jacob and colleagues (Chapter 11) enlarges our conception of
odor effects beyond perception and explains how chemical substances that are
not even smelled or do not even have any odor may affect us in different ways.
Avoiding magical explanations for marketing techniques and phenomena, they
discuss the topic of human pheromones, maintaining their necessary distance in a
field deeply invested by passions and by economy, where desires can be mistaken
for reality. Do we react to specific chemical signals in the same way as other
animals? Their recent studies, if they do not cast doubt on the physiologic effects
of some chemical signals, question the idea that chemicals can trigger complex
behaviors in humans as in other mammals; rather, they show that chemical signals
can influence mood in rather subtle ways.
Conceiving emotions as a set of basic, qualitatively different states, instead of
points on a positive–negative continuum, Phillips and Heining, in Chapter 12,
report on the use of one of the most recent tools of cognitive neuroscience,
namely, functional magnetic-resonance imaging, to highlight the complex rela-
tionships involving taste, odor, the experience of disgust, and the brain. Disgust
is especially representative of human emotion because it evolves from the uncon-
ditional, inborn responses of newborns to become elaborate social and symbolic
representations that remain deeply rooted in the body experience.
8
Acquisition and Activation of Odor Hedonics
in Everyday Situations: Conditioning
and Priming Studies
Dirk Hermans and Frank Baeyens
1. Odor Hedonics: Acquired Evaluative Meaning

Odors and the reactions of liking and disliking are so intimately intertwined that
it would be difficult to object to the statement (Richardson and Zucco, 1989)
that “it is clearly the hedonic meaning of odor that dominates odor perception”
(p. 353). The fact that the affective/emotional consequences of odor stimuli are so
powerful makes it possible for an economically important industry – perfumery –
to thrive on the production of substances whose only real function is to elicit
highly positive reactions. Also, because the principal distinctive properties of
food flavors are provided by olfaction rather than by taste cues (Rozin, 1982),
it could reasonably be argued that the whole of culinary culture is based largely
on the same strong connection between evaluative meaning and odor. Besides
eliciting the reactions of mere liking or disliking, odors can have considerable
emotional impact (Ehrlichman and Halpern, 1988; Miltner et al., 1994). This
bond between odors and emotions has long been recognized, and hence it may
not be that surprising that the subcortical limbic system, which is considered to
be of critical importance in the generation of emotions, was originally known as
the rhinencephalon or the “smell brain” (Van Toller, 1988).
Although the evaluative and emotional components and consequences of odors
have been given a lot of thought, it is less well appreciated that most human
evaluative reactions toward odor stimuli are not fixed and innate, but are largely
the products of associative learning (Engen, 1988; Bartoshuk, 1994). Remarkably
enough, the experimental evidence for evaluative learning about odors in humans
is surprisingly meager. This is true for odors perceived retronasally as part of
consumed odor/taste mixtures (“flavors”), and even more so for odors perceived
orthonasally as sniffed substances (“smells”). More specifically, the literature on
smell-preference learning in humans is limited to a few scattered demonstrations
of the mere existence of the phenomenon (e.g., Hvastja and Zanuttnni, 1989),
119
120 Dirk Hermans and Frank Baeyens
and the conditions of and the processes involved in human evaluative flavor-
taste learning have just recently begun to attract the experimental attention they
deserve (Baeyens et al., 1998), as discussed later. Hence, it remains a challenge
and an important and interesting enterprise to investigate experimentally the
(associative) processes by which odors acquire positive or negative valence, that
is to say, their affective meanings.
It seems clear that nonassociative effects of mere exposure can contribute
to changes in odor preferences (e.g., Balogh and Porter, 1988). Nevertheless,
associative processes, and more specifically Pavlovian associative conditioning,
have been suggested as major sources of evaluative odor learning. The theory
of Pavlovian learning as it applies here is that when an odor that is perceived as
neutral is paired with any liked or disliked event, that may be sufficient to change
one’s perception of the originally neutral odor into perception of a stimulus with
positive or negative valence. A study by Hvastja and Zanuttini (1989) provides
a good example of that phenomenon. They exposed groups of six- and eight-
year-old children to simultaneous presentations of various odors and positive or
negative images on photographic slides. One month after that learning phase,
there were significantly more favorable ratings for odors that had previously been
paired with the positive images. As the odors were presented equally often in both
the positive and negative contexts, mere exposure cannot account for the acquired
evaluative differentiation. Also, given the fact that testing took place one month
after the original odor–slide pairings, a nonassociative mood effect can be ruled
out as an alternative explanation. Although it was not conducted fully within the
parameters of fundamental research on learning processes, that study provides
an empirical demonstration of the idea that associative processes may play an
important role in the acquisition of odor hedonics. It shows a laboratory analogue
of an experience that most of us will have encountered before, namely, that a
previously neutral odor acquired a positive or negative valence for us because
of its contiguous presentation with a positive or negative event. For instance,
the odor of a given perfume originally perceived as neutral may have taken on a
positive valence through its association with an attractive and charming person
who used to wear that fragrance, perhaps the person with whom you were in
love at the time.
If we conceptualize the odor as a conditioned stimulus (CS), and the positive/
negative stimulus or event as an unconditioned stimulus (US), both the per-
fume anecdote and isolated studies, such as the one by Hvastja and Zanuttini
(1989), can be situated within the empirically rich research tradition on evaluative
conditioning that has been studied extensively in our laboratory in Leuven. In the
remainder of this chapter we shall explore the concept of evaluative condition-
ing and describe two experimental field studies of evaluative odor conditioning
Acquisition and Activation of Odor Valence 121
that were conducted at our laboratory. Next, we shall discuss how associa-
tive learning might contribute to the emotional influence that odors can have
in our daily lives. A replication of an odor-conditioning study that was originally
conducted by Kirk-Smith, Van Toller, and Dodd (1983) will be the basis for
a more fundamental reflection on the automatic (unconscious) affective influ-
ences of odors. This discussion will be in the context of research on automatic
affective processing, which has been a second major line of research at our
laboratory.
2. Acquisition of Odor Hedonics: Evaluative

Odor-Conditioning Studies
“Evaluative conditioning” refers to the situation in which simultaneous exposure
to a neutral stimulus (conditioned stimulus, CS) and a positively or negatively
valenced stimulus (unconditioned stimulus, US) can result in the originally neu-
tral CS itself acquiring a valence congruent with the affective value of the US
(Levey and Martin, 1987). For example, after a neutral picture of a human face
has repeatedly been paired with a liked (or disliked) picture of another face,
research participants typically demonstrate an acquired liking (or disliking) for
the originally neutral face (e.g., Baeyens et al., 1992). That pattern has now been
demonstrated using stimuli from different sensory modalities. Besides a wide
range of studies using visual stimuli as CSs and USs, evaluative conditioning
has also been demonstrated with olfactory and gustatory stimuli. Although in the
bulk of this chapter we shall discuss some interesting studies from our laboratory
in which evaluative learning with odors was demonstrated, we shall first focus
on a series of flavor-conditioning studies to clarify some of the most important
characteristics of evaluative conditioning in general.
The evaluative flavor–flavor learning paradigm is a conditioning framework
that has proved to be a very efficient tool for study of human evaluative learning.
In this differential-conditioning paradigm, which was first developed by Zellner
et al. (1983) and extended at our laboratory, research participants were exposed
to a series of flavored and colored water solutions containing the appropriate
CS+ /US and CS− contingencies. Several experiments showed that after an orig-
inally neutral fruit flavor A (CS+) had been presented several times mixed with
the bad-tasting substance Tween 20 (Polysorbate 20) as the US, research partic-
ipants developed a dislike for the pure flavor A relative to a similar fruit flavor B
(CS−) that had been presented equally often in plain water (e.g., Baeyens et al.,
1990b).
We are beginning to achieve a more detailed understanding of the conditions
and characteristics of this type of evaluative learning with flavors. The available
evidence indicates that this learning effect is quite robust, in that (1) it involves
rapid learning, (2) it survives the passage of time, (3) it is not influenced by
the color of the solutions, (4) it can be achieved with sequential rather than
simultaneous presentations of CS and US flavors, albeit in a weaker form, and
(5) it allows for an observational mode rather than a direct mode of presenting
the crucial CS–US information (Baeyens et al., 1990b, 1995a, 1998).
Two properties of evaluative flavor–flavor learning bring it into line with the
functional characteristics of other evaluative-conditioning designs and at the
same time justify a distinction between evaluative learning and other forms of
Pavlovian learning, such as expectancy learning (Baeyens, Eelen, and Crombez,
1995b). The first property concerns the role of explicit knowledge about the
CS–US relation (i.e., “contingency awareness”). Expectancy learning, involving
the acquisition of preparatory (defensive, appetitive, or orienting) conditioned
responses, has repeatedly been shown to require awareness of the CS–US con-
tingency (Dawson and Shell, 1982). In contrast, evidence is accumulating from
several study designs that contingency awareness is not a necessary condition
for evaluative conditioning (e.g., Baeyens, Eelen, and Van den Bergh, 1990a;
De Houwer, Baeyens, and Eelen, 1994). In line with this, evaluative flavor–
flavor learning has been demonstrated to proceed orthogonally to conscious
identification of the CS–US flavor contingencies. For example, in two studies
(Baeyens et al., 1990b, 1996a) a double dissociation between evaluative learn-
ing and conscious acquisition of knowledge was observed, in that with flavors
functioning as the CS+/CS−, none of the participants demonstrated awareness
of the stimulus relations, but they evidenced clear conditioning; on the other
hand, when colors acted as the CS+/CS−, a substantial number of participants
were contingency-aware, but no evaluative conditioning was observed (Baeyens
et al., 1996a).
The second important functional property of evaluative learning for flavors per-
tains to the interrelated phenomena of “extinction” and “contingency sensitivity.”
In cases of expectancy learning, unreinforced CS presentations after the acqui-
sition phase (i.e., an extinction procedure, during which the CS+ is no longer
followed by the US) result in a decrease or complete disappearance of the condi-
tioned preparatory responses. Similarly, presentation of unreinforced CSs during
the learning phase, thus lowering the CS–US contingency, clearly attenuates the
acquisition of conditioned responses. Descriptively, both phenomena can be
thought of as the result of expectancy disconfirmation (the expected US does
not arrive). The main reason to conceive of evaluative learning as qualitatively
different from expectancy learning is that unreinforced CS presentations, either
during or after acquisition, do not seem to have an effect on this type of condi-
tioning: Evaluative conditioning is resistant to extinction (Baeyens et al., 1988,
1995b, 1989) and to CS–US contingency manipulations (Baeyens, Hermans,

and Eelen, 1993). In line with this, in the evaluative flavor–flavor paradigm it
was observed that post-acquisition unreinforced CS presentations (extinction
procedure) did not attenuate the acquired flavor dislike (Baeyens et al., 1995a,
1996a) and that an acquisition schedule containing equal numbers of Tween-20-
reinforced and nonreinforced flavor trials resulted in an acquired flavor dislike
equally as strong as that produced by an acquisition schedule containing the
same number of reinforced, but no unreinforced, learning trials (Baeyens et al.,
1996a).
These findings justify considering evaluative learning as a prototypical ex-
ample of a Pavlovian learning process mediated by what we have named the
“referential system” (Baeyens et al., 1995a). According to this hypothesis, dur-
ing acquisition an association is built up (consciously or unconsciously) be-
tween CS and US representations following a rudimentary learning algorithm,
the parameters of which include only temporal contiguity and stimulus salience:
Synchronous activation of CS and US representations results in an increase in as-
sociative strength, whereas activation of the representation of the CS alone (or of
the US alone) is causally ineffective. Because of this associative link, activation
of the representation of the CS flavor activates (consciously or unconsciously)
a representation of the US (i.e., the bad-tasting substance Tween 20) that is be-
haviorally expressed in a dislike for the CS flavor. Thus, it is hypothesized that
this whole process can (but will not necessarily) take place in the absence of any
engendered expectation that the US is really going to arrive momentarily, and
without triggering defensive preparatory responses.
Translated to the study of odors, all this information would seem to imply that
an originally neutral odor could acquire a positive or negative valence through a
contiguous occurrence of a positive or negative event, even without the person
being aware of the crucial association between the odor (the CS) and the US with
which it was associated. Nevertheless, it is assumed that the newly acquired odor
valence is based on this CS–US association, in that the odor is linked, consciously
or unconsciously, to the positive or negative US. From this perspective, the fra-
grance mentioned in the earlier perfume anecdote is assumed to be evaluated
as pleasant and agreeable not because it has gained any new “intrinsic” valence
but because it makes one think (unconsciously) of the person who wore it and
with whom one was in love. Moreover, one would expect the odor to retain its
acquired positive valence, even if the real-life contingency between the perfume
and one’s beloved no longer held. Although the evaluative differentiation re-
ported in the study of Hvastja and Zanuttini (1989) likely was due to such a
process of evaluative conditioning, the potential for extraneous effects of social
desirability or other demand effects was not clearly eliminated in their study.
Therefore, in two experimental field studies, we attempted to further investigate

the possibility of evaluative odor conditioning.
2.1. Bathroom Study

In a first study, Baeyens et al. (1996b) investigated whether or not a room’s
background odor (CS) that was quite “natural” for the specific environment
could be perceived as acquiring the affective-evaluative tone of the situation and
activities with which it was associated. In this study, we implemented a real-life
contingency between an odor as the CS and toilet rooms or toilet-room activities
as the conceptual US. We made use of the fact that each unit in our department
has its own nearby bathroom, and the majority of people frequent only their own
unit’s bathroom. Also, at the time of this study, air-refreshers were not used in the
toilet rooms. Thus it was possible to establish a multi-trial real-life conditioning
schedule with simultaneous presentations of one particular odorant (CS) and the
toilet-room and toilet-activity stimuli (US).
During the conditioning phase, two different odors were used on a between-
subjects basis: lavender and pine. The odors were presented by means of stand-
alone automatic odor dispensers that were placed inconspicuously above the
ceiling slats of 10 toilet rooms in the faculty building. Five were located in toilet
rooms on the back side of the building (location A), and five were located on two
floors on the front side of the building (location B). Participants from location
A in the building received several days of exposure to the lavender odor in their
toilet rooms. For that group, pine was the control odor. Participants from location
B in the building were exposed to the pine odor in their toilet rooms, and for
them lavender functioned as the control odor.
After the conditioning phase, the odor dispensers were removed from the bath-
rooms, and after a delay of several days, employees whose offices were in the
proximity of the toilet rooms treated with the odors were invited to participate in
“a short pilot study on odor perception.” During that part of the experiment, par-
ticipants were asked to rate the two odors on 11 semantic rating scales covering
Osgood’s three dimensions of semantic meaning: “valence” (5 items), “potency”
(3 items), and “activity” (3 items) (Osgood, Suci, and Tannenbaum, 1957). To
assess the participants’ awareness of the fact that one of the odors was the same
as the one that had earlier been presented in their toilet rooms, they were asked
if they had ever smelled either odor before, and if so, in what context or product.
Finally, because it was assumed that the people probably differed in terms of the
frequency with which they visited the toilet rooms (some might visit the toilet
room as a relaxing break from work, whereas others might experience it as a
necessary evil), they were asked to indicate whether or not they usually liked
entering the toilet room, using a −10 (“necessary evil”) to +10 (“agreeable break
from work”) rating scale.
When the group of participants was subdivided on the basis of the latter ratings,
it was possible to demonstrate an evaluative odor discrimination in line with what
would be expected on the basis of the evaluative-conditioning hypothesis. That
is, the participants who rather liked going to the toilet room evaluated the
toilet-paired conditioning odor more positively than the control odor, whereas
the reverse was true for people who rather disliked going to the toilet room.
That effect was observed in a situation in which few of the participants (15%)
recognized the CS odor as being the odor that had earlier been presented in the
toilet rooms, making it very implausible that experimental demand could account
for the observed differences. Moreover, when the data for the participants who
were aware of the CS (odor)–US (toilet) contingency were excluded from the
analysis, a similar result was obtained. Also, no conditioning effects could be
demonstrated for the “activity” and “potency” ratings.
Consequently, these data provide clear support for the possibility of Pavlovian
evaluative learning about odors in adult human participants. A second study
(Baeyens et al., 1996b) was devised in an attempt to replicate those findings
conceptually in the context of therapeutic massages performed by a professional
physiotherapist.
2.2. Massage Study

In this second experimental field study, we obtained the cooperation of a physio-
therapist who was instructed to use massage oil containing one of two CS odors
during a series of therapeutic massages (US) on clients who frequented his prac-
tice. On the basis of their medical diagnoses, half of the participants were treated
with positive-relaxing massages, whereas the other half of the participants were
treated with less positive, and sometimes even negative-painful, massages.
Orthogonal to that manipulation, and also on a between-subjects basis, two differ-
ent odors were used during the conditioning phase. Half of the patients were treat-
ed with odor A, and half with odor B. Both odors were etheric oils and were selec-
ted on the basis of a pilot study in which they were similarly rated for Osgood’s
semantic dimensions (valence, potency, and activity) (Osgood et al., 1957).
The main purpose of the study was to demonstrate in an adult population that
a rather salient odor (the CS) that was quite natural in the given setting might
acquire the affective-evaluative tone of the events with which it was associ-
ated. That was achieved by establishing a contingency between an odor (the CS)
and the bodily sensations resulting from either positive (relaxing) or less posi-
tive (negative-painful) massage treatments (USs). Hence, it was predicted that
participants in the “positive” massage group would rate the treatment odor
more positively than the control odor, whereas the reverse was expected for the
“negative” massage group. That was indeed confirmed. About one week after
the final treatment session, the patients returned to the physiotherapist for the
standard follow-up visit. At that time the physiotherapist explained that a pharma-
cological company had asked him to invite his patients to evaluate two massage
oils that they were planning to bring onto the market, and they were interested
primarily in the odors of the oils. Next the patients were asked to rate the two
odors on a series of items in the “valence” and “dynamism” dimensions (where
“dynamism” is a combination of Osgood’s original “activity” and “potency”
dimensions; see also Osgood et al., 1957). Patients were also asked to rate the
massage treatment they had gone through during the preceding weeks.
As predicted, the crucial interaction involving conditioning (experimental odor
versus control odor) and massage type (positive versus negative reactions to
massage) was highly significant. Subsequent analyses demonstrated that for the
“positive” massage group, the odor that was used in the massage oil was rated as
more pleasant than the control odor. Also, the massage odor was experienced as
less dynamic (active/potent) than the control odor. For the “negative” massage
group, however, there was no significant impact of conditioning on the “valence”
and “dynamism” ratings of the odors. However, that was not really surprising,
given that we apparently failed to administer a negatively valenced US (massage),
because the intended negative-painful massage treatments were experienced by
the patients as rather neutral events.
Interesting from a theoretical point of view was that the conditioning effect in
the “positive” massage group was not dependent on conscious recognition of the
experimental odor. In fact, when participants were explicitly questioned whether
or not they had ever smelled the experimental odor before, quite surprisingly
only 13 of the 34 participants recognized the experimental odor as the odor
to which they had been exposed during the massage treatments. When only
those participants who were unaware of the crucial CS (odor)–US (massage)
contingency were taken into account, the conditioning effects for odor “valence”
and odor “dynamism” could still be demonstrated in the “positive” massage
group. In other words, awareness of the fact that the odor had been encountered
before during the therapeutic massage treatment was not a necessary precondition
for the conditioning effect to occur.
In sum, the data of the massage study demonstrate that not only odor “valence”
but also odor “dynamism” can be influenced by Pavlovian contingencies. As it
has often been argued that “valence” and “dynamism” (or “activity/arousal”) are
the two basic dimensions underlying emotional meaning (Osgood et al., 1957;
Lang, Bradley, and Cuthbert, 1990), these data seem to indicate that Pavlovian
conditioning may be able to shape or modify the core emotional meanings evoked
by odors.
3. Acquisition and Activation of Odor Hedonics: Emotional

Influences of Aversive Conditioning
In the two preceding studies it was demonstrated that an evaluative-conditioning
process can take place even if the subject is unaware of the crucial CS–US contin-
gency. In both studies, most of the participants were unaware of the CS–US con-
tingency, for although the odors were used at clearly noticeable concentrations,
they were used in situations in which people are accustomed to the presence of
odor stimuli (scented massage oil, air-refreshers in toilets). Another strategy was
used by Kirk-Smith et al.(1983), who published the article “Unconscious Odour
Conditioning in Human Subjects” in Biological Psychology. There the CS–US
contingency was masked by using an unfamiliar odor that was presented at a
very low, hardly noticeable concentration. Their study is particularly interesting
because it demonstrated that the associative learning that occurs in the relation-
ship between an odor (CS) and an emotionally toned event (US) not only can
change one’s evaluation of that odor but also can have other affective/emotional
influences when that odor is encountered later in another situation.
3.1. The Study by Kirk-Smith et al. (1983)

In that study, participants were subjected to the stressful task of completing block
patterns at a rather demanding rate. On completion of the task, participants were
told that their performances were below average. For half of the participants
(experimental group), a low-intensity odor (trimethylundecylenic aldehyde,
TUA) was present, but for the control group the unobtrusive odor was not pre-
sented. In what the participants were led to believe was an unrelated exercise,
several days later, they were invited to participate in an experimental task on
“moods and the assessment of people.” They were instructed to fill in mood-
rating sheets and to assess a series of photographs of people in terms of pairs of
attributes. During that second phase, the odor was present for both the experi-
mental group and the control group. It was hypothesized that participants who
had experienced the association between the odor (CS) and the stressful task
(US) would describe themselves and the photographs of people as more anxious
than would the control participants, for whom the odor had not been associated
with the stressful experience.
Although the expected group differences in these ratings were not significant,
the data showed that women made more mistakes and were slower on the block-
pattern task than men. Hence it was concluded that the task may have been
more stressful for the women and that as a result the women would be more
likely to be conditioned to the odor than would the men. Indeed, the mood
scales indicated increased anxiety ratings for the female experimental group in
that second phase, relative to the control group. In addition, women rated the
photographs as showing more anxiety. A post-experimental test of awareness
indicated that those participants were not aware of any association between
the odor and the stressful experience. It was therefore concluded that the data
provided support for the theory of unconscious emotional conditioning with
odors. The one-trial contingency between the odor (CS) and the stressful situation
(US) seems to have been sufficient to change the previously neutral reactions to
the odor (CS) such that it would elicit affective reactions in those subjects when
the odor was subsequently encountered in a situation unrelated to the original
conditioning context.
Nevertheless, that study by Kirk-Smith and colleagues has been severely crit-
icized on methodological as well as statistical grounds (Black and Smith, 1994);
see Kirk-Smith (1994) for a reply to those comments. One of the comments by
Black and Smith was that no evidence was presented to show that the block-
pattern task was effective in inducing stress/anxiety as intended. Also, and more
importantly, they argued that it could not be excluded that initial group differ-
ences in the extent to which the block-pattern task was experienced as stressful
might have been responsible for the observed findings (that was not explicitly
tested ), rather than (group) differences due to being exposed to the CS (odor)–US
(stressful-task) contingency.
In spite of those methodological and statistical flaws, we still believe that the
procedure proposed by Kirk-Smith and colleagues provides an elegant way of
investigating the behavioral and emotional impacts of aversive conditioning with
odors in a laboratory analogue of typical natural situations. For that reason, we
decided to replicate their experiment conceptually in a more controlled study
(Hermans, Pauwels, and Baeyens, 1992).
3.2. Conceptual Replication of the Study by Kirk-Smith et al. (1983)

We collected data from a group of psychology students who were submitted to
the stressful task of completing patterns in a Chinese tangram puzzle. They were
told that they were participating in the validation of a new intelligence test and
that the puzzle was a measure of their “general problem-solving ability and level
of motor skill.” A pilot study in our department had shown that the “tangram task”
was rather stressful, with the mean total of correctly assembled patterns in that
pilot study only about one pattern in 15 minutes. However, we told our students
that related studies abroad had indicated that an average person should be capable
of assembling one pattern every two minutes, adding that we did not expect any
differences for the Flemish population, and certainly not for university students.
During a period of 15 minutes the participants were to assemble as many patterns
as possible. As in the original study by Kirk-Smith and associates, the TUA odor
was present at an unobtrusive intensity for the participants in the “stress, odor”
condition, whereas participants in the “stress, no odor” condition did not receive
the odor during that first session. And in order to accommodate the Black and
Smith (1994) critique of the original study by Kirk-Smith et al. (1983), at the end
of that first phase a brief “test-stress evaluation questionnaire” was presented. It
consisted of five bipolar 10-point visual-analogue scales to assess the extent to
which the task had been experienced as stressful.
Six days after the first session, all participants received letters in which they
were invited to participate in “a brief study on moods and the assessment of
people.” No reference was made to the first session, and the letter was signed
by a second experimenter. On arrival, participants entered a TUA-odorless room
and were informed that the purpose of the study was to investigate how cer-
tain moods may affect a person’s perception and assessment of other people.
Then they were asked to complete the “General Mood Ratings” for the first
time. In that questionnaire, which is similar to the one used by Kirk-Smith and
associates, participants have to rate themselves in terms of “current affective
state” (“anxiety,” “depression,” and “hostility”) on a series of 11-point visual-
analogue scales (0 = not at all; 10 = very). Next, participants were invited into
another room in which the odor was present. During that phase of the exper-
iment, the odor was present for both the experimental group and the control
group. As was the case during the first phase of the experiment (the stressor
task), the concentration of the odor was such that it would not be noticed unless
one’s attention were drawn to it. In that room, the participants were asked to
complete the “mood” scale for a second time, as well as both the “state” and
“trait” parts of the Dutch version of the State Trait Anxiety Inventory (STAI)
(Van der Ploeg, Defares, and Spielberger, 1980). In addition, just as in the proce-
dure employed by Kirk-Smith and associates, participants were asked to judge
a set of photographs of four male and female persons on a series of bipolar
semantic differential scales. After completion, participants were asked to eval-
uate the room’s odor on a 10-point visual-analogue scale (pleasant–unpleasant)
and were asked where they had encountered that odor before. Subsequently
they were asked (1) if they had noticed anything unusual about the conditions
of the experiment, (2) what they thought the experiment was really about, and
(3) if they had noticed any similarity between the conditions of the most re-
cent experiment and those of the tangram task they had carried out six days
earlier.
Initial analysis revealed that the “stress, odor” group and the “stress, no odor”
group did not differ in the way they had experienced the stressor task, as indicated
by their answers on the five questions of the “test-stress evaluation questionnaire”
and their numbers of completed puzzles. Although all participants experienced
the task as difficult and rather stressful, there were nonetheless strong inter-
individual differences in their ratings.
Because emotional effects from the odor (CS) would be expected for only
those participants who experienced the tangram task as rather unpleasant and
distressing, we subdivided the total sample of participants by means of a cluster
analysis for the data from the “test-stress evaluation questionnaire” and the num-
bers of completed puzzles. That analysis revealed two clusters of participants:
cluster 1 = highly stressed participants (N = 18); cluster 2 = slightly stressed
participants (N = 15). Second, a principal-components analysis was performed
on all “emotional/affective” ratings that were carried out in the presence of the
odor during the second part of the study, including the photograph ratings, the
different items of the General Mood Ratings, the “state” and “trait” scores on
the STAI, and the evaluative ratings of the odor. That analysis (varimax rota-
tion) revealed three major factors (Mood 1, Mood 2, Mood 3) that explained the
majority of variance (34%, 15%, and 10%, respectively).
Next, a multivariate analysis of variance (manova) for the participants’ rat-
ings on those mood factors (Mood 1, Mood 2, Mood 3), with “condition”
(odor group/no-odor group) and “stress” (low/high) as between-subject vari-
ables, showed that the crucial “condition” × “stress” interaction was marginally
significant [Pillais F(3, 27) = 2.6; p = .072]. Subsequent univariate analyses for
the three mood factors separately revealed a significant interaction for Mood 3
[F(1, 29) = 7.6; p = .01]. The three variables that loaded highest in that mood
factor were the “assertiveness,” “hostility,” and “sexiness” ratings for the pictures.
Relative to the control group, participants in the experimental condition (odor
group) rated the photograph images as more hostile, more assertive, and less
sexy when that odor had been associated with an experience of stress during the
first session. That was not the case, however, for those who described the stressor
test as not so stressful.
So although the data did not reveal a main effect of odor, we can nevertheless
conclude that for those participants who actually experienced the stress-inducing
task as difficult and stressful, encountering the odor again in an apparently un-
related context influenced their affective ratings for a series of pictures. The
fact that the effect was restricted to that group is not really surprising, given
that the stressor task could be regarded as a genuine negative US only for those
participants.
4. Automatic Activation of Odor Hedonics:

Affective Odor-Priming Studies
An important aspect of the Kirk-Smith paradigm is that the data suggest that
after the subjects were exposed to the odor (the CS), they became noncon-
sciously susceptible to its influence in their affective/emotional behavior. The
idea of automatic/unconscious/implicit emotional influences by affectively va-
lenced stimuli is certainly not new. Whereas most older studies had investigated
the emotional influence of subliminally presented stimuli, recent research on
automatic affective influences has focused more on the automatic affective im-
pact of supraliminal and clearly perceptible emotional stimuli. This approach is
more attractive from the perspective of ecological validity. One possible method
within this approach is to study the impact of perceptible stimuli that are not
within the focus of attention. A second method is to employ clearly percepti-
ble stimuli that can be within the central focus of attention, but to assess their
emotional impact by means of a procedure that cannot be influenced by con-
sciously controlled strategies: Emotional effects should hence be attributed to
automatic (unconscious) processes. A good example of such a research paradigm
is the affective-priming procedure, which was introduced by Fazio et al. (1986)
and has been under further investigation in our laboratory (e.g., Hermans,
De Houwer, and Eelen, 1994, 1996, 2001). Before describing some very recent
data from affective-priming studies using odor stimuli, it seems appropriate to
first introduce some basic findings on affective priming that were obtained using
stimuli from a sensory modality other than olfaction: vision. In an extensive series
of affective-priming experiments it has been demonstrated that response laten-
cies to affectively valenced stimuli are mediated by the affective context against
which they are presented. In a standard affective-priming study, a series of target
words (e.g., “constructive,” “jealous”) is presented, to be evaluated as quickly
as possible as either “positive” or “negative.” Each target word is preceded by
a priming stimulus, which can be positive, negative, or neutral (e.g., “music,”
“dentist,” “circle”) and is to be ignored by the subject. Of crucial importance in
these priming studies is the affective relation between the valence of the prime
and the valence of the target, which typically is manipulated over three lev-
els. Prime–target pairs can be affectively congruent (e.g., “music-constructive;”
“dentist-jealous”), affectively incongruent (e.g., “dentist-constructive;” “music-
jealous”), or affectively unrelated (e.g., “circle-constructive;” “circle-jealous;” or
control pairs). It has now repeatedly been demonstrated that this affective relation
mediates the time needed to respond to the target stimulus. Response latencies are
shortened for affectively congruent prime–target trials, as compared with control
trials, and are relatively lengthened for affectively incongruent trials. This data
pattern can be explained only if one assumes that the participants have evaluated
the primes, even though they have been asked to ignore those stimuli. Moreover,
the parameters that typically are used in affective-priming research preclude
consciously controlled processes that could be responsible for these priming
effects. For instance, in most affective-priming studies, the interval between the
onset of the prime and the onset of the target – the stimulus-onset asynchrony
(SOA) – has been only 300 msec [prime = 200 msec; inter-stimulus interval
(ISI) = 100 msec], which is assumed to be too brief for participants to deploy
controlled response strategies. Hence, affective-priming effects that are observed
under these conditions should be attributable to automatic processes. Given the
importance of the automatic character of the affective-priming effects, it has been
thoroughly investigated (Hermans, Van den Broeck, and Eelen, 1998b); it is at-
tributed to fast-acting, goal-independent, relatively efficient processes that can
operate even without any awareness of the instigating stimulus. Taken together,
these data indicate that humans are able to evaluate stimuli as “positive” or
“negative” in a rather unconditional and automatic fashion, an idea that has been
one of the central tenets of several modern cognitive-representational theories of
emotion.
Following the original study by Fazio et al. (1986), wide generality of this
affective-priming effect has now been demonstrated. Not only has it been pos-
sible to demonstrate affective-priming effects using different types of response
tasks (target evaluation, target pronunciation, lexical decision tasks), but also the
evidence for automatic stimulus evaluation, derived from the affective-priming
paradigm, has been generalized toward different types of stimulus materials,
such as words (e.g., Fazio et al., 1986; Hermans et al., 1994), nonsense words
for which affective meanings have only recently been learned (De Houwer,
Hermans, and Eelen, 1998), simple line drawings (Giner-Sorolla, Garcia, and
Bargh, 1994), and complex real-life color pictures (Hermans et al., 1994, 1996).
Moreover, the effect has been obtained with a wide range of stimuli varying
in content as well as in the accessibility of their affective valence in memory.
But whereas the models of automatic affective processing have assumed that
automatic stimulus evaluation (and hence affective priming) should apply to all
sensory modalities, in all of the studies of the affective-priming effect that have
been published, the stimulus material has been visual in nature. In that context
(here we return to the main issue of this chapter) we decided to use odors as
primes in an affective-priming procedure. Accordingly, to test whether or not
the affective-priming effect could be generalized to nonvisual stimuli, we used a
cross-modal affective-priming paradigm in which selected positive and negative

odors provided the affective-processing context for word evaluation.
4.1. Affective Odor-Priming Study

In this study (Hermans, Baeyens, and Eelen, 1998a), each participant selected
a most liked odor and a most disliked odor from a series of 10 odors. Ten
positive and 10 negative target words were also selected on an individual ba-
sis. In the second phase of the experiment, the individually selected positive
and negative odors and words served as primes and targets, respectively, in an
affective-priming procedure. During the priming procedure, participants were
asked to evaluate each target word as quickly as possible by saying, out loud,
“Positive” or “Negative.” Each word was immediately preceded by a 10-sec pre-
sentation of either the “positive” odor or the “negative” odor. Analysis of the
evaluative-response latencies to the words demonstrated a significant main effect
of “affective congruence.” Target words were evaluated significantly faster when
preceded by a similarly valenced prime (odor), as compared with trials in which
prime and target were of opposite valence. Because of known gender differences
in the way odors are processed, the gender of the participants was also entered
into the analysis as a between-subjects variable. The analysis showed that the
effect of “affective congruence” was moderated by “gender.” For female partic-
ipants, the data were clearly in line with the affective-priming hypothesis. For
the male group, however, there was no difference between response latencies for
affectively congruent and incongruent trials.
The fact that the affective-priming effect was limited to the female participants
may simply be attributable to the fact that the female olfactory sense is superior
in most respects to that of males (Doty et al., 1985; Doty, 1991). Thresholds for
odor identification are much lower in women for several odorants, and odors are
experienced as more intense by women; they have a better capacity to discrimi-
nate odors and are more pronounced in their judgments of whether a particular
odor is pleasant or unpleasant (Vroon, Van Amerongen, and De Vries, 1994,
p. 95). That would seem to imply that the absence of affective priming for males
is not a consequence of their inability to automatically evaluate odors, but of
their lower capacity to detect and/or discriminate odors. The fact that additional
analyses showed that the means for the males were in the expected direction in
the second experimental block supports this hypothesis. The olfactory system of
a male participant probably needed more time to perceive the odor primes. All in
all, given the presentation parameters that were employed, the data of this study
provide support for the idea that the positive/negative valence of odor stimuli
can be processed automatically (Hermans et al., 1998a).
4.2. Evaluative Odor Conditioning and Priming Combined

The first part of this chapter focused on the role of associative processes in the
acquisition of odor valence. But given the predominance of like/dislike reactions
in the perception of odors, and given the fact that affective-priming data suggest
that these like/dislike reactions can be triggered automatically on perception of
odors, the question can also be reversed: How do odors, once they have acquired
a positive or negative valence for an individual, in turn influence evaluative reac-
tions to non-odor stimuli, and, more specifically, what is the role of associative
learning here? Again, this is a largely unexplored research issue, but the little ev-
idence that is available seems promising. For example, Todrank et al. (1995)
convincingly demonstrated that pairings of valenced odors with pictures of
human faces resulted in reliable shifts in evaluation during subsequent view-
ing of the pictures presented without odors. Similar results have been described
by Schneider et al. (1999).
In the final experiment to be discussed here, we wanted to take these obser-
vations one step further (Hermans, Baeyens, and Natens, 2000): (1) Would it be
possible to effectively use positive and negative odors as USs in an evaluative-
conditioning procedure, with neutral pictures of objects as CSs? (2) Would the
newly acquired valences of the CSs (the pictures) in turn exert an automatic
affective influence, as measured by an affective-priming procedure?
The CSs used in this study were four different color pictures of a bottle of
liquid soap, each placed in a transparent plastic freezer bag together with a cotton
ball. For one of the pictures (CSpositive), a pleasant odor (lemon; essential oil)
was applied to the cotton ball, and for a second picture (CSnegative) a negative
odor (civet; dissolved in ethyl alcohol) was applied to the cotton. For the last
two pictures (CSneutral), which served as controls, there was no odor. As part
of the cover story, an electrode was attached to the participant’s right hand, and
each was told that the experiment was designed to determine whether or not
there was a relationship between preferences for complex sensory stimuli and
physiological (skin-conductance) responses to those stimuli, and whether or not
those skin-conductance responses depended on preferences for those visual and
olfactory stimuli. On each trial, the participant was asked to take a look at the
picture, to open the bag and to sniff it, to close the bag again, and finally to take
a second look at the picture. For each CS–US pair there were eight acquisition
trials. At the end of the acquisition phase, participants were asked to rate each
of the four CSs on a number of dimensions. The first two dimensions were
evaluative: to what extent they thought the product (the bottle of liquid soap)
was attractive, and to what extent they thought the CS was pleasant/unpleasant.
Also, it was asked to what extent this product would attract their attention in a
supermarket, what they anticipated the quality of the product to be, and to what
extent they would be inclined to buy this product on seeing it in a supermarket.
The results showed that there was a strong effect of evaluative conditioning.
The CSpositive was rated as more attractive and pleasant than the CSnegative.
Also, participants indicated that the CSpositive probably would attract their
attention more in a supermarket and probably would be of better quality. Finally,
participants indicated that they would be more inclined to buy the CSpositive
than the CSnegative. We can thus conclude from these data that the mere pairing
of relatively neutral pictorial CSs with a positive or negative odor (the US) can
result in an evaluative shift for these visual CSs.
However, it cannot be excluded that those effects may have been due in part to
demand effects. Most participants probably were aware of the specific CS–US
contingencies, and it is possible that effects of social desirability or other demand
effects may have influenced their ratings. Therefore, in the second phase of
the experiment, the four CSs were entered as primes in an affective-priming
procedure, which, as argued earlier, can be viewed as an indirect and unobtrusive
measure of stimulus valence that is not likely to be influenced by demand effects
(Hermans et al., 1999). During the priming phase, participants were asked to
evaluate a series of positive and negative target words that were preceded by one
of the four CSs. It was predicted that if the conditioning phase had indeed changed
the valences of the CSs in the expected directions, presentation of the CSpositive
would facilitate the processing of a positive target, but inhibit the processing
of a negative target, whereas an opposite pattern would be expected for the
CSnegative. The results showed that there was a significant effect of “affective
congruence” for the male subgroup. Response latencies for affectively congruent
prime–target pairs were significantly shorter than for affectively incongruent
trials. For the female participants, an effect of “affective congruence” was not
seen. We have no valid explanation for this gender difference in the affective-
priming data, but the data from the male subgroup offer a clear indication that
contingent pairing of a neutral visual CS with a positive or negative odor (US)
can result in reliable evaluative shifts for these non-odor CSs. Moreover, this
newly acquired valence can be automatically activated, as was shown by the
results of the affective-priming procedure.
5. Conclusion
This chapter has focused on recent research into the acquisition and activa-
tion of odor valence. With respect to the acquisition of odor likes and dislikes,
we can conclude that associative processes are justifiably assumed to play an
important role. Even in natural situations such as toilets and therapeutic mas-
sages, processes of evaluative conditioning seem to provide a sufficient basis
to modify odor preferences. An important observation from the reported stud-
ies is that awareness of the contingency between the CS and the US is not a
necessary precondition for evaluative odor conditioning. In other words, the
mere contingency between a relatively neutral odor and a positive or negative
stimulus/event is sufficient to change one’s evaluation of that odor, even if one
is unaware of the fact that the odor was presented together with the positive or
negative stimulus/event. Hence, these data provide a fine demonstration that the
acquisition of odor hedonics can take place outside our conscious awareness. In
addition, it is important to note that to our knowledge these data represent the
first clear demonstration of plasticity in adults’ odor hedonics due to a Pavlo-
vian stimulus contingency. Hence, even though it still may be the case that the
fundamentals of odor hedonics are acquired during childhood, there is certainly
room left for additional evaluative plasticity during adulthood. Moreover, there
is no reason to assume that such Pavlovian associative processes should not
play an equally important role in the acquisition of odor likes and dislikes in
early childhood. Hence, it is our conviction that the kind of studies discussed
here, founded on theoretical and empirical knowledge regarding evaluative con-
ditioning, provide a firm and attractive basis for studying the acquisition of odor
hedonics over all age groups. Not only can associative processes alter the liking
or disliking of an odor, but also the results of our conceptual replication of the
study by Kirk-Smith et al. (1983) suggest that these associative processes can
even be the basis for unconscious affective/emotional influences of odors on our
behavior. This observation is commensurate with recent more general studies
of the automatic affective/emotional impact of stimuli employing experimental
paradigms borrowed from experimental cognitive psychology, as modified to
study automatic affective influences. The affective-priming procedure discussed
here is a good example of such a paradigm. On the basis of studies that have
employed this methodology, we can now conclude that humans are capable of
automatically evaluating external stimuli as positive or negative. The data of
our affective odor study (Hermans et al., 1998a) show that this postulate not
only holds for visual stimuli but also can be generalized to olfactory stimuli.
Odors are capable of automatically activating positive or negative connotations.
All in all, the data presented here lead to the conclusion that acquisition of
odor hedonics can take place outside conscious awareness, and once acquired,
odor valence can exert an automatic (unconscious) influence on our behavior.
And according to the data from the liquid-soap study, odor valence not only
can directly influence our perception and behavior but also can have an indi-
rect impact, as a clearly valenced odor can by itself act as an evaluative US
and alter the valence of stimuli that go together with that odor. Moreover, these
latter stimuli can in turn be evaluated automatically, as was indicated by the
data from the affective-priming procedure. Relating this to the perfume exam-
ple from our introduction, this can be translated as follows: Not only can an
attractive or beloved person change one’s perception of the perfume that per-
son is wearing, but once it has come to be seen as pleasant, that perfume can
subsequently elicit positive feelings for an unknown person wearing the same
perfume.
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9
Is There a Hedonic Dimension to Odors?
Catherine Rouby and Moustafa Bensafi
The goal of psychophysics is to understand the relationships between varia-

tions in the physical environment and variations in our mental states. During
the past century, psychophysics has evolved from pure sensory and physicalist
conceptions to more perceptive and ecological ones, allowing us to include deci-
sion, attention, and expectation in the processing of sensory stimuli (Tiberghien,
1984). In the olfactory domain, memory psychophysics has been compared to
perception psychophysics (Algom and Cain, 1991), and multidimensional scal-
ing methods have been used to compare perception and imagery (Carrasco and
Ridout, 1993). Thus, psychophysics has come to include more and more cog-
nitive issues. Perception is recognized as categorical, inferential, and generic,
leading to meaning and knowledge.
Hedonic responses to odors are very salient in folk psychology (David, Dubois,
and Rouby, 2000) as well as in scientific accounts (see Rouby and Sicard, 1997,
for a review). But can we study hedonic responses to odors with the usual
psychophysical tools? Empirical descriptions and measures of preferences are
clearly possible (Moncrieff, 1966; Köster, 1975), allowing a kind of affective
psychophysics. But beyond preferences, if one is interested in the links between
emotional responses and cognitive processing of odors, methodological ques-
tions arise concerning what is measured and how. Three main questions will be
examined in this chapter:
1. Are the degree of pleasantness and the intensity of an odor reflecting the same
dimension?
2. Is there a hedonic axis? Is a representation of affect possible on a psychophysical
continuum, or are there clear-cut odor categories?
3. Are unpleasant odors symmetric with pleasant odors in relation to “zero
affect”? That is, do they carry the same weight with respect to a neutral
reference?
140
Hedonic Dimension to Odors 141
To discuss these theoretically important questions, we shall gather contri-

butions from different sciences, namely, psychology, anthropology, psycholin-
guistics, and neurophysiology. Insights from these disciplines will show that
pleasantness and intensity can be considered as separable aspects of odor
perception, relying on different neural networks, that a hedonic continuum is
only partially adequate for an understanding of the affects accompanying odors,
and that the negative pole of the hedonic axis is more relevant for humans.
1. Pleasantness and Intensity: A Single Dimension?

Strong odors are perceived as being unpleasant: A negative correlation is often
found between intensity and pleasantness, leading some authors to consider them
as reflective of a single dimension (Henion, 1971). Doty (1975), in comparing
the pleasantness and intensity curves with concentrations for 10 odorants, did not
support that view: For 3 of them (anethole, eugenol, geraniol), no correlation was
found. He also found that the range of variation was smaller for pleasantness than
for intensity, pleasantness being not described by a power function. Moreover,
even when a strong correlation was found, the relationship of pleasantness
and intensity to one another, as well as their relationship to concentration, var-
ied strongly across odorants. Royet et al. (1999), using a very large sample of
185 odorants, found no correlation between intensity and pleasantness, a result
they attributed to the wide range of odors they studied, from very pleasant to very
aversive, which was not the case in the Doty study. However, they found sig-
nificant correlations between intensity and familiarity and between pleasantness
and familiarity, thus supporting earlier observations (Engen and Ross, 1973) of
a link between familiarity and preferences that is addressed in food sciences as
neophobia (Rozin and Vollmecke, 1986). Neophobia appears to be a key to he-
donic responses, because only familiar foods lead to a confident approach, with
unfamiliar ones entailing avoidance or minimal, cautious consumption. Trans-
cultural studies have shown that these familiarity/novelty effects extend to non-
food odors and that familiarity seems to influence not only hedonic evaluation
but also intensity psychophysical evaluation, suggesting that perceived intensity
itself does not depend solely on stimulus concentration, but also on cultural and
ecological influences. These top-down influences are reflected in different biases
characterizing different groups: Japanese, Mexican, German (Ayabe-Kanamura
et al., 1998; Distel et al., 1999).
Thus, one attributing an intensity level to an odorant could be relying not only
on a “pure” sensory coding but also on recognition of the intensity of a fami-
liar object. This interpretation is evident when the familiar object is a food:
For example, de Graaf, van Staveren, and Burema (1996) measured perceived
142 Catherine Rouby and Moustafa Bensafi
Pleasantness
8
1
1 2 3 4 5 6 7 8 9 10
Perceived intensity
Figure 9.1. Mean responses on the pleasantness of bouillon as a function of per-

ceived intensity, judged by elderly (dashed line) and young (solid line) subjects.
The possible range in responses was from 1 (very weak) to 10 (very strong) for
intensity, and from 1 (very unpleasant) to 10 (very pleasant) for pleasantness.
(Adapted from de Graaf et al., 1996.)
intensity for foods like bouillon, tomato soup, chocolate custard, and orange
lemonade, according to concentration (Figure 9.1). They found that different
psychophysical curves characterized the variation of pleasantness with concen-
tration. The psychohedonic function relates two psychological variables: per-
ceived intensity and pleasantness. When perceived intensity rises, pleasantness
goes up to a maximum, before going down. Our understanding of this phe-
nomenon is that this optimum corresponds to a memory of what should be a
good bouillon or chocolate custard, or what it was in the past: The apex of this
curve will correspond to the intensity that best matches the memory the sub-
ject has of this particular food. The difference between the curves for older and
yonger subjects in Figure 9.1 derives from the elevated thresholds of the elderly,
but the optima are nevertheless very similar.
These diverse data show that the pleasantness/intensity relationship is far from
simple, being linked to bottom-up sensory processes as well as to top-down mech-
anisms (Figure 9.2). This is in accordance with psychophysical models that take
into account context effects and anchor effects in judgments (Parducci, 1995).
From a theoretical point of view, it is important to know if pleasantness can
be dissociated from intensity and if these aspects of olfactory perception reflect
different cognitive processes. But assessing the independence of these processes,
from a practical point of view, has been difficult because of lack of a hedonic test.
Thus we had to design one in which a set of odorants could be rated by subjects
Familiarity
Pleasantness Intensity
Stimulus quality Stimulus concentration
Figure 9.2. Schematic representation of the observed relationships among in-

tensity, pleasantness, and familiarity. Arrows indicate top-down and bottom-up
processes.
according to their intensity, on the one hand, and according to their pleasantness,
on the other (Rouby, Jones-Gotman, and Zatorre, in press). Such a design was
used to measure the response times for hedonic judgments.
According to Craik and Lockhart (1972), various sensory stimuli may be pro-
cessed at different levels, from superficial processing (such as pitch or intensity
in the case of audition) to deep semantic processing (such as identification of
a sound, noise, word, or melody). The influence of the depth of processing on
word-recognition performance has been shown by Craik and Tulving (1975).
Response times are commonly used in cognitive psychology in order to evaluate
the complexity of cognitive tasks: Short response times are most often seen when
there is superficial encoding of stimuli, whereas semantic processing involves
longer response times. Thus we used response times to determine the depth of
processing for hedonic judgments, intensity judgments, and judgments of the
dangerousness of odorants.
Our hypothesis was that response times would be shortest for the intensity
judgments, and longest for the dangerousness judgments, the latter requiring se-
mantic processing before a decision would be possible. If the hedonic judgments
were dependent only on stimulus properties, we would expect that they would
not differ from intensity judgments in terms of response times; alternatively,
if the hedonic judgments required deeper processing, we would expect longer
response times (Burnet, Dubois, and Rouby, 1997).
To measure response times, we used a device combining a respiratory sensor
placed in one nostril, a timer, and a response box with two keys. The respiratory
sensor was inserted in the left nostril. Pairs of odorant vials were presented
to the right nostril. Each subject was instructed to sniff at each presentation
of an odorant vial (only one sniff was allowed) and, after sniffing the second
odor of the pair, to respond as quickly as possible by pressing one key on the
response box; for the second odor, the sniff was detected by the sensor, which
started the timer; the timer was stopped when the subject pressed one of the two
3500
3000
Response time (ms)

2500
2000
1500
1000
500
0
Intensity Pleasantness Dangerousness
Figure 9.3. Mean response times for 31 subjects making pair comparisons
during three judgments: intensity, pleasantness, and dangerousness.
keys to respond. Six odors [thymol, pyridine, isovaleric acid, isoamyl acetate,
cyclodecanone, R-(+)-limonene] were presented by pairs (15 pairings, each pair
presented twice). The order of the pairs was random and different for each task
(intensity, pleasantness, dangerousness), as was the order of tasks across subjects.
After some training trials to synchronize the subject’s sniff and the odor pre-
sentation by the experimenter, the test began and responses were recorded after
presentation of the second odor of each pair: The subject had to press the right
button if the second odor was less intense, or the left button if the second odor was
more intense than the first one. The same procedure was used for pleasantness
judgments and for dangerousness judgments, with subjects having to decide if
the second odor was more or less pleasant (or dangerous) than the first one.
The results are shown in Figure 9.3. Dangerousness and pleasantness com-
parisons did not differ in response times, but both took significantly longer than
the intensity judgments. The difference between each of them and the intensity
judgments revealed a 345-msec mean effect (F[1, 29] = 15, p < .001). This is
a large effect, if we consider that the apparatus allowed a temporal resolution of
10–20 msec for sniff detection, 0.1 msec for the timer, and 0.1 msec for the
response box. Of course, the natural sniff action of the subject was the main
source of measurement error: It is possible that some subjects may have detected
an odor before it was 1 cm from the nostril, and thus some response times may
have been shortened in an undetermined way; the large standard deviations in
response times (intensity, 1,185 msec; dangerousness, 1,340 msec; pleasantness,
1,550 msec) may in part reflect such variation in stimulus input. However, that
was not the sole explanation, because in sets of odorants that were judged for
intensity, pleasantness, and dangerousness, only for the intensity judgments were
both the mean and standard deviation smaller. Therefore, it is unlikely that varia-
tions in the onset of sniffing and in the presentation of the odorant under the sub-
ject’s nostril could explain the robust difference of 345 msec between judgments.
These findings indicate that hedonic judgment is elaborated beyond the percep-
tive level and that perceived intensity does not require a deep level of processing.
Although this does not mean that hedonic and intensity judgments cannot be
correlated in psychophysical tasks, it lends support to the idea that they rely on
different processes. Such processes could differ in two ways: Either they could
be completely dissociated, or they could rely on the same early neural process,
which might be sufficient for the intensity judgment, but not for the pleasantness
and dangerousness judgments. Such an issue is too difficult to resolve using only
response times.
Other support for the idea of dissociation between intensity and pleasant-
ness can be found in neuropsychological observations: The well-known patient
H.M., whose surgery produced bilateral medial temporal damage, was unable to
identify odors or to describe them, but was completely normal in terms of odor-
detection and odor-intensity tasks (Eichenbaum et al., 1983). To our knowledge,
no example of the reverse pattern has been reported, that is, subjects discriminat-
ing and describing odors, but impaired in terms of intensity processing. Unfor-
tunately, H. M. was not tested for his hedonic responses to odors. Nevertheless,
we have tried to document in normal subjects a possible dissociation between
intensity and pleasantness. In collaboration with neuropsychologists, we have
sought to further test the specificity of hedonic judgment using brain-imaging
techniques, namely, positron-emission tomography (PET), with the same kind
of intensity/pleasantness test, in order to try to determine if intensity and pleas-
antness rely on different neural networks.
The tests showed right orbitofrontal activation that was common to both tasks,
but robust activation of the hypothalamic area that was specifically attributable
to the situation of judging pleasantness/unpleasantness (Zatorre, Jones-Gotman,
and Rouby, 2000; Zatorre, Chapter 20, this volume). Thus, in the absence of
evidence of double dissociation between pleasantness and intensity, which would
argue in favor of completely distinct neural networks, the response times and
the PET study tend to indicate that intensity and pleasantness ratings share
common processes and activate common cortical structures, but nevertheless
rely on different neural networks and require different computing durations.
2. Is There a Hedonic Axis? Or Discontinuous

Hedonic Categories?
The second question concerns the ecological validity of the idea of a continuous
hedonic axis to study the affective processing of odors. To tackle this problem, we
shall consider different attempts that have been made to understand and describe
the psychological odor space, as well as the linguistic odor space, across cultures.
A first problem transcends the odor space: the existence of an emotional

continuum. Theorists of emotion do not agree on this point. To present things
briefly, there are two main positions: One group argues that there is a single emo-
tional dimension, characterizing and underlying approach/withdrawal behaviors
(Davidson and Irwin, 1999; Rolls, 1999). The other group believes in a limited
number of primary, basic emotions (sadness, happiness, fear, surprise, anger,
disgust) with distinctive facial expressions that are associated with distinctive
physiological events (Ekman, Levenson, and Friesen, 1983): Basic emotions
rely on innate mechanisms, and during ontogeny they give rise to secondary
emotions, evoked by a variety of stimuli, situations, and meanings, that shape
individual and cultural differences by association with the primary, basic emo-
tions (Damasio, 1994). For the historical grounds for those positions, see Phillips
and Heining (Chapter 12, this volume).
Thus, in the olfactory domain, the idea of continuous hedonic axis presupposes
that odors can be ranked at least on an ordinal scale, at best on an interval scale.
If the assumption of a continuum does not hold, and if different odors evoke differ-
ent psychological and physiological events, then their placement on a continuous
scale will mask its purely nominal character and will not help us to understand the
psychological and physiological mechanisms underlying subjects’ responses.
The status of the hedonic “dimension” can be evaluated by reviewing the sci-
entific attempts to organize the olfactory space. All psychophysical odor classifi-
cations and odor-similarity descriptions in the twentieth century have attributed
great weight to the dimension “pleasantness” (Harper et al., 1966; Schiffman,
1974; Schiffman, Robinson, and Erickson, 1977). Berglund et al. (1973) consid-
ered that dimension to be the only one that was common among the olfactory
spaces of individuals. But as we do not know much about the organization of
this space (or spaces), the number of dimensions can only be approximated, and
their physiological meanings are still undetermined (Chastrette, Chapter 7, this
volume).
Scientific attempts at odor classification in the eighteenth century (Table 9.1),
when the language of science was Latin, tried to impose some order with crude
tools: categories. Albrecht von Haller (1763) erected three categories: good
(literally, “sweet-smelling”), neutral, and bad (stinking/infectious odors). The
well-known Linnaeus (1765) believed in seven groups, three of which referred
to unpleasant odors: odores fragrantes (fragrant odors), odores tetri (repelling
odors), and odores nausei (nauseating odors). A fourth category, odores hircini
(male-goat smell), also would seem to include a hedonic characteristic, al-
though its description did not explicitly refer to affect or evaluation; however,
that odor is a prototypical malodor in the Mediterranean world. More recently,
Zwaardemaker (1925) proposed a classification that kept and refined most of
Table 9.1. Examples of European scientific and popular odor classifications
Odor classifications by scientists

Date Authors and laypeople
1763 von Haller 1. odores suaveolentes (musk,
camphor, mint, apple, violet,
rose)
2. odores medii (wine, vinegar,
empyreumatic odors)
3. odores foetores (animal
perspiration, corpses,
corrupted organic compounds)
1765 Linnaeus 1. odores aromatici (laurel)
2. odores fragrantes (lime or
jasmine blossom)
3. odores ambrosiaci (amber,
musk)
4. odores alliacei (garlic)
5. odores hircini (male goat)
6. odores tetri (solanaceous plants)
7. odores nausei (foul-smelling
plants)
1925 Zwaardemaker 1. ethereal odors
2. aromatic odors
3. floral and balsamic odors
4. ambrosiac odors
5. alliaceous odors
6. empyreumatic odors
7. caprylic odors (capronic acids
and homologs)
8. repelling odors (pyridine,
alkaloids)
9. nauseating odors (indole,
scatole)
1997 David et al. Descriptions referring to % of responses
effect 40.75
source 27.75
effect /source 13.5
effect /memory 5
effect /intensity 3.75
effect /intensity/memory 2.25
others 7
the seven Linnaean categories, including the same three malodorous groups
(Table 9.1: group 7, caprylic odors; group 8, repelling odors; group 9, nauseating
odors). Thus, all scientific attempts at odor classification have paid considerable
attention to the hedonic and affective aspects of odor perception.
Up to this point, several terms have been used somewhat indifferently:

“pleasantness,” “hedonicity,” “preference,” “affect,” “hedonic judgment,” and
“emotional value.” From a psychological and linguistic point of view, it is in-
teresting to consider to what extent these different expressions refer to the same
reality. Can we speak of hedonic valence or hedonic connotation as describing
some attribute of a stimulus – nothing more than a side effect of the perception
of an odor? Can we speak of emotional reactions triggered by some odorants?
Can we speak of emotional judgments attributable to an external stimulus?
Linguistic inquiries have led to a more thorough examination of the hedonic
dimension (David et al., 1997). We asked 250 subjects to write their own answers
to open questions such as “What is an odor for you?” and obtained a wide
diversity of responses. But the linguistic analysis showed that the words used
to speak about odors were constructed mainly on verbs referring to an effect
of an odor on the perceiver (disgusting, nauseating). Moreover, descriptions
referring to the effect were far more frequent than descriptions referring to the
source: Spontaneous expressions tend to replicate scientific classifications using
essentially the same words (Table 9.1).
Thus, what linguistics tells us about odor perception is that it is subjective,
which we already knew, but also that this hedonic valence is not referred to as
external; it is a relationship between the odor and one’s body. What laypeople put
into words in a spontaneous, nonscientific way is not a description of objective,
simply quantitative external “dimensions,” symbolized by positions on a contin-
uous line, but rather descriptions of effects on their bodies or their well-being.
We must remember that when we use psychophysical hedonic “scales,” the sci-
entific classifications also take into account the hedonic valence, in almost the
same words as laypeople (nauseating, repelling), mainly on the negative side of
the ledger. Thus the supposed continuum between good and bad could rather
imply, in the case of olfaction, that there are two types of odors, those that have
qualities that can be processed semantically and described (mainly by their
sources), and those that have effects: For some aspects of the olfactory space
that appear to be most important for human beings, an auto-centered reference
is used (the effect); for some other aspects, an allo-centered reference is possible
(a semantic processing referring to the source). This duality of representation
has also been deployed in the cognitive representations of space (Berthoz and
Viaud-Delmon, 1999).
3. Are Pleasant Odors Symmetric with Unpleasant Ones?

In an inquiry into odor descriptions in 60 languages from nine language families,
Boisson (1997) confirmed that the hedonic dimension is dominant everywhere,
an observation reported earlier by Buck (1949) for Indo-European languages:
Table 9.2. Summary of transcultural studies of odor denomination and hedonic

categorization
Odor classification
Date Authors or comments
1997 Boisson Among 60 languages:
35 have specific terms for sweat and body odor
34 have specific terms for strong animal odors
31 have specific terms for rotten-things odor
31 have specific terms for burnt-things odor
26 have specific terms for odor of molded things or places
23 have specific terms for odor of fish, rotten (15)
or fresh (8)
13 have specific terms for urine odor
12 have specific terms for fresh-meat odor
11 have specific terms for rancid-food odor
8 have specific terms for dampness odor
6 have specific terms for breath malodor
4 have specific terms for feces odor
1998 Schaal et al. There is better agreement between and within cultures on the
negative side of the hedonic dimension. Far more
variability is found on the positive and neutral sides.
1997 Mouélé et al. The negative pole is the one that is linguistically dominant.
“The only widespread popular distinction is that of pleasant and unpleasant

smells – good and bad smells, to use the briefest terms – and this is linguistically
more important than any similar distinction, that is, of good and bad, in the
case of other senses.” Thus the ecological value of the hedonic dimension has
been fully confirmed using a very large sample from different language families.
Some malodors are the most frequently named odors across languages, probably
because they are more salient for perceptual reasons and/or for cultural rea-
sons (Table 9.2). Boisson distinguishes four main groups: body odors, decaying
organic substrates, animal foods, and live animals.
A comparative olfactory ethnography remains to be done, but this survey
shows that negative terms are always more numerous in a given language than
are positive terms: Even in Hawaii, where there are many different terms for
pleasant odors, they are outnumbered by words for unpleasant odors.
Although many different odorant sources are employed in various cultures to
represent the positive and negative poles of the hedonic dimension, the portion
of the ecological environment that is common across cultures may have room
for at least some olfactory universals: body odors or any of the four main groups
described by Boisson (1997).
A review of studies on preferences by children and adults from different
cultures (Schaal et al., 1998) revealed a strong consensus between and within
cultures on the negative side of the hedonic dimension; that agreement was
little influenced by age and sex variables. Far more variability was found on the
positive and neutral sides, with strong influences from age and sex variables.
Thus, malodors and human body odors may be olfactory universals in the sense
that they are common to all cultures and salient for most of them. Moreover,
perceived pleasantness and unpleasantness seem to be rather independent of
each other during early development, and negative facial responses appear to be
acquired earlier than positive responses in newborns (Schaal, Soussignan, and
Marlier, Chapter 26, this volume).
Some ethnolinguistic studies have confirmed that view: In a short inquiry
into five Bantu languages in Gabon, Hombert (1992) found that they had from
6 to 14 specific odor terms, each referring not to a source, as in Indo-European
languages, but to the odor of that source. Those languages have names for odors
for which the Indo-European lexicon is empty. Those names refer mainly to body
odors or to strong odors: In Li Wanzi and in four other languages, the odor of
the civet has its specific name. Comparisons with other populations of hunter-
gatherers have yielded similar findings. Moreover, ethnolinguistic studies have
confirmed the differential attention given to malodors: The negative pole is the
one that is linguistically marked (Mouélé et al., 1997; Mouélé, 1997).
Our detour through linguistics and psychology led us to examine further the
negative side of the supposed hedonic continuum and to ask whether or not un-
pleasant odors are symmetrical with pleasant odors. Linguistic studies indicate
that such is not the case. What does neuroscience suggest? Psychophysiology
and neurophysiology do not trust only in words; they consider behavior and
its neural correlates. Behavioral responses to odors have been studied through
facial expressions (Steiner, 1979; Gilbert, Fridlund, and Sabini, 1987; Soussignan
et al., 1997; Schaal et al., Chapter 26, this volume) and psychophysical measures
of preferences with different methodologies (Herz, Chapter 10, Hermans and
Baeyens, Chapter 8, this volume). Here we shall focus only on the recording
of physiological responses, using two main approaches: One relies on record-
ings of response times or responses of the autonomic nervous system (startle
reflex, changes in skin conductance, heart rate). The other approach uses cere-
bral imaging: evoked potentials, functional magnetic-resonance imaging (fMRI),
and positron-emission tomography (PET). Their main results are summarized in
Table 9.3.
One of the first reports of differential treatment of unpleasant versus pleasant
odors in the brain was that of Kobal, Hummel, and Van Toller (1992), who showed
differences in the latency and amplitude of the P2 wave, with a positive potential
appearing around 500 msec after odorant stimulation: Latencies were shorter
and amplitudes smaller after stimulation of the left nostril by an unpleasant odor
Table 9.3. Main results of psychophysiological studies contrasting pleasant

and unpleasant odors
Parameters
Date Authors studied Pleasant odors Unpleasant Odors
1997b Alaoui- Skin Shorter duration Longer duration

Ismaı̈li et al. conductance
1997a Alaoui- Skin ohmic Shorter duration Longer duration
Ismaı̈li et al. perturbation
1995 Brauchli et al. Skin No difference Increase in
conductance with odorless air conductance
1997b Alaoui- Heart rate Decrease Increase
Ismaı̈li et al.
1997a Alaoui- Heart rate Decrease Increase
Ismaı̈li et al.
1995 Brauchli et al. Heart rate Decrease Increase
1997 Ehrlichman et al. Heart rate No effect Increase
1994 Miltner et al. Startle reflex No effect Increase
1995 Ehrlichman et al. Startle reflex No effect Increase
1997 Ehrlichman et al. Startle reflex Decrease in Increase in
(between- amplitude amplitude
subjects design)
1992 Kobal et al. Odor-evoked Short latencies Short latencies
potentials and smaller and smaller
(P2 wave, amplitude after amplitude after
∼500 msec) stimulation of stimulation of
the right nostril the left nostril
1997 Zald & Pardo Cerebral Amygdala: no Amygdala (left
blood flow difference with a and right): more
no-odor condition. activated than
Orbito-frontal in a no-odor
cortex (left and condition. Left
right): more orbito-frontal
activated than in a cortex: more
no-odor condition activated than in
a no-odor condition
1998 Fulbright et al. fMRI Brodmann area 32, Brodmann
(left) BA 46/9 BA 6 area 32, BA
(right). Insula BA 8 46/9 BA 6. Insula
2000 Bensafi et al. Response times Around 1,300 msec to Around 1,000 msec
perform a to perform an
pleasantness unpleasantness
judgment judgment
(hydrogen disulfide), whereas for a pleasant odor (vanillin) shorter latencies and
smaller amplitudes were obtained after stimulation of the right nostril. Those
authors interpreted their data as showing a predominance of the left hemisphere
for positive emotions, and of the right hemisphere for negative ones. Zald and
Pardo (1997) also found hemispheric differences in neuronal activation, with
unpleasant odors activating the left orbito-frontal cortex (OFC) and the amygdala
on both sides, whereas less unpleasant odors activated the OFC bilaterally and
caused no difference in amygdala activation compared with a no-odor condition.
The fMRI study of Fulbright et al. (1998) also revealed hemispheric differences:
The left Brodmann area 8 was activated specifically by pleasant odors.
Autonomic activity evoked by olfactory stimuli presents two patterns: either
opposite effects for pleasant and unpleasant odors, which is the case for skin
conductance and heart rate (Alaoui-Ismaı̈li et al., 1997a,b; Brauchli et al., 1995;
Ehrlichman et al., 1997), or effects due to unpleasant odors only, which is the
case for the startle reflex (Miltner et al., 1994; Ehrlichman et al., 1995). These
latter results favor the idea of automatic emotional arousal by malodors.
Recent psychophysical studies have shown that the right nostril dominates in
discrimination of unfamiliar odors, but not of familiar odors (Savic and Gulyas,
2000), and familiar, moderately pleasant odors are rated as more pleasant when
sniffed by the right nostril (Herz, McCall, and Cahill, 1999). Thus far, it is not
possible to describe clear hemispheric patterns of activation for pleasant and
unpleasant odors, but evidence seems to be accumulating to suggest differential
involvements of brain hemispheres according to the pleasantness/unpleasantness
of odors. Royet et al. (2000) have shown that such hemispheric differences are
not limited to olfaction, but extend to reactions to emotional stimuli in the visual
and auditory modalities. Regarding our questioning of the idea of a continuous
hedonic dimension, it is important to emphasize that Zald and Pardo (1997)
considered the odors they presented as “aversive” rather than “ unpleasant”: They
may have elicited fear, anger, or disgust. Some evidence from the study of Alaoui-
Ismaı̈li et al. (1997a) shows that unpleasant odorants (methyl methacrylate and
propionic acid) activate primarily the autonomic responses of disgust and anger.
As recent neuropsychological studies have shown differential brain activations
for disgust (Phillips and Heining, Chapter 12, this volume) and have lent support
to theories of distinct basic emotions, it seems likely that the situation is as
follows:
1. Unpleasant odors do not form a continuum with pleasant odors.
2. Unpleasant odors do not form a homogeneous group with respect to the emo-
tional experience.
Fear has been studied extensively by LeDoux and collaborators (Armony

et al., 1997) with animal models, in the form of fear conditioning in the auditory
modality. Their studies have revealed the critical role of the amygdala in fear
conditioning, and they converge with human studies implicating the amygdala
in emotional processing, especially of negative emotions (Aggleton, 1992). Fear
conditioning with odors has also been studied (Otto, Cousens, and Herzog, 2000),
and a crucial role for the amygdala in odor-mediated fear conditioning has been
confirmed in animals. Although amygdala lesions in humans do not produce the

same drastic emotional disturbances observed in animals, the amygdala’s role
in emotional processing is clear (Halgren, 1992): Aversions and other negative
emotions like fear imply amygdala activation (Morris et al., 1996).
A study by Hermann et al. (2000) used odors to study aversive and appeti-
tive conditioning in humans, that is, building conditioned approach / withdrawal
responses based on unconditioned odor stimuli in the laboratory. In that elec-
troencephalographic (EEG) study, autonomic correlates of the startle reflex and
emotional activation were also recorded. Neutral images of faces were paired
with either an aversive unconditioned stimulus (fermented yeast) or a pleasant
unconditioned stimulus (vanilla); the experiment produced differential aversive
conditioning with yeast, but failed to achieve any appetitive conditioning with the
vanilla odorant. EEG and autonomic recordings showed no effect of the aversive
conditioning on EEG tracings nor on the startle reflex, but there were effects on
skin conductance and muscular nonvoluntary responses. The authors interpreted
their data as indicating subcortical processing of aversive responses induced via
olfaction.
Although one may be surprised by the certitude of the latter authors concerning
the idea of olfactory unconditioned stimuli driving appetitive as well as aversive
behaviors in humans (Chapters 8, 10, and 26, this volume), the important point
for our purpose is that a negative affect (aversion) could be manipulated with
odors, but not a positive affect. That is in agreement with the work of Zald and
Pardo (1997), who found activation of the amygdala only for aversive odors.
Thus, several studies using different techniques to record activities in the cen-
tral nervous system and autonomic nervous system argue for asymmetry between
responses to pleasant odors and responses to unpleasant odors. For that reason,
we decided to use response times to check for possible differences between he-
donic judgment and other judgments, as well as differences between the process-
ing of pleasant and unpleasant odors (Bensafi et al., 2001). The hypotheses were
as follows:
1. Hedonic judgment of odors differs in kind from detection, intensity, and famil-
iarity judgments.
2. The processing of unpleasant odors differs from the processing of neutral or
pleasant odors.
Twelve odorants were chosen after perusal of a larger sample of 20 studied by

Godinot (1999). There were 4 pleasant, 4 neutral, and 4 unpleasant odorants,
according to the mean hedonic judgments of 40 subjects. Sixty-four subjects
performed four different tasks: detection and intensity, pleasantness, and famil-
iarity judgments. In contrast with our first response-time study, the judgments
were not comparative, but were absolute judgments: Subjects were instructed to
answer yes or no as quickly as possible by pressing one of two keys to indicate
if an odor was detected (yes/no) and if it was intense (yes/no), pleasant (yes/no),
or familiar (yes/no). Task order was randomized.
A three-way analysis of variance showed a significant effect of “task”
( p < .05), and the interaction between “task” and the hedonic class of the odor
was significant ( p < .05). Comparison of means showed no response-time dif-
ferences for the detection and intensity tasks, which is in accordance with the
hypothesis that these judgments rely on a perceptive process. But detection and
intensity responses were faster than hedonic and familiarity responses ( p < .05),
and familiarity judgments required more time than hedonic judgments ( p < .05).
But more interesting, pair comparisons showed that response times to the un-
pleasant odors were significantly shorter than response times to either the neutral
or pleasant odors: The swiftness of responses to unpleasant odors accounted for
the differences in pleasantness and familiarity judgments (Figure 9.4). Hedonic
response times to unpleasant odorants did not differ from response times for
intensity judgments.
That speed of processing seen only with the unpleasant odors could be in-
terpreted as further evidence of differential processing of malodors. However,
different response times are not sufficient to allow us to conclude that there are
separate neural substrates. As shown by Royet et al. (1999), some judgments that
require the same response times, such as familiarity and comestibility, depend
on different neural networks. Our hypothesis is that the faster hedonic responses
to unpleasant odorants may be explainable by parallel routes of processing: a
2500
2000
Response time (ms)
Pleasant
1500
Neutral
1000
Unpleasant
500
0
Detection Intensity Pleasantness Familiarity
Figure 9.4. Mean response times for 64 subjects in four tasks (detection, in-
tensity, pleasantness, and familiarity) and according to odor hedonic valence
(pleasant, neutral, and unpleasant). The interaction between odor pleasantness
and task was significant (F = 2.260; p < .04). Post-hoc comparisons showed
that response times for unpleasant odors were significantly different from those
for neutral and pleasant odors.
“quick and dirty” route for perception and reaction to potentially harmful odorant
stimuli, and a slower, cognitively more complex route for neutral and pleasant
stimuli. Brain imaging and autonomic recordings will be helpful in testing this
hypothesis.
Concerning the hedonic dimension of odors, it is not entirely superposable
onto the hedonic judgments we considered: Emotional responses and reactions
imply that there are also autonomic responses, attentional shifts, and unconscious
processes. It is important that the differences we found in hedonic and intensity
judgments were not odor-specific, but task-specific: Hedonic judgment, which
has been shown to activate the hypothalamic area (Zatorre et al., 2000), may be
primed by unconscious processes.
In a more general vein, we have gathered evidence that the hedonic dimension
is not to be found in an external and objective frame of reference, but rather
in a complex of different categories of meaningful odors. These meanings are
mainly ego-centered. This is in accordance with two lines of research: One
states that a hedonic ecology cannot consider objects and goals of desire as
independent of the perceiver (Rosch, 1996), nor decisions as independent of the
hedonic context (Tversky and Kahneman, 1981). The other demonstrates that
categorization itself is influenced by emotional states, and ultimately it considers
that any categorization implies hedonics (Isen and Daubman, 1984; Niedenthal,
Halberstadt, and Innes-Ker, 1999).
Finally, evidence of asymmetry in the processing of unpleasant and pleas-
ant odors, both in language and in hedonic tasks, is in keeping with a re-
search line called affective neuroscience, which works to elucidate different
circuits underlying positive and negative emotions in the human brain (Davidson
and Irwin, 1999). Thus, the complexity of olfactory hedonics certainly poses
a challenge for psychophysics, but it also offers an unparalleled opportu-
nity to improve our understanding of the relationship between cognition and
emotion.
Acknowledgments
This research was funded by the French National Program in Cognition Sciences
(Catégorisation et invariance dans la perception des odeurs) and by G.I.S. Sci-
ences de la cognition (Relations entre affectivité et cognition dans la percep-
tion des odeurs). This chapter has benefited from discussions with G. Sicard,
B. Schaal, S. David, D. Dubois, M. Mouélé, N. Godinot, R. Burnet, R. Gervais,
R. Versace, V. Farget, M. Vigouroux, and, last but not least, M. Jones-Gotman
and R. Zatorre.
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10
Influences of Odors on Mood and
Affective Cognition
Rachel S. Herz
In this chapter we shall review a wide range of research that shows how odors
can influence mood, cognition, and behavior. This review, though not exhaustive,
offers a comprehensive overview of the field. As background for this analysis,
a discussion of odor-associative learning will first be given. The topics to be
covered will then include the effects of odor exposure on (1) mood and specific
emotions, (2) attitudes, work efficiency, and perceived health, (3) emotional
memory, and (4) emotionally conditioned behavior. In addition to the behavioral
evidence, neuroanatomic substantiation for the special relationship between odor
and emotional associations will be presented.
1. Odor-associative Learning
The aim of the following paragraphs is to illustrate that almost all our responses
to odors are learned, rather than innate. Evidence to support this idea comes pri-
marily from research with infants and children. Although some work suggests
that young children show adult-like preferences for certain odors (Schmidt and
Beauchamp, 1988), most research with this age group indicates that children of-
ten do not differentiate between odors that adults find either very unpleasant or
pleasant, such as butyric acid (rancid butter) versus amyl acetate (banana) (Engen,
1988; Schaal, Soussignan, and Marlier, Chapter 26, this volume), or they may
have responses opposite to adult preferences, such as liking the smell of synthetic
sweat and feces (Stein, Ottenberg, and Roulet, 1958; Engen, 1982). By age eight,
however, most children’s hedonic responses to odors mimic those of adults. Odor
learning begins prior to birth. The olfactory system is functional in utero by 12
weeks of gestation (Schaal, Marlier, and Soussignan, 1998; Winberg and Porter,
1998), and there is considerable evidence that the specific odor characteristics of
a mother’s amniotic fluid (AF) are learned during gestation (Schaal and Rouby,
1990; Marlier, Schaal, and Soussignan, 1988; Winberg and Porter, 1998; Schaal
160
Olfaction and Affective Cognition 161
et al., 1998, and Chapter 26, this volume). AF also contains flavor compounds
from the mother’s diet (Mennella, Johnson, and Beauchamp, 1995) that also
can be incorporated into maternal milk (Mennella and Beauchamp, 1993). For
example, it has been found that the infants of mothers who consume distinctive-
smelling volatiles (e.g., garlic, alcohol, cigarette smoke) during pregnancy or lac-
tation show preferences for those smells, as compared with infants who have not
been exposed to those scents (Mennella and Beauchamp, 1991, 1993; Mennella
et al., 1995). The consequences of odor learning go well beyond preferences
for familiar smells and are not limited to biologically meaningful odorants. It
has been shown that through simple exposure and reinforced conditioning (e.g.,
cuddling), preferences for odors such as cherry oil or the mother’s perfume
are readily developed by young infants (Balogh and Porter, 1986; Schleidt and
Genzel, 1990; Sullivan et al., 1991).
Among adults, some of the most common instances of learned odor associ-
ations are the various hedonic responses to fine fragrances, which often have
earned their associative connotations through their connections to significant
others. Thus an individual’s personal history with particular odorants tends to
shape that individual’s responses to those odors for life. The exception to this rule
is that odors that cause strong trigeminal stimulation (e.g., ammonia) often are
immediately repelling, because the irritation caused by trigeminal nerve activity
at the moment of odor exposure produces a concomitant avoidance response.
Thus there may be odors that an individual will automatically and instantly dis-
like. However, the proposition that there are odors that are automatically liked
without prior experience seems unlikely. Even the smell of vanilla, which has
been touted as universally appealing, is first experienced during suckling by
both breast-fed and bottle-fed infants, for it is a primary odor compound in milk
(Mennella and Beauchamp, 1996), and that context is certainly an instance of
very salient emotional and nutritive reinforcement.
An area as yet unexplored is the extent to which individual differences in sensi-
tivities to certain volatiles may differentially predispose people to like or dislike
specific smells. It is known that anosmias to specific odors vary within popula-
tions and that this is largely determined genetically (Wysocki and Beauchamp,
1984). It is therefore possible that weakened or heightened sensitivities to certain
chemicals might explain why some people enjoy the smell of skunk (and in the
United States may even be members of the “Whiffy Club”), whereas most dislike
it intensely. Empirical investigations into the relationships between individual
physiological sensitivities and individual learning histories are clearly needed.
In addition to idiosyncratic experience, cultural modeling has been shown to
play an important role in the development of odor preferences. We see this contin-
ually in ethnic differences in food preferences: “One man’s meat is another man’s
162 Rachel S. Herz
poison.” Evidence for culturally learned odor associations has been presented
in two empirical studies examining olfactory hedonic responses: One study was
conducted in the United Kingdom in the mid-1960s (Moncrieff, 1966), and the
other in the United States in the late 1970s (Cain and Johnson, 1978). One might
not think that those populations would have very different responses to flavors
and smells, but the two studies demonstrated striking differences between the
two cultures. Among the odors examined in both studies was methyl salicylate
(wintergreen). In the U.K. study, that smell was given one of the lowest pleas-
antness ratings. By contrast, in the U.S. study, wintergreen was given the highest
pleasantness rating among all the odors tested. Why would that be the case? The
most likely explanation for the difference lies in cultural history. In the United
Kingdom, the smell of wintergreen is associated with medicine, particularly so
for the subjects in that 1966 study, who would have remembered the rub-on
analgesics that were widely used during World War II, a time they may not have
remembered fondly. Conversely, in the United States, the smell of wintergreen
is exclusively a candy “mint” smell, and one that has very positive connotations.
A similar pattern has been reported anecdotally for the smell of sarsaparilla,
which in the United Kingdom is a disliked medicinal odor, but in the United
States is the smell of root beer, a popular soft drink. It should always be kept in
mind that because of the many idiosyncratic odor associations of individuals, it
is often difficult to predict an individual’s reaction to a specific odor, despite the
existence of cultural norms.
Another factor that influences the type of association that an odor will evoke
is the frequency with which the odor is encountered. For example, frequently
experienced odors such as coffee lose their ability to elicit specific associations,
and rather evoke general hedonic responses (e.g., pleasant, soothing, alerting),
whereas an odor that is rarely encountered and has already been linked to a
unique event may be able to elicit intense responses when smelled later: for
example, the smell of eugenol (clove) and fear of the dentist’s drill (Robin et al.,
1998). The concept of odor-associative learning, vis-à-vis individual experience,
culture, and odor–event specificity, provides the background for the following
sections.
2. Effects of Odors on Mood and Specific Emotions

Many studies have shown that environmental manipulations such as exposure
to pleasant or unpleasant music (Eich and Metcalf, 1989) or variations in in-
door lighting (Baron, Rea, and Daniels, 1993) can have directional influences
on emotional states. In a similar vein, exposures to pleasant and unpleasant
odors have been found to impact moods. For example, in one study, pleasant
fragrances used in a “real-life setting” were shown to improve mood for women
and men during midlife and to alleviate some of the problems associated with
menopause (Schiffman, et al., 1995b,c). In contrast, odors emanating from pig-
holding facilities resulted in mood ratings that were significantly worse than those
for control subjects (Schiffman et al., 1995a). Ludvigson and Rottman (1989)
demonstrated that presentation of a pleasant odor (lavender) affected mood in
a positive direction for subjects performing a stressful arithmetic task, though
their performances on the task were inferior to those of subjects who did the
task in a clove-odor or no-odor condition. Knasko (1995) found that exposure
to an ambient smell of chocolate or baby powder caused people to look longer
at photographic slides and to report being in a better mood, as compared with
a no-odor condition. In contrast, exposure to the unpleasant odor of dimethyl
disulfide caused subjects to report less pleasant mood ratings than did subjects
exposed to lavender (Knasko, 1992). Thus it would seem that pleasant odors
make people feel good, and unpleasant odors make them feel bad. In support of
that contention, a study assessing a series of flower, herb, and fruit odors for their
effects on emotion found that the scents that subjects liked best were those that
they also found most relaxing (Nakano et al., 1992). Notably, it has been found
that the mere suggestion of an ambient pleasant or unpleasant odor in a unscented
room can produce the changes in mood that would be expected if such stimuli
were present (Knasko, Gilbert, and Sabini, 1990). This implies that it is sufficient
to have had past experience with the hedonic attributes of an odor for it to induce
concordant mood changes. However, it also suggests a general caveat for any
findings regarding odor and mood: It might be that any reported mood changes
will have been influenced by demand characteristics, because subjects will ex-
plicitly have been aware of the presence of an ambient odor. Experiments using
ambient odors at concentrations near the detection threshold, with no explicit
mention of odor having been made, would offer the most revealing approach.
Within the odor–mood paradigm, only one study to date has tested with a barely
detectable ambient odor (Kirk-Smith, Van Toller, and Dodd, 1983; Hermans
and Baeyens, Chapter 8, this volume). In that experiment, subjects worked on
a stressful task in the presence of a low concentration of trimethylundecylenic
aldehyde (TUA) that they later reported being unable to detect. Nevertheless, at
a subsequent nonchallenging task, those same subjects reported feeling anxious
when that odor was present, as compared with subjects who had not been ex-
posed to TUA during the stress task. That finding corroborates some results from
studies in which the odor presence was not hidden and lends further support to
the argument for the potency of odor-associative emotional learning.
In addition to self-reported mood changes, the physiological correlates of
emotional states have been shown to be affected by odors. Miltner et al. (1994)
164 Rachel S. Herz
found that the presence of a negative odor (hydrogen sulfide) increased the am-
plitude of the eye-blink startle reflexes of subjects relative to a no-odor condition,
whereas the presence of a positive odor (vanillin) decreased the startle reflex.
Ehrlichman et al. (1997) reported similar results. Consistent with those obser-
vations, Vrana, Spence, and Lang (1988) have shown that the startle reflex is
more pronounced during negative emotion, and muted during positive emotion.
Changes in patterns of EEG theta rhythms have also been observed after exposure
to different odorants, suggesting that various odors can differentially influence
mental activity and mood (Lorig and Schwartz, 1988). Critical to the develop-
ment of emotional associations to odor are first experiences, especially when
they are emotionally salient. Reexposure to an odor that earlier was involved
in such an episode can induce a spontaneous and intense emotional reaction
commensurate with one’s prior associational history with that odor. Initiation or
reoccurrences of post-traumatic stress disorder often are triggered by an odor that
was associated with the traumatic event (Kline and Rausch, 1985). For exam-
ple, many Vietnam veterans have experienced physiological and psychological
stress responses to odors associated with combat long after leaving the context
of war (Kline and Rausch, 1985; McCaffrey et al., 1993). In less severe cases,
patients who fear dental procedures show more stress-indicative autonomic re-
sponses to eugenol (clove odor, from dental cement) than do unafraid patients
(Robin et al., 1998). Smells can also influence the cravings of drug addicts, and
their contribution to the craving clearly is based on the associative-conditioning
history that such odors have with particular drugs. For example, for a “crack”
addict, the smell of a burning match can readily trigger a craving for cocaine
(A. R. Childress, personal communication, 1995). Acquired odor–emotion asso-
ciations have also been used therapeutically. Schiffman and Sieber (1991) trained
subjects to associate an odor with muscle-relaxation exercises and found that the
odor alone could later elicit relaxation responses. Odor–emotion associations
have been used to increase patients’ comfort and reduce anxiety during therapy
(King, 1988). Thus, when odors have previously been associated with specific
emotional states, they can have considerable capacity, when later encountered,
to rekindle those emotions and influence both the cognitive and physiological
parameters of experience.
On the basis of what is known about odor-associative learning, it seems evident
that the directional effects on mood that are seen following exposure to certain
odors are due to the hedonic connotations of those odors. An exception to that
pattern, however, was recently reported by Chen and Haviland-Jones (1999), who
found that an odor that was rated as smelling unpleasant could reduce feelings of
depressive affect in subjects. In that study, college students rated their moods and
then evaluated either (1) underarm odors from one of six donor groups (young
boys, young girls, college women, college men, older women, older men) or (2)
the smell of “home,” using various hedonic dimensions. The subjects were later
exposed to their target odors again, and their changes in mood were recorded. It
was found that subjects who were exposed to the smell of older women rated it
as unpleasant and intense (though not as unpleasant or intense as one of the other
groups rated the smell of college males), but they also reported reduced feelings
of depressed affect on the mood-assessment questionnaire. Reductions in de-
pressed affect were also reported by subjects who smelled the odor of “home.”
Notably, the smell of older women was given a fairly high familiarity rating,
so it may be that odors that are familiar, whether pleasant or unpleasant, are
also comforting. Unfortunately, there was no determination of what associations
were evoked by the smell of older women, or by any of the other odors tested.
Therefore it is not possible to determine whether or not the subjects’ prior per-
sonal associations (independent of the hedonic ratings) induced the observed
effect. In the absence of such information, these data beg the question whether
or not there was some biologically significant information carried by the smell
of older women that was soothing.
“Aromatherapy” consists in application of the contention that various “natural”
odors have intrinsic (essentially pharmacological) abilities to influence mood,
behavior (cognition), and health. For example, some contend that the odor of jas-
mine oil has a stimulating effect, whereas lavender has a sedative effect, on mood
and physical state (I. Imberger, personal communication, 1993). From an empir-
ical standpoint there is nothing to suggest that the effects of these odors extend
any further than the extent of one’s associative learning, especially at a cultural
level. That is, the claim that certain odors are experienced as relaxing, and others
as stimulating, may be true, but that likely is due to the acquired reputations or
meanings of the odors, not their intrinsic power; for example, in Western culture,
lavender is commonly found in bath oils and soaps. Nevertheless, the findings
of Chen and Haviland-Jones (1999) emphasize the need to determine whether or
not any emotionally (or cognitively) significant information can be transmitted
through exposure to such putatively biologically meaningful odorants (Jacob
et al., Chapter 11, this volume).
3. Effects of Odors on Attitudes, Work Efficiency,

and Perceived Health
The influence of odor hedonics on affective cognition is further illustrated by
their effects on attitudes, performances, and perceptions of health. In a study to
investigate how odor exposure would affect subjective evaluations, participants
exposed to a malodor (1) judged paintings as less professional and inferior and
166 Rachel S. Herz
(2) assessed significantly lower ratings of well-being for people in photographs

than did participants in a no-odor control group (Rotton, 1983). Baron (1983)
reported that job applicants were evaluated more positively and credited with
greater emotional competence when interviewed in a room that was scented with
a pleasant odor prior to or during the interview, though certain complex interac-
tions involving odor, gender, and style of dress were also observed. Pro-social
behavior has been shown to be enhanced in the presence of positive ambient
odors: Baron (1997) reported that assistive behavior toward strangers was much
more likely to occur when subjects were exposed to pleasant ambient odors (bak-
ing cookies, roasting coffee) than in the absence of such odors, and respondents
also reported significantly higher levels of positive affect in the presence of those
smells. Results from several studies have demonstrated that pleasant odors have
a positive influence on task performance: Baron (1990) showed that subjects who
worked in the presence of a pleasant ambient odor reported higher self-efficacy,
set higher goals, and were more likely to employ efficient work strategies than
subjects who worked in a no-odor condition (Baron, 1990).
Similarly, Warm, Dember, and Parasuraman (1990) reported that pleasant
odors enhanced vigilance during a tedious task, and Ehrlichman and Bastone
(1992) found that the presence of a pleasant odor improved creative problem-
solving relative to an unpleasant-odor condition. In studies examining the effects
of pleasant ambient odors on anagram and word-completion tests (Baron and
Bronfen, 1994; Baron and Thomley, 1994) it was found that in both low-stress
and high-stress conditions subjects did better in the presence of pleasant odors.
Notably, receipt of a small gift had similar positive effects on performance in
those experiments. Many studies have shown that manipulations such as being
given a small gift or being complimented can increase one’s positive mood and
improve behavior (Isen, 1984; Clark, 1991). Thus pleasant fragrances appear to
be able to modify mood and behavior in a manner comparable to other mood
manipulations.
Another way that odors have been shown to influence cognition is through
the connotations they have for environments and for people’s beliefs about
the health risks or benefits of scented spaces. Historically, unpleasant odors
long were viewed as carriers of disease, and good odors as curative (Levine
and McBurney, 1986; Le Guérer, 1994). Today such negative perceptions are
manifested as complaints about “multiple-chemical-sensitivity syndrome,” in
which severe allergic reactions and emotional distress are caused by the presence
of malodorous environmental pollutants (Kjaergaard, Pederson, and Molhave,
1992), and “sick-building syndrome,” in which individuals perceive that some-
thing in their indoor space is causing various health problems (Colligan and
Murphy, 1982), and there is a sort of generic increase in symptom reporting
in the presence of unfamiliar or unpleasant ambient odors (Neutra et al., 1991;

Stahl and Lebedun, 1996). On the positive side, certain pleasant ambient odors
are heralded in aromatherapy circles as natural healers (Lawless, 1991). Thus,
contemporary beliefs are not so different from ancient beliefs. Whether exces-
sively fearful, justifiably concerned, or indifferent to ambient odors, it is clear that
the vast majority of people automatically make assumptions about the healthful-
ness or harmfulness of an environment on the basis of their hedonic evaluations
of the ambient smells (Cain, 1987).
Notably, Dalton and colleagues (Dalton, 1996, 1999; Dalton et al., 1997) have
shown that subjective beliefs about odors appear to be responsible for many in-
stances of health complaints. In a study examining odor perception and cognitive
bias, odors typically rated as healthful (wintergreen), harmful (alcohol), or am-
biguous (balsam) were presented in three cognitive-bias conditions (healthful,
harmful, and neutral). The subjects reported significantly more health symptoms
and gave more intense odor ratings and higher irritation ratings to an odor (re-
gardless of what it was) when it was presented in the “harmful” cognitive-bias
context than when it was presented with a neutral or healthful bias (Dalton,
1999). There was also a synergistic effect between odorant and bias condition,
such that the worst effects of odorant irritation were reported when alcohol
was presented in the harmful context. In other studies (Dalton, 1996; Dalton
et al., 1997), giving subjects false information about the health consequences
of exposure (positive, negative, or neutral) altered their adaptations to isobornyl
acetate (balsam) and acetone (nail-polish remover). Subjects who were in the
positive- or neutral-bias context reported a decrease in perceived odor intensity
(normal adaptation response) over time. In contrast, subjects who were in the
negative-bias context showed initial adaptation, but then a sensitization effect
that resulted in later odor ratings that in some cases were higher than the initial
ratings.
Thus, just as with emotional perceptions, the physical aspects (health symp-
toms) of odor exposure can be mediated by subjects’ beliefs, where the beliefs
stem from the hedonic connotations of the odorants. This effect can be so extreme
that the mere suggestion of an odor, without it actually being present, can cause
people to report physical distress. For example, a tone played over the radio in-
duced olfactory hallucinations in a number of listeners, some of whom reported
discomfort from the “odor exposure” (O’Mahoney, 1978). Similarly, in a labo-
ratory study, Knasko et al. (1990) found that feigned exposure to an unpleasant
ambient odor produced increased ratings of discomfort and health symptoms.
If such responses are not due to the actual presence of an odor stimulus, then
they must be learned; and as can be seen, the response is consistent with the
acquired hedonic connotation of the smell (real or imagined). The phenomenon
168 Rachel S. Herz
of associative health effects produced by odors is further witnessed by the find-

ing that subjects reported fewer health symptoms when exposed to baby powder
than when exposed to chocolate or to no odor (Knasko, 1995). Such mood effects
clearly are in line with the learned connotation of baby powder as comforting
and clean.
4. Effects of Odor Exposure on Emotional Memory

The way in which odors elicit hedonically congruent mood and attitudinal
states is by evoking memories of past experiences. In studies to examine the
hedonic congruence between odor pleasantness and the valence of memories
evoked, it was found that the personal memories that subjects recalled were
significantly more positive when they were in the presence of a pleasant ambi-
ent odor (almond) than when in the presence of an unpleasant odor (pyridine)
(Ehrlichman and Halpern, 1988). Notably, the subjects’ memories in that study,
though personal, were not directly related to the ambient odors present, but
rather were simply congruently toned with the hedonic valences of the odors.
That is, the ambient odor influenced the subject’s overall mood, and the subject’s
mood then influenced the tendency to remember more good or bad life events.
This effect is an extension of the same associative mechanisms that determine
hedonic influences of odors on moods, beliefs, and behaviors. Another, more
direct way in which odors can influence memory is in their links to specific
“autobiographical” events (e.g., the Proust phenomenon). Several investigators
have used the autobiographical-memory method to explore the specific charac-
teristics of odor-evoked memories. Those studies have shown that odor-evoked
memories are reported as very evocative and that odors seem to be especially
good reminders (see Chu and Downes, 2000, for a review). Most importantly,
such studies have shown that odor-evoked memories are experienced as highly
emotional, as measured by both self-reports and increased heart-rate responses
(Laird, 1935; Herz and Cupchik, 1992; Herz, 1998a).
The most comprehensive method for assessing the special characteristics
of odor-evoked memories is with a cross-modal approach, where memories
elicited by stimuli presented in various sensory modalities are compared. In the
first cross-modal olfactory-memory experiment of that type, Rubin, Groth, and
Goldsmith (1984) showed participants 15 familiar stimuli (e.g., coffee, Band-
Aids, cigarettes) to be assessed in olfactory, verbal, or picture form. For each
item, the participant described the memory that was evoked and rated it on sev-
eral scales: age of the memory, vividness, emotionality at the time of the event,
emotionality at the time of recall, how many times it had been recalled, and
when it was last recalled (prior to the experiment). From those measures, the
only finding that was statistically reliable was that memories evoked by odors
were thought of and talked about less often than memories evoked by words and
pictures. There was a trend for odor-evoked memories to be more emotional, but
that effect was not statistically significant.
Hinton and Henley (1993) compared subjects’ free associations (via word,
odor, and visual perceptions) to six familiar items (coffee, tobacco, carnations,
oranges, Ivory soap, pine). Confirming the intuition that odors have a special
capacity to elicit hedonic responses, they found that the free associations elicited
by odors were more emotional, as evaluated by independent judges, than the free
associations elicited by words or visual versions of the same items. Moreover,
when the free associations resembled autobiographical recollections, they most
often had been elicited by odor cues, thus suggesting that associations elicited
by odors are more hedonically toned and personally involving than those elicited
by other sensory stimuli.
Several cross-modal experiments from our laboratory have further demon-
strated that memories evoked by odors are distinguished by their emotional
potency, as compared with memories cued by other modalities (visual, tactile,
verbal, music) (Herz and Cupchik, 1995; Herz, 1998b; Herz, 2001; Herz and
Schooler, 2002). In one set of experiments, familiar objects (cues) were pre-
sented to participants in olfactory, verbal, visual, or tactile form (e.g., the smell
of popcorn, the word “popcorn,” seeing popcorn, or feeling popcorn) while the
participants viewed emotionally evocative pictures. The participants were told
that the experiment concerned the effects of different environmental cues on
the perception of pictures. Memory was never mentioned. Two days later, how-
ever, when participants returned to the laboratory, they were given a surprise
cued-recall test concerning their picture experiences, and the accuracy and emo-
tionality of their memories were assessed. In each experiment it was found that
the memories evoked by the various types of cues did not differ in accuracy (the
same numbers of pictures were correctly recalled for each cue type); however,
memories evoked by odor cues were significantly more emotional than mem-
ories prompted by any other cue. In a second series of experiments in which
abstract odors, music, and visual images were compared as memory cues, it was
found that odor-evoked memories caused higher heart rates during recall than
did memories evoked by the other sensory cues, and again memory accuracy
was unaffected by cue type. Most recently, we have combined autobiographical
and cross-modal methods and have demonstrated that autobiographical mem-
ories elicited by odors are more emotional and evocative than recollections of
the same personal events triggered by visual or verbal stimuli. Together, these
findings show that odor-associated memory is distinctively more emotional than
memory elicited through other sensory modalities.
170 Rachel S. Herz
5. Effects of Odors on Emotionally Conditioned Behavior

From the literature reviewed in this chapter, it is clear that odors have a special
propensity to become associated with events and to cue recall. Perceptions of
odors can also be emotionally conditioned. In a recent study it was shown that
when a neutral odor was unobtrusively paired with toilet stimuli, subjects with
negative attitudes toward “going to the toilet” rated the paired odor more nega-
tively than they rated a non-toilet-paired control scent one week later (Baeyens
et al., 1996; Hermans and Baeyens, Chapter 8, this volume). Thus, Pavlovian
conditioning can modify perceptions of odors. Odors can also influence moods,
either through an individual’s specific associational history or because of the
acquired cultural connotation of an odor. We also know that moods can in-
fluence behavior. For example, a positive affect is generally associated with an
increase in work productivity and an inclination to help others (Isen, 1984; Clark,
1991), whereas negative feelings have been shown to reduce the propensity to
assist (e.g., Underwood, Froming, and Moore, 1977) and to increase aggression
(Baron and Bell, 1976). Following logically from that, one would predict that an
odor experienced during an emotionally significant event could, when reintro-
duced, elicit an emotional response consistent with the past event and perhaps
alter behavior accordingly.
To test that idea, we investigated whether or not an odor that had been as-
sociated with failure and frustration could, when later encountered, produce a
detrimental effect on performance in an unrelated task. In that study (Epple and
Herz, 1999), we gave five-year-olds the task of trying to solve an impossible
maze (the “failure maze”). All subjects worked at the task while in a scented
room. As the task was unsolvable, the result was failure and frustration, as subse-
quently confirmed by independent analyses of videotapes from the session. After
the failure-maze task, the subjects were given a 20-minute break in an unscented
area. They were then divided into three groups and taken to other experimental
rooms that were scented with the same odor as in the failure-maze task, a novel
odor, or no odor and were given a cognitively challenging test. It was found
that subjects who performed the test in the presence of the same odor as in the
failure-maze task did significantly worse than subjects in the other groups. Sub-
jects in the novel-odor and no-odor groups did not differ in performance. Such
findings show that subjects can become experientially conditioned to odors and
that later exposure to such odors can have direct impacts on behavior. Although
our study demonstrated a negative effect produced by emotional conditioning
to an odor, many positive extrapolations are possible from such findings. For
example, positive conditioning with odor manipulations could be implemented
to improve scholastic performances for children with low self-confidence and
poor academic orientation. Additionally, the underlying concepts and methods of

odor-associated conditioning can be applied toward a variety of health-enhancing
and positive-behavior-promoting techniques for both children and adults.
6. Neuroanatomic Connections between Olfaction

and Associative Emotional Processing
The behavioral findings that indicate the highly associative and emotionally
evocative properties of odors are being substantiated on neuroanatomical
grounds. Olfactory afferent mechanisms have a uniquely direct connection with
the neural substrates for emotional processing (amygdala-hippocampal complex)
(Turner, Mishkin, and Knapp, 1980; Cahill et al., 1995). Only two synapses sep-
arate the olfactory nerve from the amygdala – critical for experiencing and ex-
pressing emotion (Aggleton and Young, 2000) and maintaining human emotional
memory (Cahill et al., 1995). And only three synapses separate the olfactory
nerve from the hippocampus, involved in the selection and transmission of in-
formation in working memory, in transfers between short-term and long-term
memory, and in various declarative memory functions (Staubli, Ivy, and Lynch,
1984; Schwerdtfeger Buhl, and Gemroth, 1990; Eichenbaum, 1996). Addition-
ally, the orbitofrontal cortex and amygdala have been shown to play major roles
in stimulus-reinforced associative learning (Rolls, 1999), and olfactory process-
ing has been shown to activate the orbitofrontal cortex and to some extent the
amygdala (Zatorre et al., 1992; Phillips and Heining, Chapter 12, this volume).
The fact that no other sensory system makes this kind of direct, dynamic contact
with the neural substrates for emotion and memory provides strong support for
the emotional distinctiveness of olfactory cognition.
The existence of a unique relationship between olfaction and emotional pro-
cessing can also be defended on neuroevolutionary grounds. Olfaction was the
first sense to evolve and is the most fundamental in terms of the information that
it imparts. Even for the most simple creatures of one or a few cells the chemical
sense enables the organisms to know what to approach (chemotaxis) for nu-
tritional and reproductive reasons, that is, knowing what to approach for their
survival. In more complex animals, such as mammals, olfactory information is
the key form of communication for all of the most critical aspects of behavior –
knowing which are one’s kin, scenting out the reproductively available con-
specifics, finding food, sniffing out the sources of danger – again, information
that tells the animal what to approach and what to avoid in order to survive and
thrive. We humans no longer rely on olfactory information as the key to our sur-
vival; rather, visual and verbal communications have become the major means
172 Rachel S. Herz
by which we maneuver ourselves adaptively through the world, though olfaction

still retains some of its basic functions.
The most immediate response we have to a smell is to like or dislike it, that is,
approach or avoid. This basic hedonic choice is an affective response (Livesey,
1986). It is also the case that when one thinks abstractly about what emotions
tell us, they are about what is good (to approach) and what is bad (to avoid).
For example, positive emotions such as joy encourage our approach to the joy-
ful stimulus and thus presumably foster our survival and reproductive potential,
whereas negative emotions such as fear enable us to avoid or counter dangers,
thus fostering our survival through avoidance of death. Thus, conceptually, emo-
tions tell us the same things that smells tell our animal brethren, that is, what
to approach and what to avoid for maximal reproductive advantage. In other
words, emotions and olfaction are functionally and ultimately analogous; both
are fundamentally geared to prompt either an approach or avoid response that
will enable the organism to react appropriately to best ensure its survival.
It is also notable that during human phylogenetic development, the most an-
cient part of the brain, called the rhinencephalon (literally, “nose-brain”), which
comprises the olfactory and limbic areas, developed from olfactory structures
first, and the limbic structures (e.g., amygdala-hippocampal complex) then fol-
lowed (McLean, 1969). In other words, the ability to experience and express
emotion grew directly out of the ability to cognitively process smell. In sum,
there appears to be neuroanatomical and neuroevolutionary convergence linking
the perception of smell and the experience of emotion (Phillips and Heining,
Chapter 12, this volume).
7. Conclusion
The literature reviewed in this chapter has shown that exposure to odors can alter
moods, change attitudes, influence perceptions of health, affect task performance,
and evoke memories. In general, pleasant-smelling odors induce positive moods,
attitudes, and behavioral changes, and unpleasant odors induce negative moods,
attitudes, and behavior. Almost all of these effects can be explained by associative
learning and conditioning principles, where the acquired hedonic connotation of
an odor is responsible for inducing congruent moods and behaviors; in more
specific cases, a particular odor is tied to a past event and induces reactions con-
sistent with its associational history. The neuroanatomical, phylogenetic, and
functional relationships between olfaction and limbic-system structures provide
strong support for the special and perhaps unique emotional potency and asso-
ciative propensity of our perceptions of odors. Despite our current knowledge,
our understanding of how odors influence mood and affective cognition is still
in its infancy. Many topics await further exploration, and many new questions
await answers. It is envisioned that neuroimaging techniques in conjunction with
behavioral studies will greatly expand our capacity to deal with these questions
and use wisely the answers we shall find.
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11
Assessing Putative Human Pheromones
Suma Jacob, Bethanne Zelano, Davinder J. S. Hayreh,
and Martha K. McClintock
Whether or not human pheromones exist and how they might influence human
physiology and behavior have been debated for decades; for a review, see Preti
and Wysocki (1999). In this chapter, we present the concepts and data that are
shaping our understanding of pheromones and pheromone-like effects in humans
and other species. This will include the semantic issues associated with use of the
term “pheromone” and descriptions of experiments designed to determine the
psychological effects of two putative human pheromones. The expectation that
human pheromones can consistently elicit stereotyped behavior is unrealistic.
We argue that it is more likely that airborne signals are context-dependent and
have more general, modulatory effects that can best be captured conceptually
in terms of “modulatory pheromones” or “social chemosignals” (McClintock,
2000). Research with humans also presents a unique opportunity to consider the
functional role of an awareness or conscious experience of pheromones and social
chemosignals, whereas animal research is limited to studies of overt behavior.
1. Definition of “Pheromone”
According to the classic definition (Karlson and Lüscher, 1959), pheromones are
airborne chemical signals emitted by an individual that trigger specific neuroen-
docrine, behavioral, or developmental responses in other individuals of the same
species. Early pheromone research began with insects (Karlson and Butenandt,
1959), and the term “pheromone” was coined to designate a group of externally
released “active substances” that triggered specific behavioral responses and
were similar to, but could not be called, hormones. An example is bombykol, a
substance emitted by female silkworm moths. A male will follow the bombykol
up its concentration gradient to find the female and mate (Schneider, 1974).
As pheromone research broadened, pheromones were divided into three gen-
eral classes based on their functional effects. In one class of pheromones are the
178
Human Pheromones 179
releaser pheromones (Wilson and Bossert, 1963), which trigger or “release” a

stereotyped behavior, (such as the male moth following the trail of bombykol
(Schneider, 1974), or mating behavior in cattle (Rivard and Klemm, 1990). In a
second class are priming pheromones (Wilson and Bossert, 1963), which trigger
a regulatory or developmental neuroendocrine change in the receiving organ-
ism (van der Lee and Boot, 1955, 1956; Bruce, 1960a,b; Vandenbergh, Witsett,
and Lombardi, 1975). The third class comprises the signaling pheromones that
indicate or signal to members of the same species information such as iden-
tity or reproductive status of an individual (Bronson, 1968). Recently, we have
proposed the concept of a fourth class, modulating pheromones (McClintock,
2000), largely in response to the research with humans described later in this
chapter. These modulate behavioral or psychological reactions to a particular
context, without triggering specific behaviors or thoughts.
Although it may be simplest to categorize a pheromone by its clear and obvious
behavioral or physiological effects, some have called for more specific criteria
concerning a signal’s cognitive attributes and developmental program, especially
in regard to mammalian chemosensory communication. For example, it has
been proposed that a pheromone should be chemically discrete (just one or a
few compounds) and that pheromonal responses must be shaped minimally by
olfactory qualities or learning and primarily by genetics (Beauchamp et al., 1976;
Goldfoot, 1981).
The idea that olfaction and cognitive recognition do not play roles in
pheromonal communication arose in part from the observation that in many
mammals, pheromones do not always initiate their effects by binding at the
main olfactory epithelium. Instead, they may bind at specialized chemoreceptors
within the vomeronasal organ (Wysocki and Meredith, 1987; Keverne, 1999).
The vomeronasal organ is the receptor organ of the vomeronasal system, and
neural projections from the vomeronasal organ extend to the accessory olfactory
bulb and to parts of the brain associated with emotional responses, social behav-
ior, and reproduction, such as the limbic system and the anterior hypothalamus
(Wysocki and Meredith, 1987). There are no known projections directly to the
primary and secondary olfactory cortices, which are understood to be necessary
for recognition and categorization of odors.
It has become clear, however, that some mammalian pheromones are indeed
processed by the main olfactory system. Androstenone is the pig pheromone
produced and released by the boar that causes the sow to assume her mat-
ing stance. Simply spraying this steroid from an aerosol can, without a boar
present, is sufficient, along with a light touch, to trigger the behavior (Melrose,
Reed, and Patterson, 1971). Nonetheless, the vomeronasal organ is not necessary
for this response. Sows will respond after their vomeronasal organs have been
180 Jacob, Zelano, Hayreh, and McClintock
plugged, implicating involvement of the main olfactory system in the response

(Dorries, Adkins-Regan, and Halpern, 1997). Moreover, androstenone has a
strong odor detectable by about 50% of human adults and presumably by sows
(Wysocki, Dorries, and Beauchamp, 1989; Dorries et al., 1995). Thus, demon-
strating involvement of the olfactory system is not evidence that a chemosignal
is not a pheromone. Humans are the species in which questions concerning
the roles of olfaction and cognition in pheromonal communication can best be
explored.
2. Chemical Communication in Humans

The presence of the vomeronasal organ in human adults has been quite contro-
versial and marked by conflicting reports. Reports of vomeronasal frequency
in humans have been inconsistent, ranging from 39% (Johnson, Josephson,
and Hawke, 1985) to 100% (Moran, Jafek, and Rowley, 1991), possibly be-
cause some investigators may mistakenly have identified other nasal structures
as the vomeronasal organ (Jacob et al., 2000). At present, it can be concluded
only that human adults have at least a remnant of a vomeronasal organ in the
nose, but whether or not it is functional in adults remains debatable (Keverne,
1999; Preti and Wysocki, 1999; Smith et al., 1999). Recent claims for a func-
tional vomeronasal organ have stemmed mainly from surface-potential changes
recorded from the putative human vomeronasal epithelium during exposure to
steroidal compounds (Berliner et al., 1996; Grosser et al., 2000). However, there
has been valid criticism of the interpretation of those results as proof of function-
ality (Preti and Wysocki, 1999), and evidence for receptor potentials and neural
transmission to the brain is needed. Furthermore, attempts to locate vomeronasal
receptor genes in human vomeronasal tissue have thus far found only pseudo-
genes (Tirindelli, Mucignat-Caretta, and Ryba, 1998), although one, V1RL1,
has been isolated from nasal epithelium (Rodriguez et al., 2000).
Regardless of whether or not humans have or need a functional vomeronasal
system for processing pheromones, the important issue facing experimenters
is what effects of pheromones to look for. At present, there is evidence in hu-
mans only for priming pheromones that regulate endocrine function (Stern and
McClintock, 1998): Axillary secretions collected from women were found to
modulate the duration of the follicular phase and the timing of the preovulatory
surge in luteinizing hormone (LH) in recipient women who had the secretions
applied just under their noses. We hypothesized that, as in other species, human
pheromones might be produced by apocrine glands (active only during reproduc-
tive maturity), eccrine glands (which produce sweat that contains compounds
found also in saliva and urine), exfoliated epithelial cells, hair, or bacterial action
(Nixon, Mallet, and Gower, 1988). We collected compounds from the axillae
(armpits) because they contain all five of those potential sources.
After those compounds had been collected on pads, frozen, and then thawed,
they did not have an odor that was detectable by the women in the study. It
was also of central theoretical importance that all participants in our study be
blind to the experiment’s hypothesis and the source of the compounds. The study
was presented to the subjects as being focused primarily on the development of
noninvasive methods for detecting ovulation, and only secondarily on sensitivity
to the odor of small amounts of “natural essences” (consent was obtained for a
list of 30 compounds).
We do not yet know the structures of the compounds that regulate ovulation
without being consciously detectable as odors. Axillary compounds, such as 5α-
androst-16-en-3β-ol or (E)-3-methyl-2-hexenoic acid, at first would not seem
likely to be the active compounds, because they have a strong odor. On the other
hand, the latter compound is odorless when bound tightly with its carrier protein,
which would be the case in natural secretions (Spielman et al., 1995). Thus it
could be that the larger molecule is odorless, even though the smaller component
that has a pheromonal action does have an odor.
Whereas we have shown that these chemosignals affect endocrine function
without having detectable odors, there is some evidence for odors affecting
human behavior and psychological states, presumably acting through the main
olfactory pathway. For example, living within smelling distance of a pig farm has
been shown to significantly depress mood (Schiffman et al., 1995), and there is
some evidence for consistent emotional influences by low levels of odors (Kirk-
Smith, Van Toller, and Dodd, 1983; Lorig et al., 1990; Schwartz et al., 1994).
The power of odors to evoke emotional memories of past experiences in humans
has often been noted (Proust, 1922; Degel and Köster, 1998), and the hedonic
qualities of odors in everyday life are commonly recognized and inescapable
(Tassinary, 1985).
Suggestive evidence for human signaling odors (if not for pheromones) comes
from studies of the major histocompatibility complex (MHC). Ober and col-
leagues demonstrated that marriages between people with identical human leuko-
cyte antigen (HLA; the human MHC) haplotypes are less frequent than expected
(Ober et al., 1997, 1999) and that a high degree of HLA similarity between
partners increases the chance of miscarriage (Ober et al., 1998).
Furthermore, studies have shown that people find unpleasant the odors from
individuals whose HLA genes are similar to their own (Wedekind et al., 1995;
Wedekind and Füri, 1997). Together, these intriguing findings suggest that people
may use chemosignals in mate-choice decisions to reduce the fitness costs due
to early fetal loss or miscarriage.
Whether this observed pattern of disassortative mating in humans is mediated

by olfaction, as it is in rodents (Yamazaki et al., 1979; Boyse, Beauchamp,
and Yamazaki, 1987), or mediated by some other mode of action has yet to be
determined. If social chemosignals do play a role (regardless of which pathway
mediates their effects), we do not suggest that they induce an instinctive attraction
at a level below conscious control or awareness. However, it is conceivable to
think that, in appropriate social contexts, pheromones or other chemosignals
could modulate behavior and attraction and be one of the many influencing
factors that lead to decisions and actions with long-lasting effects.
To date, research on specific behavioral effects (rather than physiological
effects) of putative human pheromones has been conceptually limited to identi-
fying releaser pheromones. The focus has been on sociosexual behaviors similar
to those in some animal models, such as sex attraction in silkworm moths, ham-
sters, and rhesus monkeys (Michael, Keverne, and Bonsall, 1971; Schneider,
1974; Singer et al., 1986; Singer, 1991; Wood, 1998) and mating reflexes in pigs
and rats (Gower, 1972; Sachs, 1997). Despite the fact that chemical communi-
cation among non-human animals is often complex and context-dependent (see
Izard, 1983, for a review), the entertainment media and perfume industry have
championed the idea that dramatic sexual behaviors or drives can be triggered
in humans (see Table 2 of Preti and Wysocki, 1999).
In general, the search for human pheromones involved in sexual behavior has
produced mixed results. For example, when Morris and Udry (1978) studied
married couples in their homes, they failed to find that aliphatic acids increased
the frequency of intercourse. Cutler and colleagues, however, reported that an
unidentified compound increased sexual interactions of men (Cutler, Friedman,
and McCoy, 1998). Unfortunately, that study did not address whether or not the
behaviors were influenced by learned associations with consciously perceived
odors, nor whether it was the women themselves who were affected or their male
partners. However, even if the effects are not as dramatic as the perfume industry
touts them to be, the idea that there may be detectable influences on behavior is
certainly intriguing.
The expectation that discrete behaviors and states, specifically sexual inter-
course or sexual desire, can be triggered in humans exceeds what can be predicted
from our knowledge of human cognition and behavior. The inherent multimodal,
multidimensional complexities of human behavior render such a strict model
inappropriate, and the elaborate neocortical cognitive systems of the human ner-
vous system preclude the initiation of complex behaviors by a simple signal.
Just as in many other mammals (Signoret, 1976, 1991; Goldfoot et al., 1980;
Sorensen, 1996), human chemical communication likely is inextricably linked
with other sensory and emotional systems.
Rather than focusing on releaser effects and a limited range of observable

behaviors, what seems more justifiable and productive is investigation into the
more fundamental and well-studied aspects of psychological state and function.
Using methodologies currently employed in psychological and physiological
research to test on-line fluctuations would make investigations into the behavioral
effects of putative human pheromones more flexible, sensitive, and comparable
to extant knowledge in related fields. Specifically, pheromonal influences might
be studied by measuring variations in common state measures such as mood
and arousal, with corresponding concurrent psychophysiological measures (e.g.,
phasic and/or tonic autonomic nervous system variations or evoked-response
measures).
The hypothesis that pheromonal effects can be detected in mood and auto-
nomic measures is supported by the mammalian literature. The vomeronasal
and olfactory inputs project to regions of the amygdala and hypothalamus in
other mammals (Wysocki and Meredith, 1987; Risold and Swanson, 1995).
Both of these areas of the brain play roles in causing changes in emotional tone
(Aggleton, 1993) and in regulation of physical states such as body temperature,
autonomic nervous system tone, appetite, and reproductive function. Thus, in-
vestigating changes in emotional, physical, and body states not only is a viable
research avenue but also can provide a fundamental foundation for characteriz-
ing the full range of potential-circuit-based effects produced by putative human
pheromones. We have employed such an approach in the research described next.
3. Psychological Effects of Androstadienone and Estratetraenol

In our laboratory we have recently been investigating a tantalizing development
in the human pheromone field. Claims that two steroids, 4,16-androstadien-3-
one (androstadienone) and 1,3,5,(10),16-estratetraen-3-ol (estratetraenol), are
human pheromones have generated much debate. Androstadienone is found in
men’s sweat (Labows, 1988), semen (Kwan et al., 1992), and axillary hair (Nixon
et al., 1988; Rennie et al., 1990), and estratetraenol has been isolated from the
urine of pregnant women in the third trimester (Thysen, Elliott, and Katzman,
1968). Perfume marketers and their associated scientists claim behavioral re-
leaser effects for these compounds, including stimulation of specific social cog-
nitions or thoughts, such as increased friendliness, sociability, self-confidence,
and sense of well-being (Blakeslee, 1993; Taylor, 1994). More recent findings,
using a 70-item modification of the Derogatis Inventory, suggest a decrease in
negative emotional self-ratings (not specifically related to social qualities) after
exposure to androstadienone (Grosser et al., 2000). It also was reported that
these compounds generated electrical responses from the human vomeronasal
organ, not the olfactory epithelium, and that subjects did not detect any odors
(Monti-Bloch and Grosser, 1991; Monti-Bloch et al., 1994). Furthermore, those
electrophysiological responses were sex-specific: Androstadienone significantly
stimulated only the female vomeronasal organ, whereas estratetraenol signifi-
cantly stimulated only the male vomeronasal organ.
Although the electrophysiological findings have elicited considerable skep-
ticism (Preti and Wysocki, 1999), those data presented not only an interesting
development in the field but also an opportunity to investigate the effects of spe-
cific compounds. Our interest was to test the claims of specific effects on specific
social cognitions or thoughts, such as increased self-confidence in social situa-
tions, as well as the sex specificity of the steroids, a claim based to date only on
electrophysiological evidence.
Our hypothesis was that sex-specific releasing effects were unlikely in humans.
Our alternative hypothesis was that human behavioral pheromones or social
chemosignals would only modulate basic drive states, attention, or subcortical
affect systems. Chemosignals might do this in several ways: (1) by affecting
particular neurotransmitter systems in the brain (similar to the psychoactive
effects of specific drug classes), (2) by activating or inhibiting brain circuits
involved in emotion or motivation, or (3) by influencing arousal, attention, or
memory-biasing systems. The predicted primary effect on behavior would be a
change in the underlying tone or valence for perceiving external stimuli, in other
words, a mood. We further hypothesized that cortical inputs could easily override
a behavioral response. In that scenario, neither behavior nor specific cognitions
would be expected to be reflexively associated with chemosignal exposure, as is
the case in classical releasing pheromone systems.
We conducted two experiments (Jacob and McClintock, 2000). In both, we
exposed our subjects to no more than 900 micromoles of either steroid in a
propylene glycol carrier, applied under the nose with a cotton swab so that
subjects would be exposed to it continuously. In order to minimize the chance
of falsely accepting negative results, our concentrations were higher than those
used by the perfumers, who directly delivered steroids to the vomeronasal organ
or olfactory epithelium. In the initial study, we masked the steroids with a carrier
of propylene glycol, which has a weak odor and was used by Monti-Bloch and
colleagues (Monti-Bloch and Grosser, 1991; Monti-Bloch et al., 1994). In the
second, replication study, we masked any odor from the steroids with a strong
odor of clove oil added to the propylene glycol carrier.
To determine whether or not the steroids had psychological and sex-specific
effects, we used a 15–20-minute psychometric battery consisting of well-
established and validated scales for assessing the subjective effects of pharma-
cological agents on mood and psychological state (de Wit and Griffiths, 1991).
The Profile of Mood States (POMS) (McNair, Lorr, and Droppleman, 1971) was
selected because it is an established measure that is sensitive to mood changes
related to olfactory cues (Schiffman et al., 1995), to drug-induced changes in
mood (de Wit and Griffiths, 1991; Fischman and Foltin, 1991), to hormonal-
state influences (Kraemer et al., 1990), and to normal transient mood shifts in a
wide range of circumstances (Lieberman et al., 1982; Der and Lewington, 1990;
Horswill et al., 1990; Cockerill, Nevill, and Lyons, 1991; Williams, Krahenbuhl,
and Morgan, 1991). The POMS scale we used in this study had 72 items in an
adjective checklist format. From that extensive checklist, eight factors have been
derived empirically, and these clusters of items are called Anxiety, Depression,
Anger, Vigor, Fatigue, Confusion, Friendliness, and Elation.
The pharmacological-state Addiction Research Center Inventory (ARCI)
(Haertzen, 1974a,b) questionnaire was originally developed to provide empiri-
cally derived scales to distinguish the sensations and perceptions uniquely as-
sociated with specific drugs or classes of drugs. The ARCI has five empirically
derived scales: the morphine-benzedrine group (MBG) scale, which reflects drug
euphoria; the lysergic acid diethylamide (LSD) scale, which reflects drug dys-
phoria and mental confusion; the pentobarbital-chlorpromazine-alcohol group
(PCAG) scale, which measures level of sedation; the amphetamine (A) scale,
which measures amphetamine-like stimulant effects; and the benzedrine group
(BG) scale, which measures stimulant-like effects or intellectual efficacy.
A visual-analogue scale (VAS) is often used to assess momentary changes in
affect (Folstein and Luria, 1973). We chose an established scale used in psy-
chopharmacological research (Zacny, Bodker, and de Wit, 1992; Brauer and
de Wit, 1997; de Wit, Clark, and Brauer, 1997; Kirk, Doty, and de Wit, 1998)
that measures participants’ responses to six adjectives (“stimulated,” “high,”
“anxious,” “sedated,” “down,” and “hungry”).
In the initial experiment, we studied 10 women and 10 men in our laboratory.
In each of three randomized, counterbalanced, and double-blind sessions, we
applied a solution (estratetraenol, androstadienone, or propylene glycol carrier
control) and then tested the participants’ psychological responses. After an initial
hour in our testing room, participants returned to their everyday lives and self-
administered the test-battery questionnaires approximately 2, 4, and 9 hours after
we had applied the test solutions.
We used similar methods in the replication experiment with the strong odor
mask. However, we focused only on women and their responses to androsta-
dienone within the first 2 hours (in contrast to the 9 hours covered in the first
study). In order to increase statistical sensitivity, we measured psychological
responses in terms of changes from their responses to a baseline battery admin-
istered prior to exposure to chemosignals, but after acclimation to the testing
environment. All questionnaires were filled out in the testing room, except for
one that was filled out 2 hours after application, roughly 1 hour after the subject
had left the laboratory.
We found no support for a releaser effect nor for the marketing claims that
androstadienone and estratetraenol have exclusively sex-specific effects and that
they make individuals feel more social, self-confident, and friendly. At least in
the context of everyday life in and around the university or within a labora-
tory setting, these steroids did not act as simple, sex-specific behavior releasers,
cognitive releasers, or mental-state releasers. Nonetheless, in both settings, we
did identify effects on general emotional states and demonstrated that these
compounds were not exclusively mimicking psychoactive drugs in the major
pharmacological classes (e.g., alcohol or opiates). Furthermore, at the low con-
centrations of androstadienone and estratetraenol that we presented, most people
could not verbally describe a difference between the odor of the carrier with the
steroids and its odor without the steroids (Figure 11.1). Subjects also did not
distinguish between the strongly masked steroid and control presentations in the
replication study. Thus, our data indicate that these steroids do not have to be
detected consciously and identified as odors in order to exert their psychological
effects.
Contrary to the sex-exclusive claims based on surface-potential activity of the
vomeronasal organ (Monti-Bloch and Grosser, 1991; Berliner, 1994), both men
and women responded to each steroid on a number of our measures. Compared
with the control context, women responded positively to both steroids, but men
Androstadienone Estratetraene
16 + pg + pg pg
Total # of Responses
12
Figure 11.1. Smell descriptors and associations from 20 participants presented

with androstadienone with propylene glycol (pg), estratetraene with pg, and pg
alone. Unfilled bars indicate no smell was reported, solid bars indicate chemi-
cal descriptors, horizontal lines indicate musky descriptors, vertical lines indi-
cate sweet/sour/bitter descriptors, and diagonal lines indicate floral descriptors.
(Adapted from Jacob and McClintock, 2000.)
Euphoria (MBG-ARCI) Amphetamine (A-ARCI)

8 * * 8
6 6 * *
Women 4 4
2 2
0 0
pg A+pg E+pg pg A+pg E+pg
8 8
6 6
* *
4 4
Men
2 2
0 0
pg A+pg E+pg pg A+pg E+pg
Figure 11.2. Absence of sex-exclusive psychological responses. Women re-

ported initial euphoric and amphetamine-like responses to the estratetraenol
(E) and propylene glycol mixture (E + pg; ∗p = .05), as well as to the an-
drostadienone (A) and pg mixture (A + pg). Men reported decreased euphoria
(MBG-ARCI) and amphetamine-like responses to estratetraenol (∗p = .05).
responded negatively, especially in response to estratetraenol (Figure 11.2).

There are several possible explanations for the lack of sex-specific results. Dif-
ferences in methodologies and procedures between our study and previous ones
could account for the difference in results. We used a repeated-measures design
and controlled heavily for the context of the subjects’ experience (e.g., odor-
controlled room, trained testers, scripted procedures). In addition, our study
looked at effects of long-term exposure to the steroids, as opposed to the imme-
diate effects tested in previous studies (Monti-Bloch and Grosser, 1991; Berliner,
1994). We may have presented the steroids in a mode or concentration that af-
fected other sensory processing systems – both steroids might produce their psy-
chological effects via one or more systems that do not involve the vomeronasal
organ. Given the possibility of multiple sensory systems responding to the stim-
uli (i.e., vomeronasal organ and olfactory epithelium), we may have obtained
results that represent an interaction of the detection signals. Finally, psycholog-
ical measures could simply be more sensitive to an overall response than are
certain end-organ surface potentials.
The observed effects of androstadienone do not support a simple story of how
these compunds affect attitudes related to social interactions. Androstadienone
did not trigger feelings of self-assurance, sociability (VAS measures), or friendli-
ness (POMS) at any time (Figure 11.3). It did, however, modulate women’s mood
states by preventing deterioration in general mood. Under the control condition,
1 0.2
Friendly Positive Mood
0.1
0.6
POMS Scores
POMS Scores
0
0.2 -0.1
-0.2 -0.2
-0.3
-0.6
-0.4
NS
-1 -0.5 *
20 16
Self-assured Irritated
15
12
10
VAS Scores
VAS Scores
5 8
0 4
-5
0
-10
-15 -4
NS
-20 -8 * * *
16 0.1hr 1hr 2hr
Social
12 Time
8
VAS Scores
4
0
-4
-8
-12
-16 *
0.1hr 1hr 2hr
Time
Figure 11.3. Time courses for subscales related to mood in women in the sec-
ond replication study. Filled squares, androstadienone condition; open circles,
propylene glycol odor-carrier condition; NS, no significant effects; ∗ significant
contrasts, p = .05. Included is a composite POMS Positive Mood score.
there was a gradual increase in negative mood that did not occur or was prevented
under the androstadienone condition (see VAS, “Irritated,” Figure 11.3). Simi-
larly, there was a decrease in positive mood under the control condition that was
prevented in the same subjects under the androstadienone condition (see POMS,
“Positive Mood,” Figure 11.3). As discussed in previous reports related to these
data (Jacob and McClintock, 2000), the overall effect observed was determined
most simply by calculating factors using factor analysis and varimax rotation.
Androstadienone produced an overall positive shift in mood states in both stud-
ies, and estratetraenol had this effect in the first study. Inspection of individual
measures from the initial study also suggested a drop in positive mood and an
increase in negative mood at 9 hours after application. This suggests a rebound
or “crash” from the influence of the steroids. This rebound pattern could be
consistent with a withdrawal from a positive state. Alternatively, it could result
from exposure to the steroids without an appropriate sociosexual context or in
a manner not normally encountered in everyday life (e.g., concentration or time
course at which the steroids evaporated and presented themselves to sensory
epithelia). Characterizing the mechanisms of these longer-term psychological
responses will require further study.
4. Putative Behavioral Pheromones?

Determining whether or not androstadienone and estratetraenol are pheromones
will require more data. These steroids are not simply odors, because they ex-
ert their effects without being consciously detected or cognitively related to a
particular odor or valenced memory. Although they do have characteristic odors
at high concentrations, recognizable by a subset of people, their effects at low
concentrations do not depend on the recipient being able to describe a particu-
lar odor, memory, or association. Thus, it is clear that the functional effects of
these steroids do not necessitate that they be smelled consciously, an insight not
possible with animal research.
How conscious versus unconscious odor detection contributes to the definition
of a pheromone in higher mammals, and humans in particular, is something that
can be determined only through additional research and discussion. To clarify
existing terminology and concepts of chemical signals, we shall need to ascertain
the functions of relevant compounds in a variety of contexts. We shall also need
to ascertain their mechanisms of action. Where are their receptor sites? Are
their effects neural or neuroendocrine? Are the primary and secondary olfactory
cortices involved, and what other neural circuits ultimately process the chemical
information? Finally, how do the various sensory systems integrate, if at all?
Because these steroids occur naturally in humans, they are strong candidates
for being social signals, if not modulator pheromones, among humans. However,
we do not yet know if these steroids, which have been tested only in a pure
form, are produced, detected, and functional at natural levels and are social
chemosignals that have evolved over time to mediate social interactions within
the human physical environment. Moreover, there is always the possibility that
these particular steroids are not themselves social signals, but merely agonists
binding at a receptor for a different natural compound.
In sum, our data do demonstrate that these chemosignals are not classic
behavior-releasing pheromones, because they are not prepotent stimuli driving
a stereotyped behavior across a wide range of contexts and social environments.
Instead, these steroids modulate emotional reactivity or mood associated with
a social context, such as participating in our experiment. They may exert these
effects by modulating the limbic system and prefrontal areas that regulate mood.
They may also modulate attention, perception, and sensory integration involved
in a variety of cognitive tasks or ongoing behaviors. Such effects would, of
course, be highly context-dependent.
It must also be recognized that we cannot exclude the possibility that our
observations reflect responses derived from a learned association with androsta-
dienone. This raises the question whether or not all human “pheromone” effects
can be completely dissociated from any learning or cognitive integration, as in
more restrictive definitions of pheromones (Beauchamp et al., 1976). Determina-
tion of whether or not these particular steroids are “modulating pheromones,” in
parallel with releaser and primer pheromones, must await data on their bioavail-
ability during human social interactions and a consensus on the use of the
term “pheromone.” In a natural setting, androstadienone and estratetraenol will
be present alongside many other chemical and nonchemical signals adding to
the overall sensory landscape of a particular social environment and context.
What roles these consciously undetectable compounds play in the larger scheme
of human chemical communication is an intriguing question that requires
future research at the interface of chemosensory cognition, neurophysiology,
and psychology.
Acknowledgments
This work was supported by the Mind-Body Network of the John D. and
Catherine T. MacArthur Foundation, the NIH MERIT award R37 MH41788
to Martha K. McClintock, and the Olfactory Research Fund’s Tova Fellowship
to Suma Jacob.
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12
Neural Correlates of Emotion Perception:
From Faces to Taste
Mary L. Phillips and Maike Heining
Is there a relationship between the brain regions involved in perception of others’

emotions and those important for olfaction and taste? The aim of this chapter is
to discuss the nature of emotions, and in particular the studies that have examined
brain regions important in the perception of distinct emotions, such as fear and
disgust, and then to demonstrate that similar brain regions are involved in the
perception of odors and flavors and emotive stimuli presented in other sensory
modalities.
1. What Is the Relationship among Olfaction, Taste,

and Emotion?
1.1. Emotions
What are emotions, and why do we have them? Dualist, or “feeling,” theories
proposed by Descartes and, in later years, by James (1890) describe emotions
as epiphenomena, or nonfunctional feelings, separate from the physiological
changes or behavior seen in response to provoking stimuli. Behaviorist theories,
such as that of Skinner (1974), define emotions in terms of reinforced patterns
of behavior. Cognitive theories dating from Aristotle emphasize the importance
of cognitions as causal to emotions, with theorists such as Lyons (1992) describ-
ing the appraisal or interpretation of events, which then leads to physiological
changes, as central to the formation of an emotion. Ekman (1992) has described
emotions as “having evolved through their adaptive value in dealing with funda-
mental life-tasks.” He argues that emotions are characterized by several unique
features, including distinctive facial expressions, distinctive physiology, their
presence in other primates, and distinctive antecedent events (Ekman, 1992).
Intact perception and experience of emotion would thus appear to be vital, in
evolutionary terms, for survival in the social environment.
196
Neural Correlates of Emotion Perception 197
How many different emotions are there? One theory (Cannon, 1927; Lyons,
1992) argues against separate, basic emotions, and instead suggests that a general
level of arousal will be interpreted by an individual in terms of the events and
evaluations with which it is associated. Davidson (1992) has proposed a single
emotion continuum built on primitive adaptive responses: the range from ap-
proach (positive) to withdrawal (negative). The other type of theory (Darwin,
1965; Ekman, Friesen, and Ellsworth, 1982) argues for the existence of separate,
basic emotions, proposing six: sadness, happiness, anger, surprise, fear, and dis-
gust. This theory has become more popular in recent years as studies have begun
to elucidate the neurobiological substrates for different emotions, as discussed
later.
1.2. Olfaction, Taste, Fear, and Disgust

Odors and flavors can be classified as either pleasant or unpleasant, and enjoyed
or avoided, respectively. Two specific emotions that therefore would appear to be
of relevance to olfaction and taste are fear, important in prompting appropriate
avoidance of unpleasant and threatening stimuli in the environment (LeDoux,
1996), and disgust (literally, “bad taste”). Disgust has, indeed, been defined in
terms of a food-related emotion. Darwin (1965) wrote that disgust was “some-
thing offensive to the taste,” and later authors described the emotion as “revulsion
at the prospect of (oral) incorporation of an offensive object” (Rozin and Fallon,
1987). Often the objects of disgust have been identified as waste products of
human and animal bodies (Angyal, 1941). In addition, the concept of disgust
can be expanded to involve causes such as violation of body borders at points
other than the mouth (Rozin and Fallon, 1987; Rozin, Lowery, and Ebert, 1994).
This core concept of disgust has been further elaborated to include animal-origin
disgust, encompassing the tendency of humans to emphasize the human–animal
boundary, avoiding unnecessary contact with animals (Rozin and Fallon, 1987;
Rozin et al., 1994). Other causes of disgust include interpersonal contamination,
with disgust elicited by physical contact with unpleasant or unknown people
(Rozin et al., 1994), and, finally, disgust can arise from the moral or sociocul-
tural domain (Miller, 1997), with disgust at certain beliefs or behaviors, such as
sexual abuse of children, acting as powerful means of transmitting social val-
ues (Rozin and Fallon, 1987). It has been argued that other complex emotions,
such as shame, guilt, and embarrassment, are derived from the basic emotion
of disgust, with the focus of disgust being on the self (Power and Dalgleish,
1997).
Are there similarities in the neural correlates of taste and olfaction and fear and
disgust? The nature of the neural substrates underlying perceptions of different
198 Mary L. Phillips and Maike Heining
emotions will be reviewed, followed by a discussion of recent studies examining

the neural correlates of olfaction and taste.
2. The Neurology of Emotion Perception: Current Issues

Despite increased interest in studies of the neurobiological basis of emotion
perception in recent years (LeDoux, 1996), there are several areas in need of
further study.
2.1. Do Different Emotions Have Specific Neural Substrates?

Lesion studies have implicated both the left hemisphere (Young et al., 1993) and
the right hemisphere (Adolphs et al., 1996) in the perception of facial expressions.
The valence hypothesis links positive (approach-related) emotions with the left,
and negative (withdrawal-related) emotions with the right, frontotemporal brain
regions (Davidson, 1995; Davidson and Irwin, 1999), and further evidence for
that comes from a recent functional imaging study (Canli et al., 1998). Other
authors have provided evidence indicating roles for the orbitofrontal cortex (e.g.,
Rolls, 1990; Hornak, Rolls, and Wade, 1996; Angrilli et al., 1999) and the ret-
rosplenial cortex (Maddock, 1999) in emotion perception.
Lesion studies and functional neuroimaging studies have also been successful
in demonstrating roles for different brain regions in neural responses to different
specific emotions in humans. Many of those studies have employed as stimuli
the facial expressions from the series of Ekman and Friesen (1976), in which
subjects view depictions of faces displaying expressions of fear, disgust, anger,
sadness, happiness, and surprise, in addition to a neutral expression. Those fa-
cial expressions can be transformed with computer software to depict different
intensities of the emotions (Calder et al., 1997). There has been an assumption,
which has not yet been refuted, that when viewing a facial expression, subjects
empathize with the emotion displayed. The neural response to a specific facial
expression therefore reflects not only recognition by the subject of that emotion
in another but also the experience, in part, of the emotion.
With the use of such stimuli, it has been demonstrated that the amygdala is
critical to perception of fearful facial expressions (Adolphs et al., 1994, 1995;
Young et al., 1995; Breiter et al., 1996; Calder et al., 1996; Morris et al., 1996).
Adolphs et al. (1994) demonstrated that patients with bilateral amygdala lesions
were impaired in their ability to perceive facial expressions of fear, as well as
their ability to match facial expressions. In a functional neuroimaging study em-
ploying positron-emission tomography (PET), Morris et al. (1996) demonstrated
a positive correlation between the rate of amygdala blood flow and the intensity
of fear depicted in a facial expression.
Although there have been fewer studies examining the nature of neural re-
sponses to other specific emotions, the anterior insula and components of a
cortico-striatal-thalamic circuit implicated in perception of offensive stimuli in
primates (Alexander, Crutcher, and DeLong, 1990), but not the amygdala, have
been demonstrated to be important in the perception of facial expressions of
disgust (Phillips et al., 1997). That study was the first to demonstrate differential
neural responses to stimuli depicting different specific emotions.
Other recent studies have employed facial expressions to examine the neural
correlates of perception of other basic emotions. Such studies have demon-
strated the importance of the medial frontal cortex and the amygdala (Schneider
et al., 1997; Blair et al., 1999) for recognition of sad facial expressions, and
the orbitofrontal cortex and anterior cingulate gyrus for recognition of angry
facial expressions (Blair et al., 1999). Studies examining the neural correlates
of happiness have been inconclusive. Several different brain regions have been
implicated in the neural response to this emotion, such as widespread decreases
in blood flow over the whole brain (George et al., 1995), amygdala activation
(Schneider et al., 1997), and activation in bilateral posterior cingulate gyri and
medial frontal cortex and the left anterior cingulate gyrus (Phillips et al., 1998a).
Such findings suggest that perception of a given positive emotion may not be
dependent on activity in a discrete brain region, but instead may be associated
with simultaneous activities in several different brain regions. Furthermore, pos-
itive emotions such as happiness may be processed in terms of the environmental
context in which they exist, so that happiness occurring in the context of fear
might be associated with activity in brain regions different from these activated
during the processing of happiness occurring in an otherwise neutral context.
It is possible, therefore, that happiness may be a more complicated and less
“basic” emotion than previously thought. That problem will be the subject of
future studies.
Other types of visual stimuli have been employed in studying the neural cor-
relates of emotion perception. Emotive scenes from the International Affective
Picture System (IAPS) (Lang, Bradley, and Cuthbert, 1997) have been employed
in several studies. The IAPS comprises scenes rated as depicting different in-
tensities of positive (pleasant), negative (aversive), and neutral emotions. When
subjects have viewed those scenes, activation has been demonstrated predomi-
nantly in bilateral visual cortical regions (e.g., Lane et al., 1997; Lang et al., 1998;
Lane, Chua, and Dolan, 1999). Other studies have employed emotive film ex-
cerpts, demonstrating in response to those stimuli activation in occipitotemporal
cortex and limbic structures (Reiman et al., 1997) and medial prefrontal cortex
(Paradiso et al., 1997). The results of those studies indicate that regions impor-
tant for visual-object processing are activated to a greater extent by emotionally
salient stimuli than by neutral, complex visual stimuli, despite efforts to control
for the degree of visual complexity (luminance, color, detail) contained in the two
types of stimuli. Some authors have suggested that that may reflect a modulation
of activation in visual regions by regions important for emotion perception, such
as the amygdala (Morris et al., 1998).
2.2. Are Specific Neural Substrates for Perception of Different

Basic Emotions Supramodal?
It is important in evolutionary terms that an appropriate behavioral response be
made to an emotionally salient stimulus, regardless of the sensory modality in
which the stimulus is presented. There have been fewer studies examining neu-
ral responses to emotional stimuli presented in nonvisual modalities. One study
to investigate perception and evaluation of the emotions projected by spoken
words has demonstrated increased blood flow in the frontal cortex and cerebel-
lum (Imaizumi et al., 1997). Impaired perception of fearful and angry vocaliza-
tions has been reported in a patient with bilateral amygdala lesions (Scott et al.,
1997), and perception of fearful vocalizations has been reported to be associated
with interactions between the amygdala and brainstem regions (Morris, Scott,
and Dolan, 1999). In another study, amygdala activation to both fearful faces
and sounds was reported in the same group of individuals, with the findings also
suggesting a possible general role in emotional behavior for the superior tempo-
ral gyrus (Phillips et al., 1998b). A recent study (Blood et al., 1999) has shown a
correlation between increasing dissonance or consonance of music and activity
in areas of the brain involved in emotion processing, including the right parahip-
pocampal gyrus and precuneus, bilateral orbitofrontal cortex, medial subcallosal
cingulate gyrus, and right frontal polar regions.
Processing of painful tactile stimuli is thought to occur in many regions of
the brain, but has been associated in particular with increased activity in pri-
mary and secondary sensory cortices, the anterior cingulate gyrus, the thala-
mus, and the insula (Casey et al., 1994; Oshiro et al., 1998). Other types of
unpleasant sensory stimulation, including nonpainful and painful gastric stim-
ulation, have been shown to activate bilateral central sulcal regions, the insula,
and the frontoparietal operculum, with painful gastric stimulation associated
with activation in bilateral insulae and the anterior cingulate gyrus (Aziz et al.,
1997). Those findings are further support for the roles of limbic, frontal, and sen-
sory cortical regions in the perception of emotionally salient stimuli, but further
studies are needed to increase our understanding of the nature of the neural re-
sponses to different types of emotional stimuli presented in different sensory
modalities.
2.3. Emotional Learning

Some authors have examined the neural correlates of the processes of learning
and recalling emotionally salient events by asking subjects to view and subse-
quently remember events with either an emotional or nonemotional significance.
Activation in the amygdala has been associated with the ability to remember
emotionally salient stimuli and events (Cahill et al., 1996; Phelps and Anderson,
1997; Hamann et al., 1999), but further studies are needed to clarify the nature
of the different neural systems underlying the learning and recall of emotional
material.
Other studies have employed conditioning paradigms to determine the neural
correlates of emotional learning. It has been well established from studies with
non-human primates that fear conditioning involves the amygdala (e.g., LeDoux,
1996; Quirk, Armony, and LeDoux, 1997). In some functional imaging studies,
human subjects have been allowed to develop a conditioned fear response to a
stimulus such as an angry face paired with the nonconditioning stimulus (often
a burst of white noise), with subsequent examination of the neural correlates of
their perceptions of the conditioning stimulus (Buchel et al., 1998; LaBar et al.,
1998). The results indicate that the amygdala is important for fear conditioning.
Those and other studies (e.g., Breiter et al., 1996) have also highlighted the
phenomenon of habituation of the amygdala response to fearful stimuli over
time. Further studies employing more sophisticated methods of analysis, in which
the temporal nature of the responses of specific brain regions implicated in the
perception of specific emotions (time-series analysis and event-related fMRI
paradigms), will help to clarify our understanding of the neural networks involved
in emotion conditioning and learning.
3. Neural Correlates of Olfaction and Taste

The neural correlates of perceptions of negative emotions, particularly fear and
disgust, have been shown to include the amygdala and insula, in addition to sen-
sory and medial frontal cortices. The neural correlates of perceptions of pleasant
and unpleasant odors and flavors might be predicted to include those struc-
tures. There have been fewer studies examining the neural correlates of olfaction
and taste, and especially few examining neural responses to emotionally salient
odors and flavors. In this review, we attempt in particular to compare the neural
correlates of perceptions of emotionally salient odors and flavors with the neural
responses to the basic emotions of fear and disgust.
3.1. Neural Correlates of Olfaction

Receptor cells from the olfactory epithelium project across the cribriform plate
and innervate the olfactory bulb; the primary projection of the olfactory bulb
neurons are to the piriform cortex, olfactory tubercle, anterior olfactory nucleus,
amygdala, and entorhinal cortex (Price, 1987). The olfactory system is in fact the
only sensory system that bypasses the thalamus and has direct projections to cor-
tical areas. Lesion studies have highlighted the importance of the orbitofrontal
cortex and temporal lobes in olfactory identification (Jones-Gotman and
Zatorre, 1988) and discrimination tasks (Zatorre and Jones-Gotman, 1991), and
the greater importance of the right, rather than left, anterior temporal cortex in
olfactory memory (Rausch, Serafetinides, and Crandall, 1977). Furthermore, the
role of the amygdala in olfaction is indicated by the demonstration that amyg-
dalotomy is a successful treatment for olfactory hallucinations in patients with
seizure disorders (Chitanondh, 1966).
Neuroimaging studies have highlighted the roles of the orbitofrontal cortex
(e.g., Zatorre et al., 1992; Sobel et al., 1998) and the right frontal lobe in olfaction,
with the latter activated to a greater extent in females than in males (Yousem et al.,
1999). The roles of the piriform cortex, orbitofrontal cortex, amygdala, and en-
torhinal/hippocampal region in olfaction have been emphasized in a recent review
of PET and fMRI studies of the human olfactory system (Zald and Pardo, 2000).
With regard to examination of the neural correlates of perceptions of emotion-
ally salient odors, activation of the left medial frontal lobe, inferior frontal cortex,
and bilateral insulae has been demonstrated during olfaction per se, with pleasant
odors producing increased left insula activation, as compared with unpleasant
odors (Fulbright et al., 1998). Another study has reported increased blood flow
in the left orbitofrontal cortex and bilateral amygdalae in response to perception
of unpleasant (although not specifically disgusting) odorants (Zald and Pardo,
1997). Perceptions of familiar odorants have also been associated with right or-
bitofrontal cortical activation (Royet et al., 1999). Although such studies have
been few, the findings to date indicate that many of the brain regions associated
with emotion perception are also involved in perception of olfactory stimuli:
the orbitofrontal cortex, amygdala, and insula. Because odors are rarely devoid
of emotional salience, it is probable that the involvement of the orbitofrontal
cortex, amygdala, and insula demonstrated in the neural response to olfactory
stimulation reflects, at least in part, processing of the emotional component of
such a stimulus.
3.2. Neural Correlates of Taste Perception

There have been few lesion studies examining taste perception in subjects with
lesions in higher cortical areas, rather than the brainstem or midbrain. Some
epilepsy patients experience gustatory hallucinations, which can be induced by
stimulation of the parietal or rolandic operculum (Hausser-Haw and Bancaud,
1987). According to a comprehensive review of studies investigating neural sub-
strates for taste perception (Small et al., 1999), the insula, parietal and frontal
opercula, and orbitofrontal cortex have been demonstrated to play important
roles, predominantly within the right hemisphere. Those authors have suggested
that orbitofrontal activity may be dependent on the motivational features of spe-
cific taste tasks, whereas the right hemisphere predominance for taste perception
may be a result of the specialization of the left hemisphere for language. One
study has also reported activation of the anterior cingulate gyrus and thalamus,
in addition to the areas mentioned earlier (Faurion et al., 1998). Others have
emphasized the importance of activation in the insula and perisylvian region and
have reported functional lateralization of taste perception related to handedness
in the inferior part of the insula (Cerf et al., 1998; Faurion et al., 1999). In one
study in which neural responses to aversive gustatory stimulation were exam-
ined, amygdala and orbitofrontal cortex activation was demonstrated specifically
in response to such stimulation (Zald et al., 1998).
The findings in such studies indicate that there is significant overlap between
regions important for perception of distinct flavors and those involved in emotion
perception. Flavors, like odors, frequently have emotional significance, and it is
probable that they too are processed to a large extent in terms of their emotional
component.
3.3. Examination of the Overlap among Neural Responses to

Emotional, Olfactory, and Gustatory Stimuli
The results from the studies just discussed indicate that similar brain regions
are activated by emotional stimuli presented in the visual modality and by odors
and flavors – both pleasant and unpleasant. The potential overlap between brain
regions activated by emotional stimuli presented in different sensory modalities,
including the olfactory and gustatory modalities, was investigated directly in a
recent study (Francis et al., 1999). Neural responses to a pleasant touch (velvet), a
pleasant olfactory stimulus (vanilla), and a pleasant gustatory stimulus (glucose)
were examined in the same group of four subjects. Similar (medial) regions of
the orbitofrontal cortex were activated by all three types of stimuli, particularly
right-sided. The pleasant olfactory and gustatory stimuli also activated simi-
lar regions of the bilateral anterior insulae. Those authors suggested that their
findings provided evidence of a role for the orbitofrontal cortex in particular in

the learning and representation of rewards, and they argued that emotions per se
can be defined in terms of states elicited by reward (or punishing) stimuli. The
findings of that and other studies therefore highlight the role of the orbitofrontal
cortex and insula in emotion processing. Furthermore, odors and flavors appear
to activate these regions in particular, suggesting that these stimuli are processed
primarily in terms of their emotional salience.
4. Conclusion: From Faces to Olfaction and Taste

With the advent of functional neuroimaging techniques, it has become possible
to examine the neural correlates of sensory and emotion perception. The ear-
lier studies concentrated on investigation of neural substrates for perceptions of
visual stimuli depicting facial expressions and unpleasant and pleasant scenes.
Later studies have employed techniques to present emotionally salient stimuli
in other sensory modalities: auditory, tactile, olfactory, and gustatory. It is clear
from these studies that similar regions, in particular the insula, amygdala, and
primary sensory and orbitofrontal cortical regions, are implicated in the percep-
tion of aversive stimuli presented in all five sensory modalities. The orbitofrontal
cortex and insula are also activated by several different types of odors and fla-
vors. This suggests that emotion processing and perception of odors and flavors
have similar neural bases and that olfactory and gustatory stimuli seem to be
processed to a significant extent in terms of their emotional content, even if not
presented in an emotional context. The aim of future studies in this area will be
to determine the nature of the specific neural systems involved in olfaction, taste,
and emotion perceptions by employing analysis techniques to allow examination
of the temporal and functional relationships between the different brain regions
identified in these processes.
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Section Four
Memory
Concerning memory processes in olfaction, most of the authors herein note

that the evidence is sparse, mainly because the standard procedures used in the
fields of vision and hearing are difficult to transfer to olfaction. Early research
in olfaction, mimicking studies of the processing of visual information, was
oriented toward episodic and semantic functions. However, recently there has
been increasing interest in olfaction specificity, therefore shifting the focus to
implicit forms of odor memory and to priming effects.
Chapter 13, by Sylvie Issanchou and colleagues, explains how the study of
odor memory specificity in everyday life led them to contrast (1) incidental
(nonintentional) learning and implicit recollection and (2) consciously learned
and consciously recollected memories of odors in laboratory studies. They exam-
ine the ecological validity of traditional laboratory experiments and of incidental-
learning paradigms in the study of olfaction by trying to get at the experimental
conditions that can best predict memory performances in everyday life. They
prefer priming and same/different judgments to identification tasks. However,
Issanchou and associates, like Maria Larsson (Chapter 14) and Mats Olsson and
his colleagues (Chapter 15), note that in spite of their efforts, it has been unex-
pectedly difficult to show priming effects in olfaction, as compared with priming
in other modalities, the challenge being to figure out whether priming effects
depend on perceptual processes or on conceptual (naming) processes.
Maria Larsson, in questioning whether priming is conceptually driven (medi-
ated by subvocal naming) or simply perceptually driven, finds that the evidence
for priming effects in olfaction is still sparse and presents a mixed pattern of
results. In sorting out the different memory processes traditionally identified
in visual (and verbal) memory research, she finds that olfactory research has
yielded puzzling evidence and that the links either to neurophysiological bases
or to language (naming) remain much less straightforward than in the case of
visual information.
210 Section 4: Memory
In the introductory overview of their Chapter 15, Mats Olsson and his col-
leagues report on three experiments published in German by Wippich et al.
(1993) that therefore may not have come to the general awareness of the interna-
tional scientific community. They further present new data on olfactory repetition
priming. That experimental paradigm was designed to avoid the problem that
priming has tended to be too dependent on the processing of odor names, whereas
the attention of participants should be turned toward the quality of odors during
both study and test phases. However, in spite of their efforts, and in line with
previous research, they find no statistically reliable evidence regarding percep-
tual repetition priming. They are therefore led to conclude that, when observed,
priming effects rely mainly on verbal priming.
Steven Nordin and Claire Murphy, in Chapter 16, address the question whether
or not studies of odor memory in populations with specific neurological or geri-
atric disorders, such as Alzheimer’s disease, can provide a better understanding
of the neural processes underlying odor memory. More precisely, they examine
whether or not specific olfactory memory impairments rely on specific neuro-
logical abnormalities. A secondary issue in their chapter is the potential for use
of olfactory memory tests for early diagnosis of Alzheimer’s disease.
In Chapter 17, Johannes Lehrner and Peter Walla point out that although a
considerable literature has been accumulated on odor perception, memory, and
naming in studies of adults or newborns (see Schaal and colleagues, Chapter 26),
less attention has been paid to the developmental processes of olfactory functions
in childhood and young adulthood. The observation that consistent use of odor
labels is strongly dependent on the relevance of the label given to a particular
odor, with “veridical naming” producing the highest level of consistent naming,
led them to conclude that more research is needed on semantic processing of
odor memory in childhood.
In short, the reviews and the original studies of memory for odors presented
here reveal many contrasts and a somewhat puzzling picture. The difficulties
encountered in getting at reliable data similar to those obtained in the visual
domain suggest the importance of olfactory memory specificity: incidentally
learned and unnamed in everyday conditions. However, that contrasts with the
fact that perceptual priming is not observed, but that evaluative and even hedonic
(semantic?) priming seems possible. This last remark suggests that memory for
odors relies on principles that are at variance with the principles of memory for
visual and auditory stimuli and rather would seem to be connected to emotional
and affective values, as discussed in the preceding section.
13
Testing Odor Memory: Incidental versus
Intentional Learning, Implicit versus
Explicit Memory
Sylvie Issanchou, Dominique Valentin, Claire Sulmont,
Joachim Degel, and Egon Peter Köster
1. Introduction
How good is human memory for odors? Tests of memory involve two phases: an
exposure or learning phase and a testing phase, separated by a retention period.
During the exposure phase, stimuli are presented, and, depending on the instruc-
tions and experimental conditions, the odors can be memorized incidentally or
intentionally. During the testing phase, the same odor stimuli are presented
again, generally accompanied by new stimuli, and memory can be tested
explicitly or implicitly (i.e., intentional retrieval by the subject may or may not
be involved). Compared with other kinds of memory, such as verbal memory,
pictorial memory, and face memory, there have been very few studies of odor
memory. Moreover, most of those few studies investigated consciously learned
and consciously recollected memories of odors. But in everyday life, odors are
generally learned incidentally. Rarely does anyone decide “I should memorize
this odor” (Baeyens et al., 1996; Haller et al., 1999, Sulmont, 2000). In other
words, whereas in everyday life odor learning is nonintentional and its recollec-
tion is usually implicit, in laboratory studies odor memory has been evaluated
using intentional learning and explicit recollection. That raises the question of
the ecological validity of traditional laboratory experiments to test odor memory.
Indeed, following Neisser (1976), we must wonder if that type of approach has
not been ignoring some of the main features of odor memory as they occur in
ordinary life.
To examine the effects of experimental paradigms on memory performance
for odors is the main goal of this chapter. More precisely, we are interested
in finding the experimental conditions that can best predict memory perfor-
mance in everyday life. We shall begin by defining the testing procedures that
are generally referred to as explicit and implicit memory tasks. Then we shall
review the literature on odor memory to examine the effects of experimental
211
212 Issanchou, Valentin, Sulmont, Degel, and Köster
conditions on memory performance. Previous work has suggested that the pro-
cesses governing odor memory are different from those governing other types
of nonverbal memory, or at least that odor memory has a variety of important
distinguishing characteristics (Herz and Engen, 1996). Thus, we shall, when
possible, compare the results obtained for odors with the results obtained with
other nonverbal stimuli. In agreement with Murphy et al. (1991), we have chosen
human faces as comparative nonverbal stimuli. Though there are obvious differ-
ences between these two types of stimuli, it is our opinion that odors and faces
have some important common features. Like faces, odors provide social sig-
nals, elicit emotions, are difficult to describe, seem to be perceived holistically,
elicit context-dependent memory effects, and are quite resistant to forgetting. To
some extent these common features may have their origins in the way we ac-
quire knowledge about these two types of stimuli. Like other nonverbal stimuli,
such as music or paintings, odors and faces are learned through repeated expo-
sures without explicit learning intention. During those exposures, sets of features
useful for distinguishing among the stimuli are assembled little by little. For ex-
ample, whereas at first two burgundy wines such as a Pommard and a Chambolle
may seem rather similar, the difference between them will become increasingly
clear over several exposures. In general, this type of learning, called perceptual
learning (Gibson, 1969), is characterized by difficulty in precisely describing the
features used to distinguish between stimuli, difficulty in generalizing to new
stimuli, and the phenomenon of recognition/naming dissociation. Who has not
experienced the feeling of recognizing a face, a melody, or an odor, but then
being unable to recall anything else about it? When it applies to an odor, this
phenomenon has been called the tip-of-the-nose effect by Lawless and Engen
(1977).
What makes identifying faces different from identifying odors, however, is our
great expertise in identifying faces. This great expertise results from the social
importance of faces. Indeed, the face not only provides the most distinctive and
useful information for identifying a known person but also enables us to infer
the gender, the age, the emotional state, and perhaps even the health condition
of an unfamiliar person. Earlier work on odors (Engen and Ross, 1973) showed
that we are far from being able to identify large numbers of odors. Yet it seems
that even though we are not very good at identifying odors, our capacity to
discriminate between odors is as impressive as our capacity to discriminate
faces (Holley, 1999). One plausible explanation for the discrepancy between
our good discrimination performance and our poor recognition/identification
performance is that although we are physiologically well equipped for perceiving
odors, we do not use all our capacities, because the sense of smell is not crucial in
day-to-day life. Congenitally anosmic individuals are not always aware of their
Testing Odor Memory 213
loss (Engen, Gilmore, and Mair, 1991), whereas prosopagnosic individuals are
severely impaired (Wacholtz, 1996).
2. Explicit versus Implicit Memory

It is now a well-known fact that even deeply amnesic patients are capable of
learning. Thus, the often-described amnesic patient H.M. (Milner, Corkin, and
Teuber, 1968) was able to learn new motor skills such as tracking a moving target.
His performance in that task improved gradually with practice, even though he
was not aware of having performed the task before. That type of memory has
been called implicit memory, because subjects do not need to remember having
encountered the situation before to perform better. The tasks used to evaluate
implicit memory differ greatly from the explicit memory tasks usually used in a
laboratory. Explicit memory tasks require conscious recollection of previously
experienced events “through some sort of directed controlled search into stored
information” (Perruchet and Baveux, 1989). In contrast, conscious or voluntary
recollection of previous experiences is not necessary in implicit memory tasks.
In an implicit memory task, memory is demonstrated by a change in perfor-
mance, shorter latency or greater accuracy, on tasks involving either previously
experienced items (i.e., repetition priming effect) or items closely associated to
previously experienced items (i.e., semantic priming effect).
2.1. Explicit Tasks

The explicit tasks most commonly used are recall and recognition tasks. In
a recall task, subjects are exposed to a series of stimuli (acquisition phase).
Some time later, they are asked to recall as many of the stimuli as possible
with (cued recall) or without (free recall) the help of a list of cues. Recall tasks
typically are used to probe verbal memory. In that case, the stimuli would be a
list of words, and the cues could be, for example, the first two letters of each
word. Strict recall tasks would be quite difficult to use with faces and odors,
as they would require that subjects re-create the stimuli (i.e., draw previously
seen faces or recompose odors). Such tasks would be possible only for painters
or perfumers. However, it is worth mentioning that such procedures have been
used by Tuorila, Theunissen, and Ahlström (1996) and by Vanne, Tuorila, and
Laurinen (1998) for testing quantitative memory for taste. Those authors asked
their subjects to reproduce the subjective taste intensity of a tastant solution
previously tasted, by mixing portions of a pure medium (with no tastant) and
a high concentration of the tastant. Both studies showed that subjects tended
to recall tastes as more intense than they had actually been. It is also worth
mentioning that some authors have used a “recall” task with odors and faces,
but in fact have asked their subjects either to provide a verbal description of the
stimulus or to recall not the stimulus itself but the name of the stimulus. That last
task, however, is possible only with familiar stimuli for which subjects already
have names. That paradigm has been used, for example, by Hanley, Pearson, and
Howard (1990) with photographs and by Annett and Lorimer (1995) for familiar
odors of common household substances. For faces, subjects were first presented
with a series of famous faces and then asked to write down the names of as many
faces as they could remember. For odors, authors asked their subjects to write
down the names, or brief descriptions, of as many of the previously smelled
odors as they could remember. Then participants were presented with each odor
again and asked to provide a verbal label or a brief description for it. Because of
the idiosyncratic nature of odor labeling, that procedure was chosen to facilitate
the scoring of recall responses. It is clear that such recall tasks with odors and
faces are not equivalent to the recall task with words, because subjects are not
asked to recall the stimuli per se, but to give the names of the stimuli.
The recognition task is the experimental paradigm most frequently used to
study explicit memory for odors and faces. The acquisition phase is identical
with that of a recall task, but the testing phase differs in that subjects have to
recognize the target stimuli among distractor stimuli. This is usually done in one
of two different ways: a two-alternative forced choice (2AFC) or a yes/no task.
In a 2AFC task, stimuli are presented by pairs composed of an “old” stimulus
(presented during the learning stage) and a “new” one. Subjects are asked to
determine which stimulus in a pair is the old one. In a yes/no task, old or new
stimuli are presented one at a time, and subjects are asked to answer “yes” or
“no” to the question “Were you presented with this stimulus in the first part of
the experiment?”
2.2. Implicit Tasks

Implicit memory tests were first designed to study implicit memory for words.
The general principle of these tests is as follows: First subjects are presented
with a list of words. Then they are asked to perform a task such as word-stem
completion, word-fragment completion, tachistoscopic identification, or ana-
gram resolution (Table 13.1). Half of the words presented during this task will
have been in the list presented in the first part of the experiment (targets); the
other half will be distractors. Implicit memory is demonstrated if the perfor-
mance on the second task is greater for targets than for distractors. That type of
test has been extended to the study of visual memory using picture-completion
or picture-clarification tasks (Table 13.2). The general idea of “completion,”
Table 13.1. Classic paradigms for implicit word-memory tasks
Test Learning stage Retention Retrieval stage Retrieval task Dependent variable
Word-fragment Visual or auditory Distractor task Visual or auditory Give the first word Number of completed
completion presentation of the presentation of the that comes to mind words (new and old)
target stimuli target stimuli and
of the new stimuli
autumn a- - - m -
orange f-o---
tuning o--n--
-un---
vi----
ca - - - -
Anagram Visual presentation Distractor task Visual presentation of Give the first solution Number of solved
of the target stimuli the target stimuli and that comes to mind words (new and old)
of the new stimuli
autumn antumu
orange fwoler
tuning oeangr
gunint
vinlio
ctrroa
Tachistoscopic Brief visual exposure Distractor task Give the first solution Number of identified
identification to the target stimuli that comes to mind words (new and old)
Perceptual Visual presentation Distractor task Words embedded within Give the word as soon Latency (new old words)
clarification of the target stimuli a mask that gradually as it has been
vanished identified
Table 13.2. Classic paradigms for implicit picture-memory tasks
Test Learning stage Retention Retrieval stage Retrieval task Dependent variable
Picture Identification of Distractor task Visual presentation Same as learning Gain between the first and the
completion target stimuli of the target stimuli stage second presentations for the
presented from the and of the new perceptual identification
most incomplete stimuli threshold (i.e., the level of
version to the fragmentation at which the
complete version picture was identified)
or
Identification of Distractor task Visual presentation Identification of Difference in perceptual
target stimuli of the target stimuli target stimuli identification threshold
presented at one and of the new presented from for old and new stimuli
level of stimuli the most incomplete
fragmentation version to the
complete version
however, is rather difficult to apply to odors and faces. Thus slightly different
paradigms are generally used for those stimuli. They rely on the assumption that
the presentation of a first stimulus sharing some properties (visual, olfactory,
or semantic) with a second stimulus should affect the processing of the second
stimulus more than would the presentation of an irrelevant stimulus.
Bruce and Valentine (1985) were the first to use that type of paradigm to study
implicit memory for faces. They presented subjects with a series of famous-face
pictures or names. The subjects’ task was to identify the faces from their pictures
or to read their names. After a 20-minute break they were asked to identify (exp. 1)
or recognize (exp. 2) a second series of face images. That second series was
composed of faces whose pictures had been presented in the first series, faces
whose names had been presented in the first series, and new faces (control).
Implicit memory was demonstrated when performance was better for faces from
the first list than for new faces. Since that first work, numerous variations of that
procedure have been used, but the general principle remains the same (see Bruyer,
1990, for a review). All such variations have converged to the finding that face
identification is facilitated by previous presentation of either the faces themselves
or their names, whereas face recognition (i.e., familiarity judgment) is facilitated
only by previous presentation of the faces, not by previous presentation of their
names.
In comparison, as discussed by Mair, Harrison, and Flint (1995), implicit mem-
ory for odors has received scant attention in the literature. Schab and Crowder
(1995) were the first to report experiments testing implicit memory for odors.
Their paradigm was similar to that used with faces. During the learning phase,
subjects were exposed to a series of jars filled either with an odorant or with
water. As each jar was presented, they were given the name of the odor they
were actually (odor-and-name condition) or supposedly (name-only condition)
smelling. During the testing phase, subjects were presented with a second se-
ries of jars containing an odorant. That series included the odorants presented
during the learning phase in the odor-and-name condition and in the name-only
condition, as well as new odorants. Their task was to identify (exp. 1) or detect
(exp. 2 and 3) the odors, or judge their pleasantness (exp. 4). As before, implicit
memory was demonstrated if performance was better for odors presented in the
first series than for new odors. The data showed that, as was the case for faces,
a name priming effect was observed in the identification task (i.e., a significant
difference between the name-only condition and the control condition was ob-
served) but not in the detection task. Because that effect was even larger in the
name-plus-odor condition, the authors concluded that there was odor priming.
However, it is important to note that the paradigm used by Schab and Crowder
differed on one point from that used by Bruce and Valentine (1985): In Schab
and Crowder’s experiments, odors were always presented with their names in
the learning stage, but Bruce and Valentine’s experiment included a learning
condition in which faces were presented alone. As pointed out by Degel and
Köster (1998), it is not clear that, given such conditions, a “pure” implicit memory
for odors was tested. In fact, Schab and Crowder’s experiments would allow
to study the impact of verbal mediation in odor identification. As indicated
by the authors themselves, the superior performances in identification scores
and reaction times for the odor-and-name learning condition compared with
the name-only learning condition may have been caused by a strengthening of
the association between a perceptual representation and its related verbal label
or by an increased availability of a verbal label because of prior activation of
the perceptual representation in combination with its verbal label. That could
explain why a priming effect was observed only in their first experiment, when
the test task was an identification task. Nevertheless, because our identification
capacity for odors is not crucial in day-to-day life, the identification task should
be replaced by another task based on discrimination. In particular, it would seem
possible to adapt the paradigm used for faces to odors by presenting an odors-only
condition during the learning stage, and not an odors-and-labels condition.
In an attempt to minimize the effect of verbal processing, Olsson and Cain
(1995) used a subvocal identification paradigm to demonstrate odor priming.
Subjects were asked to indicate when they had last smelled six mono-rhinally
presented odors. After a 10-minute break, they were presented with the same
odors as well as six new odors. Their task was to press a button when they realized
what they were smelling, without giving a verbal label. A positive priming effect
(i.e., primed odors were identified faster than control ones) was observed when
odors were presented to the left nostril. However, as pointed out later by Olsson
(1999), even though subvocal identification was used, the testing task was a
verbal task, and consequently that was not “a process-pure test of priming.”
In a later paper, Olsson (1999) reported another repetition priming experiment
based on latency of identity rejection. A positive priming effect was observed for
odors that could not be identified. On the contrary, a negative priming effect was
observed for odors that could be identified. Thus, it seems that identification may
interfere with the encoding or retrieval of odor memory. However, the task used
during the learning stage (i.e., to judge when they had last smelled the odor),
because of its emphasis on remembering, almost certainly would have precluded
true measures of implicit memory in the final phase.
Recently, Degel and Köster (1999) reported a new method to analyze im-
plicit memory for odors. During the learning stage, subjects completed a cre-
ativity test, a letter-counting concentration test, and a mathematical test in several
weakly odorized rooms without being aware of the odors. In that experiment the
presentation of the stimuli during the learning stage was somewhat similar to a
tachistoscopic word presentation in that subjects were not aware of the stimuli.
After a 30-minute retention time, subjects were shown photographic slides of
different surroundings, including the room they had been in, and were asked to
rate how well each of 12 odors, including the one they had been exposed to,
fitted with each context shown in the pictures. The hypothesis was that if there
was an effect of implicit memory for odors, the ratings of fit between odors and
contexts would be positively influenced by odors previously experienced uncon-
sciously and subliminally in the test rooms. The data showed that subjects who
had worked in a room with a given odor subsequently assigned a higher fit for
that odor to the picture of that room than did subjects who had worked in rooms
with other odors, but that was true only for people who could not identify the
odor by its name.
In summary, explicit and implicit tasks differ on several points. In an implicit
memory test, learning is unintentional, retrieval is involuntary, and memory is
tested indirectly, as subjects are not required to remember past events. In an
explicit task, retrieval is voluntary, and memory is tested directly, whereas learn-
ing can be intentional or incidental. The notion of the intentionality versus the
nonintentionality of learning and retrieval plays a crucial role in subjects’ perfor-
mances. The task at the learning stage determines the encoding process, which
also has a key role in memory performance. We shall illustrate these points in
the following sections.
3. Effects of Experimental Conditions on Memory Performance

3.1. Intentional versus Incidental Learning
Since the frequently cited study by Craik and Lockhart (1972), we know that
all methods of encoding information are not equally useful. In particular, labo-
ratory studies have shown that the simple intention to remember something is
not enough if that intention is not followed by an effective elaborative encoding.
Real-life experiences suggest that the intention to learn is not even a necessary
condition. Indeed, most of the experiences that we recall from our day-to-day
lives were not encoded with the deliberate intention to remember them. Accord-
ingly, Engen and Ross (1973), in a study reporting three memory experiments
with odors, the first one using intentional learning, and the other two incidental
learning, noted that “when due allowance was made for experimental differ-
ences, the retention percentages found for incidental learning (experiments II
and III) appear to be in line with the percentages found for intentional memory
(in experiment I).” Likewise, Ayabe-Kanamura, Kikuchi, and Saito (1997), in
Table 13.3. Impact of intentionality on recognition performances for

faces and odors
Type of Number of
stimulus Group subjects Type of learning d mean
Faces 1 25 incidental 1.46a *
2 27 intentional 1.32a
Odors 1 25 incidental 1.69a
2 27 intentional 1.62a
*d values followed by the same letter within a cell are not significantly
different.
studying the effects of verbal cues on recognition memory for unfamiliar odors,
observed no difference in performance between intentional and incidental learn-
ing. Although both studies should be interpreted with caution, as different sets
of odors were used in the intentional and incidental conditions, they suggest
that odor can be learned incidentally. That conclusion has been supported more
recently in a study by Senouci (1999) to evaluate the effect of learning intention-
ality on memory for unfamiliar odors and unfamiliar faces: During the learning
phase, subjects were presented with a series of pairs of odors and a series of
pairs of faces. Their task was to decide which odor, or which face, in each pair
they preferred. In addition, half of the subjects were asked to memorize the stim-
uli. After a delay of a week, all subjects participated in a recognition task. The
data show that, for both odors and faces, no significant difference was observed
between the incidental and intentional learning conditions (Table 13.3).
3.2. Encoding Processes

Warrington and Ackroyd (1975) were the first to demonstrate that subjects’
knowledge of the fact that a subsequent recognition test was to be taken had no
effect on memory performance for faces. Those authors showed that the intention
to learn per se was not a determining factor, but that how the subjects processed
the information was most important. In particular, they showed that memory for
faces was better following a judgment-of-pleasantness condition than following
either a judgment-of-height condition or an intention-to-learn condition. Since
that first work, many studies have been carried out to examine the effect of
the type of processing on facial recognition (see Coin and Tiberghien, 1997,
for a review). Those studies showed that the more elaborate and rich one’s
memory representations are, the better the memory performance. In line with
that conclusion, Hanley et al. (1990) showed that subjects who were asked to
name familiar faces performed better at a recognition test than did subjects who
had been asked to make occupation or familiarity decisions. They hypothesized
that the better performance in the naming task was due to the fact that naming a
face gives rise to the elaboration of pictorial, semantic, and lexical codes.
A positive effect of naming has also been shown by most recent studies on odor
memory. Lyman and McDaniel (1986, 1990) showed that recognition of odors
was higher when subjects were asked to name odors at the inspection phase, as
compared with control groups who were asked to remember or simply smell the
odors. Several authors did not compare performances obtained when some sub-
jects were asked to identify the odors and some were not, but rather tested only
one group of subjects (who were asked to describe odors at the learning stage)
and compared the results obtained for odors that were correctly identified or
consistently named to the results obtained for odors that were not correctly iden-
tified or were inconsistently named. Whatever the type of learning – incidental
for Lehrner (1993), and intentional for Rabin and Cain (1984) and Lehrner,
Glück, and Laska (1999a) – they showed that correctly identified odors and
consistently named odors were better recognized than incorrectly identified and
inconsistently named odors, and respectively, they also found that consistency
in labeling had a positive effect on odor recognition.
Sulmont (2000) also observed a positive effect of labeling consistency when
subjects had to perform paired preference tests at learning, indicating that sub-
jects could have spontaneously tried to identify odors. That positive effect of
labeling is consistent with the results obtained by Jehl, Royet, and Holley (1992),
who compared the recognition performances of subjects previously familiarized
with the odors in different labeling conditions (no label, veridical label, chemical
name, label personally generated by the subject) (on odor labeling, see Dubois
and Rouby, Chapter 4, this volume). Indeed, those authors observed the highest
recognition performances for the veridical label and the personally generated
label, and the worst score for the no-label condition.
Finally, Lesschaeve and Issanchou (1996), who analyzed odor descriptions
given by subjects in terms of precision (i.e., categorization level: orchard, fruit,
apple) rather than in terms of accuracy (compared with a veridical name), also
observed a positive effect of precision in labeling on odor recognition. From all
those results, it appears that the key point for improving recognition is not the
presence of a label but the “quality” of the label. To help subjects memorize
an odor, the label must be appropriate (i.e., it must evoke personal experiences
and/or evoke a relevant source of that odor for the subject). As an explanation,
Lehrner et al. (1999b) suggested that the way odors are processed depends not
only on the task but also on the way the task is performed. They assumed that
odors that could not be correctly named were processed on a more perceptual
and lower level than were correctly named odors. They found no age effect in
recognition performances for incorrectly named odors, but young adults per-
formed better than did children and the elderly for correctly named odors. Those
authors concluded that there are two different forms of human odor memory: a
perceptual memory and a semantic memory.
Most authors agree that naming is not necessary for memory, but enhances
it, and most would agree that that can be accounted for by a dual-coding theory
(Paivio, 1986). Lyman and McDaniel (1990) observed that recognition perfor-
mance was higher when odors were presented with their names or with pho-
tographs of their sources than when only odors were presented, and the highest
recognition was obtained when odors were presented together with their names
and photographs of their sources. Consequently, those authors suggested an
alternative to the dual-coding theory: a general elaborative-network model in
which encoding representations from different modalities would provide more
retrieval paths than would encoding in a single modality. They suggested that
the key point was not the verbal coding, but the multimodality coding. In order
to test the relevance of the dual-coding theory in olfactory memory, Perkins and
McLaughlin Cook (1990) used a suppression paradigm: During the acquisition
stage, subjects were presented odors in one of four different conditions. Subjects
in the visual-suppression group had to play a computer game. Subjects in the
verbal-suppression group had to listen through headphones to a random sequence
of numbers and had to repeat each number as soon as they heard it. Subjects in
the visual-plus-verbal-suppression group had to perform both tasks. There was
no suppression for the control group. Recognition was tested 2.5 minutes and
one week after the learning stage. As expected by the authors, recognition perfor-
mance after one week decreased in the following order: control, visual, verbal,
and visual-plus-verbal. After a delay of 2.5 minutes, only the verbal condition
was significantly different from the control condition. However, as pointed out
by the authors, the effects seen for those suppression tasks may simply have
reflected the relative complexity of the total task.
In contrast to the foregoing, it should be noted that verbalization can also have
a negative effect on memory performance. Fallshore and Schooler (1996), in
an experiment on recognition performance for own-race faces versus other-race
faces, observed that verbalization at the learning stage impaired recognition in
the case of other-race faces. From those findings and from other data on music
and visual forms, Melcher and Schooler (1996) hypothesized that verbal over-
shadowing occurs when the level of perceptual expertise and the level of verbal
expertise differ. Their hypothesis was confirmed in an experiment conducted on
wine, using subjects who did not drink wine, untrained wine drinkers, and trained
wine experts. Degel and Köster (1999, 2001) also reported a negative effect of
verbal knowledge in observing that implicit memory for odors was found only
in subjects who were unable to give the right names for the odors, but in their
case, explicit verbalization did not come into play. As mentioned in Section 1.2,
Olsson (1999) also observed a negative impact of odor identification on implicit
memory.
3.3. Implicit versus Explicit Recollection

As pointed out by Mandler (1980), most examples of remembering involve both
conscious and subconscious processes. First, it must be noted that even if the task
instructions for tests of indirect measures of memory do not make any reference
to the old/new character of the stimuli (i.e., presented or not presented during
the learning phase), it is possible that uninformed subjects will realize early
in the test session that some items have previously been presented, as noted by
several investigators (e.g., Light and Singh, 1987). Consequently, as pointed out
by Schacter (1990), even though subjects are not required to think back to the
stimuli presented during the exposure phase, it is possible that some of them will
adopt intentional, explicit retrieval strategies, thus turning the indirect test into
a direct test.
3.4. Match or Mismatch between Encoding Operations

and Retrieval Operations
As mentioned by Schab and Crowder (1995), dissociations between indirect tests
could also be due to the degree to which the types of processing at encoding and
at retrieval match. In the domain of face memory, Wells and Hryciw (1984), for
example, observed that trait judgments (e.g., honesty–dishonesty) at the encod-
ing stage yielded higher performances in full-face recognition than did feature
judgments (e.g., narrow nose–wide nose). Even more interesting, they observed
that feature judgments produced better reconstructions than did trait judgments.
Those authors explained their findings by suggesting that making trait judgments
involves holistic encoding processes and that face recognition involves a holistic
process rather than a feature-based process. Likewise, in a second experiment,
Lyman and McDaniel (1990) observed that when subjects were presented with
a set of names of common objects, asking them to imagine the odors of those
objects facilitated later odor recognition, and asking them to visually imagine
those objects facilitated later visual recognition. The authors explained that
effect in terms of the concept of “transfer-appropriate processing.” According to
that concept, the usefulness of different types of processing will depend on the
degree to which the processing performed at encoding matches the demands of

the retrieval task.
4. Similarity between Experimental Conditions

and Real-Life Conditions
Like Neisser (1976), we think that memory research should have ecological
validity. This means that we should examine naturally occurring memory phe-
nomena and develop experimental designs that will allow us to place subjects
in conditions as representative as possible of everyday situations. So, before
concluding, we would like to point out the important differences between odor
memory as it is studied in the laboratory and odor memory as it occurs in real life.
How do we learn odors in everyday life? As mentioned by Köster (Chapter 3,
this volume), we generally do not learn to name odors. The only people who
actively learn to recognize odors and to match odors and labels are perfumers,
flavorists, and members of sensory panels. For those of us who are not profes-
sionally involved in the world of odors, there are nevertheless some particular
odors that we probably learn to identify in everyday life. The learning of odor
names generally is limited to cases where odors are associated with toxic or dan-
gerous substances, such as leaking gas and decaying products, and some taints,
such as cork taint in wines, or rancid butter. Only a few of the names for the
odors of commonly used foods are learned, more as a convenience for referring
to the foods than as a reference to their odors, and as a consequence we find it
difficult to identify those odors when they are presented without their foods. It
is thus surprising that most research on odor memory has been focused on the
impact of naming. Moreover, odors are learned incidentally, and subjects are not
always aware of the presence of odorants.
It is also important to keep in mind that odors are remembered very differ-
ently, as compared with faces, for example. In everyday life, we have occasions
to recognize faces, but also to identify a person’s face, and occasionally we even
need to recall faces when we “try to describe a face verbally to someone else,
when we try to draw a face from memory, or when we try to picture a face by
forming a mental image of it” (Cohen, 1989). As pointed out by Cohen, mem-
ory for people is “a crucial element in everyday life, both in social interaction
and in work and family life.” As mentioned earlier, odor identification usually
is performed only in particular occupations and activities, such as perfumers’
and flavorists’ work and sensory analysis, but odor identification is also car-
ried out spontaneously by wine amateurs who regularly try to identify origins,
and vintages. But except in rare cases, odor identification is not performed in
everyday life.
Odor recall is even more unusual. Odor recognition tends to occur in a sponta-
neous way, as when one perceives a familiar perfume at the cinema. The memory
phenomenon that has most frequently been reported is that an odor cue can evoke
memories of events that long ago were associated with the presence of that odor.
Perhaps the most famous example was provided by Proust, who described how
the flavor of a madeleine soaked in tea reminded him of his aunt’s house. It is
clear that the association between a particular odor and a particular context is
learned incidentally and that such memories are retrieved automatically, with-
out any effort. Moreover, several features of this phenomenon are worth noting.
The first is the remarkable duration of the effect, with memories being evoked
from months, years, even decades earlier (Degel and Köster, 1998; Aggleton
and Waskett, 1999; Haller et al., 1999). The second feature is the precision
and detail of the autobiographical events associated with the odor. It should
be noted that such features are not exclusive to memories prompted by odors,
but also can be observed with word and picture evocations (Rubin, Groth, and
Goldsmith, 1984). However, it appears that memories evoked by odors elicit the
strongest affective reactions. Herz and Cupchik (1995) reported that memory
accuracy in recalling paintings was no better with an olfactory cue than with a
verbal label, but odor-evoked memories were more emotional than verbally cued
memories. So the majority of the experiments would seem to confirm the auto-
biographical reports, and there is also evidence for the strong emotional content
of odor-evoked memories, which is one of the particular features of the Proust
phenomenon. However, in all those laboratory experiments the retention interval
was short (24 or 48 hours) compared with the retention interval that is typical
for autobiographical accounts.
Aggleton and Waskett (1999) reported a study conducted in a real-world set-
ting. In a test to determine if reexposure to the unique combination of odors
present in a museum would aid subjects’ recall of their visit to the museum,
they asked subjects who had visited the museum in different odor conditions
to complete questionnaires about the contents of the museum. Their findings
indicated that the odors that had been present in the museum at the time of en-
coding could improve recall memory of various displays that had been seen, on
average six years earlier, in the same odor context. Likewise, a study conducted
by Haller et al. (1999) with 133 German adults revealed an influence of early
experience with vanillin on food preferences later in life. In Germany, bottled
milk for infants and babies had been flavored with vanilla for many years. When
preferences for ketchup without or with vanilla were measured, it was found that
those who had been bottle-fed as infants preferred ketchup with vanilla, whereas
the breast-fed group preferred ketchup without it. That result demonstrates the
effectiveness and the duration of unintentional learning in olfaction.
What do we learn about odors in everyday life? Though we do not learn to

name odors, we learn to associate hedonic values to odors through various mech-
anisms that all involve memory. The first such mechanism is the mere exposure
effect. Zajonc (1968) has suggested that repeated exposures constitute a suffi-
cient condition for increased liking of stimuli: For foods, that effect has been
demonstrated in adults by Pliner (1982) and in children by Birch and Marlin
(1982), and their findings have recently been confirmed by Sulmont (2000).
However, a detailed analysis of such results has revealed that the effect of re-
peated exposures on hedonic values is very dependent on both the stimulus and
the subject. In many instances, repeated exposures to novel stimuli can even
lead to a decrease in appreciation (Lévy and Köster, 1999). The second type of
mechanism that can induce changes in our hedonic valuations of odors is asso-
ciative conditioning. For example, Zellner et al. (1983) demonstrated that after
pairing a neutral flavor with sugar (a hedonically positive test), subjects assessed
increased hedonic value to the combination at the end of the presentation and one
week later. Baeyens et al. (1990) reported a negative taste-flavor conditioning
effect, but no significant taste-flavor conditioning and no color-flavor condition-
ing when the conditioned stimulus was hedonically positive. Those results reveal
an asymmetry between negative and positive conditioning and show that not all
associations are effective in inducing a hedonic shift. Social conditioning can
also occur and can have a positive or negative effect on the hedonic value of a
food, as demonstrated by the following experiments: Birch, Zimmerman, and
Hind (1980) reported that if a neutral food was given to children either as a reward
contingent on a pro-social behavior or paired with an adult’s positive attention, a
positive hedonic shift was observed, as compared with children who received
the food in a non-social-affective context. To the contrary, Birch, Marlin, and
Rotter (1984) reported a negative shift in preferences for foods eaten to obtain a
reward. In the three preceding experiments, a hedonic reaction evoked by a stim-
ulus (the unconditioned stimulus, US) was transferred to a previously neutral
stimulus (conditioned stimulus, CS) presented with the US. To be effective, such
simultaneous presentation of the US and the CS must be repeated several times.
As reported by Baeyens et al. (1990), subjects had no explicit knowledge about
the CS–US contingency relationship. Conditioning can also occur when a flavor
is associated with positive or negative post-ingestion consequences. For exam-
ple, Booth, Mather, and Fuller (1982) found a positive hedonic shift for a flavor
paired with a high caloric content and offered to hungry subjects, as compared
with a flavor presented an equal number of times, but with low caloric content.
Using a questionnaire filled out by 198 subjects, Pelchat and Rozin (1982) found
that when nausea follows ingestion of a food, people tend to develop a dislike
for the taste of that food, but a negative hedonic shift is not reported for ingestion
that is followed by other negative consequences, such as headache, diarrhea, or

rash. Compared with the previously described cases of conditioning, this nausea
conditioning is unique, because a single negative experience is sufficient.
5. Conclusion
Several features of odor memory as it occurs in the real world have been de-
scribed, and they should be taken into account by anyone attempting to design
better experimental procedures to study odor memory in the laboratory. First,
odors are learned unintentionally, and in most cases without one’s awareness.
Consequently, future experiments with odor memory should take place in a con-
text such that the subject’s attention is not specifically drawn to the odor at
learning time. That is, no task related to the odors should be given at the learn-
ing stage. When studying environmental odors, each odor should be diffused
in a room in which subjects perform tasks or activities unrelated to the odor,
as in the study of Degel and Köster (1999), or dissolved into the instruction
sheets, as in the study by Kirk-Smith, Van Toller, and Dodd (1983). As the hu-
man olfactory system is not well oriented toward description, tasks presented
to evaluate retrieval should avoid verbalization and preferably should be based
on priming for hedonic judgments or for different–same judgments, rather than
on identification. The previously discussed reports of conditioning effects seem
to reveal an asymmetry between positive association and negative association
in odor learning, the latter being more efficient, and possibly more resistant to
change. Such possible asymmetry should be considered in future experiments on
odor learning with conditioning. The major difficulty in trying to create a truly
natural experimental condition is in reproducing associations involving emo-
tions that will be as strong as they originally were when they occurred naturally.
Then one must test those long-term memories so common in real life. However,
we think that combining “field” studies and laboratory studies should lead to a
better understanding of how odor memory works and what importance it has in
food-preference dynamics.
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14
Odor Memory: A Memory Systems Approach
Maria Larsson
Research focusing on human memory suggests that memory is not a single

or unitary faculty of the mind. Instead, it can be conceived of as a variety of
distinct and dissociable processes and systems that are subserved by particular
constellations of neural networks that mediate different forms of learning (e.g.,
Gabrieli et al., 1995; Tulving, 1995; McDonald, Ergis, and Winocur, 1999).
One categorical distinction within human memory is that between declara-
tive memory and non-declarative memory (Tulving, 1995). According to this
division, non-declarative memory is characterized by unintentional learning, or
learning without awareness, and by inability to access conscious recall. This form
of memory is manifested in multiple dissociable processes and is measured in
terms of changes in performance (produced by conditioning and priming) in the
learning of motor skills (e.g., Schacter, 1992). In contrast, declarative memory
can be conceptualized as learning with awareness and refers to the acquisition
and retention of information about events and facts, and is typically assessed by
accuracy in tests of recall and recognition. The available evidence suggests that
medial temporal/diencephalic structures are critical for the integrity of declar-
ative memory, whereas non-declarative forms of memory rely on other brain
areas, such as occipital structures (visual priming) (Gabrieli et al., 1995) and
basal ganglia (procedural memory) (Heindel et al., 1989).
Although based on hypothetical constructs and still under considerable de-
bate, the view that human memory is composed of at least five different systems
has been highly influential (e.g., Nyberg and Tulving, 1996; Roediger, Buckner,
and McDermott, 1999). According to the fivefold classification system described
by Schacter and Tulving (1994), the non-declarative and declarative classes of
human memory can be decomposed into five interrelated memory systems that
have evolved both phylogenetically and ontogenetically in the following order:
procedural memory, perceptual representation system (PRS), semantic memory,
working memory, and episodic memory. The latter three systems typically are
231
232 Maria Larsson
described as declarative forms of memory, whereas the first two are examples
of non-declarative expressions of memory. It is noteworthy that the system that
evolved last, episodic memory, is the form of memory that has been proved to
be the most sensitive to disturbances (e.g., aging, depression, dementia, health
status), whereas the systems that developed earliest are considerably more robust.
The highly developed neural complexity supporting the functions of episodic
memory, as contrasted with the more localized mnemonic properties of the sys-
tems developed earlier (procedural, PRS), likely underlies the sensitivity of this
form of memory. It is also of interest to note that the brain structures especially
critical to the functioning of episodic memory have been shown to undergo grad-
ual changes that start in early adulthood (Braak, Braak, and Mandelkov, 1993;
Simic et al., 1997) and mimic life-span data, covering memory functioning from
early to late adulthood (e.g., Nilsson et al., 1997).
During the past decade, several reviews of studies in olfactory memory have
been presented, but none has explicitly tried to conceptualize the various ex-
pressions of olfactory memory in the realm of a memory-systems framework
(Richardson and Zucco, 1989; Schab, 1991; Herz and Engen, 1996). Most re-
search on odor memory has been oriented toward episodic and semantic mem-
ory functions, with little attention paid to non-declarative aspects of olfactory
memory. However, increasing interest in implicit forms of odor memory has been
noted, and this is particularly true for the principles governing odor condition-
ing (Otto, Cousens, and Rajewski, 1997; Robin et al., 1999). Also, researchers
have been trying to determine whether or not priming effects can be shown
for olfactory information (e.g., Olsson, 1999; Olsson et al., Chapter 15, this
volume).
The main aim of this chapter is to organize some of the available knowledge
on the behavioral and psychological manifestations of odor memory using a
memory-systems approach. The review is highly selective, and the reports cited
serve only as examples to be used in constructing a theoretical framework that
potentially may further our understanding of the various expressions of olfac-
tory memory. Also, we shall consider some neuropsychological evidence and
some brain-imaging evidence indicating that various olfactory functions draw
on different neural correlates. A classification scheme for the different olfactory
functions as they relate to each memory system is provided in Table 14.1.
1. Non-declarative Memory
1.1. Procedural Memory
Procedural memory is a form of memory underlying the acquisition of skills and
other aspects of knowledge that are not directly accessible to consciousness and
Odor Memory: A Systems Approach 233
Table 14.1. Classification scheme
Memory system Olfactory function

Procedural memory Odor conditioning; aversions
Perceptual representation system Odor priming
Semantic memory Hedonics; familiarity;
identification; metamemory
Working memory Odor discrimination
Episodic memory Odor-recognition memory
whose presence can be demonstrated only indirectly by action (e.g., walking,

skiing, conditioned responses). Procedural memory has been subdivided into
a number of other systems, including (1) skills and habits, (2) simple associa-
tive learning or conditioning, and (3) nonassociative forms of learning such as
habituation and sensitization (Schacter and Tulving, 1994).
Procedural memory may have appeared early during evolution and is shared
in various forms by most living organisms (Tulving, 1993). In contrast to other
forms of memory, non-declarative memory is little influenced by the passage
of time, which is reflected in the fact that we can adequately perform tasks
that we have not carried out in years, and we can experience conditioned re-
sponses to stimuli that we may not have encountered for decades (Robin et al.,
1999).
Procedural memory comes into play in one of the most prominent features
of the olfactory sensory system: the production of odor and taste aversions. The
development of aversions occurs as a response to the ingestion of a sickness-
provoking substance, which from an evolutionary perspective makes sense in that
the aversion works as self-protection against food poisoning (Borison, 1989). It
is of interest to note that the ability to learn to avoid ingesting toxic substances
is present in simple invertebrates, which implies that relatively primitive neu-
ral networks can mediate this form of learning (Sahley, Gelperin, and Rudy,
1981).
However, there are situations in which elicitation of conditioned aversions can
be problematic. For instance, patients undergoing anti-cancer treatment often
experience nausea and vomiting, which tends to make them averse to further
treatment. That can eventually result in the anticipatory syndrome in which the
patient experiences nausea and vomiting when thinking of the treatment, or
when visiting the hospital environment and being exposed to the sights, sounds,
and smells associated with the treatment (Andrews and Sanger, 1993). Cancer
patients can also develop an aversion to food that is consumed in close association
with the treatment. Conditioned odor/taste aversions can be difficult to extinguish
234 Maria Larsson
because of the lengthy association between the particular food and previous
illness (Bernstein, 1978; Garcia et al., 1985; Hursti et al., 1992).
In a similar vein, recent evidence suggests that the principles governing ac-
quisition of conditioned emotional (fear) responses to auditory and visual in-
formation are also valid for olfactory information, although it is not clear that
odor-conditioned fear is acquired more rapidly or is more robust than other forms
of conditioned fear (Otto et al., 1997). Robin et al. (1999) examined negative
conditioning for the odorant eugenol. Eugenol is a substance commonly used in
tooth fillings and in restorative dentistry, and it is responsible for the typical odor
of dental offices. When fearful and nonfearful dental patients were exposed to
eugenol, it was seen that the evoked responses of the autonomic nervous system
were associated with positive basic emotions (happiness, surprise) in nonfearful
subjects, whereas fearful subjects displayed negative basic emotions (fear, anger,
disgust). That finding provides evidence of the potential for olfactory stimuli to
serve as conditioning elicitors of negative or positive responses, depending on
the previous associations with specific odors.
1.2. Perceptual Representation System

“Repetition priming” refers to the unconscious facilitation of performance fol-
lowing prior exposure to a target item or a related stimulus (Schacter, 1992). Like
tasks in procedural memory, priming tasks have been referred to as “implicit,”
because the test instructions do not inform the participants to actively think back
to a previous study episode. Considerable research efforts have been devoted
to exploration of lexical and visual priming, but the available evidence on the
possibility of priming for olfactory information is sparse and presents a mixed
pattern of results (Schab and Crowder, 1995; Olsson, 1999; Olsson et al., Chapter
15, this volume).
In a series of experiments attempting to explore the potential for odor priming,
Schab and Crowder (1995) examined the effects of previous exposure to an odor
and/or exposure to its name on odor-detection and odor-identification thresholds.
Their data yielded only weak support for the idea of odor priming, although
presentation of a suprathreshold odor enhanced subsequent ability to identify
that particular odor. Likewise, Olsson and Cain (1995) reported that primed
odors were identified faster than control odors and that the priming effect was
more pronounced when the olfactory information was presented in the left nostril
rather than in the right nostril. Although the possibility of subvocal naming was
not controlled for, that pattern of results might indicate that the priming effect
was related to subvocal naming, suggesting a conceptually driven priming effect
rather than a perceptually driven priming effect.
2. Declarative Memory
2.1. Semantic Memory
“Semantic memory” or “generic memory” refers to our general knowledge of
the world. It encompasses the meanings of words, concepts, and symbols and
their associations, as well as rules for manipulating these concepts and symbols
(Tulving, 1993). As opposed to episodic memory, the information in semantic
memory is stored without reference to the temporal and spatial context that was
present at the time of its storage. Semantic memory also involves knowledge
about one’s own memory proficiency and one’s own memory processes. This as-
pect of semantic memory has been termed “metamemory” (Flavell and Wellman,
1977).
Semantic memory in an olfactory context concerns a person’s knowledge or
experience with a specific odorant and typically is exemplified in odor identi-
fication and perceptions of familiarity. However, semantic memory also comes
into play in perceptual experiences of hedonic odor properties and in tip-of-the-
nose states. The following sections describe a number of olfactory functions and
states tapping reservoirs of prior knowledge about odors.
Hedonic Valence. A fundamental question in olfactory research is

whether hedonic responses to odors are present at birth or whether affective
reponses are acquired postnatally, in interaction with experience (Menella and
Beauchamp, 1997). The available data show a mixed pattern of findings that
most likely is related to difficulties in assessing affective reactions in pre-verbal
children, as well as to problems in selecting test odorants (i.e., whether affective
responses are the results of olfactory or trigeminal stimulation).
Engen (1982) postulated that all odor preferences are learned relatively late
in the pre-school period. That position is based on reports indicating that chil-
dren less than five years old do not show systematic, adult-like odor-preference
patterns. For example, Stein, Ottenberg, and Roulet (1958) reported that four-
year-old children were as likely to say that they liked the smell of amyl acetate
as they were to say that they liked the smell of synthetic sweat and feces. That
response pattern was reversed among six-year-olds, who reported aversive sen-
sations for feces and sweat smells, and pleasant sensations for amyl acetate. In
opposition to those findings, several studies have shown that affective odor reac-
tions may begin in early infancy, suggesting that some odors may be inherently
pleasant or unpleasant (Steiner, 1979; Strickland, Jessee, and Filsinger, 1988).
Further research into the developmental aspects of semantic memory is
needed. Much more research into the relationships among genetic mecha-
nisms, physiological maturation, and various experiential factors is of critical
236 Maria Larsson
importance if we are to achieve a better understanding of the development of odor

preferences.
Odor Familiarity. In contrast to identification tasks, which require ex-

plicit retrieval of verbal descriptors of odorants, familiarity ratings require only
that a subject indicate a perceived familiarity on a scale varying from low to high.
Thus familiarity can be regarded as a continuum covering the subject’s implicit
level of odor knowledge. A low familiarity rating may reflect an extremely vague
perception, with no distinct semantic cues elicited by the olfactory experience.
A medium rating may involve moderately meaningful associations, whereas a
high familiarity rating presumably reflects the experience of having access to
more specific knowledge about the odor. Occasionally, a high familiarity rating
may simply reflect knowledge of the odor name, which would make this measure
equivalent to identification. That presumably is true in some cases, but consid-
ering the high incidence of tip-of-the-nose experiences for olfactory stimuli,
an item rated as highly familiar may truly reflect access to a more general or
idiosyncratic knowledge of the odor.
Odor Identification. Performance at odor identification can be assessed

by free identification or in a multiple-choice format. It is widely accepted that
naming odors spontaneously is extremely difficult. Reviews indicate that unaided
free identification of odors by young laypersons varies between 22% and 57%,
with set sizes ranging from 7 to 80 items (e.g., Cain, 1979; Richardson and
Zucco, 1989; Chobor, 1992). In contrast, when subjects have access to a number
of response alternatives, they perform better (Doty, Shaman, and Dann, 1984;
Larsson et al., 1999). Most likely that superiority is related to a decrease in
cognitive demands: The provision of label alternatives reduces the effort an
individual has to invest in searching for an appropriate label, which ultimately
yields a more supportive task situation.
Related studies oriented toward life-span changes in olfactory function-
ing have indicated that aging effects are minor in perceptions of familiarity,
whereas aging has deleterious effects on odor-identification ability (Larsson and
Bäckman, 1993; Lehrner et al., 1999). This dissociative pattern of results sug-
gests that increasing age is associated with retrieval impairment regarding the
specificity of information (i.e., the verbal label), although semantic knowledge,
as reflected in perceptions of familiarity, remains unaffected by aging. Similar
findings have been reported for visual information (Kempler and Zelinski,
1994).
A somewhat neglected area of interest is the relationship between general
semantic functioning (e.g., vocabulary, information) and proficiency in odor
identification. Consequently, we examined this issue in a recent study (Larsson,

Finkel, and Pedersen, 2000) in which we found evidence of that odor-
identification aptitude is strongly and positively related to performance in other
semantic memory tasks (i.e., analogies, vocabulary, information). We noted that
odor identification proved to be unrelated to performance in other cognitive
functions, such as visuospatial functioning, short-term-memory functioning, and
episodic-memory functioning. This observation strengthens the notion that se-
mantic memory (i.e., crystallized intelligence) and odor identification tap the
same cognitive domain. Further support for this was provided in a follow-up
study addressing the heritability aspects of various odor functions. There the re-
sults indicated that the relationship between odor identification and measures of
verbal ability was primarily genetically mediated (Finkel, Pedersen, and Larsson,
2001).
Metamemory. The general definition given for “metamemory” is that

it involves knowledge of and monitoring of one’s own memory proficiency and
one’s own memory processes (Flavell and Wellman, 1977). Studies examining
the relationship between predicted and actual olfactory performances are sparse,
although there is some evidence that subjects tend to overestimate their odor-
memory performances and odor-identification abilities (Schab, 1991).
One element of metamemory knowledge is the commonly experienced feeling
of knowing that underlies tip-of-the-tongue experiences (i.e., to know a word, but
not be able to recall it) (Brown and McNeill, 1966; Brown, 1991). The olfactory
analogue of this phenomenon was described by Lawless and Engen (1977) as
the tip-of-the-nose experience. However, in contrast to the former, persons in
the tip-of-the-nose state typically cannot answer any questions about the name
of the odor, such as the initial letter, the number of syllables, or the general
configuration of the word. Subjects can, however, answer questions about the
odor’s quality, such as its taxonomic category, or say something about objects
associated with it (Lawless and Engen, 1977).
2.2. Short-Term Memory/Working Memory

Short-term memory can be divided into two components: primary memory and
working memory. Both types of memory are indices of short-term memory,
because the items to be remembered reside in consciousness. Where they differ
has to do with whether or not additional processing operations are performed
on the information to be remembered. Specifically, items in primary memory
are maintained passively, whereas items in working memory are manipulated in
some fashion (Baddeley, 1986).
238 Maria Larsson
It is well established that working memory can be subdivided into a central

executive system and at least two slave systems – one specialized for verbal
information, and the other for nonverbal (visual) information (Baddeley, 1992) –
that depend on slightly different cortical regions (Vallar and Papagno, 1995;
Owen, 1997).
Although earlier research suggested that olfactory memory consisted only
of long-term-memory components (e.g., Engen, 1982, 1991), today the gen-
eral picture suggests the presence of a viable short-term/working-memory olfac-
tory system (see White, 1998, for a review), although its storage capacity and
processing efficiency remain unclear. Two olfactory abilities that immediately
involve working memory are discrimination and odor matching. In these tasks,
the subject must be able to form a transient representation of the target odor and
use that representation for comparison with the subsequent odorant. It has been
noted that odor discrimination seems to be particularly affected by age, which
is in keeping with age effects in working memory for verbal and visual infor-
mation (Salthouse, 1995; Larsson et al., 1999). It is important to remember that
some of the earlier research that focused on short-term retention for olfactory
information may have confounded output from short-term memory with actual
retrieval from episodic memory. For example, in traditional memory research, a
simple and effective way of discriminating items residing in short-term memory
from items in long-term memory (i.e., episodic memory) is to evaluate recency
effects in recall tasks (Tulving and Colotla, 1970). Odor memory is assessed by
means of recognition with a fixed test order, making the interpretation of any re-
cency effects difficult. Recency effects in recognition memory should be treated
with caution, because it is highly likely that they reflect a temporal gradient in
episodic memory, thus suggesting that the most recently consolidated episodic
information will be best remembered.
As noted earlier, working memory is composed of at least two slave systems;
verbal and nonverbal. As compared with the verbal system, the nonverbal system
in working memory is yet relatively unexplored. Speculatively, it is possible
that working memory may be composed of an additional number of modality-
specific short-term stores (e.g., olfactory working memory). Whether that is true
or whether all incoming olfactory information is manipulated and processed in
either or both of the slave systems remains to be addressed in future research.
2.3. Episodic Memory

Episodic memory deals with the acquisition and retrieval of information that was
acquired in a particular place at a particular time. It involves traveling back in
time to remember personally experienced events through conscious recollective

processes (Tulving, 1993). That orientation toward the past makes episodic mem-
ory phenomenologically different from other varieties of memory. In the labo-
ratory, episodic memory typically is assessed by asking persons to recall or
recognize some information encountered earlier in an experimental setting.
It is well known that episodic-memory performance is a context-dependent
phenomenon related to encoding/retrieval factors (e.g., encoding activity, recall
or recognition), the nature of the information to be remembered (e.g., visual,
verbal), and subject-related factors (e.g., health status), as well as to the multiple
interactions among those factors (Jenkins, 1979). Earlier work suggested that
episodic memory for odors differed fundamentally from episodic retention of
verbal and visual information. That dissimilarity was reflected in a flat forgetting
function, no influence of semantic factors, and a negligible impact of retroactive
interference (e.g., Lawless and Cain, 1975; Engen, 1987). However, that view
has changed, as later research has revealed that episodic memory for odors is to
a large extent governed by the same principles that govern information acquired
via other modalities (see Larsson, 1997, for a review).
Addressing the interdependence between the memory systems, it is of interest
to highlight some of the interplay observed among working memory, seman-
tic memory, and proficiency in episodic-memory odor recognition. Episodic
memory for odors has been proved to vary according to the degree and type of
elaboration (imagery, verbal elaboration) the subjects engage in during encod-
ing or during exposure to an odorant that relates to working-memory processing
(Lyman and McDaniel, 1990; Larsson and Bäckman, 1993). Also, recognition
memory for odors is sensitive to the degree of familiarity and identifiability of
the olfactory information, which are instances of semantic memory (Rabin and
Cain, 1984; Larsson, 1997).
2.4. Neuropsychological and Physiological Evidence

As noted at the outset, one implication of the memory-systems theory is that
different memory functions are subserved by certain constellations of neural
networks responsible for different forms of learning. Although the available evi-
dence speaking to this issue is sparse, there have been some clinical observations
and neuroimaging studies suggesting that different olfactory functions are indeed
mediated by and dependent on different underlying substrates (Eichenbaum et al.,
1983; Savic et al., 2000).
The most striking illustration that olfactory functions can be dissociated
by cerebral damage was manifested in H.M., a patient with bilateral medial
240 Maria Larsson
temporal lobe resection (Eichenbaum et al., 1983). In contrast to a normal

capacity to detect odors, to make intensity discriminations, and to adapt to
odors, H.M. was unable to discriminate the quality of odors, whether tested
by same–different judgments or matching-to-sample tasks. Moreover, although
H.M. was successful in naming common objects using visual and tactile cues,
he could not identify them by smell. Those findings suggest that structures in
the medial temporal lobe play critical roles in quality discrimination and odor
identification.
Relatedly, Savic et al. (1997) examined episodic odor recognition and odor-
quality discrimination in two groups of epileptic patients and a healthy con-
trol group. The epilepsia groups included one group with mesial temporal lobe
seizures (MTLS) and a group of patients suffering from neocortical seizures
(NS). The results showed that MTLS patients were selectively impaired in odor
discrimination relative the NS group and controls, whereas odor-memory perfor-
mances were equal for the two epileptic groups, but lower than for controls. That
pattern of results indicates that different pathological states can induce dissocia-
ble impairments in higher olfactory functions such as quality discrimination and
episodic memory for odors, which ultimately implies that the two functions are
mediated by different neurological structures.
In order to investigate whether or not odor perception, discrimination, and
episodic-memory odor recognition are mediated by different sets of brain struc-
tures, and to explore the neurobiological correlates of those specific tasks, we
used positron-emission tomography (PET) to measure regional cerebral blood
flow in a group of healthy adults (Savic et al., 2000). The different tasks varied
in degree of complexity and differed in terms of the cognitive demands imposed
by the tasks (from low to high demands): passive smelling of odorless air, pas-
sive smelling of single odors, intensity discrimination, quality discrimination,
and episodic-memory odor recognition. In agreement with earlier findings, pas-
sive smelling of olfactory information activated the amygdala-piriform cortex,
right orbitofrontal cortex, right thalamus, and insula (Zatorre et al., 1992; Sobel
et al., 1998). Depending on the task, different subsets of those regions were re-
cruited, along with other areas interconnected with them. Both discrimination
tasks engaged the left insula and right cerebellum. However, discrimination of
quality proved also to involve structures hierarchically above those engaged in
intensity discrimination: the thalamus, cingulum, orbitofrontal and prefrontal
cortex, the frontal operculum, caudatus, insula, and subiculum. Several studies
have shown that the prefrontal cortex is a major area of activation in tasks tap-
ping working memory, which implies that odor-quality discrimination draws on
the same neural structures that have been shown to support working-memory
functions (Cabeza and Nyberg, 2000). The absence of a prefrontal effect for
intensity discrimination is less clear, but may be related to the fact that the task
is more perceptual/sensory-mediated (stronger/weaker), whereas discrimination
by quality is more cognitively loaded (similar/dissimilar).
Furthermore, episodic memory for odors, which was considered to be the task
posing the highest cognitive demands, also proved to show the most extensive
activation pattern. It activated the same areas as the quality-discrimination task,
with the exception of caudatus, subiculum, and insula. However, episodic mem-
ory for odors activated the piriform cortex and two remote neocortical areas: the
temporal and parietal cortices. That outcome is in accordance with a number of
studies addressing neuroanatomical correlates of episodic-memory functioning
for other types of sensory information (e.g., Buckner et al., 1995; Cabeza and
Nyberg, 2000). Thus, the activation pattern of episodic memory for odors maps
well to what is known for verbal and visual episodic memory.
3. Concluding Comments
According to systems theory, different kinds of information about an event
are “stored” in different memory systems and subsystems and used as needed
(Tulving, 1995). Whether that is also valid for olfaction or whether odor memory
is best described as a form of memory governed by its own premises remains to
be explored in future research. Here, the cognitive neuroscience approach will
provide valuable insights into the organization and representation of olfactory
memory in the human brain.
Acknowledgments
This work was supported by a post-doctoral fellowship from The Swedish
Council for Research in the Humanities and the Social Sciences (F1484/1997)
to Dr. Maria Larsson. I am grateful to Drs. Timo Hursti and Mats J. Olsson for
providing me with materials and stimulating discussions.
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15
Repetition Priming in Odor Memory
Mats J. Olsson, Maria Faxbrink, and Fredrik U. Jönsson
1. Introduction
1.1. Implicit Memory
Tests for implicit memory have been pursued extensively for about two decades,
and the findings from such memory experiments are commonly considered to
have confirmed the phenomenon of implicit memory. Schacter (1987) defined
“implicit memory” as facilitation of task performance because of prior experi-
ence, in the absence of conscious or intentional recollection (explicit memory).
That rather broad definition might seem to encompass the definitions of implicit
learning, conditioned learning, motor-skills learning, and perceptual adaptation
(Roediger and McDermott, 1993), but will not be considered to do so here.
Instead, our focus will be on the branch of implicit memory known as repeti-
tion priming. In our terminology, repetition priming is tested when the stimuli
presented are the same (identical) or of the same type (essentially the same, but
varying in some way) at priming and at testing. In this type of experiment, the
response to a repeated stimulus is facilitated without the influence of explicit
memory from the first encounter.
Implicit memory can also be measured using cross-modal priming, where
the sensory modalities used differ between priming and testing. This review
will cover cases of cross-modal priming in which odor names are presented at
priming, and odors at testing. Several recent studies have examined cross-modal
priming using the olfactory and visual modalities, assessing the influence of
processing an odor on the later processing of a visual stimulus (e.g., Hermans,
Baeyens, and Eelen, 1998; Grigor et al., 1999; Pauli et al., 1999; Sarfarazi et al.,
1999). Those (visual) priming studies will not be covered in this review. Other
studies of related interest have been conducted by Degel and Köster (1998,
1999) to address implicit learning (Buchner and Wippich, 1998) associated with
surreptitious presentation of odors.
246
Repetition Priming 247
A common way to probe repetition priming in the visual domain has been
with tests of word-stem or word-fragment completion (e.g., Warrington and
Weiskrantz, 1974; Tulving, Schacter, and Stark, 1982). In such tests, participants
are exposed to a list of words in the priming phase. In a later testing phase they are
presented with word stems or fragments that they are asked to complete with the
first word that comes to mind. Although participants’ attention is directed away
from the earlier priming list, they nevertheless tend to select words from that
list. In fact, even in the absence of episodic recognition (i.e., explicit memory
for the words on the priming list) (Tulving et al., 1982), participants use the
priming words significantly more often than would be expected. In a similar
vein, amnesic patients have performed well on this type of test, whereas they
have done very poorly on tests of explicit memory (Graf, Squire, and Mandler,
1984).
Repetition priming has most often been interpreted as involving perceptual
processes (e.g., Jacoby and Dallas, 1981). It has also been proposed that prim-
ing largely reflects the operation of a separate perceptual representation system
(Tulving and Schacter, 1990). But even for versions of repetition priming tests
that have been considered to be of the perceptual type, there are now findings
that imply that these tests are driven by conceptual processing as well as by
perceptual processing (e.g., Keane and Gabrieli, 1991). The issue of what type
of priming a certain test is tapping is important and will emerge as one of the
key issues in our empirical review of repetition priming in olfaction.
1.2. Objectives
Although there is considerable interest in implicit memory, only a few studies
have been performed using odors as the stimuli to be remembered. One possible
reason for that is that repetition priming for odors is difficult to investigate
with many of the standard procedures used in the fields of vision and hearing
(Issanchou et al., Chapter 13, this volume). The objectives of this review are
therefore (1) to review the empirical evidence concerning implicit memory for
odors as assessed in priming experiments, (2) to present new data on olfactory
repetition priming, (3) to provide a state-of-the-art assessment, and (4) to suggest
what further research is needed in these areas.
2. Review of Priming Experiments

Basically, three groups of researchers have performed experiments on priming
in olfaction. We shall review the experiments of each group in order to follow
the lines of reasoning behind their work.
248 Mats J. Olsson, Maria Faxbrink, Fredrik U. Jönsson
2.1. The Schab and Crowder Experiments

When Schab and Crowder (1995) published their study on implicit memory for
odors, there was nothing on this topic in English. They designed their experi-
ments with reference to how implicit-memory tests are typically structured in the
visual realm, and they hypothesized that odors would lend themselves to prim-
ing much as did visual, auditory, and tactile stimuli. In four experiments they
investigated the effects of previous exposure on identification scores and reac-
tion times: olfactory detection thresholds, identification thresholds, and latency
of pleasantness ratings.
In the priming phase of their first experiment, Schab and Crowder exposed
participants to 10 odor names alone and 10 other odor names together with
their respective odors. The stimuli were at all times presented in jars (for the
name-only condition, the jars did not contain any odorants). To try to offset that
potential problem, participants were told that some odors could be very faint.
Five minutes later, the participants attempted to identify the 20 experimental
odors and 10 control odors. Both identification scores and reaction times (RTs)
were measured. Exposure to name and odor at priming led to significantly better
identification and shorter RTs in the test phase than did the name-only condition
(which by itself yielded significant priming). Schab and Crowder argued that
this “name priming” was a common finding in lexical research, but did not
necessarily demonstrate odor-specific priming. More interesting, the name-and-
odor condition showed higher facilitation, both for identification scores and
for RTs, than did the name-only condition. Those findings were interpreted
as showing that “(a) the activation of an odor’s perceptual representation, in
conjunction with the activation of its verbal label, enhances subsequent odor
identification by temporarily strengthening the association between the odor’s
perceptual representation and its verbal code or (b) the presentation of an odor
with its corresponding verbal label strengthens the accessibility of that verbal
label until the subsequent odor identification task more than does presentation
of the label only” (p. 75).
In the detection experiment (exp. 2), thresholds for nine different odors were
measured after previous exposure to the name or to the name and the odor. The
data showed that neither of those conditions generated enhanced sensitivity as
compared with control odors. Because in the experiment on detection they did
not obtain the same results as in the first experiment on identification, Schab and
Crowder suggested that if participants had to make decisions on odor quality,
one would observe priming effects.
To test that hypothesis, Schab and Crowder performed an identification thresh-
old experiment (exp. 3). The experiment entailed three separate parts and sought
to determine if the concentration at which odors were identifiable would de-

crease because of previous exposure to names or to names plus odors. In the
priming phase (part 1), six odors distributed over two study conditions were
rated for pleasantness and familiarity. The two conditions were name and name
plus odor. In the name-only condition, the participants “smelled” a labeled “odor”
consisting of de-ionized water, which they were told was “very faint.” Shortly
after that, the participants were asked to identify the six experimental odors and
three control odors presented at 10 concentrations each. They were to select
among four odor names, one of which was correct. The data showed that the
odor-identification scores for the experimental conditions were not significantly
different from those for the control condition, in which only new odors were
presented.
At that point, Schab and Crowder argued that the difference between the prim-
ing condition and test task could have been detrimental to the aim of observing
priming. That idea rests on the theory of transfer-appropriate processing (Morris,
Bransford, and Franks, 1977), stressing that memory performance is dependent
on whether or not the encoded information is appropriate for the memory test
used to measure retention. The importance of transfer-appropriate processing for
priming has been pointed out in a number of studies (Roediger and McDermott,
1993). In part 2, Schab and Crowder tested participants for identification thresh-
olds twice. The first time, two stimuli were presented by name only, and two
were presented as names plus odors. Although the means lined up according
to the hypothesis that the name-plus-odor condition would generate lower iden-
tification thresholds than the name-only condition (which in turn would show
lower thresholds than the control condition), the differences fell short of being
statistically significant.
Encouraged by the pattern of results in part 2, Schab and Crowder replicated
that part with more participants (20), this time achieving a significant main effect
for condition. However, a pairwise comparison of the name-only and name-
plus-odor conditions yielded a small and nonsignificant difference, as in part 2.
Because the pairing of the odor and the name did not significantly increase the
priming effect, Schab and Crowder concluded that they had not shown “odor
priming,” but simply “name priming.”
In their final experiment, Schab and Crowder returned to their testing of
repetition priming with odors above threshold, this time measuring only RTs.
Participants rated the perceived intensities of 24 common odors, half of which
were presented as odors along with their names, and the other half as names
alone, but with the instruction to try to imagine the corresponding odor. At
testing five minutes later, participants rated those odors and 12 control odors
for pleasantness. RTs were also measured for these ratings. The data revealed
that the means for the three conditions were almost identical and hence did not
demonstrate any priming at all.
Schab and Crowder concluded that their efforts to demonstrate priming of
odor memory “paint a surprisingly bleak picture” and that the phenomenon
was “not yet on a solid factual basis.” Regarding those statements, a comment
might be made concerning their decision not to use a condition in which only
the odor would be presented in the priming phase. They discussed that exten-
sively and concluded that an odor-only condition would have yielded ambigu-
ous results with regard to the type of priming found (odor priming or name
priming), because it would have been impossible to control the participants’
thought processes. On the other hand, using the difference between name prim-
ing and name-plus-odor priming as a measure of “odor priming” is questionable
(Olsson and Fridén, 2001). The fact that identification rates for familiar odors
seldom exceed 50% (de Wijk, Schab, and Cain, 1995) means that inclusion of
odor names along with the odors in the priming phase would have introduced new
information to the participants that could have been used later in the test phase.
Therefore it is doubtful that the name-plus-odor condition taps only implicit
memory.
2.2. The Wippich Experiments

We shall review three studies by Wippich and colleagues (Wippich, Meck-
lenbräuker, and Trouet, 1989; Wippich, 1990; Wippich, Mecklenbräuker, and
Banning, 1993). They were published in German and therefore may not have
come to the general awareness of the international scientific community. We re-
alize, of course, that more studies on this topic can be found in other languages.
Wippich et al. (1989) wanted to study the commonly observed dissociation
between implicit memory and explicit memory for different levels of processing.
Typically, implicit-memory tests are not sensitive to levels of processing, whereas
explicit-memory tests are (Jacoby and Dallas, 1981; Graf et al., 1984). The prim-
ing phase of the first experiment by Wippich et al. (1989) entailed three condi-
tions: (1) estimation of the subjective duration of exposure (Darbietungsdauer)
(which was 3 sec at all times), (2) condition 1 plus an attempt to identify the
odor, and (3) condition 2 plus a rating of pleasantness. In the test phase shortly
thereafter, odors were presented in pairs (one old and one new odor), and partic-
ipants judged each odor with regard to subjective duration. In addition, for half
of the pairs they judged which of the two pair members was the more pleasant.
The data indicated no difference between new and old odors for any of the study
conditions, either for ratings of duration or ratings of pleasantness. In other
words, no priming was observed.
In a second experiment, Wippich et al. (1989) used two priming conditions:

Group 1 judged the lingering time for presented (3-sec) odors, and group 2 made
an additional attempt to identify the odors. The identification was cued with one
correct name and one distractor name. In the test phase, directly following the
priming phase, all participants judged each odor for lingering time, pleasant-
ness, and identity. Identification was once again cued with a correct name and
a distractor name. The results showed that neither the ratings of lingering time
(Nachwirkungsdauer) nor the ratings of pleasantness were significantly affected
by previous exposure in any of the groups. With regard to odor-identification
scores, the following results were obtained: Odors that had been smelled in the
priming phase (group 1) were better identified than control odors. Odors that
had been smelled before and whose identification had been attempted with the
aid of the two cues (group 2) were not identified significantly better at testing
than were the control odors that had not been smelled before but whose names
had appeared as distractors in the priming phase. The results for identification
RTs did not prove significant, but there was a tendency in group 2 toward shorter
RTs for old odors than for new odors. The authors concluded that it appeared
that verbal mediation was necessary in order for priming to be observed.
In order to differentiate between odor priming and name priming, Wippich
(1990) exposed participants either to odors or to their names. For each exposure,
participants were asked either to relate an autobiographical memory or to judge
the odor/name for edibility. Three dependent measures were registered in the
test phase in response to new and old odors: RTs for relating an autobiographical
memory, scores and RTs for identification. The data showed that identification
of previously presented odors (without names) was better and faster than identi-
fication of new odors. In the case in which only names had been presented in the
priming phase, there was no significant priming effect. At that point, the authors
concluded that repetition priming for naming odors was not purely a verbal-
priming effect, but also presupposed olfactory processing in the priming phase.
With regard to RTs for autobiographical memory, a priming effect was observ-
able only in the condition in which autobiographical memories had been reported
in the priming phase, not for the condition in which edibility had been judged.
Another main result was that the level of processing did not seem to matter for
measures of implicit memory, but it did for some measures of explicit memory.
A third study (Wippich et al., 1993) sought further proof for olfactory-specific
priming. In the priming phase, there were three encoding conditions: exposure
to single odors, to their names, or to pairs of odors. For the group that was
presented names, the instructions were that they should try to imagine the odor
corresponding to a name and rate the degree of clarity at which they could evoke
that phenomenon. The group that was presented with single odors was similarly
asked to rate the degrees of clarity with which they perceived the odors. The
group that was presented with pairs judged whether they were the same or
different. The test phase, directly following the priming phase, was identical
for all participants. Odors were presented in pairs, with the two members of
each pair being identical or different, and the test task was to judge whether they
were the same or different. Participants who responded “different” were asked
to judge which odor was the more pleasant. For the group that had received odor
pairs in the priming phase, the pairs in the test phase appeared as either old pairs
(identical or different) or new pairs (identical or different). If old, the order of
the odors was reversed relative to the order in the priming phase. For the group
that studied odor pairs, the data showed that old pairs were more quickly judged
for whether they were composed of identical or different odors than were new
pairs. That effect was observed to the same extent whether different or identical
odors were repeated. Participants who were exposed to single odors or to their
names in the priming phase were only nonsignificantly faster to judge old pairs
as compared with new pairs.
With regard to preference judgments, priming effects were observed. The
group that had been exposed to single odors and had rated them for perceptual
clarity in the priming phase preferred old odors over new ones in significantly
more than 50% of cases. In a related experiment, Cain and Johnson (1978)
showed that unpleasant odors were rated as less unpleasant after previous ex-
posure; on the other hand, pleasant odors were judged less pleasant. Cain and
Johnson discussed their results using the notion of “affective habituation.” It
should be noted that the odors used by Wippich et al. (1993), according to the
few examples that were given, were on the positive side in terms of preference
ratings. Therefore, those two studies may be somewhat at odds.
As noted, the group that studied odor pairs judged old pairs more quickly
than new pairs with respect to whether they were composed of identical or
different odors, whereas the group that had been presented single odors in
the priming phase did not. Two observations regarding that pattern of results
were discussed by Wippich et al. (1993). First, in accordance with a transfer-
appropriate-processing account of priming effects, the findings suggest that in
order to observe priming, task-specific processes, not only the activation of odor
representations, need to be repeated between priming and testing. Second, an
alternative interpretation of that pattern of results would be that the presentation
of one member of a pair triggered the episodic memory of the other member.
The short RTs when judging old pairs, therefore, might possibly be attributable
to explicit-memory processes.
On the basis of their efforts to show repetition priming in olfaction (Wippich
et al., 1989, 1993; Wippich, 1990), those authors, in their third paper, concluded
that it had been unexpectedly difficult to show priming in olfaction as compared

with priming in other modalities. It will be remembered that Schab and Crowder
(1995) had a similar comment, suggesting that the observed priming in their
experiments may have been verbally mediated. However, Wippich et al. (1993)
concluded that priming occurs not only as a function of name activation but also
as a function of odor activation in the priming phase.
2.3. The Olsson Experiments

Following the Schab and Crowder (1995) experiments, Olsson and Cain (1995, in
press) attempted to design a repetition priming experiment that would not draw on
the processing of odor names as heavily as had the study by Schab and Crowder.
In addition, the design entailed only mono-rhinal smelling. Data on the nostril
used (left or right) at priming and testing were factorially combined. Mono-rhinal
testing is supposed to reflect functional characteristics of the ipsilateral cerebral
hemisphere (Brodal, 1981; Doty et al., 1997).
In the priming phase used by Olsson and Cain (exp. 1), participants estimated
how long it had been since they had last smelled each of six very familiar odors.
In doing that, participants had no access to names or visual cues to the identity
of each odor. Five minutes later, they smelled 12 odors (6 old and 6 new) and
indicated by pressing a response key when they thought they knew the identity
of an odor. They were not required to know the names of the odors at the time
of pressing the key; a visualization of the odorous object itself would qualify.
Measured that way, the findings revealed faster RTs for identification of old odors
than for new ones.
When the data were broken down by nostril, the following pattern emerged.
Which nostril had been used at priming did not matter at all. Which was used
as the test nostril, however, did matter: Priming was evident only when testing
was via the left nostril, irrespective of the side used at priming, and therefore
it was believed to reflect left-hemisphere (LH) functioning. Because the LH is
associated with verbal processing, the left-nostril priming we observed may be
also. That is, the observed priming may again represent name priming rather
than odor priming.
In a follow-up experiment, Olsson (1999) tried to draw even less on verbal
processes. The idea was to restrict the requirements of verbal processing by
intervening in the naming process to see if odor priming in the LH was still
evident. It should be noted that most theories of object naming would agree
that at least three stages are present in the naming process: object identification,
name activation, and response generation (Johnson, Paivio, and Clark, 1996). In
Olsson’s experiment, the priming task required participants to rate how long it
had been since they had last smelled the odors (because Olsson and Cain had
found priming only when tested from the LH, participants used the left nostril
throughout the whole experiment). In the test phase, participants were introduced
to a comparison odor (orange or coffee). They were then presented with old and
new odors. The task was to decide, as quickly as possible, whether or not the
old and new odors were identical with the comparison odor. The general idea
was that only early (perceptual) processing should be necessary in order to reject
the proposition that a test odor was identical with the comparison odor. Prim-
ing was then supposed to reveal itself as faster rejections for old odors than for
new ones. The results showed that old and new odors were rejected equally fast,
suggesting that the original experiment by Olsson and Cain had tapped some
type of conceptual priming rather than perceptual priming. However, the results
proved more complicated than first realized. After the priming test, participants
had been asked to identify each odor, and as is commonly observed in odor-
identification experiments, their correct identifications had been low (48%). A
post-hoc analysis of the RT data, dividing the trials into two categories, one
for trials that were followed by successful identification and one for trials fol-
lowed by incorrect identification, showed that unidentifiable odors had been
associated with shorter latencies than had control odors and hence had exhibited
repetition priming. Identifiable odors, on the other hand, had been associated
with slower RTs. That latter result was discussed in terms of negative repetition
priming (Tipper, 1985), that is, an expression of memory in which the process-
ing of a stimulus is in some sense inhibited because of a previous encounter
with it.
Another attempt to reduce the impact of verbal processing in the quest to show
repetition priming in olfaction is seen in a study by Olsson and Fridén (2001).
They argued that perceptions of edibility would be less laden with verbal process-
ing and that judgments thereof could be made without prior identification. In their
first experiment, participants were asked to judge the edibility of 24 bi-rhinally
presented odors, half of which were edible. Ten minutes later, they repeated such
judgments for 48 odors, 24 old and 24 new, that were presented mono-rhinally.
The results indicated that edibility judgments for old odors were significantly
faster, but not more accurate. There were no differences in performance for the
two nostrils.
A second experiment followed the lines of the first, with one major change.
The participants attempted to identify the odors in the priming phase and judged
old and new odors for edibility in the test phase. The results showed that priming,
in terms of faster RTs, was observable only when testing was via the right nostril.
It can be noted that testing via the left nostril was associated with more correct
judgments of edibility, as compared with the right nostril.
The main finding of Olsson and Fridèn (2001) that pertains to our review is that
edibility judgments were faster when repeated for the same odors. The authors
reported two observations that support the notion that edibility judgments are
not conditional on name activation: First, the reaction times were quite fast for
edibility judgments. The RTs for judging whether or not an odor was edible
were at least 30–35% shorter than those for making a decision on the odor
source (Olsson and Cain, in press). Second, there was no correlation across odors
between the primability and identifiability of odors. On the other hand, Olsson
and Fridén discussed the possibility that the observed priming could be based on
categorization of odors into some number of edible and inedible subcategories,
such as spices, cleaning products, and so forth (see Dubois and Rouby, Chapter 4,
this volume, on this point). In other words, this type of priming may tap into
conceptual processes other than the strictly perceptual ones.
3. An Experiment Probing Perceptual Repetition Priming

One of the critical points in the search for evidence of olfactory repetition priming
concerns the development of methods that can measure odor priming, or per-
ceptual priming, rather than name priming. We shall present some original data
from an experiment aimed at investigating such perceptual priming: The design
was based on an experiment by Wippich et al. (1993) that in our opinion seems
adequate for tapping perceptual priming. Although their data showed nominal,
but not significant, priming effects, it seemed possible that a more focused ex-
perimental effort might. The idea was to see if exposure to odors in conjunction
with an orienting task focusing on odor quality during the priming phase would
influence perceptions of odor quality at a later test, thereby facilitating judgments
on perceptual clarity and same/different judgments of odor pairs.
3.1. Method
Participants. Twenty male and 20 female participants, primarily stu-
dents from Uppsala University, took part in the experiment, either for course
credit or for a movie ticket. They ranged in age from 19 to 52 years (mean =
26.8). Their olfactory functioning was normal, according to self-assessments.
Smokers (n = 6) were asked to refrain from smoking for one hour before the
experiment. Anyone suffering from a cold or a temporary nasal obstruction was
excluded.
Stimuli. The stimulus set consisted of 48 different odorous items that

were placed in amber-tinted glass jars and occluded from visual inspection by
cotton pads. The odors represented common everyday objects, both edible and
inedible, such as coffee, cinnamon, shoe polish, and so forth.
Design and Procedure. In the priming phase, participants judged the

similarities of 24 odors to a comparison odor (pine) on a scale from zero (very
dissimilar) to 100 (identical). To suppress verbal processing of the odors during
the priming phase, participants were required to perform a verbal-fluency test
(Benton and Hamsher, 1976) between the odor presentations. To prevent verbal
processing during the retention interval between the priming and test phases,
participants engaged in a working-memory test (Skandinaviska Testförlaget,
1967).
In the test phase, participants were presented with 32 odor pairs, half of which
were made up of old odors, and the other half of new odors. Identical pairs
and different pairs were equally represented among the new and old pairs. At
the presentation of the first member of a pair, participants sampled the odor
on hearing a tone signal and then indicated when they had perceived the odor
quality “clearly” by pressing a timer button. For the second member of the pair,
participants indicated whether the odor was the same as or different from the
first member of the pair. For that judgment, both correctness and RTs were
noted.
3.2. Results and Discussion

Three analyses of variance (anova) were performed to investigate repetition
priming. First, the RT for perceptual clarity in response to the first member of a
pair in the priming phase was analyzed in a two-way anova (Old/New × Sex),
with repeated measures on the first factor. The results showed that old and new
odors were perceived with clarity equally fast (1,450 msec and 1,440 msec, re-
spectively) [F(1, 38) = 0.17, p = ns]. The dependent variable for the second
analysis was the RT for giving a same/different judgment (for pairs whose two
members were different) when presented the second odor of a pair. The rea-
son for omitting the responses to pairs of identical odors from the analysis was
that in those trials the same odor was presented twice, and therefore the sec-
ond presentation could not be considered “new.” An anova (Old/New × Sex)
yielded no significant difference between old odors (1,230 msec) and new odors
(1,257 msec) [F(1, 38) = 1.29, p = ns], and hence no indication of repeti-
tion priming. The third test of priming concerned correctness scores for the
same/different judgments. For the same reasons as before, that analysis was per-
formed only for pairs whose two members differed. An anova (Old/New × Sex)
yielded no significant difference between old (95.5%) and new (95.7%) pairs
[F(1, 38) = 0.03, p = ns]. It should be noted, however, that performance levels
were quite high, indicating that ceiling effects may have prevented detection of a
difference between old and new pairs. On the other hand, performance levels for
new and old pairs were close to identical. Women performed nominally faster and
better than men in all three analyses, but those differences were not statistically
significant.
To conclude, a repetition priming experiment designed to tap perceptual prim-
ing was performed. Task requirements oriented the participants toward the quality
rather than the identity of odors at both priming and testing. In addition, distrac-
tion tasks prevented additional processing of odor identities or other semantic
processing. The effects of repetition were assessed in three ways. No statistically
reliable evidence could be found for perceptual repetition priming. Our findings
are in line with previous results from Wippich et al. (1993).
4. Discussion
This review of the literature indicates that several priming effects for a number of
tasks in olfaction have been observed. Moreover, such priming can be seen to be
lateralized between the cerebral hemispheres, as assessed by mono-rhinal testing.
However, several authors have concluded that repetition priming in olfaction
has received weaker empirical support than would have been expected on the
basis of findings for other modalities. Moreover, the effects that were observed
could have been due to verbal processing rather than perceptual processing.
Given that background, we conducted an experiment aimed at probing further
into perceptual priming. Our results supported the notion that strictly perceptual
processing (in this case, attending to sensory quality) may not suffice to generate
repetition priming effects in olfaction.
A second major issue regarding the existence and nature of olfactory repeti-
tion priming concerns the issue of external validation. Typically, investigators
in olfaction have adopted procedures similar to those that have been developed
and validated for probing repetition priming in the field of visual memory. How-
ever, as can be noted in this review, there is no proof that the methods used to
probe olfactory repetition priming really tap the operations of implicit memory.
Therefore, we need tests to show independence between explicit memory and
implicit memory for odors at the level of individual items (cf., Tulving et al.,
1982). Another way to validate the existence of olfactory priming would be to
show that amnesics exhibit olfactory priming in the absence of normal perfor-
mance on other explicit tests of odor memory (Cave and Squire, 1992). A third
possibility concerns assessment of the effects of surreptitiously presented odors
on subsequent performance (Degel and Köster, 1999).
5. Conclusions
This review of different experimental conditions attempting to assess repetition
priming in olfaction has led to the following conclusions: Response facilita-
tion due to repetition (priming) in olfaction can be observed for several tasks.
However, several authors have argued that such priming experiments have had
limited success as compared with tests of priming in other modalities, especially
vision. Experimental procedures that target odor identity/naming typically are
more successful in exhibiting priming than are other procedures. This indicates
that the observed effects concern “name priming” rather than “odor priming” or
“perceptual priming.”
Other experimental procedures, drawing less on the ability to identify odors
by their names, have also been developed. Repeated edibility judgments, for
instance, have shown reliable priming effects in terms of shorter RTs. Other
procedures designed to focus on strictly perceptual processing (e.g., comparing
odor qualities) have found little to no priming.
Transfer-appropriate processing shows more priming than transfer-inappro-
priate processing. In other words, priming is more likely to be observed if
the priming and test tasks are repeated or otherwise overlap with respect to
information or processing.
Results from several experimental conditions indicate that priming effects
differ for the two hemispheres (nostrils). This is an interesting finding that could
further our understanding of functional cerebral lateralization, as well as the
processes/neural substrates that are associated with priming in olfaction.
It should be noted that there has been no validation of the methods used to probe
repetition priming in olfaction, that is, whether or not they tap the operations of
implicit memory, thereby avoiding “leakage” between priming and testing via
explicit memory. Such methods have been developed within the field of visual
memory, and we need to find ways to extend them to olfaction.
Acknowledgments
This work was supported by The Bank of Sweden Tercentenary Foundation and
The Alrutz Fund.
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16
Odor Memory in Alzheimer’s Disease
Steven Nordin and Claire Murphy
1. Introduction
The neuropsychology of olfactory cognition is a relatively young scientific do-
main that in recent years has in many respects advanced from explorative research
to more focused and hypothesis-driven investigations. That advancement can be
attributed in part to important studies of certain neurological and geriatric dis-
orders. A question of interest here is whether or not research in odor memory
in populations with those disorders can provide a better understanding of the
neural processes underlying odor memory. For example, there is evidence that
Korsakoff patients experience rapid forgetting in the visual, auditory, and tactile
modes, but not in the olfactory realm (Jones, Moscowitz, and Butters, 1975;
Mair, Harrison, and Flint, 1995). That has been used as part of the evidence
that odor memory may be a specialized subsystem of memory (Herz and Eich,
1995). If so, it might be expected that a pattern quite opposite to that of Korsakoff
patients would be possible. Thus, memory impairment for olfaction may, under
certain neuropathologic conditions, be more severe than memory deficits in other
sensory modalities.
The notion of olfactory-specific memory impairment can be linked to the
possibility of odor memory being particularly vulnerable to certain cortical neu-
ropathologic conditions. In a rather extensive review of the neuropsychological
literature involving human olfaction, Mair et al. (1995) concluded that, in contrast
to the situation for other sensory modalities, there is no evidence for morpho-
logically distinct centers mediating memory for and perception of odors. Thus,
impairment of odor memory is strongly associated with impairment in the ability
to perceive the quality of an odor. The general association between impairments
in perception and memory for odors suggests that relatively limited cortical areas
serve a relatively wide range of olfactory functions. That, in turn, might imply
that odor memory could be more sensitive than other sensory systems to focal
261
262 Steven Nordin and Claire Murphy
neuropathologic changes, because both perceptual functions (prerequisites for

the encoding of odors) and odor memory per se would be affected.
Patients with Alzheimer’s disease (AD) constitute an interesting population
with regard to questions concerning olfactory-specific memory impairment and
an understanding of the neural processes underlying odor memory. Of particular
interest are cases of AD in its very early stages, because it is assumed that cortical
abnormalities at an early stage of the disease progression are relatively focal and
limited to the entorhinal and transentorhinal areas (Braak and Braak, 1997).
The main issue to be addressed in this chapter is the question of what can be
learned about the neuropsychology of odor memory from studies of patients with
AD. At present, several criteria are used to assess AD (McKhann et al., 1984),
though unfortunately a determination of disease status can be made definitively
only by neurological examination at autopsy. More sensitive tools clearly are
needed for diagnosis in the early stages of the disease progression. Because of
early, pronounced neuropathologic changes in olfactory brain areas in AD, this
sensory system is of particular interest for the development of diagnostic tools.
Consequently, a secondary issue of this chapter is the potential for using memory-
based olfactory tests for early diagnosis of AD. To approach these two issues,
we shall review the state of research into the neural and behavioral abnormalities
of the olfactory system at various stages of the disease. Finally, our review will
be integrated with the most recent scientific findings to address our two issues
and to shed light on further research needs.
2. Neuropathology of AD
AD is a neurological disorder characterized by progressive memory loss, and the
most common cause of dementia. About 5% of people over the age of 65 years
suffer from dementia (Jorm, Korten, and Henderson, 1987), and AD accounts
for 50% to 60% of the dementing diseases (Katzman, 1986). Although cognitive
symptoms dominate, other symptoms such as anxiety, depression, delusions, and
hallucinations plague many of these patients (Folstein and Bylsma, 1994). The
most prominent cognitive deficit typically associated with AD is amnesia, with
additional deficits in language, abstract reasoning, certain executive functions,
and visuospatial abilities (Bondi, Salmon, and Butters, 1994b).
The neuropathology of AD is characterized by the presence of neuritic plaques
(NP), neurofibrillary tangles (NFT), and cell loss. As mentioned earlier, it has
been suggested that regions of importance for olfactory processing are among
those most affected, and they may even be sites of initial involvement in the
disease (e.g., Pearson et al., 1985; Braak and Braak, 1997). NPs, NFTs, and
neuropil threads have been found in the anterior olfactory nucleus (Ohm and
Odor Memory in Alzheimer’s Disease 263
Braak, 1987; Price et al., 1991), and NFTs, neuropil threads (Esiri and Wilcock,
1984), and axonal loss (Davies, Brooks, and Lewis, 1993) have been reported in
the olfactory bulb. Signs of abnormalities in the olfactory epithelium have been
less consistent; some researchers have reported changes (Talamo et al., 1989),
whereas others have reported no significant abnormalities (Davies et al., 1993).
Such findings tend to focus the search for olfactory deficits on more central
regions of this sensory system.
Van Hoesen and Solodkin (1994) pointed out that olfactory brain areas appear
uniquely affected, given the relative sparing of other sensory areas. For exam-
ple, the entorhinal cortex and periamygdaloid nucleus, which are parts of the
olfactory cortex, are especially damaged. The work of Price et al. (1991) has
confirmed the presence of tangles in areas that mediate olfactory function, par-
ticularly the anterior olfactory nucleus, entorhinal cortex, and amygdala, in AD
patients with very mild dementia. Reyes, Deems, and Suarez (1993) reported NPs
and especially NFTs in the entorhinal and prepiriform cortices and in the peri-
amygdaloid nucleus and concluded that there was greater evidence of pathologic
changes in the olfactory cortex than in the hippocampus, which is the area char-
acteristically associated with damage in AD. Hyman (1997) reported the most
severe lesions to be in the entorhinal and perirhinal cortices, the CA1/subicular
area of the hippocampus, the amygdala, and the association cortices. Braak and
Braak (1992) have argued that the lesions in the entorhinal and transentorhinal
areas effectively disconnect the hippocampus from the isocortex, preventing the
transfer of information essential to memory function.
3. Odor Detection and Discrimination

Although the focus of this chapter is on odor memory, it is important to understand
that more sensory-based olfactory functions required for memory performance
are also affected in AD. Losses in absolute detection sensitivity have been demon-
strated for a large number of substances (Richard and Bizzini, 1981; Knupfer
and Spiegel, 1986; Doty, Reyes, and Gregor, 1987; Rezek, 1987; Murphy et al.,
1990; Serby, Larson, and Kalkstein, 1991; Lehrner et al., 1997; Nordin et al.,
1997). That poor performance in odor detection most likely is due to neurological
rather than rhinological status (Feldman et al., 1991) and to sensory loss rather
than lack of comprehension of the detection task per se (e.g., Nordin, Monsch,
and Murphy, 1995). The loss in detection sensitivity is further illustrated by its
association with the degree of dementia (Murphy et al., 1990; Nordin et al.,
1997) and by an association between a rapid progression in dementia and a swift
decline in sensitivity (Nordin et al., 1993). A patient’s odor threshold has, inter-
estingly, also been found to correlate with a family history of AD (Schiffman,
Clark, and Warwick, 1990). Obviously AD patients are at considerable risk with
respect to safety issues (detection of smoke, gas leaks, spoiled food, etc.), be-
cause many anosmic AD patients are unaware of their olfactory loss (Doty et al.,
1987; Nordin et al., 1995).
Another sensory function underlying performance on tests of odor memory is
quality discrimination. Impairment in that olfactory function has been shown in
AD when using same-or-different (Koss, 1986) and match-to-sample paradigms
(Kesslak et al., 1988; Buchsbaum et al., 1991; Kesslak, Nalcioglu, and Cotman,
1991). The roles of detection and discrimination sensitivity for accurate odor
memory will be discussed next.
4. Odor Memory
Considering the severe olfactory neuropathologic abnormalities found in the
medial temporal lobe in AD, it is of particular interest to study behavioral im-
pairment of memory for odors in this population. Thus far, much research has
been directed toward explicit memory (see Issanchou et al., Chapter 13, this
volume). Hence the memory domains to be reviewed here are of the episodic
and/or semantic nature. Episodic memory is commonly defined as memory for
personal episodes, and it is the type of memory for which the most pronounced
auditory and visual deficits have been reported in AD (Welsh et al., 1991). Poor
performances in these two sensory modalities on tests of recognition memory,
inability to learn new information over repeated learning trials, and rapid forget-
ting suggest impairment in storing (i.e., encoding) and retaining new information
in AD (e.g., Delis et al., 1991; Welsh et al., 1991). Such findings suggest that var-
ious dimensions of episodic odor memory are of potential interest with respect
to AD.
Impairment in semantic processing in AD has also been well documented
for visual and auditory material. It includes identification by naming and ver-
bal fluency with respect to both categories and letters (Butters et al., 1987;
Chertkow and Bub, 1990). This impairment may well reflect breakdown of se-
mantic networks in AD, as has been demonstrated by applying various graphic
scaling techniques (Chan et al., 1993, 1995), including multidimensional scaling
(MDS). Findings from our laboratory obtained with the technique of MDS, with
triads of odor stimuli being compared for similarity, suggest a breakdown in
the semantic network for odors, but not colors, in term of associations between
odors (Chan et al., 1998). Not surprisingly, our patients also showed losses in the
ability to identify odors. Another memory function that requires intact seman-
tic memory, but also episodic memory, is verbal recall of previously presented
odors. Preliminary findings from our laboratory suggest that AD patients perform
particularly poorly on this task and show basically no ability to improve across
repeated trials. This includes immediate recall as well as short- and long-delay
recall, both with and without semantic cues (Razani et al., 1996). Analyses of
the data suggest that impaired odor identification underlies much of the failure
of recall.
4.1. Recognition memory

The ability to recognize previously experienced odors is predominantly a matter
of episodic memory, but also is influenced by semantic knowledge of the odor
item (e.g., Larsson and Bäckman, 1997). Deficits in recognition memory for
odors have been documented in mild to moderate cases of AD for both short-
term memory (retention intervals of 5–30 sec) (Knupfer and Spiegel, 1986)
and long-term memory (10–20 min) (Moberg et al., 1987; Murphy, Lasker, and
Salmon, 1987; Lehrner et al., 1997). Preliminary data from our laboratory also
suggest that AD patients have limited trust in their recognition memory for odors
even when they in fact remember correctly (Wilhite et al., 1993).
We have examined the question of when in the disease progression a decline
in recognition memory for odors begins (Murphy, Nordin, and Jinich, 1999).
That was addressed by studying 78 patients with probable AD, categorized as
very mild, mild, or moderate in degree of dementia, and 78 controls. Common
household odors were used as stimuli, as were visual stimuli of common faces
and abstract, uncommon symbols for comparison. Ten stimuli for each modality
were presented for inspection. After intervals averaging 20 min, half of the
stimuli were presented again, together with the same number of new stimuli and
the instruction to tell which stimuli had been presented before. In addition, odor-
detection sensitivity for n-butyl alcohol was assessed for comparison. The results
showed that whereas the earliest declines in odor sensitivity and visual memory
were found in patients with mild dementia, a decline in odor memory was found in
patients with very mild dementia. That suggested that odor-recognition memory
may be affected earlier in the disease progression than are visual-recognition
memory and odor sensitivity.
To further our understanding of the early decline in odor-recognition mem-
ory in AD, we shifted our focus to persons with the diagnosis of questionable
AD. These persons are rare, but ideal for studying the early changes in AD.
They show impairment in cognitive functions, similar to patients with proba-
ble AD, but, in contrast, they do not yet show changes in everyday function-
ing as reported by significant others (Bondi et al., 1994a). Using the same test
procedures as in the study described earlier (Murphy et al., 1999), we inves-
tigated 16 persons diagnosed with questionable AD and 16 controls (Nordin
1.0
Controls
Questionable AD
0.9
Proportion Correct
0.8
0.7
0.6
0.5
Odors Faces Symbols
Figure 16.1. Mean (±SE) proportions of correct responses for odors, faces,
and symbols on tests of recognition memory in questionable AD and normal
controls. (From Nordin and Murphy, 1996. Reprinted by permission of the
American Psychological Association.)
and Murphy, 1996). Six of the questionable-AD subjects were diagnosed again
one to three years after the odor-memory testing, and at that time all six were
given the diagnosis of probable AD. Thus, those subjects can be considered
to represent preclinical AD. The results are presented in Figure 16.1 and sug-
gest a relative olfactory-specific impairment in recognition memory. Thus, per-
sons with questionable AD performed significantly poorer than did controls
for odors, but showed only a tendency toward poorer performance for visual
material.
4.2. Familiarity
Familiarity with a certain object or event can be considered as a form of remote
memory – memories for stimuli encoded at some unspecified previous time.
Besides episodic memory (e.g., “This is familiar; it is something I had for break-
fast some time ago”), familiarity may also involve semantic memory (e.g., “This
is familiar; it is some kind of spice”). Research in the visual and auditory domains
in AD patients has demonstrated deficits in retrieval from remote memory (e.g.,
Beatty et al., 1988; Mitrushina et al., 1994). In a study to compare familiarity
performances for visual and olfactory materials, test stimuli of odors, faces, and
symbols were used when studying 32 mild to moderately demented patients with
probable AD and 32 controls (Niccoli-Waller et al., 1999). The subjects were
instructed to rate the stimuli for familiarity on a visual-analogue scale. It was
found that AD patients rated odors, but not faces or symbols, as significantly
less familiar than did controls, indicative of deficits in remote odor memory.
Follow-up testing one year later in 12 of the AD patients and 12 of the controls
again showed the same result.
4.3. Identification
The ability to identify odors by name depends on semantic memory, but also
requires a great deal of perceptual processing such as quality discrimination
(e.g., Cain and Potts, 1996). This is especially true when response alternatives
are available, which eases the cognitive load. Difficulties in odor identification by
naming have been demonstrated in AD when assessed by a test to match odors to
names (Corwin et al., 1985; Knupfer and Spiegel, 1986), without presentation of
response alternatives (Rezek, 1987; Bacon Moore, Paulsen, and Murphy, 1999).
However, the most commonly used means to study odor identification in AD has
been the University of Pennsylvania Smell Identification Test (UPSIT), which
is a lexical-based test using four written response alternatives for each test odor
(Doty, Shaman, and Dann, 1984). Results from such studies consistently show
losses in the ability to name odors (Warner et al., 1986; Doty et al., 1987, 1991;
Kesslak et al., 1991; Serby et al., 1991; Moberg et al., 1997).
The studies of odor identification cited earlier relied on lexical functioning as
the response mode, such as the interpretation or formulation of words. There-
fore, we wondered if odor identification that did not rely on lexical function
would also show impairments (Morgan, Nordin, and Murphy, 1995). Eighteen
patients with probable AD at mild to moderate stages of dementia were compared
with 18 controls, and 8 persons diagnosed with questionable (preclinical) AD
were compared with 8 controls. The participants were given the UPSIT and the
San Diego Odor Identification Test (SDOIT) (Anderson, Maxwell, and Murphy,
1992). The latter is an eight-item test (of which six were used for our purpose)
developed for children, with pictures as the response alternatives from which to
choose. Thus, the participant would point at the picture representing the odor
item, which eliminated lexical demands. To verify earlier findings of relatively
spared visual identification in AD (Doty et al., 1987, 1991), the Picture Identifi-
cation Test (PIT) (Vollmecke and Doty, 1985) was administrated. It is identical
in content and format with the UPSIT except that pictures, instead of odors, serve
as stimulus items. The results are presented in Figure 16.2 and show impairments
in both lexical-based (UPSIT) and picture-based (SDOIT) odor identifications
for both probable and questionable AD. With the same items represented by
pictures (PIT), the AD groups, in contrast, performed at the same level as their
control groups.
These findings suggest that the impairments in odor identification commonly
found in AD cannot be attributed predominantly to lexical difficulties. That
Controls (Questionable AD)

Questionable AD
Controls (Probable AD)
Probable AD
Correctly Identified Item
Odors (UPSIT) Odors (SDOIT) Pictures (PIT)

40 6 40
5
30 4 30
20 3 20
2
10 10
1
0 0 0
Figure 16.2. Mean (±SE) numbers of correctly identified odors and pictures
in questionable AD, probable AD, and normal controls. (From Morgan et al.,
1995. Reprinted by permission of Swets & Zeitlinger.)
conclusion is supported by the findings of Larsson et al. (1999), who compared

performances in odor identification when support was provided (either written
response alternatives or real-life objects as alternatives, or no support). The AD
patients performed very similarly on both tasks with support, but considerably
better with support than without support, and significantly poorer than controls on
all three tasks. The degrees of improvement due to support were equally large in
AD patients and controls. Such similarity in support-induced improvements, also
reported by Peabody and Tinklenberg (1985) and Rezek (1987), was interpreted
by the authors as showing that degeneration of olfactory knowledge plays a more
important role than lexical-access problems in AD.
In a recent study (Devanand et al., 2000) it was demonstrated that a large
proportion of patients with mild cognitive impairment have difficulty in iden-
tifying odors (UPSIT) and that those patients with such difficulties are more
likely to develop AD than are other patients with mild cognitive impairment. In-
terestingly, it was reported that the combination of poor odor identification and
lack of awareness of one’s olfactory deficit predicted the time of development
of AD.
Still another approach to investigation of early, possible AD is by means of
typing apolipoprotein E (ApoE). This protein is found in increased amounts
in patients with AD, specifically in plaques and tangles (Namba et al., 1991),
suggesting that ApoE is a genetic risk factor for AD (Corder et al., 1993). Pairs
of three primary alleles, 2, 3, and 4, determine an individual’s ApoE status.
About 25% of the general population will have at least one 4-allele, yet 80%
of patients with familial AD and 64% of patients with the sporadic form of the
disease have one or both of the 4-alleles (Sing and Davignon, 1985). In a study
of healthy elderly people, the participants were categorized as allele-positive

(having at least one 4-allele: 2/4, 3/4, 4/4) or allele-negative (2/2, 2/3, 3/3) and
tested on odor identification (SDOIT) (Murphy et al., 1998). The results showed
that the allele-positive elderly performed significantly poorer than the allele-
negative participants on that olfactory task. Further support for a genetic link
between odor identification and AD has been provided by data suggesting that
performance on odor identification (UPSIT) is impaired in first-degree relatives
of patients with probable AD (Serby et al., 1996).
4.4. Verbal Fluency

Some well-documented difficulties in verbal fluency, as seen when subjects are
instructed to generate names of items with respect to a given category or an
initial letter, motivated a study of name generation for items specifically related
to the olfactory domain (Bacon Moore et al., 1999). Forty patients with probable
AD and 40 controls were asked to generate (within 60 sec) as many names as
possible for (1) odors belonging to a given category, (2) odors beginning with
the letters P, C, and S, and (3) odors that came to mind when presented with two
odorants. The results demonstrated impairments in AD for all three measures,
and in accordance with findings from conventional testing of verbal fluency (e.g.,
Monsch et al., 1994), category fluency was more impaired than letter fluency.
Those findings also support the claim that the poor odor identification in AD
is better explained by cognitive than by sensory impairment. Furthermore, the
difficulties in generating names for odorants may reflect a breakdown in the
semantic network for odors.
5. Discussion and Perspective

From our review of the neuropathology of AD, the very early changes appear to be
found predominantly in the entorhinal cortex, but also in the amygdala, piriform
and prepiriform cortices, and to some extent in the anterior olfactory nucleus. As
the disease progresses, the pathologic processes also involve the hippocampus
(CA1 and subiculum) and the olfactory bulb. Whereas the olfactory epithelium
may be affected to some extent, there are no indications of neurodegeneration in
the orbitofrontal cortex.
In the behavioral arena, as described in our review, the very early olfactory
impairments in AD that have been demonstrated thus far concern the abilities to
recognize and identify odors, with the latter being the more severe. Early declines
in odor identification have been demonstrated in questionable AD, in patients
with mild cognitive impairment, and in first-degree relatives of AD patients,
often by means of ApoE typing. In mild to moderate cases of AD, various other
sensory- and cognition-based olfactory functions are affected, including absolute
detection, quality discrimination, familiarity, verbal fluency for odor items, and,
probably, any type of semantic memory requiring an intact semantic network for
odors. To what extent these functional impairments are present at a very early
stage of AD remains to be studied.
The question of peripheral versus central contributions to poor task perfor-
mance may in this context determine to what extent losses in odor-detection
sensitivity can explain poor performances on tests of odor memory in AD. Al-
though a decline in detection sensitivity may contribute, there is strong support
for the view that semantic odor memory, rather than odor sensitivity, is predomi-
nantly affected in early AD. Thus, deficits in odor identification have been found
in AD in the absence of significant odor-detection deficits (St. Clair et al., 1985;
Rezek, 1987; Koss et al., 1988; Larsson et al., 1999). Impairment in identifi-
cation ability has also been found at an earlier disease stage than impairment
in detection ability (Serby et al., 1991), and the former has more commonly
been found to correlate with global cognitive status (Knupfer and Spiegel, 1986;
Kesslak et al., 1988, 1991; Serby et al., 1991; Larsson et al., 1999). Finally,
identification deficits appear to be present before detection deficits in persons at
risk for AD due to ApoE 4-allele status (Bacon et al., 1998; Murphy et al., 1998).
In accordance with this, impairment in recognition memory for odors has been
found in AD in the absence of significant odor-detection deficits (e.g., Nordin
and Murphy, 1996; Murphy et al., 1999).
5.1. Neuropsychology of Odor Memory

A difficulty in developing an understanding of the neuropsychology of odor
memory based on findings in AD is that a relatively wide range of areas already
show pathologic involvement by the time a diagnosis of probable AD can be
made. Therefore, very early cases of AD play an important role in our under-
standing, for the neuropathologic changes at that stage are still relatively focal.
The combination of very early abnormality in the entorhinal cortex and a very
early decline in odor identification, as shown in many studies to be prominent at
more advanced stages of AD, suggests that the entorhinal cortex plays an impor-
tant role in the ability to identify odors. Although this cortical region may play
a key role for odor identification, other areas may be important as well. In MRI
studies of patients who had undergone temporal-lobe resection, Jones-Gotman
et al. (1997) discussed the possibility of the piriform cortex being a critical site
for odor identification, with periamygdaloid damage causing disconnection from
the piriform cortex and thus affecting odor identification.
The theory of the entorhinal and transentorhinal areas disconnecting the hip-
pocampus from the isocortex early in AD, preventing the transfer of information
essential to memory function (Braak and Braak, 1992), directs further attention
to the entorhinal cortex, but also to the hippocampus. There is, unfortunately,
a lack of documentation of any relationship between olfactory performance in
early AD and neuroimaging data. However, some information about the more
advanced progression of AD is available. For example, lower metabolic activ-
ity, as compared with controls, has been found in the parahippocampal gyrus
(entorhinal cortex) in AD while performing an odor-discrimination task (match-
to-sample task, with a 10-sec load on working memory). Furthermore, Kesslak
et al. (1991) used MRI to show significant atrophy in the entorhinal cortex and
hippocampus in AD patients post mortem. The volumes for those areas were also
found to correlate with performances on quality discrimination and identification
of odors, but poorly with visual discrimination.
High correlations with atrophy in the entorhinal cortex and hippocampus for
both quality discrimination and identification (Kesslak et al., 1991) support the
notion that relatively limited cortical areas serve a relatively wide range of ol-
factory functions (Mair et al., 1995). That implies that the entorhinal cortex
and possibly the hippocampus may serve both quality discrimination and iden-
tification of odors. Regarding the hippocampus, Otto and Eichenbaum (1991)
suggested, with reference to animal models, that this structure is necessary to
encode relationships between odors, thus affecting discrimination. The claim that
poor odor identification in AD cannot be explained simply by loss in discrimi-
nation sensitivity is supported by findings of breakdown in semantic networks
for odors (Chan et al., 1998; Bacon Moore et al., 1999).
The demonstrated impairment in recognition memory for odors in very early
AD (Figure 16.1) raises the question whether or not the entorhinal cortex also
plays a major role in episodic odor memory. Although further investigations
clearly are needed to answer this question, such a role seems reasonable in
view of the well-established opinion that the entorhinal-hippocampal-subicular
complex is a key structure in the encoding of memory, independent of type of
sensory modality (e.g., Kandel, Schwartz, and Jessell, 2000).
Documentation of past research involving neuropsychological approaches to
an understanding of odor familiarity is sparse. However, Royet et al. (1999)
have used positron-emission tomography to show selective activation in the
right medial orbitofrontal area in normal subjects during familiarity judgments.
Considering the spared orbitofrontal areas in AD, and yet a decline in familiarity
judgment in AD (Nordin and Murphy, 1996; Niccoli-Waller et al., 1999), those
additional regions probably are involved in this process. Hypothetically, the
task of asking oneself whether or not a certain odor is familiar may activate
the orbitofrontal cortex, whereas activation in other areas, presumably in the

medial temporal lobe, may be critical for successful retrieval of the memory trace
(generating an experience of familiarity). Future studies will have to untangle
this question.
5.2. Memory-based Olfactory Tests for Early Diagnosis of AD

A first prerequisite for the introduction of an olfactory test for diagnosis of
AD in clinical settings is that there be both a neuroanatomical rationale and a
functional rationale for such an introduction. In this respect it can be concluded
that the very early and predominant abnormalities are found in cerebral areas
that are crucial for basic olfactory processing: the prepiriform and piriform
cortices (primary olfactory cortex), entorhinal cortex and amygdala (secondary
olfactory cortex), and the anterior olfactory nucleus. A second prerequisite
is that the olfactory test either detect the disease with more accuracy than
conventional tests or that it be faster to administer with equal accuracy. In
this context it is of interest to note that identification testing with the six-item
SDOIT (∼5 min) has shown an 83% correct classification rate (the ability of
the test to correctly classify subjects as healthy or diseased) for persons with
questionable AD and for controls. With the 40-item UPSIT (15–20 min), the
correct rate increased to 100% (Morgan et al., 1995).
Despite the need for further investigation into whether or not odor memory
is more affected than memory for other sensory modalities in AD, a few studies
have already compared odor memory and visual memory. Recognition memory
and familiarity (Nordin and Murphy, 1996; Niccoli-Waller et al., 1999) as well
as identification (Morgan et al., 1995) and semantic networks (Chan et al., 1998)
have been found to be more affected for odorous material than for visual material.
From our review of studies of odor memory, it appears evident that odor-
identification testing is a strong candidate for use in a battery of conventional
tests for early diagnosis of AD. Although it is tempting to suggest the use of
this test to clinical practitioners, more research is needed. In particular, this
includes direct comparisons on different odor-memory modalities (recognition,
identification, recall, etc.) in AD.
It is important to point out that olfactory changes have also been demonstrated
in other forms of dementia, the best documented being Parkinson’s disease,
Huntington’s disease, and Down’s syndrome. Attempts have been made to pro-
vide overviews of the research conducted on olfactory similarities and differences
in the various forms of dementia (e.g., Harrison and Pearson, 1989: Mesholam
et al., 1998; Murphy, 1999). However, far more research is needed before a clear
picture will emerge regarding the impairment patterns for different olfactory
functions and dementia causes. Such information will prove most valuable for
differential diagnosis.
Acknowledgments
Supported by NIH grants AG08203 and AG04085 (to Claire Murphy), by the
Bank of Sweden Tercentenary Foundation (1998-0270:01), and by the Swedish
Council for Research in the Humanities and Social Sciences (to Steven Nordin).
The excellent assistance of Anna Bacon Moore, Jodi Harvey, Samuel Jinich,
Stacy Markison, Charlie D. Morgan, Caprice Niccoli-Waller, and Jill Razani is
gratefully acknowledged.
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17
Development of Odor Naming and Odor
Memory from Childhood to Young Adulthood
Johannes Lehrner and Peter Walla
The early experiences of children have been of considerable interest in memory

research, because it is assumed that those experiences lay the foundation for
their later behavioral and cognitive development. Implicit in that assumption
is a capacity for long-term memory in children. Earlier, memories from the
first year of life had been characterized by some researchers as being short-
lived, highly generalized and diffuse, and devoid of place information (Nadel
and Zola-Morgan, 1984; Nelson, 1984; Olson and Strauss, 1984; Schacter and
Moscovitch, 1984; Mandler, 1990). More recently, however, there have been
reports of intact memory functions in infants and very young children, using
tests such as novelty-preference procedures, conditioning paradigms, auditory
localization, and deferred-imitation procedures (reviewed by Rovee-Collier and
Gerhardstein, 1997). Moreover, recent research indicates that young children
can accurately recall specific events after delays of weeks and even months.
Such long-term recall of events by young children would seem to depend on
the temporal relationships among the components of the event, the familiarity or
repeated experiencing of the event (Mandler, 1986), and the availability of cues
or remainders of the event (Bauer, 1997).
Several explanations have been proposed for developmental differences in
memory performance. The most important are different stores of resources in
short-term memory (Cowan, 1997), different uses of mnemonic strategies
(Guttentag, 1997), and different conditions of metamemory (Joyner and Kurtz-
Costes, 1997). Further, it has been argued that developmental differences in
memory performance may be attributable to age-related changes in the knowl-
edge base (Kail, 1990). Still, memory performance in recalling events is inferior
in children as compared with adults.
Memory functions in humans are not controlled by a single system. Rather,
memory can be divided into several different and independent subsystems that
278
Developmental Aspects of Olfaction 279
serve distinct functions and are characterized by fundamentally different rules of

operation (Tulving, 1985a,b; Sherry and Schacter, 1987; Squire, 1992). Evidence
for the independence of memory systems has come mainly from clinical studies in
which selective memory impairments have been reported (Tulving and Schacter,
1990). The distinction between memory based on conscious recollection (explicit
memory) and memory resulting from unperceived influences (implicit memory)
is fundamental. Explicit memory involves the capacity for conscious recollection
of names, places, dates, and events. In contrast, implicit memory encompasses
a variety of nonconscious abilities, including the capacity to learn habits and
skills and receptivity to priming and some forms of classic conditioning. A
defining feature of implicit memory is that the impact of experience is evidenced
in a change in behavior or performance, though the experience that led to the
change was not consciously accessible (Zola-Morgan and Squire, 1993). Recent
studies of childhood changes in memory performance have revealed evidence
for intact implicit memory but poorly developed explicit memory in children
(Graf, 1990; Mitchell, 1993; Naito and Komatsu, 1993; Parkin, 1997). That is,
studies of picture completion and word completion have reliably shown priming
effects (Parkin and Streete, 1988; Naito, 1990; Russo et al., 1995). Studies to
assess priming effects for recognition of faces revealed no apparent age effect
on the implicit measures, despite age-related improvements in explicit measures
(Lorsbach and Morris, 1991; Ellis, Ellis, and Hosie, 1993; Newcombe and Lie,
1995).
A considerable literature on odor perception in adults has been accumu-
lated, particularly for odor naming and odor memory (Engen, 1982; Schab and
Crowder, 1995). However, less attention has been paid to the developmental pro-
cesses of olfactory functions in children. In this chapter, we shall delineate the
current status of research on children’s olfactory functions. We shall start with
the development of odor naming and compare it to findings on the development
of visual naming. We shall consider odor-memory functions in children, and
recent findings in olfactory explicit/implicit memory will be discussed. Lastly,
we shall provide a framework to describe the development of olfaction from
childhood to young adulthood and suggest some new experimental approaches.
Before we go on, it is important to note that developmental differences be-
tween children and adults in odor naming and memory cannot be attributed to
sensory differences, because recent studies of olfactory sensitivity in children
have documented comparable olfactory thresholds in children and young adults
(Koelega and Köster, 1974; Perry et al., 1980; Cain et al., 1988, 1995; Dorries
et al., 1989; Solbu, Jellestad, and Straetkvern, 1989; Lehrner, Glück, and Laska,
1999a).
280 Johannes Lehrner and Peter Walla
1. Odor Naming
The literature on the development of childhood cognition in general, and nam-
ing in particular, has been reviewed by Schneider and Pressley (1989). One
method of testing naming capacity is by means of confrontation naming. Recent
neuropsychological data suggest that children have poorer naming capabilities
for common objects than do young adults (La Barge, Edwards, and Knesevich,
1986; Cain et al., 1995). With advancing age, that effect disappears because of
a steadily increasing lexicon.
For odor identification, which is a form of confrontation naming, similar
findings have been reported. Prior studies using the multiple-choice University
of Pennsylvania Smell Identification Test (UPSIT) found odor-naming perfor-
mance to be poorer in children than in young adults (Doty et al., 1985); however,
improvement was observed with increasing age from 4 to 17 years using both a
shortened version of the UPSIT (Richman, Wallace, and Sheehe, 1995) and the
University of California, San Diego, odorant-identification test with 20 common
odorants and corresponding pictures and names adapted for use with children
(Rothschild, Myer, and Duncan, 1995), In an odor-naming task with com-
mon household odors, similar results were obtained (De Wijk and Cain, 1994;
Cain et al., 1995; Lehrner et al., 1999a).
Taken together, the available studies document gradual improvements in odor
naming with increasing age. Because olfactory sensitivities are comparable for
different ages, the inferior naming ability probably is due to children’s poor
semantic knowledge of odors. Whether this is due to limitations in cognitive-
processing ability or to the fact that children will not have encountered odors as
often as young adults, and thus will not have acquired an extensive odor-name
lexicon, remains to be determined.
2. Stability of Odor Naming

The stability of odor-naming ability over time is a measure of retrieval/encoding
consistency. Similar naming stabilities in children and young adults would
suggest that cognitive operations for olfactory retrieval/encoding are also similar.
Recent research with young adults suggests that there is something less than
perfect consistency in label use after only a 10–15-minute time interval (Rabin
and Cain, 1984; Lehrner, 1993). The only developmental study comparing chil-
dren and young adults found inferior naming stability in children as compared
with young adults, indicating developmental differences in olfactory retrieving/
encoding (Lehrner et al., 1999a).
Consistency of label use and label quality
0
Young children Older children Young Adults
Figure 17.1. Numbers of consistently named odors across three age groups and
three classes of label quality. White bars illustrate veridical naming: anova
[F(2, 94) = 21.3; p < .001]; single Scheffe post-hoc comparisons were signif-
icant between young adults and both child groups (all pairs p < .001). The child
groups did not differ ( p > .9). Cross-hatched bars indicate near misses: anova
[F(2, 94) = 1.8; p > .16]. Black bars indicate far misses: anova [F(2, 94) =
0.9; p > .41]. (Data adapted from Lehrner et al., 1999a.)
For the purposes of this chapter, we analyzed the relationship between label
quality (i.e., how much prior information a participant had about an odor) and
consistency of labeling (Figure 17.1). Rabin and Cain (1984) reported a strong
association between the consistency of labeling and the quality of labels in
adults. As in the Rabin and Cain study, we found that veridical labeling produced
the highest number of consistently labeled odors after a retention interval of
10 minutes. Statistical analysis revealed that our three age groups differed only
for veridically named odors, with young adults performing best, whereas the two
child groups did not differ.
These results indicate that consistent use of odor labels is strongly dependent
on the quality of the label given to each odor, with veridical naming producing
the highest level of consistent naming. That effect was particularly evident for
the young adults, showing that if young adults had specific information about
odors available to them, they could use that information to retrieve the specific
odor name. In children, such consistency was still developing.
3. Explicit Memory for Odors

Memory research has documented the fact that explicit-memory performance im-
proves with age in terms of quantity and quality. This has been shown for differ-
ent explicit-memory procedures, such as free recall, cued recall, and recognition
Table 17.1. Mean olfactory performances for three age groups
Young childrena Older childrenb Young adultsc

Variable (n = 20) (n = 21) (n = 56)
Odor namingd 15.4 ± 5.5 17.7 ± 5.1 26.1 ± 6.3
Consistency of labelinge 4.2 ± 2.0 4.9 ± 2.2 6.8 ± 2.2
Hit rate f 0.78 ± 0.16 0.82 ± 0.16 0.86 ± 0.11
False-alarm rateg 0.22 ± 0.17 0.17 ± 0.14 0.12 ± 0.12
Odor memory (Pr)h 0.56 ± 0.25 0.64 ± 0.23 0.74 ± 0.19
Response criterion (Br)i 0.49 ± 0.22 0.53 ± 0.22 0.47 ± 0.20
a
Ages 4–8 years (mean 6.8 ± 1.2).
b
Ages 9–11 years (mean 9.6 ± 0.7).
c
Ages 18–30 years (mean 24.9 ± 2.7).
d
[F(2, 94) = 31.2; p < .001]. Single Scheffe post-hoc comparisons were significant
between young adults and both child groups (all pairs p < .001). The child groups did
not differ significantly ( p > .7).
e
[F(2, 94) = 16.9; p < .001]. Single Scheffe post-hoc comparisons were significant
between young adults and both child groups (all pairs p < .001). The child groups did
not differ significantly ( p > .5).
f
[F(2, 94) = 3.2; p < .05]. Post-hoc Scheffe tests showed that the hit rate was signi-
ficantly higher for young adults than for young children ( p < .03). No other differences
were statistically significant (all p > .5).
g
[F(2, 94) = 3.6; p < .03]. Post-hoc Scheffe tests showed that the false-alarm rate
was significantly lower for young adults than for young children ( p < .04). No other
differences were statistically significant (all p > .4).
h
Pr was derived by subtracting the false-alarm rate from the hit rate. [F(2, 94) = 5.8;
p < .005]. Scheffe post-hoc tests showed significant differences between the young
adults and the young-child group ( p < .008). Older children did not differ from younger
children ( p > .2) or young adults ( p > .2).
i
[F(2, 94) = 0.6; p > .5]. The response criterion (Br) was calculated after Snodgrass
and Corwin (1988). Accordingly, hit and false-alarm rates were corrected by adding
0.5 to each frequency and dividing by n + 1, where n is the number of old or new trials.
For the computation of Br, the transformed values were used. A value of 0.5 indicates
neutral bias, a value > 0.5 indicates liberal bias, and a value < 0.5 indicates conservative
bias.
Source: Adapted from Lehrner et al. (1999a).
memory, with several factors influencing memory performance, both in chil-

dren and in adults (Nelson, 1986). Younger children, as well as older children
and adults, show a consistent pattern of superior memory for ordered events as
compared with events that lack such relationships (Slackman and Nelson, 1984;
Hudson and Nelson, 1986; Slackman, Hudson, and Fivush, 1986; Ratner, Smith,
and Dion, 1986; Price and Godman, 1990). Familiarity, or repeated experiences
of an event, influences recall for young as well as older children. Repeated ex-
periences aid memory in terms of both the amount of information that can be
remembered (Fivush, 1984; Hudson, 1986, 1990) and the duration of memories
(Bauer, 1995). Reminding children of previously experienced events effectively
serves to preserve event memories over longer periods of time (Sheffield and
Hudson, 1994). Events of which children are verbally reminded at the time of
retrieval also are well recalled after long delays (Fivush, 1984; Fivush, Hudson,
and Nelson, 1984; Fivush and Hamond, 1990; Hudson, 1990; Hudson and Fivush,
1991). As discussed earlier, factors known to influence recall of events by chil-
dren also influence recall by adults, thus demonstrating considerable continuity
in mnemonic processes from young childhood to adulthood.
Studies of odor-recognition memory in children have rarely been performed.
Hvastja and Zanuttini (1989), using children from three different age groups
(mean ages 6 years, 8 years, and 10 years), found no association between odor
memory and pleasant or unpleasant pictures. Jehl and Murphy (1998), using the
child version of the California Olfactory Learning Test, documented better odor-
recognition memory and lower false-alarm rates for children aged 10–14 years,
as compared with children aged 8–10 years. Improved odor memory and lower
false-alarm rates for older children (mean age 9.6 years), as compared with
younger children (mean age 6.8 years), were also documented in another study
(Table 17.1). Interestingly, performances reached adult levels by the age of
10 years. For the hit rate, false-alarm rate, and response criterion, the same
conclusion can be drawn, indicating that 10-year-olds and young adults have
similar capacities for recognition of odors. In contrast, 7-year-olds had not yet
reached the adult processing level, although they did not differ for the response
criterion.
4. Implicit Memory for Odors

Recent memory research suggests that recognition of repeated verbal stimuli
may depend on two different memory processes: “familiarity” and “recollection.”
Familiarity judgments are made on the basis of a feeling, without specific infor-
mation about the encoding episode, and thus relate to implicit memory. Recollec-
tion is seen as an elaborate, conceptually driven process that includes retrieval of
contextual information and thus relates to explicit memory (Mandler, 1980).
A method to investigate implicit/explicit memory is the level-of-processing
approach, with a large body of evidence suggesting that different “levels” of
processing lead to different memory performances (Craik and Lockhart, 1972).
Semantic processing of words leads to good memory performance, whereas non-
semantic processing leads to rather poor memory performance (Craik, 1983).
Similar results have been obtained from odor-memory studies in young adults:
It was found that (1) if the correct labels were provided by the experimenter
(Lyman and McDaniel, 1986, 1990) and (2) the quality of self-generated labels
was high (Rabin and Cain, 1984) and (3) there was consistent labeling of odors
(Rabin and Cain, 1984; Lehrner, 1993), those factors could enhance odor memory
substantially, indicating that semantic processing of odors is important for re-
tention of odor memory (Schab, 1991; Herz and Engen, 1996).
In an attempt to distinguish between explicit memory and implicit memory for
odors in children, the combination of an odor-naming task and odor-recognition
task was used to estimate the relationship between the depth or level of processing
and retention of olfactory information (Lehrner et al., 1999b). Assuming that the
name of an odor represents its semantic information, correct naming of an odor
was interpreted as indicating a high (cognitive) level of processing. Odors that
could not be correctly named were believed to be processed at a lower and more
perceptual level. The applied analysis revealed different patterns depending on
age. Odors that were not correctly named revealed no age effect. Recognition of
odors that were correctly named depended strongly on age. The results indicated
two forms of odor memory differently represented from childhood to young
adulthood. Thus, the mechanism operating for odor-recognition memory may
be similar to that for verbal-recognition memory, where the level of processing
has a strong influence on memory performance.
5. Discussion and Perspective

As this review has shown, odor-naming capabilities progressively improve with
increasing age. Whether poor odor-naming performance in children is deter-
mined by limited cognitive-processing ability or by the fact that children have not
encountered odors as often as young adults, and thus have not acquired an exten-
sive odor-name lexicon, is not clear at present. However, several lines of evidence
indicate that poor odor-specific knowledge is responsible for poor odor naming.
In laboratory testing, children have steeper explicit paired-associate learning
slopes for names of odors than do young adults, even though they start from
a lower level of semantic knowledge of odors at the beginning. This indicates
that children possess the capacity to make appropriate odor–name associations
(Cain et al., 1995). In natural language acquisition, children add more words
per month to their vocabularies than do adults, and they probably possess the
capacity to learn more odor–name associations per month as well. However, ac-
cording to Engen and Engen (1997), who reviewed naturalistic language studies,
children are more concerned with the colors, sizes, and locations of objects than
with their smells, and there are virtually no examples of children spontaneously
using the perception verb “smell” to respond to odor experiences. In the future,
the exact acquisition speed for odor–name associations with naturally occurring
odors should be determined with naturalistic field studies and compared to per-
formances involving the other senses.
What determines odor-name acquisition in children? Is it the frequency of
encounters that offers more opportunities for learning, or is it the salience of spe-
cific odors? De Wijk and Cain (1994) and Cain et al. (1995) investigated that
issue, assuming that the frequency of occurrence in English usage reflects the
frequency of occurrence of items in everyday life. They found a significant posi-
tive correlation for odor naming and frequency in English usage, indicating that
the more their opportunities to experience the odors, the better the naming of
odors by children. Salience of odors seems to be less important, because children
and young adults showed reasonable similarities in their profiles for identifying
everyday olfactory items, indicating similar acquisitions.
Consistency of label use is inferior in children as compared with young adults.
Laboratory analyses have indicated that prior knowledge of the veridical odor
name determines the stability of naming to a large degree in adults, whereas
selection of labels of poor quality produces similar naming stabilities in children
and adults. Those results suggest some advantage in cognitive-processing ability
for young adults, probably because of greater familiarity with the odors.
Taken together, the data indicate that acquisition of verbal labels is incidental,
proceeding slowly (probably on a smell-by-smell basis) during child develop-
ment, and is strongly dependent on the opportunities children are offered and on
how well each child is encouraged to use those opportunities.
Odor memory gradually develops from childhood to adulthood, reaching an
adult level at the age of 10 years. Although their performance is inferior to that
of adults, children have already acquired a substantial odor vocabulary. They
are capable of using that semantic knowledge to encode olfactory information,
as evidenced by a significant positive correlation between odor memory and
stability of odor naming (Lehrner et al., 1999a), indicating the importance of
semantic encoding for odor memory in childhood. In future studies, it will be
important to compare recognition memory for odors with recognition memory
for other stimuli (e.g., pictures) in order to be able to compare different modalities
directly and to assess the specific influence of verbal encoding on memory for
olfactory stimuli compared with other stimuli in children.
A developmental odor-memory study has provided further support for the
implicit/explicit-memory dissociation in children, documenting a fully func-
tional implicit memory for odors and a still-developing explicit memory in
children, with the former probably based more on perceptual processing, and
the latter probably based more on semantic processing. Thus the hypothesis of
distinct implicit memory and conscious or explicit memory in children can be
extended to the olfactory modality.
Further developmental studies to investigate implicit memory for odors

(e.g., priming studies) are needed, because recent reports have demonstrated (1)
the importance of perinatal and postnatal olfactory information (Schaal et al.,
Chapter 26, this volume) and (2) the influence of neonatal experience with vanilla
on food preferences later in life (Haller et al., 1999), indicating that implicit
olfactory learning takes place in children.
Acknowledgments
Peter Walla was supported by the Austrian Science Fund and partly by the
Austrian National Bank. We would like to thank Dr. Ross Cunnington for helpful
comments on the manuscript.
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Section Five
Neural Bases
As discussed in Sections 3 and 4, olfactory and gustatory cognitions have close

links to emotion and memory, from both the psychological and physiological
points of view. The chapters in this section will complement the preceding stud-
ies and focus on the neural bases supporting the neural code and chemical-sense
cognition, while most often taking into account these emotional and memory di-
mensions. In Chapter 18, Gilles Sicard reviews recent findings on neuroreceptor
identification and the patterns that have emerged in the neural representation of
odors at the level of neuroreceptors and the olfactory bulb, emphasizing a po-
tentially important role for neural assemblies in odor detection and recognition.
The chapters in this section deal with phenomena observed over different
time scales and under different experimental conditions, varying from one study
to the next, and the concepts of neural dynamics are not always easy to fol-
low. Several sets of data presented in the following chapters will illustrate this
point. For instance, in Chapter 19, Bettina Pause examines the effects of cog-
nitive dimensions such as attention, habituation, and short-term memory on the
characteristics of olfactory-related evoked potentials recorded from the scalp
in humans. She reports on pronounced modulations of some evoked-potential
components occurring within the first second after stimulus onset. In Chapter 20,
Robert Zatorre reviews the findings on the contributions of functional imaging
studies to our understanding of the processing of olfactory affective information.
Using deep local-field potential recordings in freely behaving rats, Nadine
Ravel and colleagues, in Chapter 21, study the impact of olfactory learning
on information processing at different levels of the olfactory pathways. For
instance, it was found that, on one hand, habituation over a 1-min period to
repeated olfactory presentations and, on the other hand, associative learning,
which developed over weeks, could both strongly modify neural responses to
stimuli. They report on the efficiency of synaptic transmission and the strength
of functional coupling as revealed by oscillatory activities in neuron assemblies
292 Section 5: Neural Bases
recorded at the level of the primary olfactory cortex and in plurimodal areas such
as the entorhinal cortex.
Within the same conceptual perspective, Annick Faurion and colleagues ex-
amine how familiarization to repeated presentations of novel tastes can modulate
neural reactivity, as can aversive conditioning. Such experiences are accompa-
nied by changes in neural responses both at the periphery of the gustatory system
in animals and in the primary gustatory centers in humans.
In Chapter 23, Edmund Rolls provides strong evidence that internal states such
as food repletion and depletion induce modulation of single-cell responsiveness
in primates at the level of the orbitofrontal cortex. That plurimodal associa-
tive structure is also found to be a convergence site for gustatory and olfactory
information, taking into account the consequences of long-lasting associative
learning. These chapters will illustrate in both animals and humans how recent
and remote experiences determine neural responses to odorants and tastants at
several central stages of information processing.
18
Odor Coding at the Periphery
of the Olfactory System
Gilles Sicard
During the past decade, scientists have identified a large number of genes coding
for olfactory receptor proteins in vertebrates, including humans, and in insects
and nematodes (Buck and Axel, 1991; Selbie et al., 1992; Sengupta, Colbert, and
Bargmann, 1994; Gao and Chess, 1999; Clyne et al., 1999). Much earlier, such
entities had been hypothesized to exist, probably on the intuition that the nature of
an odor was not “ethereal” but rather a material part of the odor source (Lucretius,
De rerum natura, IV) and thus could interact directly with the detecting organism.
During the twentieth century, that concept was commonly used by physiologists
to discuss the coding of odors (Zwaardemaker, 1925; Guillot, 1948) and by
pioneer chemists who postulated receptive sites for odor molecules (Amoore,
1967; Beets, 1982). Its recent implementation in identifying receptor proteins
has emitted a “strong scent of success” (Lancet, 1991). However, when the data
from molecular biology and the physiological properties of the olfactory system
are compared, it becomes clear that the final word has not yet been spoken on
olfactory coding.
When olfactory signals are detected and differentiated, they gain behavioral
significance when recognized as representing particular odor sources. In terms
of neurophysiology, such processes require highly organized neuronal circuitry,
and an important finding in recent studies of receptor proteins is that the receptors
themselves are involved in determining the neural space devoted to representa-
tion of the chemical environment. This chapter will describe anatomical and
functional aspects of the olfactory message in the peripheral olfactory system of
vertebrates, that is, features of the sensory neurons located in the olfactory mu-
cosa and their projections to the glomeruli and the second-order neurons of the
olfactory bulb. The output message of the olfactory bulb will also be considered.
Receptors recognize, and olfactory cells respond to, defined sets of molecular
stimuli, to which we refer, using terminology borrowed from visual physiology,
as “molecular receptive fields” (Mori and Shepherd, 1994). Molecular receptive
293
294 Gilles Sicard
fields are not definable spatially, and in defining them we must content ourselves
with selectivity profiles obtained from testing a limited sample of odorants. In
addition, we know that knowledge of the specificity of the receptors alone, with-
out an understanding of their relationships to one another, leaves our description
of the proximal part of the olfactory system incomplete. Although a comparison
of data from recent advances in the molecular biology of olfactory receptors and
data from electrophysiological characterization of the olfactory receptor neu-
rons reveals some contradictory elements, the rough sketch seems coherent and
provides a basis from which to further understand olfactory perception and to
suggest important ideas and new experiments.
1. Receptors for Odorants

1.1. Olfactory Receptor Families and Specificity
Olfactory receptors selectively respond to environmental signals and represent
a form of structural memory. As a result of evolution, several hundred receptors
have been selected for olfactory discrimination in vertebrates. They were dis-
covered by scientists working on the assumption that they would belong to the
G-protein-coupled receptor family, would have seven trans-membrane domains,
and would show a certain degree of homology in their amino acid sequences.
The genes coding olfactory receptors constitute the largest known gene family,
and in fact the largest family contributing to a single physiological function.
However, on the basis of differences in their amino acid sequences, they can be
grouped into subfamilies.
Whereas orthologous genes (i.e., genes with nearly identical sequences and
functions) are found across different animal species (Krautwurst, Yau, and
Reed, 1998), the total repertoire of genes available for olfactory receptor cod-
ing varies among species. For instance, in the rat, a repertoire of 1,000 genes
has been estimated (Buck and Axel, 1991). The number of genes is more
restricted for fish and, for example, has been estimated at about 100 for cat-
fish (Ngai et al., 1993). In humans, the repertoire is also smaller, believed to be
between 200 and 750 (Ressler, Sullivan, and Buck, 1994; Mombaerts, 1999).
Interestingly, half of these are pseudogenes, which cannot encode a complete
functional receptor, thus suggesting that the human olfactory receptor reper-
toire represents a phylogenetic decline in the sense of smell (Rouquier et al.,
1998; Sharon et al., 1999). In the dolphin Stenella coeruleoalba, which has no
sense of smell, only nonfunctional pseudogenes have been found (Freitag et
al., 1998). Although we have no direct evidence of this, the level of olfactory
gene expression may vary between individuals of a given species, including
Peripheral Odor Representation 295
humans. Suggestive evidence comes from studies demonstrating differences be-

tween individuals in olfactory detection thresholds, and particularly from studies
on specific hyposmia that reveal substance-specific olfactory deficits in some
subjects.
Further, it has been shown in mice, rabbits, and humans that repeated pre-
sentations of an odorant are able to increase behavioral sensitivity to it, and in
mice and rabbits that the electrophysiological response of the olfactory mucosa
to the odorant is concomitantly increased (Wysocki, Dorries, and Beauchamp,
1989; Wang, Wysocki, and Gold, 1993; Semke, Distel, and Hudson, 1995). This
observation is consistent with an exciting hypothesis: that the level of olfactory
gene expression may depend on the chemical environment.
A first dimension of receptor specificity related to animal ecology is the par-
titioning of olfactory stimuli in hydrophilic and lipophilic chemicals. Indeed, it
has been shown that aquatic vertebrates express an olfactory receptor subfam-
ily, class I, that differs structurally from class II, found in terrestrial animals.
Interestingly, amphibians express both classes (Freitag et al., 1998).
Regarding their chemical selectivity, most olfactory receptors currently must
be considered to be orphan receptors, as we do not know their ligands. However,
different approaches have been developed to describe their ranges of chemical
selectivity, and further investigations are in progress (Raming et al., 1993; Zhao
et al., 1998; Krautwurst et al., 1998; Touhara et al., 1999). In a few cases, trans-
fections of olfactory receptor genes have been shown to confer chemosensitivity
on different host cells. Thus, in the rat, overexpression of gene I7 in the olfactory
mucosa enhanced the electrical responses to a small number of the 74 substances
tested (i.e., to linear C7–C10 saturated aldehydes), with the best response to oc-
tanal (Zhao et al., 1998). Interestingly, in the mouse, an orthologous receptor
responded best to heptanal, differing in the putative receptor pocket only by an
isoleucine (6-carbon) residue in place of a valine (5-carbon) residue (Krautwurst
et al., 1998). Such tight specificity is also illustrated by the OR17-40 human
receptor, which was reported to recognize only 1 of the 100 odorants tested
(Hatt, Gisselmann, and Wetzel, 1999).
Those observations seem to suggest that each odor receptor is tightly tuned
to a limited set of structurally related molecules. In contrast, another study of
mammalian olfactory receptors concluded that a given receptor recognized dif-
ferent molecular species (Malnic et al., 1999), although the structural difference
between the molecules tested was a change in only a single functional group.
The same study indicated that a given molecule could interact with several re-
ceptors. Thus, combinatorial coding of chemical stimuli may be occurring at the
receptor level, a form of coding that previously had been attributed to the neural
representation of odor stimuli only at the sensory neuron level!
296 Gilles Sicard
1.2. Receptor Distribution

With regard to olfactory coding, two kinds of distributional questions are of
interest: (1) How many different receptors are expressed by a given receptor
neuron? (2) Is there a spatial patterning of the receptors in the olfactory mucosa?
Because only 0.1% of olfactory neurons were found to express a particular
receptor gene in a repertoire evaluated to approximately 1,000, each neuron
presumably expresses only one receptor type (Nef et al., 1992; Strotmann et al.,
1992; Ressler et al., 1993). That assumption is consistent with allelic inactivation
of olfactory gene expression (Chess et al., 1994) and with results from studies in
which mRNAs from single olfactory neurons have been amplified (Malnic et al.,
1999; Touhara et al., 1999). However, on the basis of single olfactory cell mRNA
amplification and in situ hybridization, a recent study indicates that two different
mRNA receptor sequences can be expressed by small samples of receptor neurons
(Rawson et al., 2000). How many receptors can be expressed by a single olfactory
neuron? That, together with the question of the specificity of receptor–ligand
interactions, is a critical issue for understanding the nature of signal encoding by
the olfactory system. Assuming tightly tuned receptors and exclusive expression
of a single receptor type by a given cell, the system could simply operate by
labeled lines. On the other hand, broad receptor tuning, or alternatively, mixed
expression of receptors in one neuron, would necessitate that the stimulus be
represented by an across-fiber pattern of activation. Because the stimulus itself
is generally a combination of odorant molecules, a combinatorial representation
by several receptors seems a valid model for thinking about olfactory coding
more generally.
The second question is whether or not there is a spatial pattern of recep-
tors in the sensory sheet and whether or not that would be of advantage for
olfactory coding. A heterogeneous distribution of odorant receptors has been
shown in the olfactory mucosa in mammals. Thus, in rats, neurons expressing
mRNA of a given receptor appear to be restricted to four large zones extending
in roughly parallel bands along the anteroposterior axis of the olfactory sensory
sheet. Within those zones the distribution of receptor types appears to be random
(Ressler et al., 1993; Vassar, Ngai, and Axel, 1993), although OR37 is appar-
ently restricted to a smaller area, suggesting a different type of control for its
spatial expression (Strotmann et al., 1999). Contrasting with the former data,
such regional segregation is not found in chickens or fish (Leibovici et al., 1996;
Vogt et al., 1997), where the repertoire of olfactory receptors is possibly 10 times
smaller. Nevertheless, specific changes in sensitivity to odorants across the ol-
factory mucosa have been recorded, both in rodents and in amphibians (Daval,
Leveteau, and MacLeod, 1970; Mackay-Sim and Kesteven, 1994), which could
be a consequence of receptor segregation. It remains to evaluate the implications
of the particular spatial arrangement for olfactory coding. The data suggest at
least two comments: (1) Apparent differences among species would seem to im-
ply that peripheral odor coding principles vary among vertebrates. (2) In other
respects, as partial obstructions of the turbinates by mucus can frequently oc-
cur, the spatial representation of a given chemical can change, and the role of a
peripheral chemotopy in odor representation remains questionable.
1.3. Receptor Neuron Projections

The discovery that olfactory receptor mRNAs are also expressed in the axons
and terminals of the sensory neurons has shed new light on another topographic
aspect of the olfactory coding system. The olfactory mucosa of the rat or mouse
contains millions of sensory neurons, which send their axons to the olfactory bulb
to reach about 2,000 glomeruli. The glomeruli are well-delineated anatomical
structures. They are the sites where the receptor neurons synapse with dendrites
of the secondary neurons (i.e., the mitral and tufted cells) and with dendrites of
local interneurons such as the periglomerular cells. The primary dendrites of
only about 20 secondary neurons contribute to an individual glomerulus. Conse-
quently, there is a strong convergence of the receptor neurons on (1) the glomeruli
and (2) the secondary neuronal population (Figure 18.1).
As shown by in situ hybridization studies in rats and mice, neurons expressing
a given receptor project to just two glomeruli, one on the lateral aspect and one
on the medial aspect of the olfactory bulb (Ressler et al., 1994; Vassar et al.,
1994; Strotmann et al., 1994). Thus, in addition to the numerical convergence,
there is a functional convergence based on receptor type, meaning that the total
activation of a given receptor type is collected in the glomerular layer, resulting
in an amplification of the stimulus. The patterns of projections are similar across
individuals. In other words, the pattern of glomerular activation can be considered
as a topographically organized map of the receptors activated. The mechanisms
leading to that highly organized pattern of projections are not known, but it
has been suggested that receptor proteins could serve as surface signals in the
process of finding the target glomeruli, although other kinds of signals may
also operate, such as morphogen gradients, which are generally considered to
provide an explanation for axon targeting (O’Leary, Yates, and McLaughlin,
1999; Matsuzaki et al. 1999).
In mice, receptor neurons expressing P2 gene products converge on a pair
of glomeruli. When the P2 receptor is exchanged with the M12 receptor, the
sites of convergence shift, suggesting that the receptors themselves are involved
in the axonal guidance (Mombaerts et al., 1996). Whereas glomerular conver-
gence is precise in intact animals, following lesions of the olfactory nerve and
298 Gilles Sicard
OLFACTORY MUCOSA OLFACTORY BULB OLFACTORY BULB

DS
DP M
Gl
Gr
PG
Gl
Gr
PG
PG
Gl
Figure 18.1. Olfactory receptor convergence rule and glomerular units in the
olfactory bulb. Receptor neurons expressing a single receptor type (plain cir-
cles) are widely distributed in the olfactory mucosa. Their axons converge onto
one or two glomeruli (Gl) in the olfactory bulb, where they form excitatory
synapses with the primary dendrites (DP) of the relay neurons of the olfactory
bulb mitral cells (M) and tufted cells. In the rat, a given relay neuron contacts
only one glomerulus. Associated with a glomerulus are the dendrites of the
periglomerular cells (PG), a first group of local interneurons that are also acti-
vated by the receptor neurons. They exert an inhibitory influence on neighboring
glomeruli. Deeper in the bulb the secondary dendrites (DS) of the relay neurons
spread radially (diameter 800 µm) and synapse with a large number of granu-
lar cells (Gr), the second group of local interneurons. In addition, the granular
cells receive collaterals of mitral/tufted cell axons, with the mitral–granular cell
circuits forming feedback loops.
regeneration the target of the regenerating sensory axons is no longer so well

defined (Hudson, Distel, and Zippel, 1990; Costanzo, 2000). As a consequence,
the spatial representation of odors in the olfactory bulb should be modified. That
could explain why deficits in olfactory sensitivity (hyposmia) following nasal
viral infections in humans often are associated with alterations in the perceived
quality of stimuli (parosmia).
2. Functional Data
By means of direct recordings of the responses of receptor neurons, the structure
of the transmitted message emerging from receptor–odorant interactions can be
revealed.
2.1. Receptor Neuron Responsiveness

The selectivity profiles for olfactory receptor neurons in amphibians were char-
acterized early in a number of studies (Gesteland et al., 1963; Duchamp et al.,
1974), which showed that by considering only the output of a single receptor
neuron, the stimulus could not be unambiguously defined. More recently, elec-
trophysiological recordings have shown that the receptor neurons are able to
respond to structurally different molecules, including aliphatic, aromatic, and
spherical structures. For instance, in the frog, olfactory receptor neurons re-
sponded, on average, to 7 of 20 stimuli, although a significant percentage (19%)
failed to respond to any of those (Sicard and Holley, 1984). Some of the nonre-
sponding neurons, however, could have been tightly tuned and thus responsive to
odorants not included in the test sample. Such neurons could express receptors
as tightly tuned as that described by Zhao et al. (1998).
Although receptor neurons have been found to be more selective in the mouse
than in the frog (Sicard, 1986), they can nevertheless respond to several struc-
turally different odorants (Figure 18.2). Broad selectivity profiles for olfactory
receptor neurons have been confirmed by recent investigations in the mouse
and rat (Sato et al., 1994; Bozza and Kauer, 1998; Duchamp-Viret, Chaput, and
Duchamp, 1999). If it is assumed that only one receptor gene is expressed by
a given receptor neuron, then it should follow that some of the receptors have
broad selectivity. The problem remains that whereas most direct investigations
of receptor function suggest a high selectivity, narrow tuning is not consistent
with the bulk of the physiological data. Is it possible that the extreme sensi-
tivity of the olfactory transduction mechanisms is difficult to reproduce in host
cells? If that should be the case, then we need to consider that besides the best
ligand, other odorants may also activate the receptor, but with less efficiency.
The assumption that other types of receptors co-exist with the identified hepta-
helical receptor family constitutes an alternative hypothesis to explain the actual
molecular receptive field of the olfactory receptor cells (Gibson and Garbers,
2000).
2.2. Activity in the Bulbar Glomeruli

The olfactory glomerulus, containing no cell bodies but only fibers, is anatom-
ically an isolated structure: Locally released factors might diffuse and exert
influences over the whole glomerular neuropil, and thus the function of a given
glomerulus could be controlled independently of its neighbors. Glomeruli were
very early considered to be functional units (Leveteau and MacLeod, 1966). In
the rat, indirect evidence for that was provided by the finding that the responses
of the bulbar output neurons of a given glomerulus tended to be more similar
300 Gilles Sicard
CH3
O
e neo e
m
en xan l non
y e o a
-c le h an pt
a ra niso yclo ept -he
p a c h 2
C1 anisole
para-cymene
C2
O
C3
cyclohexanone
C4
C5
C6
heptanol OH
C7 O
2 heptanone
Figure 18.2. Responses of olfactory receptor neurons in the mouse. Upper

part: Electrophysiological response of a receptor neuron to 2-heptanone
(horizontal bar: 2-sec stimulation) recorded in an anesthetized mouse. Lower
part: Examples of the structural diversity of the molecules recognized by seven
receptor neurons recorded in the mouse. The large dots indicate an increase in
the firing rate following chemical stimulation, and the small circles the absence
of response to the stimulus: para-cymene, citrusy odor; anisole, powerful and
harsh, very sweet odor, rather chemical; cyclohexanone, minty-camphoraceous,
cool and solvent-like odor; heptanol, green-fatty, winey, and sap-like odor;
2-heptanone, fruity-spicy, light and volatile odor (Arctander, 1969).
to each other than to those of output neurons of different glomeruli (Buonviso

and Chaput, 1990). Thus, assuming that converging receptor neurons express
identical receptors, the glomeruli should have a homogeneous and unique input
as well as a homogeneous and unique output.
In fact, local neuronal circuits and centrifugal fibers from distant areas of the
brain modulate the activity of the output neurons. The first group of interneu-
rons is composed of the periglomerular cells, which are distributed around the
glomerular neuropil. They form inhibitory feedback loops with mitral/tufted cells
and also inhibit neighboring glomeruli via their short axons. These connections
tend to decrease activity in the proximity of activated glomeruli and are thought
to enhance the contrast between highly activated glomeruli and their neigh-
bors (Duchamp and Sicard, 1984a; Young and Wilson, 1999). These inhibitory
circuits may also serve to protect the olfactory system against saturation during
intense stimulation and to preserve, or further enhance, the signal-discrimination
ability at that level (Duchamp-Viret, Duchamp, and Sicard, 1990). As the sec-
ondary dendrites of mitral cells can extend over large areas (Mori, Kishi, and
Ojima, 1983) and support mitral–granular cell loops, we can also suppose that
the connections take part in shaping the representation of the stimulus linking
more distant glomeruli.
As observed in 2-deoxyglucose studies, the spatial patterns of glomerular ac-
tivation elicited in the olfactory bulb by single substances are extensive, which
appears to confirm – considering the rule by which the receptor neurons project
to the bulb – that a given chemical can interact with a large number of receptor
types. The 2-deoxyglucose method has also revealed a further type of conver-
gence involving neighboring glomeruli. For instance, stimulation with propionic
or isovaleric acid results in 2-deoxyglucose labeling of several glomeruli in a
circumscribed zone of the dorsomedial olfactory bulb (Slotnick et al., 1987;
Sicard, Royet, and Jourdan, 1989; Johnson et al., 1999), and an activation of
neighboring glomeruli by structurally related molecules has also been reported
in a recent optical recording study (Rubin and Katz, 1999). On the other hand,
because the glomerular targets of neurons expressing a given receptor are found
twice – one on the medial and one on the lateral side of the bulb – rules other than
receptor-based convergence must operate to organize the distribution of input
fibers to the glomerular layer.
The glomerular activation map is a highly structured representation of the
stimulus. Nevertheless, interactions between glomeruli (i.e., receptor inputs)
have been shown. Thus, even if epithelioglomerular convergence depends on
receptor specificity, the spatial representation of an odor in the glomerular layer
cannot be simply reduced to a list of activated receptor types.
2.3. Selectivity Profiles of Mitral Cells

Assuming that tangential intra-bulbar connections exert only modulatory influ-
ences, the selectivity of the secondary neurons should derive directly from that
302 Gilles Sicard
of the afferent receptor neurons. Indeed, the selectivity profiles of mitral/tufted

cells do not differ markedly from the selectivity profiles of the receptor neurons,
despite additional bulbar processing (Duchamp and Sicard, 1984b). In the frog,
we found the selectivity profiles of mitral cells to be similar to those of the re-
ceptor neurons, that is, neurons in the olfactory bulb were activated, on average,
by 6.4, and in the olfactory mucosa by 8.2, of the 19 odorants tested (Duchamp,
1982; Revial et al., 1982).
Similar observations have been reported in mammals, in the rabbit (Chaput
and Holley, 1985), and in the rat, in which, for instance, single mitral cells
were found to respond to limonene, carvone, amyl acetate, ethyl butyrate, and
ethyl acetate (Wellis, Scott, and Harrison, 1989). More recently, Motokizawa
(1996) observed that 69% of the secondary neurons recorded in the olfactory
bulb of the rat responded to all 5 of the 5 odorants delivered and concluded
that mitral/tufted cells respond to a broad spectrum of odorants. Once again, the
chemical structures of the 5 effective stimuli (acetophenone, limonene, isoamyl
acetate, 6-methyl-5-hepten-2-one, and butyl alcohol) were very different. If the
convergence rule for the peripheral fibers is valid, the broad chemical range in
the selectivity profiles for the secondary neurons would seem to confirm broad
response profiles in the afferent receptor neurons.
3. Use of Neural Space in Odor Coding

Because of the broad response profiles for individual receptor neurons, the re-
sponse of one neuron alone would not be able to distinguish between stimuli
belonging to its profile, and thus to discriminate stimuli would require that
groups of fibers from different receptor types be activated. Consequently, the
specificity of the transmitted message should be represented by an assembly of
neurons. Taking the selectivity profiles for single neurons into account, at the
single-neuron level the peripheral message is only slightly altered by bulbar pro-
cessing. From the olfactory bulb, a multifiber representation (i.e., an across-fiber
pattern) of the stimulus is transmitted to cortical levels via the output neurons.
The discrimination ability of the transmitted message is conserved across large
concentration ranges (Van Drongelen, Holley, and Doving, 1978; Duchamp-Viret
et al., 1990).
Theoretically, to represent olfactory stimuli adequately, no additional proper-
ties of the message need to be invoked other than the convergence of receptor
types in the glomerular layer and the spatial dimension that implies. As men-
tioned earlier, a peripheral across-fiber pattern would lead to the activation of
a glomerular assembly, resulting in amplification of receptor input and in an
increase in the signal-to-noise ratio. Conceptually, that would mean that the
treatment of the olfactory information would be massively parallel. Besides

amplification, the neuronal arrangement would favor the integration of receptor
inputs by means of lateral and modulatory feedback mechanisms, which would
result in the treatment of incoming information according to its spatial and tem-
poral properties. Some aspects of the spatial treatment have been mentioned
earlier, and increasing efforts are being made to address the temporal aspects
(Adrian, 1942; Freeman, 1978; Laurent et al., 1996). In many animal species the
oscillatory behavior of the bulbar network is a major indicator of the temporal
dimension of olfactory coding (Delanay et al., 1994; Stopfer et al., 1997; Kay
and Freeman, 1998; Kashiwadani et al., 1999; Kay and Laurent, 1999; Buonviso
et al., 2001; Lam et al., 2000). It can be affected by selective attention, learn-
ing, and memory (Freeman and Schneider, 1982; Stopfer and Laurent, 1999;
Chabaud et al., 2000; Ravel et al., Chapter 21, this volume) and thus indicates
already at the periphery high-level processing of the sensory information.
Considering the lack of effect of large bulbar lesions on olfactory-guided be-
havior (Hudson and Distel, 1987; Slotnick et al., 1987; Lu and Slotnick, 1998),
and assuming that such lesions dramatically modify the spatial representation
of chemical stimuli, some degree of flexibility must be added to the concept of
spatial coding. Thus, one might consider redundancy to account for the limited
effects of bulbar lesions. Such redundancy clearly would be supported by the
broad selectivity of the olfactory receptors and parallel inputs. That, in turn,
leads to the question whether or not amplification is the only role for glomerular
convergence. Probably not; for instance, spatial convergence could contribute to
the stabilization of the neural representation of odors during the turnover of the
receptor neuron population. Nevertheless, confirmation of a functional role for
the spatial distribution of information in the olfactory glomerular layer and, sub-
sequently, in the bulbar output neurons needs more experimental investigation.
The notion of a neuronal assembly as a prerequisite for detection and discrim-
ination of odor stimuli by the olfactory system – especially by synchronization
of activations – is opening up an important area of investigation. The olfactory
system is able to distinguish between elements simultaneously present in the
olfactory scene, distinguishing foreground from background, describing traits or
components of odorous sources, and exploring temporal clues in the olfactory
environment. In that regard, a basic task might be the formation of associations
between receptor types signaling the smell of a particular object. Although the
extraction of such information could be performed more centrally in the olfactory
system, some of the features of odor coding at the input level and in the olfactory
bulb network that would be prerequisites for that have already been mentioned.
Thus it seems, given the broad selectivity profiles for receptor neurons, that
the strategy of the olfactory system does not consist in developing receptors and
304 Gilles Sicard
corresponding labeled lines for each odor stimulus. Rather, with every stimulus
the system is required to perform pattern recognition. The multiplicity of the
receptors can be considered as an adaptation to the discontinuity of olfactory
stimuli, involving a vast number of shapes that cannot be represented by a small
number of physical dimensions. The analysis of the peripheral olfactory system
to date indicates that a combinatorial strategy operates at all levels, including
receptor selectivity and across-fiber patterning. This is most probably necessary
to ensure high adaptability in olfactory coding; that is, for any odorant, whatever
its origin or however new it may be, a specific – spatial and temporal – neural
representation can be “formed.”
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19
Human Brain Activity during the First Second
after Odor Presentation
Bettina M. Pause
Voltage fluctuations above the intact human scalp are called chemosensory event-
related potentials (CSERPs) (Evans et al., 1993) when these variations are caused
by experimental manipulations of odor presentations. CSERPs function as in-
dicators of the speed, strength, and local distribution of neuronal brain activity
related to odor perception. CSERPs are very time-sensitive, which allows odor
perception to be separated into different processing stages within the first second
after odor presentation (Pause and Krauel, 2000). The aim of this chapter is to
describe the biological and psychological meanings of the different processing
stages. Between 300 and 500 msec after odor presentation, the specific features
of the olfactory environment are encoded. This process is accompanied by a
first distinct wave that appears within the CSERP; it is negatively charged and
therefore is called the N1 component. The N1 component seems to reflect a pre-
attentive level of stimulus encoding, but also depends on the level of the subject’s
alertness. The next prominent wave within the CSERP is the positively charged
P3 component, appearing between 700 and 1,200 msec after odor presentation.
Like the N1 component, the P3 is sensitive to the attentional investment of the
subject, but in addition it is sensitive to the probability of the odor occurrence
and to the subjective significance of the odor. The extraction of the significance
of the olfactory event is an evaluative process that depends on cognitive and
emotional resources. Within this process, the olfactory information is compared
to earlier olfactory experiences stored in short- and long-term memory, and its
specific importance for the subject is identified.
This chapter aims to show the usefulness of CSERP analysis in understanding
odor processing. In the first part, CSERP indicators of the mechanisms involved
in general odor perception are presented. In the second part, a description of
how CSERPs might help to explain individual differences in odor perception
is given. As odor perception varies considerably between and within subjects,
the perception of odors will be understood as a function of the individual rather
309
310 Bettina M. Pause
than as a function of the odor itself. Within this model, differences in olfactory
perception between subjects can be explained by biological and psychological
traits, personal characteristics that remain stable over time. On the other hand,
differences in odor perception within one subject can be explained by his or her
biological and psychological state (i.e., the internal circumstances in the specific
situation).
1. The CSERP as an Indicator of General Odor Perception

About 400 msec after an odor presentation, a first wave appears within the
CSERP, called the N1 component (Figure 19.1). In response to an auditory or
visual stimulus, the N1 usually appears much sooner (e.g., 100–150 msec after
presentation) (Näätänen and Picton, 1987). Therefore, its late appearance at
about 400 msec seems to be a characteristic unique to the olfactory modality.
However, a possible explanation for the late brain response is the finding that
N1
N2b ?
N2a ?
P3a ?
P2 P3b
Odor
0 0.4 0.6 0.8 1.0 [s]
Stimulus encoding Stimulus decoding

selective attention selective attention
odor concentration expectation
odor quality odor meaning
Figure 19.1. The components of the CSERP and their relation to stimulus
encoding and decoding. This fictitious example does not refer to a real-case
CSERP, but resembles a true CSERP in its time structure. The components
are measured in microvolts and usually are detected in a voltage range from
1 to 20. Whereas the olfactory N1, P2, and P3b have been at the focus of CSERP
research, further investigation will be required to understand the functional
significance of the olfactory N2 and P3a.
The First Second after Odor Presentation 311
the olfactory receptor neuron responds to olfactory stimulation with a latency of

about 300 msec (Firestein and Werblin, 1989). The N1 component in response to
acoustic stimuli comprises several subcomponents (Näätänen, 1992) and varies
with stimulus characteristics (e.g., stimulus intensity) as well as with the internal
conditions of the subject (e.g., selective attention).
In CSERP research it is still a matter of debate whether or not the amplitude
of the N1 component varies with odor concentration. One of the difficulties is
choosing a relatively pure olfactory stimulus that does not activate the trigeminal
system (Hummel, 2000). So far, three studies using olfactory stimulants have
been conducted. Thiele and Kobal (1984) and Pause, Sojka, and Ferstl (1997)
found that the latencies of the CSERP decreased with increasing stimulus con-
centrations, whereas the amplitudes were unaffected by concentration changes.
Pause et al. (1997) concluded that olfactory concentrations are encoded as qual-
itatively different stimuli and thus do not activate a stronger neuronal response.
Those conclusions are supported by measurements of peripheral (Firestein and
Werblin, 1989) and central (Cinelli, Hamilton, and Kauer, 1995) olfactory trans-
duction, as well as by subjective rating data (O’Connell, Stevens, and Zogby,
1994). A more recent study (Tateyama et al., 1998) also found a strong effect
of odor concentration on the latencies of the CSERP. As expected, those effects
were strongest for the early components of the CSERP (e.g., the N1 component).
However, they did find a weak effect of odor concentration on the amplitudes of
the early CSERP components and a stronger effect on the late P3 component.
An effect of stimulus intensity on the P3 component had previously been shown
for auditory stimuli (Roth et al., 1980). That effect can be seen when very large
concentration differences are used and can be explained as the processing of a
higher subjective stimulus significance for very intense stimuli. A fourth very re-
cent study examined CSERPs in response to different concentrations of isoamyl
acetate (Covington et al., 1999). Even though that odor may also have trigem-
inal effects, the concentrations applied were below the threshold for irritation.
Again, only the latencies (P2, N2) decreased with higher stimulus concentra-
tions, and no tendency for the amplitudes to vary with odor concentration was
found. Summarizing, all studies so far have underlined the importance of tem-
poral characteristics in olfactory concentration encoding. Similarily, the most
promising way to differentiate odor quality by means of CSERP research seems
to be to analyze the latency differences within the N1 latency window. In a very
recent study (Pause et al., 1999d), we found a very reliable effect of odor quality
on the N1 latency that could be seen in each of 46 subjects. All of them responded
earlier to the odor of phenylethyl alcohol (rose) than to the odor of isobutyralde-
hyde (rancid butter). As the odors were rated as being equally intense (Pause and
Krauel, 2000), that effect was not due to concentration differences. However,
as isobutyraldehyde may also have activated the trigeminal nerve, those latency
differences may have resulted in part from activation of different transduction
systems. The importance of temporal characteristics in odor quality coding is
supported by studies indicating that identification of odorants in mixtures may
depend on the speed of perception of the single substances (Laing et al., 1994).
Recently, Lorig (1999) even speculated that the temporal coding of odors may
have similarities to the temporal coding of speech.
The influence of selective attention on the olfactory N1 component has been
examined by three studies. In a first study (Pause et al., 1997), two conditions
were examined. While performing a special breathing technique, subjects had
either to count the odors (active attention) or just relax (passive attention). Even
though not statistically significant, there was a tendency for the N1 component to
be larger in amplitude and to have a shorter latency when the subjects attended to
the odors actively. In a second study (Krauel et al., 1998b), the difference between
the attentional levels in two conditions was increased. In the active condition the
subjects had to actively differentiate two odors, and in the passive condition the
subjects had to count target words that served as an auditory distractor task.
That study found a significant reduction in the N1 latency in the active attention
condition. A third study should also be mentioned, one that did not explicitly
address selective attention, but its effects could easily be interpreted as effects of
attention. Pause et al. (1999b) found the N1 component to appear later when the
subjects had to perform a special breathing technique, even though their attention
was directed to the odors. Thus, carrying out two simultaneous tasks (counting
odors and artificially breathing) seems to reduce the amount of selective attention
that can be paid to the odors.
Another feature that seems to be unique to olfaction is that the N1 ampli-
tude decreases even with relatively long inter-stimulus intervals (ISI). Effects of
stimulus repetition on the N1 component in response to auditory stimuli can be
observed only with ISIs shorter than about 10 sec. The amplitude of the olfac-
tory N1, however, declines with ISIs of about 30 sec (Pause et al., 1996b). A
full recovery of the N1 has been found for ISIs of 50 sec (Pause et al., 1997).
Examining CSERPs in older subjects, Morgan et al. (1997) found a tendency for
the N1 amplitude to show a recovery time of even 90 sec. For the auditory and
visual modalities, it has been proposed that the decrease in N1 amplitude with
stimulus repetition may be related to time uncertainty, neuronal refractoriness,
or habituation (Näätänen, 1992). Time uncertainty refers to the phenomenon that
it is more difficult to predict the time of stimulus onset with long ISIs than with
short ISIs. As the effect of stimulus repetition on the olfactory N1 extends to
very large ISIs, it is unlikely that time uncertainty can explain the amplitude
reduction of the olfactory N1. However, further studies need to be carried out
to investigate whether the olfactory effect is caused by refractory periods of the

neuronal generators or by habituation. Habituation can occur only when some of
the stimulus information is stored within short-term memory (Sokolov, 1977).
If it could be proved that habituation is responsible for the amplitude decline
(e.g., by simple habituation/dishabituation studies), then the recovery time for
the olfactory N1 would indicate that the length of olfactory short-term memory
exceeds that in other modalities.
The olfactory P2 reaches its maximum amplitude about 600 msec after odor
presentation. That might reflect processing stages similar to those for the N1
component (Pause et al., 1996b; Tateyama et al., 1998) and thus probably is
also involved in stimulus encoding (for other modalities, see Rockstroh et al.,
1989). Under certain experimental conditions, a second negative component, the
N2, can follow the N1 component. The N2 component can be divided into two
subcomponents, the N2a and N2b (Figure 19.1). For the auditory modality, the
N2 component has been analyzed in great detail (Näätänen, 1990). It has been
shown that deviant, infrequent auditory stimuli presented within a train of homo-
geneous repetitive stimuli can elicit this second negativity. When the stimuli are
actively attended to, a large negative wave, the N2b, is elicited, usually followed
by a P3a. When the stimuli are not attended to, a small negative deflection, the
N2a (also called the MMN, for “mismatch negativity”), appears in association
with the deviant stimulus. The N2a precedes the N2b and can be extracted from
the ERP by subtracting the standard-stimulus ERP from the deviant-stimulus
ERP. As the N2a probably reflects mechanisms within short-term memory, it
cannot be elicited by acoustic stimuli when the ISI exceeds 10 sec (Böttcher-
Gandor and Ullsperger, 1992). To date, the N2b has not been examined using
olfactory stimuli. Some studies, however, indicate that deviant odors that are
processed on a pre-attentional level do evoke an N2a deflection (Krauel et al.,
1999). The existence of such an automatic olfactory “mismatch detector” would
indicate that olfactory information is automatically stored within a short-term
register, even without the influence of attention. Furthermore, it has been shown
that the olfactory N2a can be elicited with ISIs longer than 15 sec (Pause and
Krauel, 1998), which indicates unusually long time frames for olfactory short-
term memory.
For other modalities, the N2b has often been described as being associated
with a P3a component, both of which indicate an attentional switch to a post-
attentive evaluation of the stimulus (Näätänen, 1990). When an attentional switch
occurs, a large late positivity sometimes dominates the ERP and has been called
the P3 component (or P3b) (Figure 19.1). The P3 has a parietal dominance,
and modality-independent generators are involved in its evocation. However,
within CSERPs the P3 will also appear later (between 700 and 1,000 msec after
stimulus onset) than in the visual or auditory ERP (between 300 and 500 msec
after stimulus onset). The P3 has been described as varying with the stimulus
probability and the task relevance in an independent manner whenever attention
is directed toward the stimuli (Johnson, 1993). In fact, for the olfactory modality,
dramatic effects of attention were observed for the late positivity. When attention
was directed to another secondary task (Krauel et al., 1998b), the P3 component
was almost absent. When the attention was mildly subtracted (Pause et al., 1999b)
or not directed toward the odors (Pause et al., 1997), the P3 amplitude was
reduced.
That the P3 amplitude is larger in response to infrequent stimuli has been
interpreted in terms of a so-called context-updating model (Donchin and Coles,
1988). Donchin and Coles stated that an internal representation of the external
environment needs to be updated whenever a change occurs within the external
conditions. That process takes place whenever a change is not expected and may
correlate with the subjective feeling of surprise (Donchin, 1981). That infre-
quently presented target odors elicit a P3 has been demonstrated by Pause et al.
(1996b). Furthermore, Lorig et al. (1996) found the P3 in response to odors to
be larger during exhalation than during inhalation. They attributed that effect to
the evocation of surprise when odors are perceived during phases of exhalation.
Finally, the P3 amplitude varies considerably with the subjective stimulus
significance. Thus, when odors have to be detected (Lorig et al., 1993; Pause
et al., 1997; Krauel et al., 1998b) or to be counted (Pause et al., 1996b, 1999b), the
P3 amplitude rises. The unique feature of odors whereby they also elicit a large
P3 component when they are presented as frequent standard stimuli (Pause et al.,
1996b) might be due to their inherent emotional significance (Pause et al., 1997).
Odors mostly carry a specific hedonic value (Van Toller, 1988), and it has recently
been shown that visual emotional stimuli elicit larger P3s than do neutral stimuli
(Diedrich et al., 1997).
Summarizing, CSERP analysis divides odor processing in the central ner-
vous system into three dimensions. With respect to the high time resolution of
CSERPs, the perceptual speed of odor processing can be considered (latencies
of the CSERP). The neuronal odor transmission can be further divided into the
strength (amplitudes of the CSERP) and the distribution of the neuronal activity
(topography of the CSERP). The three CSERP measures can in turn tell us about
the perceptual dimensions of odor processing: olfactory sensitivity, odor evalua-
tion, and olfactory learning. As indicated earlier, the temporal characteristics of
the CSERPs seem to reflect quality and concentration encoding and can be taken
as indicators of olfactory sensitivity. CSERP results also indicate that olfactory
short-term memory may have longer time frames than short-term memory for
visual or acoustic stimuli; therefore basic sensory olfactory learning seems to
have modality-specific features. Moreover, findings reveal that whenever odors

are attended to (actively or passively), they will be further processed, probably
because of their emotional value.
2. The CSERP as an Indicator of Inter- and Intra-individual

Differences in Odor Perception
In the following, all dimensions of odor perception will be treated as functions
of the individual (Figure 19.2). This model will take into account that olfactory
sensitivity, odor evaluation, and olfactory learning vary considerably between
OIfactory Information Processing

Neuronal Perceptual
Speed Sensitivity
Strength Evaluation
Local Distribution Learning
Biopsychological State
Situational Factors
Attention
Cognitive Capacity
Messenger Systems
(e.g. Hormonal Status)
Age
Biopsychological Trait
Genetic Factors
Affective Style
Neuroticism/Extraversion
HLA-System
Sex
Figure 19.2. Olfactory information processing as a function of the individual.

Olfactory information processing can be measured on a neuronal or perceptual
level. CSERPs can give insight into the speed (latency), strength (amplitude),
and local distribution (source analysis in multichannel EEG recording) of the
neuronal activity related to olfactory stimulus processing. Perceptual measures
can provide information about olfactory sensitivity, odor evaluation (intensity,
quality, valence), and olfactory learning. Relating perceptual measures to neu-
ronal measures can indicate the functionality of neuronal activity. In chapter 3
Olfactory information processing has been described as a function of the indi-
vidual, and the characteristics of the individual are divided into biopsychological
state and trait factors.
and within individuals. Furthermore, the characteristics of the individual will be

separated in those that are stable over time (trait characteristics) and those that
are variable (state characteristics).
2.1. Biopsychological Trait Markers Explain Differences

in Odor Perception between Subjects
Even though CSERP studies using twins as subjects have not yet been carried out,
some studies indicate that genetic factors contribute to the perceptual speed of
processing of human body odors. In one study (Pause et al., 1999c), presentation
of the subject’s own body odor was alternated with presentation of the body odor
of a same-sex subject. It was found that subjects processed their own body odors
faster (P3 latency) than the body odors of others. It was speculated that the own-
body odor might be potentially important to the subject and, like the body odors
of others (Stern and McClintock, 1998), might even have pheromonal regulatory
properties. It is in line with those results that body odors of genetically similar
subjects are processed faster than body odors of genetically dissimilar subjects
(Pause, 1998). In such experiments, genetic similarity has been defined in terms
of identical or very similar gene loci within the HLA (human leukocyte antigen)
system. The HLA system (class I antigens) is a marker of self and non-self
within the immune system and is responsible for destruction of foreign antigens
by CD8+ T-cytotoxic cells. In addition to the latency effects, it was shown that the
body odors of subjects with similar HLA systems evoked larger P3s than did the
body odors of genetically dissimilar subjects (Krauel et al., 1998a). As the subjec-
tive ratings revealed that the body odors of HLA-similar subjects were perceived
as less positive, the P3 effects may have been related to the higher (negative)
emotional significance of odors of genetically similar subjects. Measuring sub-
jective ratings in humans, Wedekind and Füri (1997) have suggested that body
odor perception varies with the specific genetic features of the HLA system.
Some CSERP studies have indicated that females may have greater olfactory
sensitivity than males. Larger CSERP amplitudes were found in females than in
males by Becker et al. (1993) and by Evans, Cui, and Starr (1995). Moreover,
Morgan et al. (1997, 1999) found effects of age on CSERP amplitudes, which
were strongest for older male subjects. However, none of those studies were
experimentally controlled for the effects of task relevance. Given that odors are
perceived mainly as emotional stimuli, sex differences in emotional stimulus
processing (Grossman and Wood, 1993; Lang et al., 1993) may have contributed
to the described effects.
Even though personality dimensions like extraversion or neuroticism might
also contribute to olfactory perception (Pause, Ferstl, and Fehm-Wolfsdorf,
1998), CSERP studies of such factors have not yet been conducted. However,
recent EEG studies (Davidson, 1998) have suggested that the affective style of a
subject can explain differences in brain activity during perception of emotional
stimuli. In accordance with that theory, we recently recorded CSERPs in clini-
cally depressed subjects (Pause et al., 1999d, 2000) whose affective style can be
described as a function of lowered activity within the approach/appetitive motiva-
tion system. By means of threshold tests we found that depressed subjects showed
lower olfactory sensitivity than did healthy controls, and that effect was shown
very clearly for the first time. The strength of the effect may have been caused by
the selection of a homogeneous patient sample (only patients with diagnoses of
major depression participated) and by the use of olfactory (phenylethyl alcohol
and eugenol, according to Doty et al., 1978) rather than trigeminal or mixed
substances. Moreover, CSERP analyses revealed that the early components (P2)
were reduced in depressed subjects. However, the early components in response
to visual slides were similar in healthy and depressed subjects. The P3 in re-
sponse to odors and visual slides was also reduced in depressed patients. Thus,
the reduction of the late P3 complex was not modality-specific and also has been
reported by others using tones or slides as stimuli (e.g., Kayser et al., 2000). That
study again points to the useful distinction between early (N1, P2) and late (P3)
CSERP components. It was concluded that depressed subjects showed reduced
modality-specific ability to encode olfactory information. That effect could be
separated from a general deficit in selective attention that might have been re-
sponsible for the reduced P3 amplitudes. Follow-up studies that were conducted
after the patients had recovered from the severe depressive phase indicated that
their odor processing was still impaired, and that can be interpreted as a trait
marker in depressed patients.
2.2. The Biopsychological State Explains Differences

in Odor Perception within Subjects
Some CSERP studies have been conducted in order to explain differences in odor
perception within a single subject. These differences are related to effects of age,
menstrual-cycle phase, and olfactory learning. Four studies found significant ef-
fects of age on olfactory processing speed. Evans et al. (1995) examined subjects
between 18 and 83 years and found the P2 latency to decline with age at a rate
of 2.5 msec/year. A factorial design was used by Hummel et al. (1998), who
compared three age groups (age ranges 15–34, 35–54, 55–74). They found the
N1 latency to increase with increasing age. Morgan et al. (1997) and Covington
et al. (1999) compared a group of young participants with a group of elderly
participants and also found odors to be processed significantly faster in young
subjects (latencies of N1, P2, N2). Moreover, three studies demonstrated that
elderly participants also showed reduced CSERP amplitudes. Whereas Hummel
et al. (1998) and Covington et al. (1999) found similar effects of age on ampli-
tudes and latencies, Murphy et al. (1994) found the effects of age to be more
pronounced for the amplitudes (N1, P2) than for the latencies. Measuring early
olfactory stimulus processing, these results are in line with findings that olfac-
tory sensitivity is reduced in older subjects (e.g., Doty et al., 1984). Recently,
Morgan et al. (1999) focused on the olfactory P3 and found age effects for the
amplitude as well as for the latency. They discussed the importance of separating
a sensory impairment from a cognitive impairment in elderly subjects. Whereas
the former can be addressed by investigating the N1 and P2 amplitudes, the latter
can be evaluated by use of the P3 component.
In two studies, the influence of the menstrual-cycle phase on CSERPs was
examined: In the first study (Pause et al., 1996a) it was found that a citrus odor
was processed significantly faster (latencies of N1, P2, P3) during the ovulatory
phase than during the follicular or luteal phase. Interestingly, that effect was found
only after repeated stimulations, indicating that the plasticity of the olfactory
system is higher during the ovulatory phase. Additionally, it was found that the
P3 was larger during the ovulatory phase. That effect was interpreted as evidence
for a higher significance of odorous information during the ovulatory phase. In
the second study (Pause et al., 1999a), the body odors presented belonged to
two groups of odor donors, one with HLA systems similar, and one dissimilar, to
those of the subjects. It was confirmed that the largest P3s were obtained when the
females smelled HLA-similar subjects; that effect was most pronounced when
the subjects were examined during the ovulatory phase.
One of the most intriguing findings on olfactory plasticity in recent years has
come from studies showing that subjects with specific anosmias can be olfac-
torily sensitized and thus can reach normal osmia for a specific odor (Wysocki,
Dorries, and Beauchamp, 1989). Olfactory plasticity refers to the capability of
the olfactory neurons for neurogenesis and reconnection of pathways in the ol-
factory system (Costanzo and Graziadei, 1987), as well as to the capacity of
neurons within the main olfactory bulb to change their response characteristics
through olfactory learning (Brennan and Keverne, 1997). In corresponding stud-
ies in humans, the odor most frequently investigated is that of androstenone. Up
to one-third of the subjects examined were found to have a specific anosmia to
that odor (Wysocki, Pierce, and Gilbert, 1991). Androstenone has been detected
in human sweat and other body fluids and is thought to be a male pheromone
(Gower and Ruparelia, 1993). However, it has never been shown that the odor
of androstenone within the complex human body odor conveys any specific in-
formation to the perceiver. In a first CSERP study (Pause et al., 1999e), females
were exposed to a foreign, male body odor and their own body odors. Whereas
the potentials for an osmic control group became smaller in a second session con-
ducted four weeks after the first session, a group of sensitized, initially anosmic
females showed larger potentials exclusively for the male body odor during the
second session, four weeks after exposure. It was concluded that the sensitivity
to androstenone in females is associated with a stronger brain response to male
body odor.
3. Conclusion
It has been shown how measurements of event-related brain activity can be used
to better understand human odor perception. Especially the high time resolution
of CSERPs has been addressed, which may serve as a good indicator of the
temporal features in olfactory coding (Lorig, 1999). Olfactory perception has
been shown to be a function of the individual. Each individual is made up of
basic and variable psychological and biological features (Figure 19.2). Some
of them have already been examined in CSERP research and can explain inter-
and intra-individual differences in odor perception. However, further research is
needed, for example, to examine the uniqueness of olfactory plasticity. So far,
some intra-individual differences have indicated that olfactory performance can
be improved by the actions of sexual hormones (Pause et al., 1996a, 1999a) and by
repeated odor exposures (Möller, Pause, and Ferstl, 1999; Pause et al., 1999e). In
addition, our first results (Pause and Krauel, 1998) indicate that olfactory learning
can also occur unintentionally (olfactory priming), and that can be measured by
CSERPs.
Acknowledgments
I would like to thank Roman Ferstl, Kerstin Krauel, Bernfried Sojka, Claudia
Müller, and Ninja Raack for discussions and for their outstanding help in exper-
imental work. Furthermore, I would like to thank two anonymous reviewers for
their helpful suggestions on the manuscript. The preparation of the manuscript
was in part supported by the German Research Council.
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20
Processing of Olfactory Affective Information:
Contribution of Functional Imaging Studies
Robert J. Zatorre
A central concern in contemporary cognitive neuroscience is how stimulus infor-

mation is represented in the human central nervous system. One approach to this
issue is to examine the neural correlates of different types of stimuli in different
modalities to determine the functional organization of distinct cortical and/or
subcortical pathways associated with particular types of stimulus features. This
approach has proved particularly powerful for understanding how visual pro-
cesses are organized, for example. Much less is currently known about how the
brain encodes olfactory sensory information. Despite progress in understanding
the basic mechanisms of coding at the receptor level (Duchamp-Viret, Chaput,
and Duchamp, 1999), cortical processing of odor quality remains largely un-
known, especially in the human brain. One property of the chemical senses that
differentiates them from other modalities is their strong hedonic association.
Unlike visual and auditory stimuli, odors and tastes often result in strong affec-
tive reactions. That aspect of odor processing raises interesting questions about
the neural substrates that account for the salient hedonic value of odors.
In the past decade, cognitive neuroscientists have benefited enormously from
the development of functional neuroimaging, which allows noninvasive explo-
ration of the brain. Those techniques measure changes in hemodynamic re-
sponses as functions of stimulus or task demands, thus permitting assessments
of the neural activities associated with a wide variety of cognitive and perceptual
processes. Neuroimaging complements more conventional approaches such as
neurophysiological studies and lesioning studies of behavior, which continue to
be of considerable importance in understanding brain–behavior relationships.
This chapter offers a brief overview of recent studies in neuroimaging as ap-
plied to olfaction, and particularly as related to olfactory hedonics, followed
by some recently published data from our laboratory examining specifically the
processing of odor quality and intensity (Zatorre, Jones-Gotman, and Rouby,
2000).
324
Neural Correlates of Odor Judgments 325
Previous work with brain-lesioned patients has indicated that unilateral dam-
age in the temporal lobe or in the orbitofrontal cortex (OFC), particularly in
the right cerebral hemisphere, can result in significant disruptions in the higher-
order processing of odors, including odor quality discrimination and memory
tasks (Eskenazi et al., 1983; Zatorre and Jones-Gotman, 1991; Martinez et al.,
1993; Jones-Gotman and Zatorre, 1993), whereas lower-level processes such as
detection and intensity matching typically are unaffected (Eichenbaum et al.,
1983; Jones-Gotman and Zatorre, 1988). Such dissociations suggest that the
olfactory nervous system may be hierarchically organized, with the OFC re-
sponsible for more complex aspects of feature analysis and integration. Such
a model is compatible with anatomical considerations, because neurons in the
OFC receive inputs from the piriform cortex and from thalamic nuclei (Price
et al., 1991), among other areas (Figure 20.1), presumably after having under-
gone several levels of prior processing. Also, electrophysiological data from tests
with monkeys indicate greater degrees of selectivity in the profiles of neuronal
responses proceeding up the olfactory neuraxis from the olfactory bulb to the pir-
iform cortex to the OFC (Takagi, 1991). However, it remains unknown whether
or not olfactory hedonic processing is associated with the same neural substrate
as that associated with odor encoding, identification, and retention.
Figure 20.1. Diagram of known and putative primate olfactory pathways

leading to OFCs: LPOF, lateroposterior orbital frontal; CPOF, centroposterior
orbital frontal. (Adapted from Takagi, 1989.)
326 Robert J. Zatorre
Several neuroimaging studies of human olfaction using positron-emission

tomography (PET) and functional magnetic-resonance imaging (fMRI) have re-
cently been carried out, and they have helped to clarify the precise functional neu-
roanatomy of olfactory processing (for a review, see Zatorre and Jones-Gotman,
2000). Among the more relevant findings are that the piriform cortex and the
OFC usually show increased activity in response to presentation of odors, with
an asymmetry favoring the right OFC (Zatorre et al., 1992; Small et al., 1997;
Sobel et al., 1998; Savic et al., 2000). More recently, Royet et al. (1999) have
also found an asymmetry favoring the right OFC, but it was present specifically
in a condition in which familiarity judgments were elicited, suggesting that the
right OFC may be involved in processing particular stimulus features. On the
other hand, Zald and Pardo (1997) have shown that very unpleasant odors re-
sult in significant activation the left OFC, as well as limbic structures, notably
the amygdala. That latter finding raises the question whether or not hedonic
processes depend on a different hemispheric lateralization than other types of
processes and suggests that the amygdala may be involved in evaluating the
affective valence of an odor.
In what is perhaps a demonstration of scientific zeitgeist, three very recent
papers, published within a few months of one another, have used PET to ex-
plore the neural substrates associated with judgments of odor quality, intensity,
and pleasantness. Savic et al. (2000) showed that judgments of odor intensity
engaged the left insula and right cerebellum, whereas judgments of odor quality
(same/different) engaged a number of additional regions, including the OFC, cau-
date, and thalamus. Those authors concluded that their data reflected a hierar-
chical and parallel organization of olfactory processing. Royet et al. (2000)
used pleasant and unpleasant odors mixed within the same scanning condition
and asked subjects to make judgments of pleasantness; that condition was com-
pared to one where neutral odors were presented and subjects made no judgment.
The results indicated that during the hedonic judgment there was increased ac-
tivity in bilateral orbitofrontal regions, hypothalamus, and right superior frontal
gyrus. When compared with a no-odor baseline, additional activity in insular
and cerebellar regions emerged. Many of those regions were similarly active
in visual and auditory emotional tasks as well, suggesting some commonality
across modalities.
In a recent PET activation study from our laboratory (Zatorre et al., 2000), we
sought to explore directly the issue whether or not distinct pathways could be
demonstrated to participate in hedonic versus non-hedonic aspects of olfactory
information processing. We concentrated on two dimensions of odor perception,
intensity and pleasantness, because they have been shown to be dissociable. In
particular, Eichenbaum et al. (1983) found that the famous patient H.M., who
has bilateral medial-temporal-lobe damage, was utterly unable to identify odors

or assess their quality, but was nonetheless as accurate as control subjects in
performing detection and intensity scaling tasks. That result indicates that odor
intensity processing may depend on a neural substrate dissociable from that
involved in other types of olfactory processing.
One practical problem in studying odor intensity and pleasantness is that these
two dimensions typically are correlated at the behavioral level, with odors being
judged less pleasant as they become more intense; however, it is possible to
dissociate them psychophysically by a judicious choice of specific odorants and
concentrations. Specifically, we used a set of odors of various concentrations
previously selected and tested (see Rouby and Bensafi, Chapter 9, this volume)
to be independent on the two dimensions in question (Figure 20.2). In that study,
225
P HO
A CE
175
IS O
LIM
Inten s ity
125
C IN
CDN
75
MEN
PYR
CA M TH Y
25
25 75 125 175 225
U n p le a s a n tn e s s
Figure 20.2. Scattergram of pleasantness and intensity responses obtained

for 10 odorants. Each point corresponds to the ranking derived from pairwise
comparisons of each odor with each other odor, presented once for pleasantness
and once for intensity judgments. Odor concentrations were chosen to avoid a
correlation between the two variables: PHO, thiophenol; ACE, acetophenone;
ISO, isoamyl acetate; LIM, R-(+)-limonene; CIN, 1,8-cineole; CDN, cyclode-
canone; MEN, (−)-menthol; CAM, (−)(+)-camphor; THY, thymol; PYR, pyri-
dine. For the PET study, six odors were retained (excluding PHO, LIM, CAM,
and MEN). See Zatorre et al. (2000) for further details and concentrations.
subjects performed pairwise comparison tests of certain concentrations of odors,

and it was shown that judgments of relative intensity were uncorrelated with
judgments of relative pleasantness. Thus, that procedure allowed the selection
of a stimulus set that would permit us to examine odor pleasantness and intensity
judgments separately. We hypothesized that different patterns of cerebral activity
would be evoked when those two judgments were made.
The experimental design chosen was meant to control for two important issues
that have complicated the interpretation of much prior research. One such issue
is that it is often difficult to dissociate hedonic judgments from stimulus-specific
effects. That is, if one compares, say, pleasant to neutral odors and differences
are found, it is not clear whether the effects are due to differences in the stimuli
themselves or to the intended factor of pleasantness. In order to avoid such
confounding effects of the specific stimuli to be used for the two judgments, we
devised a task in which the identical pairs of odors were presented to subjects first
for intensity judgments and then for pleasantness judgments, thus ensuring that
any differences elicited would be functions of task demands and not stimulus
properties, as the stimuli were constant in all conditions. A second problem
that can cloud the interpretation of results is that differences among conditions
may emerge because of uncontrolled differences in task requirements. If one
compares a pleasantness judgment task to a neutral baseline, for example, it
is not clear whether any differences that emerge are attributable to the act of
making the judgment or to the pleasant-versus-neutral dimension of the stimuli.
The tasks used in our study involved identical nonspecific aspects, for in both the
pleasantness and intensity tasks the subjects were presented with two items and
were asked to compare the first to the second item, make a judgment, and press a
key. Thus, all cognitive components, such as working memory, decision-making
processes, and motor organization and execution, were controlled.
Twelve healthy right-handed subjects were scanned in each of three con-
ditions, termed Baseline, Affect, and Intensity. On each trial, paired stimuli
were presented, and subjects indicated whether the first or second item in the
pair was more intense (in the Intensity condition) or more pleasant (in the
Affect condition). In the Baseline condition, two odorless trials were given,
and subjects simply inhaled and responded with a random keypress. Measures
of cerebral blood flow were obtained according to standard techniques (Zatorre
et al., 2000), and the resulting functional maps were co-registered with anatom-
ical magnetic-resonance images after stereotaxic transformation. Data sets were
averaged across subjects, and paired-image subtractions were performed to iden-
tify the presence and location of significantly different voxels, according to a
t-statistic parametric map (Worsley et al., 1992).
Each of the two odor judgment conditions was compared to the baseline;
in addition, the two odor conditions were compared directly to one another.
Comparison to the common no-odor baseline revealed three main findings, each
of which will be discussed in turn: First, the expected activity in the primary
olfactory cortex, or piriform area, was not observed; second, and in accord with
what we expected based on prior studies, activation was seen in the right OFC
in both the Affect and Intensity conditions; third, the Affect condition, but not
the Intensity condition, resulted in recruitment of the hypothalamus.
The absence of increased cerebral blood flow within the piriform region in
either of the two odor conditions was somewhat surprising. There was no evi-
dence of activity in that region, even when a more liberal statistical threshold
was applied. In order to increase the power of the analysis, we pooled the data
for the two odor presentation conditions together and compared them to the no-
odor baseline to see if piriform activation could be detected, but once again no
evidence of any significant change in that region was obtained. That negative
finding cannot be dismissed simply as a false-negative response, as the analysis
performed contained sufficient observations that piriform activity should have
been detected had it been present (12 subjects scanned six times each, yielding
72 image volumes). Furthermore, previous studies in our laboratory (Zatorre
et al., 1992; Small et al., 1997) had clearly shown piriform activity, even with
fewer observations and using a less sensitive PET scanner than the one used
in the current experiment. In addition, a similar lack of piriform activity was
reported by Dade et al. (1998) in an olfactory working-memory task in which
behavioral performance clearly indicated that the stimuli were being processed.
Also, Zald and Pardo (1997) reported only weak or no activation of presumed
piriform areas in their study with very noxious odors. In other studies (e.g., Royet
et al., 2000; Savic et al., 2000), piriform activation was detected only weakly, by
using region-of-interest analyses, or only in one hemisphere.
One possible explanation for the absence of piriform activity in our study is
that sniffing odorless air can produce piriform activation (Sobel et al., 1998),
and because subjects sniffed in both the baseline condition and the two odor
conditions, it would have subtracted out. Although that possibility may account
in part for the findings, it is insufficient to explain why piriform activity is
observed in some studies but not others, all of which have used an odorless
sniffing baseline condition. It is also possible, of course, that activity in the
piriform cortex is present but is not detectable by PET methods, perhaps because
it is of a very transient nature to which PET is not sensitive.
An alternative explanation is that the piriform cortex may respond to familiar
odors, whereas the odors used in our study were chosen to be unfamiliar. That idea
is consistent with the data of Dade et al. (1998), who noted piriform activation
after odors had been familiarized, but not when they had first been presented.
Regardless of the ultimate explanation for why piriform activity is so variably
observed, the current data suggest a need to revise the traditional view of the
piriform area as a simple sensory relay in a hierarchy. Instead, the findings suggest
a more complex interaction among a network of regions including piriform
and orbitofrontal cortices, with activity in orbitofrontal areas not necessarily
dependent solely on input from piriform regions (Figure 20.1). In this regard,
a recent anatomical study is of considerable relevance: Johnson et al. (2000)
examined the connectivity of neurons in the rat piriform cortex and concluded
that the piriform region “performs correlative functions analogous to those in
association areas of neocortex rather than those typical of primary sensory areas
with which it has been traditionally classed.” Thus, the complex modulation of
piriform areas seen across the various studies would be consistent with the idea
that its function is much more complex than previously thought (see Ravel et al.,
Chapter 21, this volume).
The second result, which was in keeping with predictions, was the significant
increase in cerebral blood flow in the right OFC in both the Affect and Intensity
conditions (Figure 20.3). The positions of that OFC area were very similar across
the two conditions and, more importantly, were remarkably consistent with that
reported in several previous studies (see Zatorre and Jones-Gotman, 2000, for
a meta-analysis of OFC activation sites). Such a result therefore confirms the
greater importance of the right OFC for odor processing, as suggested by previ-
ous imaging studies (Zatorre et al., 1992; Small et al., 1997; Sobel et al., 1998;
Savic et al., 2000) and lesioning studies of behavior (Zatorre and Jones-Gotman,
1991), and more generally by several studies implicating the right hemisphere
in many, though by no means all, olfactory tasks (Abraham and Mathai, 1983;
Eskenazi et al., 1983; Zatorre and Jones-Gotman, 1990; Carroll, Richardson,
and Thompson, 1993; Martinez et al., 1993; Jones-Gotman and Zatorre, 1993).
In terms of the main point of this study, however, the OFC does not appear to
contribute differentially to affective processing, as opposed to non-affective pro-
cessing, because the activations were essentially identical in the two conditions.
The third and most relevant finding in terms of the goals of the study was that a
region of the hypothalamus was active in the Affect condition but not the Intensity
condition. To verify that the hypothalamic activity constituted the main difference
in brain activity associated with affective processing, we compared the two active
conditions directly to one another. That subtraction yielded no differences in
cerebral blood flow in the OFC areas, consistent with the fact that activation
was present in both conditions in a similar location in the orbital region. There
was, however, a region of significantly greater activity in the Affect condition
Figure 20.3. Selected areas of significant increases in cerebral blood flow in

PET study. The average PET subtraction images are shown superimposed on
averaged MRI scans. Changes in flow are shown as a t-statistic map, coded
by the color scale shown at top left. Top: Comparison of Affect condition to
Baseline condition. The two sagittal sections and the horizontal section illus-
trate the positions of activation sites in the right OFC and hypothalamic area.
Middle: Comparison of Intensity and Baseline conditions. Sagittal and horizon-
tal sections illustrate activation in right OFC. Bottom: Comparison of Affect
and Intensity conditions. Sagittal and horizontal sections illustrate activation in
hypothalamic area. (Adapted from Zatorre et al., 2000.)
compared with the Intensity condition in the vicinity of the hypothalamus, and
in essentially the same location as that seen in the Affect–Baseline comparison
(Figure 20.3).
Hypothalamic activity was also noted by Royet et al. (2000) in their odor
pleasantness/unpleasantness judgment condition, which is consistent with our
data; however, it is not clear if that effect was due to the affective state presumably
elicited by the stimuli themselves or to the cognitive demands of making the
pleasantness judgment. In our study, the hypothalamic activation appeared to be a
function of task demands, rather than being stimulus-driven, for the stimuli were
identical in the two conditions. Furthermore, because the hypothalamic activity
was observed in both the Affect–Baseline subtraction and the Affect–Intensity
comparison, it appears to be a robust finding that is specifically attributable to the
condition of judging pleasantness/unpleasantness. One possible interpretation
of that finding is that hypothalamic activity may be modulated by top-down
mechanisms. Although there is scant converging evidence for such a mechanism
from other studies, there is anatomical evidence (Takagi, 1991) that olfactory
information travels through several parallel pathways, from olfactory bulb to
OFC, and from olfactory bulb via the septal area, to the lateral hypothalamus
(Figure 20.1). Although the evidence is unclear, there may also be connections
between the hypothalamus and OFC areas (Tazawa, Onoda, and Takagi, 1983).
Those pathways could provide the means for odor-processing neural systems in
the OFC to interact with and thus influence the activity of hypothalamic neurons,
a hypothesis that would be in keeping with the clear OFC activity observed during
the odor judgment tasks.
The conventional view that the hypothalamus plays a crucial role in regulating
the internal state may be relevant to our findings as well. If the affective judgment
of relative pleasantness not only is carried out by analysis of stimulus features
but also requires access to information about the internal state, then recruitment
of the hypothalamus might be necessary. Whereas intensity can be determined
solely on the basis of the physical characteristics of a stimulus, it could be
argued that pleasantness requires one to decide how the stimulus may interact
with one’s internal environment (Might this odor indicate something good to eat?
Might this odor indicate something that could make me sick?). Thus the stimulus
features in themselves, which would be adequate for judging intensity, might
be insufficient to make that safety judgment, and reference to neural systems
involved in somatic and physiological status might be relevant. A similar function
has previously been suggested for the OFC (Rolls, 1999), which undoubtedly
plays a role in affective processes, for many neuroimaging studies have shown
that it is active in response to various types of affectively valenced stimuli (Zald
and Pardo, 1997; Blood et al., 1999; Francis et al., 1999). However, in our study
the OFC was as active during judgments of intensity as it was during judgments
of pleasantness. Clearly, much further experimental work will have to be done
before these questions can be sorted out. The current state of our understanding
of these complex systems has undoubtedly been enhanced by the contribution
of neuroimaging studies, and one may be cautiously optimistic that future work
will continue to yield additional insights.
Acknowledgments
I wish to thank my collaborators in this research, Marilyn Jones-Gotman and
Catherine Rouby, and Drs. A. C. Evans and B. Pike of the Brain Imaging Center
of the Montreal Neurological Institute. The work was supported by the Canadian
Institutes of Health Research, and G.I.S. Sciences de la Cognition, France.
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21
Experience-induced Changes Reveal Functional
Dissociation within Olfactory Pathways
Nadine Ravel, Anne-Marie Mouly, Pascal Chabaud,
and Rémi Gervais
Learning more about the neural basis of olfactory cognition should greatly im-
prove our understanding of how different brain structures deal with information.
Progress can be facilitated by simultaneous advances with animal models and
human studies, for in the olfactory system, conservatism across mammalian
species in the organization of olfactory pathways allows integration of data ob-
tained in animals and humans. In each species, output neurons from the olfactory
bulb (OB) monosynaptically reach the piriform cortex (PC), the peri-amygdaloid
cortex, and the lateral entorhinal cortex (LEC). The LEC provides massive input
to the hippocampus, and the PC sends information to the orbitofrontal neocortical
area, both directly and after a relay in the dorsomedial thalamic nuclei (Haberly,
1998). As in other sensory systems, two strategies have been developed thus far
in order to identify hierarchical organization: collecting information from one
structure at a time, and looking at the system as a network of interconnected
structures. The first strategy is typical for most animal studies and is imple-
mented through single-cell recordings in anesthetized animals (Mori, Nagao,
and Yoshiara, 1999) and active animals (Schoenbaum, Chiba, and Gallagher,
1999; Weibe and Staubli, 1999; Wood, Dudchenko, and Eichenbaum, 1999)
or through surface EEG recordings in awake restrained animals (Freeman and
Skarda, 1985). When using anesthetized animals, most studies have focused on
the OB, and fewer on the PC. When using active rats, such studies have inves-
tigated hippocampal, amygdalar, and orbitofrontal electrophysiological charac-
teristics. Those approaches provide data on cell reactivity with millisecond time
resolutions, but give no information on how information is processed simul-
taneously at different levels. The hierarchical organization of central olfactory
processing is beginning to be revealed by recent brain imaging studies in humans
(Zatorre et al., 1992; Sobel et al., 1998, 2000; Royet et al., 1999, 2000; O’Doherty
et al., 2000; Qureshy et al., 2000; Savic et al., 2000; Zatorre, Jones-Gotman, and
Rouby, 2000; Zald and Pardo, 2000). Other chapters in this volume provide an
335
336 Ravel, Mouly, Chabaud, and Gervais
overview of the main findings (see Phillips and Heining, Chapter 12, Zatorre,
Chapter 20, and Rolls, Chapter 23). However, for at least two reasons, compari-
son between electrophysiological data and brain imaging data is difficult. First,
the techniques have very different temporal and spatial resolutions. Second,
whereas most electrophysiological data have been collected in anesthetized an-
imals, brain imaging studies map alert brains involved in cognitive tasks. The
purpose of some of our recent investigations has been to contribute to filling in
the gap between the two approaches. Our experimental model relies on electro-
physiological recordings from active rats. Ideally, one would like to determine
electrophysiological activities simultaneously from the OB, several parts of the
PC, the entorhinal cortex (EC), the amygdala, several sites of the hippocampal
formation, and the orbitofrontal cortex. As a start, we focused our attention on
three structures: the OB, PC, and EC. In addition, we were particularly interested
in finding electrophysiological correlates of modulations of olfactory responses
related to internal state, recent experience, and long-term memory. But before
summarizing our findings, we shall briefly review what was available from recent
studies regarding the physiology of the OB and the PC.
1. The OB and the PC Are More than Sensory Relays

Anatomical studies have clearly shown that information converging to the OB and
PC does not originate exclusively from olfactory neuroreceptors. Indeed, both
structures are densely interconnected with several other forebrain cortical areas.
In addition, they receive dense innervations from ascending neuromodulatory
systems such as the noradrenergic system, the serotoninergic system, and the
basal forebrain cholinergic system (Gervais, Holley, and Keverne, 1988). Thus
we can predict that in an active animal, responses elicited by odorant stimuli
at the OB and PC levels are likely to be strongly modulated according to the
animal’s internal state and past experience.
At the OB level, we used three types of electrophysiogical studies to test that
prediction. First, multi-unit mitral-cell activity was recorded from one site per
bulb in response to repeated olfactory stimuli. Protocols were designed to in-
vestigate the differential rate of neuronal-response habituation according to the
behavioral value of the stimulus. For example, food odor was presented every
3 min to food-deprived animals and satiated animals (Pager et al., 1972). Second,
in awake restrained rabbits, an array of 64 electrodes recorded mass oscillatory
activity (electroencephalogram, EEG) during odor presentation. In that case,
the experimental paradigm included a simple associative-conditioning task in
which presentation of odors was paired repeatedly over days with reinforcement
(Freeman and Schneider, 1982). Both sets of data have been reviewed (Freeman
Neural Correlates of Olfactory Learning 337
and Skarda 1985; Gervais, 1993). The two key findings were that previous ex-
perience had a strong influence on populational OB responses, and that effect
depended on the action of centrifugal control exerted at the level of the OB.
However, in the two sets of experiments, the term “experience” referred to very
different time scales. Indeed, the habituation paradigm tested for a simple form
of short-term memory over minutes, whereas the associative-learning paradigm
tested for changes in OB reactivity over days and weeks. A recent study in
which single-cell mitral activity was recorded in rats engaged in a conditioning
paradigm (Kay and Laurent, 1999) confirmed earlier findings (Pager, 1983). In
fact, output cell activity was found to depend more strongly on an animal’s ex-
perience and ongoing behavior than on the olfactory stimulation. On the whole,
electrophysiological experiments show that in active animals, OB reactivity is
under strong influences from more central structures.
But what might be the role of such central influence exerted at the input level?
We hypothesized that it could be of importance for olfactory memory, and we de-
signed a series of experiments to test that hypothesis. The experiments relied on
examination of memory performances following transient perturbation of OB ac-
tivity. In one experiment, transient blockade of cholinergic modulation of the OB
(via intrabulbar injection of scopolamine) impaired short-term olfactory mem-
ory over a time scale of a few tens of seconds (Ravel, Elaagouby, and Gervais,
1994). In another experiment, transient inactivation of the OB activity (via in-
trabulbar lidocaine injection) just after each training session impaired retention
of olfactory information over a time scale of a few days (Mouly et al., 1993).
Both experiments are interpreted as evidence for OB integration into a functional
network supporting both short-term and long-term memory: That is, cooperation
between the OB and other structures such as the EC and hippocampus intervenes
to support some forms of memory processes. That also suggests that neural com-
putation performed at the OB level is doing more than “formatting” the message
addressed by olfactory neuroreceptors before transmission to other areas.
At the PC level, some lines of evidence suggest that its role is not limited to pure
sensory analysis, but also extends to olfactory learning. Electrophysiological
studies in vitro (Jung, Larson, and Lynch, 1990; Kanter and Haberly, 1990) and in
vivo (Stripling, Patneau, and Gramlich, 1988) have revealed that intrinsic PC con-
nections can express long-term potentiation (LTP), and LTP in the PC has been
shown to accompany behavioral learning (Roman, Staubli, and Lynch, 1987;
Litaudon et al., 1997). Those experimental data are reinforced by theoretical and
modeling approaches showing that the PC has several features of a network with
content-addressable memory characteristics (Haberly, 1985; Wilson and Bower,
1988; Lynch and Granger, 1989). However, that general hypothesis needs defini-
tive support from behavioral studies. In addition, the PC is commonly thought
of as being functionally homogeneous. Some recent studies have suggested a

functional dissociation along its anteroposterior axis (Litaudon and Cattarelli,
1996; Litaudon et al., 1997) although data have not been obtained from active
animals. For that reason, in our experiments we obtained electrophysiological
recordings from two sites in the PC cortex: one in the anterior part (aPC), and
the other in the posterior part (pPC).
In summary, it is likely that experience modulates responsiveness at each level
of olfactory processing, including the OB and PC. However, an overview of how
and when changes occur at each of those levels in animals performing a given
task is not yet available. Thus the purpose of our study is to provide new insights
on how the OB-PC-EC complex works for information processing. Starting with
the hypothesis that both recent and remote experiences modulate functioning at
each of the three levels, we examined the functional consequences of experience
on neural responsiveness in intact rats.
2. Local Field Potential Activity as a Measure

of Functional Anatomy
One critical step in studying brain activities is the choice of the level of analysis.
Electrophysiological investigations can rely on single-cell recordings, multi-unit
recordings, local field potentials, or surface EEGs. At a microscopic level, single-
cell recordings provide straightforward access to neural computation, but they
are very difficult to obtain simultaneously from several structures. Furthermore,
long-lasting effects of experience can be tested only with stable recordings over
days and weeks. At a macroscopic level, surface EEGs provide valuable infor-
mation on superficial brain structures such as the OB (Freeman, 1975), but are
inappropriate for in vivo recordings of deep structures such as the PC and the EC.
In a middle range between those two extremes, intracerebral local field potentials
(LFPs) provide information on population activity from identified cell layers. In
our approach, two types of LFPs were studied: electrically evoked LFPs and
naturally occurring LFP oscillatory activities.
In a first approach, electrically evoked LFPs were recorded simultaneously
in the PC and in the EC following stimulation of the OB. The characteristics
of the evoked potentials (amplitude, latency) reflect the efficiency of synaptic
functioning. Thus the characteristics of evoked field potentials (EFPs) were mea-
sured over days while animals learned an olfactory associative task, the implicit
hypothesis being that changes in synaptic transmission could reflect some neural
correlates of behavioral learning (Morris et al., 1986; Roman et al., 1987).
In a second approach, spontaneous and odor-evoked LFP activities were
studied. In the olfactory system, it is well established that the activities of neuron
populations are dominated by prominent oscillatory regimes with frequency

ranges from 1 to 100 Hz, reflecting the observation that groups of neurons have a
strong tendency to work in synchrony. One important reason for studying oscil-
latory activity is because of the current hypothesis suggesting that a widespread
common oscillatory frequency could play a critical role in transient formation
of neural assemblies. That refers to the so-called binding theory (Singer, 1999),
one key idea being that the presence of a common oscillatory rhythm within a
neuron population could favor synchronization of the individual discharges of
neurons belonging to that population. That could be particularly important in the
neural representation of odor, which is suspected to be widely distributed spa-
tially within and across olfactory structures. Whereas strong evidence supporting
that conception has been found in visual and somatosensory systems, such is not
the case in the mammalian olfactory system. However, a detailed investigation
of how oscillatory regimes arise during spontaneous activity and following odor
presentation was found to be particularly revealing of how experience modulates
the characteristics of large neuron assemblies (Freeman and Skarda, 1985). That
impressive set of data focused mainly on OB activity, and very few studies have
included data on oscillatory activities collected simultaneously from the OB, the
PC, and the LEC (Boeijinga and Lopes da Silva, 1989; Kay and Freeman, 1998).
In some recent experiments, we examined whether or not a common oscillatory
regime was expressed simultaneously in the OB-PC-EC complex during odor
processing. In addition, we tested whether or not odor-related oscillatory activ-
ities were modulated by internal states and conditioning.
3. Recent Findings
3.1. Effect of Associative Olfactory Learning
on Synaptic Transmission
In this task, rats had to learn to discriminate between two olfactory cues in order
to perform differential behavioral responses. For thirsty animals, one cue (S+)
was constantly paired with a positive reward (a sucrose solution), and the other
cue (S−) was paired with a negative reward (a quinine solution). Importantly,
the olfactory cues were not real odors, but electrical impulses directly delivered
at two different sites on the same OB (Mouly, Vigouroux, and Holley, 1985).
The main advantage of using “electrical odors” is that the same bulbar electrode
stimulated during the discrimination task can be reused following training to
elicit EFPs in target structures. In a first series of experiments, rats learned
the task within a few days. Then they were anesthetized, with a large fraction
of the PC being exposed. A voltage-sensitive-dye method was used to map
EFPs from 144 recording sites. One of the major findings was that learning
was associated with an increase in the amplitude of the early EFP component
in the posterior PC. That likely corresponded to improved synaptic efficiency at
the level of afferent fibers to the PC following stimulation of bulbar electrodes
involved in the acquisition of the task (Litaudon et al., 1997). Although that
study suggested learning-induced plasticity restricted to the posterior part of the
PC, it did not provide information on what happened in neighboring structures.
In a recent study based on the same behavioral paradigm of learning “electrical
odors,” recordings of EFPs due to OB electrode stimulation were obtained
simultaneously from the anterior piriform cortex (aPC), posterior piriform
cortex (pPC), and lateral entorhinal cortex (LEC) (Figure 21.1).
Recordings were made on the day the animals mastered the learning task
(at least 80% of correct choices for two successive daily training sessions) and
following a 20-day period of training interruption. It is important to keep in mind
that measures were not obtained during accomplishment of the task, but one
hour later and several days later. Changes in signal amplitudes likely reflected
A B
Stimulating and recording electrodes Evoked field potentials
OB1 AmV
aPC
OB2
pPC
LEC
OB
aPC 0.5 mV
pPC St
EC 20 ms
Figure 21.1. Schematic representation of the implanted electrodes and recorded

signals. A: Two bipolar stimulating electrodes (OB1 and OB2) were implanted
in the ventral mitral-cell layer of the OB. Three recording electrodes were
implanted in the aPC, pPC, and LEC. B: Examples of the EFP signals induced
at the three recording sites in response to stimulation of the OB. The amplitudes
(AmV ) of the EFP main components are measured at each site, as indicated in
the figure. St: stimulation artifact.
S+ signals
Post-learning Post-20 days
% variation % variation
60 60
* *
40 40 *
*
20 20
0 0
-20 -20
-40 -40
-60 -60
Control Trained Control Trained
aPC pPC LEC
Figure 21.2. Mean (±SEM) variations in EFP amplitudes measured in control

(n = 7) and trained (n = 11) animals at the four recording sites. In the ab-
sence of reinforcement, control animals received intrabulbar electrical pulses
with the same characteristics (intensity, duration, number) as those received
during training in the experimental group. Changes are expressed as percent-
age variations from the baseline signals collected before training. S+ signals:
signals induced by stimulation of the OB electrode (which had been associated
with delivery of sucrose in the learning task) after completion of learning (left)
and after 20 days of training interruption (right). Note the absence of variation
in the aPC following training and the significant increases in the pPC and the
LEC (*p < 0.05: significant changes compared with the signals recorded before
training).
long-lasting consequences of the learning process. That study confirmed that

learning-induced changes in the PC developed specifically in its most posterior
part. In addition, very similar increases in synaptic efficiency were revealed in
the LEC. Changes observed at both levels can be considered as durable, because
they developed just following learning completion and were still present or even
amplified 20 days later (Figure 21.2) (Mouly et al., 2001).
Thus, to summarize, multiple-site recordings clearly showed functional dis-
sociation between the aPC and the pPC and suggested that the pPC and the
LEC have some common characteristics in the context of olfactory learning.
Changes in synaptic efficiency observed at that level can be interpreted either
as reflecting a specific substrate of memory traces or as reflecting more global
changes. In the latter view, changes in electrical-signal amplitude observed fol-
lowing training could represent preferential gating of learned input. Such a gating
mechanism could represent one aspect in the formation of long-term memory,
which could result in rapid stimulus recognition and the appropriate behavioral
response. Finally, the fact that the aPC electrical response remained unchanged
following learning supports the idea of that part of the PC being related more
to sensory analysis and to simple forms of nonassociative short-term memory.
Indeed, recent data have shown that aPC neurons displayed pronounced habitua-
tion to repeated presentations of a given odor at intervals in the range of minutes
(Wilson, 1998).
3.2. Effect of Odor Valence on Odor-induced Oscillatory Activities

in Central Olfactory Pathways
The sets of experiments we have just examined do not provide information
on how the system works during odor processing. That is because recordings
were obtained following training. Another set of experiments examined how
presentation of real odors would modify ongoing neural activity in the same
olfactory structures. In freely moving rats, macroelectrodes (80 µm in diameter)
simultaneously collected activities from the OB, aPC, pPC, and LEC. When the
LFP signals were filtered between 1 and 300 Hz, each trace reflected the sum of
extracellular current generated by cellular elements near the electrode tip. In each
structure, the tip of the electrode was positioned near the layer of output cells.
As mentioned earlier, normal neuronal activity from olfactory structures de-
veloped into prominent oscillatory activity between 1 and 100 Hz. That was the
case both in the absence and in the presence of odorant stimuli. Those oscilla-
tory regimes belong to different frequency bands (theta, beta, gamma) nested
together. In addition, most oscillatory regimes are expressed as short bursts of
activity lasting for a few hundreds of milliseconds. In brief, oscillatory regimes
are highly nonstationary and complex phenomena. In order to capture transient
significant changes in signal power induced by odor presentation, signal analysis
was based on time-frequency methods. The main method relied on fast-Fourier-
transform sliding windows, which allowed the capture of changes in signal power
with a 2–4-Hz frequency resolution and a 150–400-msec time resolution. With
that technique, we had two sets of experiments aimed at identifying how the
behavioral valences of different olfactory stimuli would modulate oscillatory
regimes in neuron assemblies.
The first series of experiments tested the importance of an animal’s moti-
vation for food in its responses to food and non-food odors. The food odor
consisted of the odor of the animal’s usual diet received in its home cage for
several days before the start of the experiment. The motivational state was con-
trolled by recording an animal’s responses following a period of free access
to food (noted as “satiated condition” in the following) or after a 16-hour fast
(noted as “food-deprived condition”). Another important aspect of the proto-
col was that no conditioned behavioral response was required. Indeed, odors
were introduced into the recording cage from the top, and no other sensory cue
announced odorant onset. Because rats had to perform no special behavioral re-
sponse to the stimuli except normal exploratory sniffing, we refer to that situation
as the “passive” one. Data analysis revealed several functional differences within
central olfactory pathways. First, during spontaneous activity, power-spectrum
analysis showed high degrees of similarity between the OB and the aPC, on one
hand, and between the pPC and the LEC, on the other hand. The OB-aPC com-
plex was dominated by high-frequency gamma (60–90 Hz) bursts of activity,
and the pPC-EC complex was dominated by beta (15–40 Hz) activity (Chabaud
et al., 2000). In addition, coherence analysis revealed that during spontaneous
activity, the aPC was coupled more tightly to the OB than to the pPC (Chabaud
et al., 1999). Thus the power and coherence analyses strongly suggested that the
two parts of the PC had different functional characteristics. Another dissociation
also appeared in response to food and non-food odors: A nutritional modulation
of the food-odor response (difference in responding rate between satiated and
food-deprived conditions) was observed at the level of the OB and the LEC.
It was not expressed in the aPC and pPC. That suggests that the neuronal and
neuroendocrine systems affected by changes in nutritional states exerted more
pronounced effects on the OB and the LEC than on the PC. In addition, signal
analysis revealed that the nutritional modulation was expressed in a beta-band
oscillatory regime ranging from 15 to 30 Hz, with maximum effect near 20 Hz.
Repeated presentations of the food odor with a 1-min inter-stimulus interval
showed that habituation was expressed differentially across the recorded struc-
tures, although the responses appeared as a general increase in activity in a
wide 15–90-Hz frequency band. For example, over many repetitions, the rates
of response declined in parallel in the OB and the LEC, remained stable in the
aPC, and increased in the pPC. That was interpreted as evidence for differential
expression of this simple form of short-term memory across the four recorded
sites. In particular, the aPC and pPC seemed to react in very different manners,
for reasons that remain to be investigated (Chabaud et al., 2000).
The data collected in the “passive” condition investigated, in an indirect man-
ner, the effects of learning on neural responses. Indeed, the odor of the usual food
did not have to be learned in a conditioning paradigm controlled experimentally,
and odor presentation was not associated with a behavioral response indicating
that the animal had recognized the stimulus. Thus, a second set of experiments
was based on a more classic approach, referred to as the “active” condition: Rats
had to learn that sampling odor A (S+) in an odor port should be followed by
a “go” response, and sampling odor B (S−) should be followed by a “no-go”
response. The “go” response consisted in rapidly crossing the entire length of
the recording cage (60 cm) to obtain a food reward. For the “no-go” response the
rats were to stay near the odor port. In that experiment, rats actively sampled
the odor, and the exact time of odor onset was known. The rats had electrodes
implanted in the OB, aPC, pPC, and LEC and were recorded at the very begin-
ning of training (“beginners”) and several days later once the responses had been
learned (“experts”). Time-frequency analysis was performed with a 150-msec
temporal resolution and a 4-Hz frequency resolution. The detailed results have
been presented elsewhere (Ravel, Chabaud, and Gervais, 1999). The experiment
led to several new observations. First, even for beginners, odor sampling (average
duration 550 msec) was accompanied by clear-cut changes in ongoing oscillatory
activities. For example, during the resting state, LFP recordings from the OB
were dominated by high-frequency gamma bursts (60–90 Hz) occurring during
each inspiration phase of the respiratory cycle. Such bursts have been extensively
described (Freeman and Skarda, 1985) and are known to originate from the OB
intrinsic circuitry. Concurrently, the activity in the beta band (15–30 Hz) was
low. Active sampling of an odor was associated with a sharp decrease in rapid
gamma bursts and with a significant increase in beta oscillation (Figure 21.3).
The beta response in the OB corresponded, on average, to a twofold increase
BETA Band (15–30 Hz) GAMMA Band (60–90 Hz)

GO Odor GO Odor
OB
APC
1mV 0.5 mV
200 msec
PPC
EC
Figure 21.3. Individual example of LFP activities collected simultaneously

from the OB, aPC, pPC, and LEC. The same signals are filtered in the beta
band, on the left, and in the gamma band, on the right. In this example, the rat
recorded in the “expert” condition sampled an odor learned as a “go” signal.
Olfactory sampling, which lasted for 550 msec, was associated with obvious
increases in amplitude in the beta-band oscillations for each recorded site,
together with marked decreases in amplitude in the gamma-band oscillations
for the OB and the aPC.
Table 21.1. Differential effects of learning on odor-induced beta oscillations in

olfactory pathwaysa
Group OB aPC pPC LEC

Beginners 2.07 ± 0.11 1.84 ± 0.1 1.92 ± 0.11 2.36 ± 0.87
(n = 41) (n = 42) (n = 37) (n = 40)
Experts 3.90 ± 0.26* 2.19 ± 0.08 2.87 ± 0.12* 2.28 ± 0.07
(n = 177) (n = 157) (n = 177) (n = 153)
a
The table expresses the average ratio (±SEM) of the signal amplitude during odor
sampling to the signal amplitude within 500 msec before odor sampling. Data are from
three rats for all odors used. The total numbers of trials are indicated in parentheses. For
beginners, amplitudes varied on the order of twofold for each structure. For experts, that
increased significantly for only the OB and the pPC. *p < .001 relative to beginners for
the same structure.
in activity, which lasted for about 20% of the sampling duration, with maxi-
mum activity centered on 20 Hz. Moreover, similar responses in the beta band
were observed in the aPC, pPC, and LEC, suggesting that active, brief-duration
olfactory sampling transiently evokes oscillatory activity in neuron populations at
a common frequency near 20 Hz within a large fraction of the central olfactory
pathways. That response was found to be strongly modified following learning,
and that effect was not due to changes in sampling strategy, because the dura-
tions of odor sampling, on the order of 400–600 msec, did not differ between the
beginner and expert conditions. In contrast, for the experts, both the amplitude
and duration of the odor-induced beta activity were enhanced.
Regarding amplitude, the average variation for experts during odor sampling
reached fourfold relative to the baseline, compared with a twofold variation for
beginners. In addition, that enhancement developed selectively in two structures
only: the OB and pPC. Conversely, in the aPC and EC, response amplitudes
remained at the same levels as in beginners (Table 21.1). Regarding the OB re-
sponse duration, its values ranged from 40% to 60% of the sampling duration,
instead of the 20% seen for beginners. As seen in Figure 21.3, the oscillatory
beta-band response could be observed in experts on single trials. Finally, the de-
pression in gamma 60–90-Hz activity within the OB was even more pronounced
in experts than in beginners. Those data led to at least two conclusions: First,
multi-site LFP recording revealed the existence of a common oscillatory regime
near 20 Hz in central olfactory pathways during odor processing. In similarity
to what has been found near 40 Hz in the visual system, the beta-band activ-
ity facilitated the emergence of synchronous neural assemblies in a widespread
neuronal network. The extent of that synchronous oscillating network is still
unknown, and we need to determine if it also spreads to other limbic structures
and to neocortical areas. The cellular elements responsible for its generation
also remain to be identified. Second, the effects observed following training
suggest that learning improved the neural synchronization within each recorded
structure.
4. Conclusion
The sets of recent data we have briefly described have revealed clear-cut
functional dissociation in olfactory pathways and have led to more general
considerations. Regarding functional dissociations, the most obvious one con-
cerns the anteroposterior axis of the PC. The effects of the resting state, the
rate of habituation, and the process of learning on the synaptic transmission and
modulation of beta-band odor-induced activity revealed functional differences
between the anterior and posterior parts of the PC. The current data suggests
that the aPC is functionally more tightly linked to the OB, and the pPC is more
tightly associated with the LEC.
Finally, the more we learn about the physiology of early olfactory areas studied
in active animals, the more we realize the complexity of the computations per-
formed at those levels. In a manner similar to what is observed in auditory
pathways (Edeline, 1999), experience has profound effects on how neural re-
sponses to olfactory input are expressed. However, understanding their func-
tional significance will require identifying how these changes affect or result
from what happens in other structures. In other words, multi-site electrophys-
iological recordings in active animals can complement brain-imaging studies
in humans. Looking more closely at network functioning, instead of merely
structure, we predict that new data will reinforce our view that olfactory cog-
nition cannot be considered as resulting exclusively from hippocampal or/and
neocortical processing.
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22
Increased Taste Sensitivity by Familiarization
to Novel Stimuli: Psychophysics, fMRI,
and Electrophysiological Techniques Suggest
Modulations at Peripheral and Central Levels
Annick Faurion, Barbara Cerf, Anne-Marie Pillias,
and Nathalie Boireau
Several studies have shown that taste-aversion conditioning can modify the neu-
ral coding of taste in rodents. Chang and Scott (1984) reported that after aversive
conditioning to saccharin, rats declined to drink saccharin solution, and, simul-
taneously, the neural code in the first relay, the nucleus of the solitary tract
(NST), showed drastic changes compared with the neural code analyzed in un-
conditioned rats. Similarly, after aversive conditioning, c-fos staining showed
changes in the locations of saccharin-responding neurons in the parabrachial
nuclei (PBN) (Yamamoto, 1993) and in the NST (Houpt et al., 1994, 1996).
Preference conditioning has been shown to produce changes in neural activation
patterns in the NST (Giza et al., 1997).
In rodents, taste afferent pathways lead, on the one hand, to cortical taste ar-
eas through the NST, the PBN (the pontine taste relay), and thalamus and, on
the other hand, to the amygdala, the lateral hypothalamus, and the bed nucleus
of the stria terminalis (BST). In primates, the pontine taste relay is bypassed,
and the NST projects directly to the parvicellular region of the thalamic ven-
troposteromedial nucleus (VPMpc). Efferent pathways from the amydgala, lat-
eral hypothalamus, and BST have been traced down to the pons and the NST
(Norgren, 1985). We know from a study by Mora, Rolls, and Burton (1976)
that in primates, the lateral hypothalamus contains neurons responding to highly
integrative information, such as the sight of a taste stimulus that a monkey
likes. The rat lateral hypothalamus has been shown in operant-conditioning
experiments to contain neurons that fire during electrical self-reinforcing
self-stimulation.
The first part of the afferent pathway leads to cortical cognition-related pro-
jections, coding for quality and intensity of perception, whereas the second part,
leading to the lateral hypothalamus and to the amygdala, is believed to be related
to more subjective functions. The modifications in the neural coding of taste
quality and taste intensity that can be produced by aversive conditioning may
350
Functional Plasticity of Taste 351
have their origins in feedback from the lateral hypothalamus to the NST and/or
the pontine taste areas through efferent innervation.
Whatever the structures responsible for such modulations, it seems highly
probable that modification of the neural code at the NST or PBN level should
have consequences for taste coding at the thalamic and cortical levels because
of the organization of successive projections (Figure 22.1). Hence, we suspected
BST AGIC
CNA
HTH VPMpc
PBN
NST
AGIC
BST
CNA
HTH VPMpc
PBN
NST
Figure 22.1. Schematic diagram of the central gustatory pathways in the rat.
Top: Afferent projections to the nucleus of the solitary tract or nucleus trac-
tus solitarius (NST), the pontine parabrachial nuclei (PBN), the parvicellular
region of the thalamic ventroposteromedial nucleus (VPMpc), and the agran-
ular insular cortex (AGIC), on the one hand, and to the hypothalamus (HTH),
the central nucleus of the amygdala (CNA), and the bed nucleus of the stria
terminalis (BST), on the other hand. Dashed projections from the NST probably
convey visceral information; the function of those from the PBN is unknown.
The dotted line from the NST to the thalamus indicates that the pontine taste
relay is bypassed in the primate. Bottom: Efferent projections. Dashed arrows
represent pathways not proven to arise from the AGIC. (Adapted from Norgren,
1985.)
352 Faurion, Cerf, Pillias, and Boireau
that cortical neuronal activity would not be found to be invariant, but rather
would depend on the subject’s experience and on the nature of any stimulus
presented. In other words, is the sensitivity to tastants simply fixed by genetically
determined receptors, or can there be modulations of that sensitivity attributable
to experience?
Extensive experiments in aversive conditioning cannot be carried out in hu-
mans, for obvious ethical reasons. But conditioned taste aversion can be con-
sidered as an innocuous example of the taste conditionings that occur in our
daily lives and can be reproduced in the laboratory. Learning a novel taste, on
the one hand, and extinction of neophobia, on the other hand, are two such
situations that arise spontaneously in our lives, and they can be used as mod-
els for studying how “experience” can modulate neural signals. Often a novel
food will initially produce neophobia (Rozin, 1976), but subsequent exposures
to that food may turn neophobia into preference, or at least a neutral reaction.
Learning is an essential function in gustation. As a matter of fact, no experi-
ment can yield any relevant result in a single session. We have observed that
supraliminal sensitivity can increase by a factor of 4 during learning studies,
and detection thresholds can be lowered by a factor of 10 (A. Faurion, unpub-
lished observations; Faurion, 1994). Our experience has shown that it is only
after directed learning has taken place that humans become reliable subjects for
evaluating taste intensity (Faurion, 1993). Instead of discarding the data accumu-
lated during the learning period, as is usually done, in this study we have tried
to understand the evolution mechanisms that might be revealed by such data.
What actually happens, from the neuronal point of view, during such a learn-
ing period? Were there any changes that we might measure? Were any changes
simply a matter of central plasticity in the central nervous system? Were there
peripheral modifications involved as well? If there are modifications in taste
coding with experience, it should be possible to observe correlates of such plas-
ticity both with psychophysical sensitivity measurements and with functional
magnetic-resonance imaging (fMRI) in human subjects. Peripheral modifica-
tions of sensitivity should be measurable using electrophysiological recordings
of taste nerves in animals. Therefore, the studies we report here were aimed
at detecting clues to changes in the neural code in cognition-related taste areas
in humans, as well as changes at the chorda tympani level in hamsters, as the
status of a stimulus changed from novel (and, later, preferred or neophobic) to
familiar. The first experiment was designed to look for changes in sensitivity dur-
ing familiarization using psychophysics. The second experiment was an fMRI
study aimed at visualizing changes in the numbers of activated pixels in cortical
taste areas during familiarization. The third experiment was aimed at detecting
any modulation in signals from the peripheral taste receptors in hamsters during
familiarization.
1. Increased Sensitivity during Familiarization to

Novel Stimuli in Humans
Thirty healthy subjects, 20 to 24 years old, participated in the psychophysics
experiment. They were not aware of the aim of the experiment and were not in-
formed of their experimental performances until the end of the experiment. Five
of them took part in the simultaneously ongoing neuroimaging study with fMRI.
A group of 14 chemicals, not related to usual tastants, and chosen from a series of
182 chemicals previously tested in our laboratory, was submitted to preliminary
testing by a different panel: Two stimuli, guanosine 5 -monophosphate (5 -GMP)
and taurine, seemed to have a high probability of being judged as bad-tasting and
inducing neophobia, so they were selected. Two other stimuli, d-threonine and
glycyrrhizic acid, showed positive hedonic characteristics and were also selected.
Those four stimuli were used for iso-intense concentration measurements. Sub-
jects were submitted to a training period for 3 weeks with casual stimuli: quinine
and sucrose. Then the familiarization experiment followed: at least 10 weeks with
the four selected stimuli. Several parameters were recorded during the fami-
liarization experiment. Iso-intense concentrations (concentrations evoking the
same perceived intensity as the reference) were repetitively estimated for all
four compounds during two 2-hour sessions per week. Estimates of the strength
or concentrations of the solutions, here called “magnitude” estimations (at con-
stant concentration), were repetitively recorded, and hedonic evaluations and
semantic descriptions (“quantitative descriptive analysis”) were given during
one 90-min session per week. A food-intake questionnaire was filled out on each
experimental day, and the hormonal status of female subjects was recorded.
Subjects participated into three sessions per week, totaling 6 hours per week.
Stimuli were prepared every day with ultraviolet-sterilized water in sterile
glassware. Tests for bacterial contamination were conducted randomly every
day. The solution temperature was controlled at 0.1˚C. For iso-intense concen-
tration estimations, a forced-choice paired comparison of the stimulus with an
NaCl reference solution (1.7 g/liter) was used. The subject was asked, Which
is stronger? The stimulus concentration was varied according to the preceding
response of the subject, following the staircase procedure of Dixon and Massey
(1960), referred to as the up-and-down procedure. The dilution and distribu-
tion of solutions were computer-controlled in two home-built devices that could
accommodate up to eight subjects; those devices diluted and distributed the
solutions and controlled the opening and closing of the microvalve apertures.
The concentration of the solution distributed to a subject depended on his/her
response to the preceding paired presentation. Different up-and-down tests were
intermingled so that the staircase procedure was not apparent to the subject.
(The procedure was actually double-blind.) During each session, the up-and-
down test was repeated four times for each stimulus, which meant that the test
lasted about 30 min per stimulus (2 hours for all four stimuli), including about
30 paired presentations per stimulus. Results were calculated and printed au-
tomatically. The iso-intensity evaluations were averaged and compared from
session to session for each subject individually. The effect of learning was de-
termined by the evolution of the iso-intense concentration estimations using
statistical evaluation (t-test). For magnitude estimation, hedonic evaluation, and
quantitative descriptive analysis, three stimuli (l-valine, d-methyl mannopy-
ranoside, naringin) were added to increase the variety of stimuli so that the
subjects could not memorize their own evaluations from one session to the next.
For magnitude estimation, quantitative descriptive analysis, and hedonic eval-
uation, solutions were also sterile and were prepared with the following: gly-
cyrrhizic acid, 0.4 g/liter; 5 -GMP, 0.4 g/liter; d-threonine, 30 g/liter; taurine,
60 g/liter; d-methyl mannopyranoside, 20 g/liter; naringin, 0.15 g/liter; l-valine,
3 g/liter.
1.1. Hedonic Assessment for Each Stimulus

Preference evaluations (using a scale from −10 to +10) were positive at the
first session for 24 or 25 stimuli out of 30, for glycyrrhizic acid (m = +4.6, s.d.
1.95), and for d-threonine (m = +2.5, s.d. 0.5). Evaluations were negative for
5 -GMP (m = −1.7, s.d. 0.80) and taurine (m = −1.6, s.d. 0.65), with a few
subjects giving opposite hedonic evaluations.
1.2. Evolution of Subjects’ Sensitivity during Familiarization

Figure 22.2A shows a typical familiarization curve for individual data. The es-
timations of iso-intense concentration diminished with successive sessions until
stabilizing. Group data showed that for hedonic-positive glycyrrhizic acid and
d-threonine, the iso-intense concentrations estimated with reference to NaCl
(1.7 g/liter) diminished and then stabilized. For the hedonic-negative stimu-
lus taurine, estimates of the iso-intense concentration diminished and stabilized
as for glycyrrhizic acid and d-threonine. For the hedonic-negative stimulus 5 -
GMP, estimates of the iso-intense concentration fluctuated but never diminished.
In all cases, the group variance was much higher than the individual variances
individual results during learning

mg//l
400
300
200
100
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Sessions
Figure 22.2A. Familiarization to a novel stimulus (glycyrrhizic acid), individ-

ual data (m ± s.e.m). Iso-intensity concentrations (ordinate) were estimated
in 15 sessions (abscissa). The iso-intense concentration was determined by
comparison with a solution of NaCl (1.7 g/liter) in a forced-choice paired com-
parison test, associated with the up-and-down presentation technique. Each
point is the mean for four up-and-down tests, representing 30 min of repetitive
testing for one stimulus (about 30 paired comparisons). A learning pattern is
clearly observed: The decrease in iso-intense concentration indicates increased
sensitivity.
Taurine
isoint (group results) m. e.
g//l
50 30
40 25
30 20
20 15
10 10
1 2 3 4 5 6 7 8
weeks
Figure 22.2B. Comparison of iso-intense concentrations and magnitude

estimates. Data were averaged for the group of subjects. Iso-intensity concen-
trations (squares) diminished when magnitude estimates (diamonds) increased.
because of high and significant inter-individual differences in sensitivity. The

estimations of magnitude and iso-intense concentration varied, as expected,
as mirror images of each other for glycyrrhizic acid, d-threonine, and taurine
(Figure 22.2B). Magnitude estimates showed that all three compounds seemed
progressively stronger to subjects with increasing familiarization, and, simulta-
neously, subjects used lower and lower concentrations to match the reference
intensity in iso-intense concentration estimations. The two techniques were in
agreement in showing an increase in sensitivity due to familiarization or learning.

In contrast, the group data fluctuated, without showing a learning effect, for
5 -GMP.
The initially positive preference evaluations decreased slightly for glycyrrhizic
acid and d-threonine, with subjects showing decreasing attraction to those
stimuli; on the contrary, the initially negative group evaluation for taurine tended
to zero, indicating extinction of neophobia. Moreover, a subgroup of six subjects
tended to give positive scores, and their averaged hedonic evaluations reached the
positive value of +2. As far as 5 -GMP was concerned, the hedonic evaluations
varied randomly, and it remained neophobic, without extinction.
From those findings it appears clear that taste sensitivity increased signif-
icantly with familiarization for three stimuli out of four: taurine, a hedonic-
negative novel stimulus exhibiting extinction of neophobia; glycyrrhizic acid
and d-threonine, two hedonic-positive stimuli. On the contrary, neither a reduc-
tion in neophobia nor any learning pattern was observed for 5 -GMP.
2. fMRI Discloses Plasticity in Cortical Areas during

Familiarization to Novel Taste Stimuli
Among the 30 subjects in our first experiment, 5 participated simultaneously
in the fMRI experiment. That neuroimaging experiment (Faurion et al., 1998)
was aimed at mapping changes in the activation of cortical taste areas during
the process of familiarization with novel stimuli. Experiments were performed
using a 3-tesla whole-body MR scanner (Bruker, Germany) allowing echo-planar
imaging (EPI). At the beginning of each session, a sagittal image was acquired
to select 12 slices covering 72 mm of cortex surrounding the sylvian fissure.
Twelve high-resolution, high-contrast inversion-recovery images (256 × 256
pixels, TR = 3 sec, TE = 8 msec, IR = 800 msec) were acquired for anatomical
identification of the activated foci. During the 5-min stimulation, 50 EPI images
per slice (64 × 64 pixels, FOV = 200 mm, thickness = 6 mm, TE = 40 msec,
TR = 6 sec) were recorded.
Three stimuli from the psychophysics experiment were used: 5 -GMP,
0.4 g/liter (1-mm), glycyrrhizic acid, 0.4 g/liter (0.5-mm), d-threonine, 30 g/liter
(250-mm). The first contact of the subjects with novel stimuli occurred on the
first fMRI experimental day, prior to the psychophysical first experimental day.
The second fMRI experiment was conducted after the first psychophysical exper-
iment, by which time the subjects had experienced about 200 repetitive forced-
choice pair tests in a 2-hour experimental session. The third fMRI experiment was
conducted at the end of the familiarization (i.e., after 10 weeks of psychophysical
experimentation).
Each subject sampled three stimuli and water, as a control, at each fMRI
session. Liquids were manually pushed into the subject’s mouth through
microsyringes and silicon tubes (ID: 1.19 mm) at 50 microliters every 3 sec. Sub-
jects could swallow freely, and no peculiar head-motion artifacts were recorded
with such microquantities. The stimulation paradigm consisted in two ON
(30-sec) and OFF (90-sec) periods after a first 60-sec OFF period of reference
using water. For the wate-control experiment, the same ON and OFF periods
were alternated, water being sent to the subject during ON and OFF periods,
through two different syringes, just as tastant and water were sent during actual
taste experiments. The perceived intensity was continuously measured through-
out the fMRI experiment. Subjects used a linear potentiometer and matched the
intensity of their perceptions by the distance between the thumb and forefinger
according to the “finger-span” method (Berglund, Berglund, and Lindvall, 1978).
The resulting plot of time versus perceived intensity was AD-converted and used
for processing fMRI data by correlating the MR signal for each pixel with the
time–intensity profile. The time–intensity profile obtained with the finger-span
technique proved to be a powerful template to detect brain activation, particularly
adapted for the case of the generally slowly rising taste responses, with no bias
introduced relative to finger movement (Cerf et al., 1996a,b; Van de Moortele
et al., 1997).
Images were processed using custom IDL software (Le Bihan et al., 1993)
(Interactive Data Language, Research System Inc., Boulder, CO). Activations
were calculated for each pixel based on the correlation coefficient between the
MR signal and the perception profile recorded during the experiment. Pixels
with r > 0.4 and belonging to clusters of at least two pixels were selected.
Clusters with r > 0.4 and p < .001 (Student t-test) were finally considered as
activated. After pixels had been selected, the regions in which they were found
were identified with Duvernoy and Talairach atlases; the Voxtool 3D software
was used for localization of sulci at the surface of the brain.
Taste activations (Figure 22.3) were found bilaterally, surrounding and buried
in the sylvian fissure (Cerf et al., 1996a,b, 1997, 1998, 1999; Cerf, 1998; Faurion
et al., 1998, 1999; Cerf-Ducastel et al., 2001). The upper part of the insula, the
frontal operculum, the feet of pre-central and post-central gyri (rolandic opercu-
lum), and the temporal operculum were usually activated – hereafter collectively
referred to as the peri-insular area. The locations of the detected clusters of ac-
tivated pixels were in agreement with electrophysiological studies performed
in monkeys (Patton and Ruch, 1946; Burton and Benjamin, 1971; reviewed
by Ogawa, 1994; Norgren, 1995) and clinical observations gathered in humans
(reviewed by Norgren, 1990). Positron-emission tomography (Kinomura et al.,
1994) has revealed taste-related activations in the insula and temporal lobe,
Stimulus
Water
Figure 22.3. Examples of activation pixels observed for taste stimulation by

FMRI: horizontal anatomical sections presented according to radiological
orientation (the subject’s left side is at the right in the figure). Top: Taste
stimulation. Bottom: Control presentation of water. Activation was found in
and around the insular cortex: anterior insula, frontal operculum, superior tem-
poral gyrus (opercular part), bordering the sylvian fissure and the inferior parts
of pre- and post-central gyri. Other activation foci were observed in the tempo-
ral lobe, frontal lobe, medio dorsal thalamus, anterior cingulate gyrus, angular
gyrus, and supramarginal gyrus.
as further confirmed by Small et al. (1999). Magnetoencephalographic studies

(Kobayakawa et al., 1996, 1999; Murayama et al., 1996) have shown that some
dipoles located in the insula exhibit the shortest latencies. That finding supports
the hypothesis that regions of the insula or peri-insular area should receive the
primary sensory projection (i.e., a direct projection from the thalamus). More
recently, Barry et al. (2000) found insular activation with fMRI using “electric
taste” as a stimulus. In addition, we have recorded activations in the anterior
cingulate gyrus, the centromedial thalamus, and other areas related to emotional
or cognitive processes.
We observed that the percentages of activated pixels in the peri-insular area
increased or decreased with familiarization and hence looked for psychophysical
correlates of those modifications. We categorized experiments (one experiment
being one subject stimulated with one stimulus) according to the evolution of
the hedonic assessments. We found (Figure 22.4) that an experiment that at first
yielded a low hedonic evaluation that increased with familiarization also showed
m group I nb pixels group I
m group II % nb pixels group II
p < 0,001
p < 0,003
10 35
% activated pixels in peri insular

8
30
6
preference evaluation
25
area/whole brain
4
2 20
3
0 15
-2
1 2 10
-4
5
-6
1,2,3: fMRI sessions
-8 0
1 2 3 4 5 6 7 8 9 10 11 1 2 3
psychophysics sessions fMRI sessions
Figure 22.4. Effects of familiarization on the evolution of hedonic assessments

and the evolution of the percentages of activation pixels in the peri-insular
region. Left: Preference data for 5 subjects and 3 stimuli (from experiment I).
Experiments are grouped according to increasing (group I) or decreasing (group
II) hedonic assessments during the familiarization experiment. The difference
between the two groups of experiments was highly significant ( p < .001, χ 2 ).
Right: fMRI data for the same two groups (groups I and II). The evolutions of
the percentages of activation pixels in the peri-insular areas were significantly
different for the two groups ( p < .003, χ 2 ). High hedonic values corresponded to
high percentages of activation pixels in the peri-insular region, which decreased
in parallel with hedonic assessments during the familiarization. Low hedonic
values corresponded to low percentages of pixels in the peri-insular region,
increasing in parallel with the hedonic assessments during familiarization.
a low percentage of activated pixels in the peri-insular region, which increased

with familiarization. Conversely, experiments yielding higher hedonic evalua-
tions that diminished with familiarization also showed higher percentages of
activated pixels in the peri-insular area, which diminished with familiarization.
The differences in activated pixels occurred between the first and second fMRI
sessions, separated by only one psychophysical session, and were highly signifi-
cant ( p < .003, χ 2 ), and so were the differences between corresponding hedonic
evaluations ( p < .001, χ 2 ). Subjects needed only one session for learning before
showing significant differences in fMRI results.
In conclusion, in the peri-insular area, the percentages of activated pixels
varied with familiarization, depending on the evolution of hedonic assessments
during familiarization. If the dislike for the stimulus disappeared, the number of
pixels increased. When the positive hedonic score decreased, a phenomenon we
interpreted in terms of loss of interest in the repeated stimulus, the number of ac-
tivated pixels also diminished. Simultaneously, it should be remembered that the
perceived intensity was statistically increased for all subjects when the stimulus
became more familiar, whether it be preferred or recovering from neophobia.
Whether these findings relate to a possible encoding of preference intermin-

gled with coding of taste intensity in the areas we observed is not known, but we
suggest, for further study, the hypothesis that the so-called subjective hedonic
aspect might contribute to and structure putatively more “objective” intensity
information. Another interpretation might be that those quantitative modifica-
tions in the pixel numbers related to the subject’s “interest” in the chemical. We
can understand that familiarization might interfere with the subject’s interest in a
tastant. It should be noted that the experimental procedures included no ingestion
(except for a few microliters in the case of fMRI experiments), which prevents
any comparison with a reward situation (Rolls and Rolls, 1977, 1982).
Plasticity of taste coding was clearly shown using psychophysics and brain
imaging cooperatively. We saw that sensory information could actually be mod-
ified by the previous experience of the subject, and we saw a correlate of the
subject’s experience of modulating both the perceived intensity and the neural
code reflected in the relative numbers of activated pixels in the cortical peri-
insular area observed with fMRI. Those findings correlate with earlier results
showing modification of neural taste coding with aversive or preference condi-
tioning at the hindbrain level. Indeed, the cortical taste message does not seem
to be invariant, but rather subject to modulation in relation with the subject’s
experience. As has been well documented in the earlier literature, the effects
seen in both of the first two synaptic relays have consequences for coding in the
higher forebrain structures. Apart from aversive conditioning, which is seldom
encountered, many events in everyday life do act as mild conditionings that can
eventually modulate and shape our taste information.
3. Peripheral Electrophysiology in the Hamster: Modulation

of Sensitivity with Familiarization at the Receptor Level
After our demonstration of central plasticity, the question naturally arose whether
the peripheral chemoreceptor equipment is invariant and genetically determined
or possibly is adaptable to environmental situations. An approach to that question
is possible because of the availability of animal models. Our earlier recordings
from the chorda tympani nerve using a series of organic stimuli involved ani-
mals that had been familiarized to the stimuli before our experiments, for better
reproducibility of responses (Faurion and Courchay, 1990; Faurion, 1993). This
third experiment (Boireau, Pillias, and Faurion, 1999, in press) was designed
to detect any differences in the sensitivity of taste chemoreceptions at the pe-
ripheral level. We examined the reproducibility of chorda tympani responses
over time, looking for eventual modulation of peripheral sensitivity following
familiarization to novel stimuli. Several groups of hamsters were pre-exposed to
various novel tastants, and their responses were compared with those of control
hamsters without pre-exposure.
Pre-exposure consisted in overnight two-bottle choice tests in the home cage
lasting at least two weeks (23 nights ± 7.5). One group of hamsters was exposed
to dulcin (5-mm), a sucrose-like stimulus (Dul group), one group was exposed
to potassium glutamate (50-mm) (KGlu group), and one group was exposed to
5 -GMP (1-mm) (5 -GMP group). After the familiarization period, animals were
anesthetized, and the right chorda tympani (CT) nerve was monitored without
being cut, to prevent an eventual effect of deafferentation on the sensitivity of
the peripheral receptor system (Oakley, Jones, and Hosley, 1979; Oakley, Chu,
and Jones, 1981).
Seventeen stimuli were chosen to be used in evaluating any eventual differ-
ences in sensitivity to chemicals among the various familiarized and control
groups. The stimuli were presented six times. The chemicals were dissolved
in ultraviolet-sterilized tapwater and frozen at −24˚C. Prior to the experiment,
samples were equilibrated at controlled room temperature to avoid thermal stim-
ulation of the tongue. A continuous water flow, at a rate of 40 ml/min, was
applied to the animal’s tongue, and stimuli were applied for 12 sec at intervals
of 75 sec. The 17 stimuli were randomly ordered, and a different random order
was used for each of the six presentations, and 102 responses were recorded in
less than 2.5 hours. For each hamster and each stimulus, the percentage increase
in response amplitude was calculated by comparison to the first stimulation with
that stimulus. The individual percentage increases were averaged in each group
(m ± SD) for each stimulus and checked for significance with a paired Student
t-test for each stimulus in each group and with anova (Fischer LSD) among the
five hamster groups.
Significant increases in CT response amplitudes between the first and the
sixth presentations were observed for 15 of 17 stimuli in the control group, with
a mean percentage increase varying from 16% ± 24% for d-threonine to 109%
± 65% for KGlu (50-mm).
For animals familiarized to 5 -GMP, no increases in CT response amplitudes
to 5 -GMP were observed with repetition of stimulation (0% ± 22%), as com-
pared with groups pre-exposed to other stimuli, and with the control group
(p < .05; Fischer LSD). CT response amplitudes to KGlu were not increased
in the group familiarized to KGlu (50-mm) nor in the group familiarized to
5 -GMP. The effect of familiarization to 5 -GMP generalized to KGlu. In the
case of familiarization to dulcin, a different effect was observed. The CT re-
sponse amplitudes to the conditioning stimulus dulcin increased as much in the
Dul group as in the control group during acute recording. However, the two-week
familiarization to dulcin had effects on the amplitudes of responses recorded in
the first series of stimulations, for they were significantly higher than in the
control group ( p < .05).
From this experiment, it is clear that familiarization to novel stimuli in-
duces modifications in quantitative peripheral responses. Not only plasticity in
brain areas but also peripheral adaptation may be responsible for the objective
increases in sensitivity measured in human subjects in our first experiment in
psychophysics. Such observations may reflect enhancement of specific gene ex-
pressions in taste cells. In the liver, metabolites like glucose can influence the
regulation of specific gene expressions by receptors, an effect that is stimulus-
and concentration-dependent (Foufelle, Girard, and Ferre, 1998). The findings in
our study suggest a possible induction of supplementary synthesis of taste recep-
tor protein. Organic tastants are detected by G-protein-coupled receptors on the
apical surface of a taste cell (Striem et al., 1989; Bernhardt et al., 1996; Kinnamon
and Margolskee, 1996; Uchida and Sato, 1997; Herness and Gilbertson, 1999).
Either supplementary receptors might be induced or the transductional coupling
might be enhanced.
Immediate early genes such as c-fos, C-jun, and so forth, could be induced
during the repetitive stimulation and during familiarization. Known mechanisms
coupling neuronal activity and intracellular biochemical processes leading to
gene expression include Ca2+ influx (Finkbeiner and Greenberg, 1998), neuro-
tropic factors, and membrane-depolarizing agents. All these conditions coalesce
during the taste-cell response, along with the presence of growth factors (Nosrat
et al., 1996, 1997; Oakley et al., 1998; Cooper and Oakley, 1998). Greenberg,
Thompson, and Sheng (1992) showed that different pathways activate distinct
subsets of immediate early genes, and proteins encoded by immediate early
genes may subserve different functions – among them, long-term adaptive
responses. We suggest that the observed modulations of the increases in CT
response amplitudes might involve such immediate early genes in long-term
adaptive transcriptional responses.
4. Conclusion
Plasticity in cortical taste areas might be responsible for increases in perceived
intensity, which can be measured in human subjects during learning. There is a
hint that this increase in sensitivity might interfere with preference for the stimu-
lus or some relevant aspect of the stimulus. Our results are in accordance with the
idea that the taste neuronal code may be modifiable by learning, as suggested for
the hindbrain levels by experiments on aversive and preference conditionings by
the groups of Scott, Houpt, and Yamamoto. Moreover, we suggest that the plas-
ticity might extend to every level of the central nervous system, in accordance
with the study of Montag-Sallaz et al. (1999) on rodents, using novel stimuli.
Moreover, our study showed increases in CT response amplitudes to novel stim-
uli with repetitive stimulation, effects that could be reduced or suppressed after
a familiarization period. Not only brain plasticity but also supplementary recep-
tors or facilitation of transduction coupling, induced by stimulation, may modify
individual sensitivity after familiarization to a novel stimulus. It is clear that the
multiple small conditionings of everyday life are potential modulating agents
for taste sensitivity, either through plastic neural coding or through peripheral
modulation of receptor sensitivity, or both.
Acknowledgments
We gratefully acknowledge financial support from the Aliment Demain program
(Ministry of Agriculture), in cooperation with Danone and Orsan, for our experi-
ment 1 and from GIS (CNRS-CEA) for our experiment 2.
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23
The Cortical Representation of Taste and Smell
Edmund T. Rolls
The aims of this chapter are to describe the rules that appear to govern the corti-
cal processing of taste and smell, how taste and smell inputs combine with each
other to form flavor, how visual and oral somatosensory inputs also converge
with taste and smell, and how hunger affects the representations in different
cortical areas. Particular attention is paid to investigations in a non-human pri-
mate, the macaque, because they have provided fundamental evidence relevant
to understanding information processing in the same areas in humans, and to
neuroimaging studies in humans to complement the primate studies. A broad
perspective on the brain processing involved in emotion and motivation is pro-
vided elsewhere (Rolls, 1999a).
1. Taste Pathways in Primates

A diagram of the taste and related pathways in primates is shown in Figure 23.1.
Of particular interest is that in primates there is a direct projection from the rostral
part of the nucleus of the solitary tract (NTS) to the taste thalamus and thus to the
primary taste cortex in the frontal operculum and adjoining insula (Figure 23.2),
with no pontine taste area and associated subcortical projections as in rodents
(Norgren, 1984; Pritchard et al., 1986). The emphasis on cortical processing of
taste in primates appears to be related to the extensive development of the cerebral
cortex in primates and to the advantage of using similar cortical analyses of inputs
from every sensory modality before the analyzed representations from all modal-
ities are brought together in multimodal regions, as will be documented here.
A secondary cortical taste area in primates was discovered by Rolls, Yaxley,
and Sienkiewicz (1990) in the caudolateral orbitofrontal cortex, extending sev-
eral millimeters in front of the primary taste cortex (Figure 23.2). Injections of
horseradish peroxidase in that region produced labeled cell bodies in the primary
taste cortex (Baylis, Rolls, and Baylis, 1994).
367
368 Edmund T. Rolls
VISION
V1 V2
TASTE
Taste Nucleus of the
Receptors solitary tract
OLFACTION
Olfactory
Bulb
TOUCH
Thalamus VPL
Figure 23.1. Schematic diagram of the taste and olfactory pathways in primates
showing how they converge with each other and with visual pathways. The
gate functions refer to the finding that the responses of taste neurons in the
orbitofrontal cortex and the lateral hypothalamus are modulated by hunger.
VPMpc, parvicellular region of the ventraoposteromedial thalamic nucleus;
V1, V2, V4, visual cortical areas.
2. Taste Processing in the NTS and the Taste Thalamus

Taste neurons have been found, and their responses analyzed, in the rostral part
of the NTS in macaque monkeys (Scott et al., 1986a). It was found that different
Cortical Representation of Taste and Smell 369
Inferior temporal
V4 visual cortex
Amygdala Striatum
Thalamus Lateral
VPMpc nucleus Hypothalamus
Gate Gate
Frontal operculum/Insula function
(Primary Taste Cortex)
Orbitofrontal
Cortex
Hunger neuron controlled
by e.g. glucose utilization,
stomach distension or body
weight
Olfactory (Pyriform)
Cortex
Insula
Primary somatosensory cortex (1.2.3)
Figure 23.1. (cont.)
neurons responded best to various stimuli – orally administered glucose, NaCl,

HCl (sour), and quinine HCl (bitter) – but the tuning of the neurons was in most
cases broad, in that, for example, 84% of the neurons had at least some response
to three or four of these four prototypical taste stimuli. Pritchard, Hamilton,
and Norgren (1989) were able to confirm that the parvicellular division of the
ventroposteromedial (VPMpc) nucleus of the thalamus is the relay nucleus for
thalamic taste in primates: In macaque monkeys, single neurons in the VPMpc
responded to taste stimuli.
Frontal Opercular cortex Anterior Insular cortex Orbitofrontal cortex
0.0 A 1.0 P 6.0 A
In
Caudate Caudate
te
Int
er
rn
na
al
l
C
Ca
ap
su
psu
Putamen
le
le
Putamen
Sylvian Fissure Sylvian Fissure
Figure 23.2. Coronal sections to show the locations of the primary taste cortices in the macaque in the frontal operculum and
rostral insula and the location of the secondary taste cortex in the caudolateral orbitofrontal cortex. The coordinates are in
millimeters anterior (A) or posterior (P) to the sphenoid (Aggleton and Passingham, 1981).
3. Gustatory Responses in the Primary Taste Cortex

Taste neurons in the frontal opercular cortex and rostral insular cortex in the
cynomolgus macaque monkey, Macaca fascicularis (Figure 23.2) were found to
be more specifically tuned to the prototypical stimuli (glucose, NaCl, HCl, and
quinine HCl) than were neurons recorded in the same monkeys in the NTS (Scott
et al., 1986a,b; Yaxley, Rolls, and Sienkiewicz, 1990). With the use of glucose
and NaCl, a corresponding area has been demonstrated by fMRI investigations
in humans (e.g., Francis et al., 1999; O’Doherty et al., 2001).
4. Gustatory Responses in the Secondary Cortical Taste Area:

Caudolateral Orbitofrontal Cortex
In a study of the role of the orbitofrontal cortex in learning, Thorpe, Rolls, and
Maddison (1983) found a small proportion of neurons (7.9%) showing gustatory
responses in the main part of the orbitofrontal cortex. In recordings made from
3,120 single neurons, Rolls et al. (1990) showed that to be a secondary cortical
taste area in the dysgranular field of the orbitofrontal cortex (Ofdg) (Figure 23.2),
situated anterior to the primary taste cortical area. Quite sharp tuning to several
taste stimuli (glucose, NaCl, HCl, quinine HCl, water, blackcurrant juice) was
evident in many cases, in that some of the neurons responded primarily to one
tastant. That tuning was much finer than that seen for neurons in the NTS in
the monkey, and finer than that for neurons in the primary frontal opercular and
the insular taste cortices. With the use of glucose and NaCl, a corresponding
area in the medial orbitofrontal cortex close to the subgenual cingulate area has
been demonstrated by f MRI investigations in humans (e.g., Francis et al., 1999;
O’Doherty et al., 2001).
In the secondary taste cortex and also in the primary taste cortex, populations of
neurons were found that responded to the taste stimuli monosodium l-glutamate
(MSG), glutamic acid, and inosine 5 -monophosphate (IMP), which are tastants
that produce the protein or “umami” taste (Baylis and Rolls, 1991; Rolls et al.,
1996a; Rolls, 2000a). Across those populations of neurons, the responsiveness
to glutamate was poorly correlated with the responsiveness to NaCl, so the rep-
resentation of glutamate was clearly different from that of NaCl. Further, the
representation of glutamate was shown to be approximately as different from the
representation of each of the other four tastants as they were from each other, as
shown by multidimensional scaling and cluster analysis. It was concluded that
in primate taste cortical areas, the taste of glutamate, which produces the umami
taste in humans, is approximately as well represented as are the tastes produced
by glucose (sweet), NaCl (salty), HCl (sour), and quinine HCl (bitter). Thus the
neurophysiological evidence in primates indicates that there is a representation
Cell Be047
7
Firing Rate (Spikes/s)

2
H2O
triolene
gluc 0.5M
silicone oil
paraffin oil
NaCl 0.5M
HCl 0.01M
spontaneous
MSG 0.05M
vegetable oil
Q-HCl 0.001M
milk (0.1% fat)
cream (18% fat)
cream (47.5% fat)
Figure 23.3. Responses of a primate neuron in the orbitofrontal cortex to the texture of fat in the mouth. The cell (Be047) increased
its firing rate to cream (double and single cream), and responded to texture rather than to the chemical structure of the fat, in that it
also responded to 0.5 ml of silicone oil [Si(CH3 )2 On ] or paraffin oil (hydrocarbon). The cell also had a taste input, in that it had a
consistent but small response to umami taste (monosodium glutamate, MSG); gluc, glucose; NaCl, salt; HCl, sour; Q-HCl, quinine,
bitter. The spontaneous firing rate of the cell is also shown (data of H. Critchley, E. T. Rolls, A. D. Browning, and I. Hernadi).
of umami flavor in the cortical areas that can be distinguished from those for the
prototypical tastants sweet, salt, bitter, and sour, and in that respect umami can be
considered as a fifth prototypical taste. That representation probably is important
for the taste produced by proteins, and to complement those findings, recently
evidence has started to accumulate that there may be taste receptors on the tongue
specialized for umami taste (Chaudhari et al., 1996; Chaudhari and Roper, 1998).
5. The Mouth Feel of Fat

Texture monitored in the mouth is an important indicator of whether or not fat
is present in a food, which is important not only as a high-value energy source
but also as a potential source of essential fatty acids. In the orbitofrontal cortex,
Rolls et al. (1999) have found a population of neurons that respond when fat is
in the mouth. An example of such a neuron is shown in Figure 23.3, illustrating
that information about fat as well as information about taste can converge onto
a given neuron in that region. It was shown that such a neuron could respond to
taste, because its firing rates were significantly different for the tastants sweet,
salt, bitter, and sour. However, its response to fat in the mouth was larger. The
fat-related responses of these neurons are produced at least in part by the texture
of the food, rather than by chemical receptors sensitive to certain chemicals, in
that such neurons typically respond not only to foods such as cream and milk
containing fat but also to paraffin oil (which is a pure hydrocarbon) and to silicone
oil [Si(CH3 )2 On ]. However, some of the fat-related neurons do have convergent
inputs from the chemical senses, in that in addition to taste inputs, some of these
neurons respond to the odor associated with a fat, such as the odor of cream (Rolls
et al., 1999). Feeding to satiety with fat (e.g., cream) decreases the responses of
these neurons to zero for the food eaten to satiety, but if the neuron receives a
taste input from, for example, glucose taste, that is not decreased by feeding to
satiety with cream. Thus there is a representation of the macronutrient fat in that
brain area, and the activation produced by fat is reduced by eating fat to satiety.
6. Effects of Hunger and Satiety on Taste Processing at Different

Stages of the Taste Pathway and Their Relevance to the Control
of Eating and Sensory-specific Satiety
In order to analyze the neural control of feeding, we have been recording the ac-
tivities of single neurons during feeding in brain regions implicated in feeding in
the monkey (Rolls, 1994, 1997, 1999a, 2000c). It has been found that populations
of neurons in the lateral hypothalamus and adjoining substantia innominata in the
monkey respond to the sight and/or taste of food (Rolls, Burton, and Mora, 1976).
Part of the evidence that these neurons are involved in the control of responses
to food is that they respond to food only when the monkey is hungry (Burton,
OFC CC167
20
BJ
10
Glucose
SA
0
Pre 50 100 150 200 250
+2
+1
Acceptance
−1
−2
CC170
12
BJ
Glucose
SA
0
Pre 50 100 150 200 250
+2
+1
Acceptance
−1
−2
Figure 23.4. Effect of feeding to satiety with glucose solution on the responses
of two neurons in the secondary taste cortex to the tastes of glucose and
of blackcurrant juice (BJ). The spontaneous firing rate is also indicated (SA).
Rolls, and Mora, 1976; Rolls et al., 1986). Indeed, modulation of the reward or
incentive value of a motivationally relevant sensory stimulus, such as the taste
of food, by an animal’s motivational state (e.g., hunger) is one important way in
which motivational behavior is controlled (Rolls, 1975, 1999a). The subjective
correlate of this modulation is that food tastes pleasant when one is hungry, but
tastes hedonically neutral when it has been eaten to satiety.
These findings raise the question of the stage in sensory processing at which
satiety modulates responsiveness. We have found that this modulation of taste-
evoked signals by motivation is not a property found in the early stages of
the primate gustatory system. The responsiveness of taste neurons in the NTS
(Yaxley et al., 1985) and in the primary taste cortex – frontal opercular (Rolls
et al., 1988) and insular (Yaxley, Rolls, and Sienkiewicz, 1988) – is not atten-
uated by feeding to satiety. In contrast, in the secondary taste cortex, in the
caudolateral part of the orbitofrontal cortex, it was shown that the responses
of neurons to the taste of glucose decreased to zero when the monkey ate it
to satiety, during the course of which its behavior turned from avid accep-
tance to active rejection (Rolls, Sienkiewicz, and Yaxley, 1989). That mod-
ulation of the responsiveness of the gustatory responses of the orbitofrontal
cortex neurons by satiety could not have been due to peripheral adaptation
in the gustatory system or to altered efficacy of gustatory stimulation after
satiety was reached, because modulation of neuronal responsiveness by sati-
ety was not seen at the earlier stages of the gustatory system, including the
NTS, the frontal opercular taste cortex, and the insular taste cortex. We also
found evidence that gustatory processing involved in thirst became interfaced
to motivation in the caudolateral orbitofrontal cortex taste projection area,
in that neuronal responses there to water were decreased to zero when wa-
ter was drunk to satiety (Rolls et al., 1989). In the secondary taste cortex,
it was also found that decreases in the responsiveness of neurons were rela-
tively specific to the food with which the monkey had been fed to satiety. For
example, in seven experiments in which monkeys were fed glucose solution, neu-
ronal responsiveness to the taste of glucose decreased, but not that to the taste
of blackcurrant juice (Figure 23.4). Conversely, in two experiments in which
Figure 23.4 (cont.). Below the neuronal response data for each experiment, the
behavioral measure of the acceptance or rejection of the solution on a scale
from +2 to −2 is shown. The solution used to feed to satiety was 20% glucose.
The monkey was fed 50 ml of the solution at each stage of the experiment,
as indicated along the abscissa, until he was satiated, as shown by whether he
accepted or rejected the solution. “Pre” indicates the firing rate of the neuron
before the satiety experiment started. The values shown are the mean firing rate
and its s.e. (Adapted from Rolls et al., 1989.)
376 Edmund T. Rolls
monkeys were fed to satiety with fruit juice, the responses of the neurons de-
creased to fruit juice, but not to glucose (Rolls et al., 1989).
Such evidence shows that the reduced acceptance of food that occurs when
food is eaten to satiety and the reduction in the pleasantness of its taste (Cabanac,
1971; Rolls and Rolls, 1977, 1982; Rolls et al., 1981a,b; Rolls, Rowe, and Rolls,
1982; Rolls, Rolls, and Rowe, 1983c) are not produced by reductions in the
responses of neurons in the NTS or frontal opercular or insular gustatory cortices
to gustatory stimuli. Indeed, after eating to satiety, humans reported that the
taste of the food on which they had become satiated was almost as intense as
when they had been hungry, though much less pleasant (Rolls et al., 1983c).
That comparison is consistent with the possibility that activity in the frontal
opercular and insular taste cortices, as well as the NTS, does not reflect the
pleasantness of the taste of a food, but rather its sensory qualities independently
of motivational state. On the other hand, the responses of the neurons in the
caudolateral orbitofrontal cortex taste area and in the lateral hypothalamus (Rolls
et al., 1986) are modulated by satiety, and presumably it is in areas such as those
that neuronal activity may be related to whether or not a food tastes pleasant,
and to whether or not the food should be eaten (Scott, Yan, and Rolls, 1995;
Critchley and Rolls, 1996b; Rolls, 1996, 1999a, 2000b,c).
7. Representation of Flavor: Convergence of Olfactory

and Taste Inputs
At some stage in taste processing, it is likely that taste representations are brought
together with inputs from different modalities, such as olfactory inputs, to form a
representation of flavor. Takagi and his colleagues (Tanabe et al., 1975a,b) have
found an olfactory area in the medial orbitofrontal cortex. In a mid-mediolateral
part of the caudal orbitofrontal cortex there is an area investigated by Thorpe et al.
(1983) in which they found many neurons with visual responses and some with
gustatory responses. We therefore sought to investigate whether or not there were
neurons in the secondary taste cortex and the adjoining, more medial orbitofrontal
cortex that would respond to stimuli in other modalities, including the olfactory
and visual modalities, and whether or not single neurons in that cortical region
would in some cases respond to stimuli from more than one modality. We found
(Rolls and Baylis, 1994) that in the orbitofrontal cortex taste areas, of 112 single
neurons that responded to any of those modalities, many were unimodal (taste
34%, olfactory 13%, visual 21%), but they were found in close proximity to one
another. Some single neurons showed convergence, responding, for example, to
taste and visual inputs (13%), taste and olfactory inputs (13%), and olfactory and
visual inputs (5%). Some of those multimodal single neurons had corresponding
sensitivities in the two modalities, in that they responded best to sweet tastes
(e.g., 1-m glucose), and in a visual-discrimination task they responded more to
the visual stimulus that signified sweet fruit juice than to one that signified saline,
and in an olfactory-discrimination task they responded more to fruit odor. The
different types of neurons (unimodal in different modalities, and multimodal)
frequently were found close to one another in tracks made into that region,
consistent with the hypothesis that the multimodal representations are actually
being formed from unimodal inputs to that region.
It thus appears to be in these orbitofrontal cortex areas that flavor representa-
tions are built, where “flavor” is taken to mean a representation that is evoked
best by a combination of gustatory and olfactory inputs. This orbitofrontal region
does appear to be an important region for convergence, for there are only low
proportions of bimodal taste and olfactory neurons in the primary taste cortex
(Rolls and Baylis, 1994).
8. Rules Underlying the Formation of Olfactory Representations

in the Primate Cortex
Critchley and Rolls (1996a) showed that 35% of olfactory neurons in the or-
bitofrontal cortex categorized odors in an olfactory–taste discrimination task on
the basis of the taste–reward associations of the odorants. Rolls et al. (1996b)
found that 68% of the odor-responsive neurons in the orbitofrontal cortex mod-
ified their responses in some way following changes in the taste–reward asso-
ciations of the odorants during olfactory–taste-discrimination reversals. (In an
olfactory-discrimination experiment, if the monkey made a lick response when
one odor, the S+, was delivered, he obtained a drop of glucose reward; if the
monkey incorrectly made a lick response to another odor, the S−, he obtained
a drop of aversive saline. At some time during the experiment, the contingency
between the odor and the taste was reversed. The monkey relearned the discrim-
ination, showing reversal. It will be of interest to investigate in which parts of
the olfactory system the neurons show reversal, for where they do, it can be con-
cluded that the neuronal response to the odor depends on the taste with which it is
associated.) Full reversal of neuronal responses was seen in 25% of the neurons
analyzed. (In full reversal, the odor to which the neuron responded was reversed
when the taste with which it was associated was reversed.) Extinction of the dif-
ferential neuronal responses after task reversal was seen in 43% of the neurons.
(Those neurons simply stopped discriminating between the two odors after the
reversal.) Those findings demonstrate directly a coding principle in primate ol-
faction whereby the responses of some orbitofrontal cortex olfactory neurons are
modified by and depend upon the taste with which the odor is associated. It was of
378 Edmund T. Rolls
interest, however, that those modifications were less extensive, and much slower,
than the modifications found for orbitofrontal visual neurons during visual–taste
reversal (Rolls et al., 1996b). That relative inflexibility of olfactory responses
is consistent with the need for some stability in odor–taste associations to fa-
cilitate the formation and perception of flavors. In addition, some orbitofrontal
cortex olfactory neurons did not code in relation to the taste with which the odor
was associated (Critchley and Rolls, 1996a), so there is also a taste-independent
representation of odor in this region.
9. Olfactory and Visual Sensory-specific Satiety and

Representations in the Primate Orbitofrontal Cortex
It has also been possible to investigate whether or not the olfactory representation
in the orbitofrontal cortex is affected by hunger. In satiety experiments, Critchley
and Rolls (1996b) showed that the responses of some olfactory neurons to a food
odor were decreased when the monkey was fed to satiety with a food (e.g., fruit
juice) having that odor. In particular, seven of nine olfactory neurons that were
responsive to the odors of foods, such as blackcurrant juice, were found to
decrease their responses to the odor of the satiating food. Typically the decrease
was at least partly specific to the odor of the food that had been eaten to satiety,
potentially providing part of the basis for sensory-specific satiety. It was also
found for eight of nine neurons that had selective responses to the sight of food
that they demonstrated sensory-specific reductions in their visual responses to
foods following satiation. Those findings show that the olfactory and visual
representations of food, as well as the taste representation of food, in the primate
orbitofrontal cortex are modulated by hunger. Usually a component related to
sensory-specific satiety can be demonstrated.
Those findings link at least part of the processing of olfactory and visual
information in this brain region to the control of feeding-related behavior. This
is further evidence that part of the olfactory representation in this region is related
to the hedonic value of the olfactory stimulus, and in particular that at this level
of the olfactory system in primates, the pleasure elicited by the food odor is at
least part of what is represented.
As a result of the neurophysiological and behavioral observations showing the
specificity of satiety in the monkey, experiments were performed to determine
whether or not satiety was specific to foods eaten by humans. It was found that
the pleasantness of the taste of food eaten to satiety decreased more than that
for foods that had not been eaten (Rolls et al., 1981a). One consequence of
this is that if one food is eaten to satiety, appetite reduction for other foods is
often incomplete, and that will lead to increased eating when a variety of foods
is offered (Rolls et al., 1981a,b; Rolls, Van Duijenvoorde, and Rolls, 1984).
Because sensory factors, such as similarities in color, shape, flavor, and texture,
usually are more important than metabolic factors, such as protein, carbohydrate,
and fat content, in influencing how foods interact in this type of satiety, it has
been termed “sensory-specific satiety” (Rolls and Rolls, 1977, 1982; Rolls et al.,
1981a,b, 1982; Rolls, 1990). It should be noted that this effect is distinct from
alliesthesia, in that alliesthesia is a change in the pleasantness of sensory inputs
produced by internal signals (such as glucose in the gut) (Cabanac and Duclaux,
1970; Cabanac, 1971; Cabanac and Fantino, 1977), whereas sensory-specific
satiety is a change in the pleasantness of sensory inputs that is accounted for,
at least in part, by the external sensory stimulation received (such as the taste
of a particular food), in that, as shown earlier, it is at least partly specific to the
external sensory stimulation received.
The parallel between these studies of eating by humans and studies of the
neurophysiology of hypothalamic and orbitofrontal cortex neurons in the monkey
has been extended by observations that in humans, sensory-specific satiety occurs
for the sight of food as well as for the taste of food (Rolls et al., 1982). Further, to
complement the finding that in the hypothalamus there are neurons that respond
differently to food and to water (Rolls, 1999a), and that satiety with water can
decrease the responsiveness of hypothalamic neurons that respond to water, it
has been shown that in humans, motivation-specific satiety can also be detected.
For example, satiety with water decreases the pleasantness of the sight and taste
of water, but not of food (Rolls et al., 1983c).
To investigate whether or not the sensory-specific reduction in the respon-
siveness of orbitofrontal olfactory neurons might be related to a sensory-specific
reduction in the pleasure produced by the odor of a food when it has been eaten
to satiety, Rolls and Rolls (1997) measured humans’ responses to the smell of a
food that was eaten to satiety. It was found that the pleasantness of the odor of
a food (and also, but much less significantly, the perceived intensity of its odor)
was decreased when the subjects ate it to satiety (Figure 23.5). It was also found
that pleasantness ratings for the smells of other foods (i.e., foods not eaten in
the meal) showed much smaller decreases. That finding has clear implications
for the control of food intake, for ways to make foods presented in a meal ap-
pealing, and for odor pleasantness ratings following meals. In an investigation
of the mechanisms of this odor-specific sensory-specific satiety, Rolls and Rolls
(1997) had humans chew a food, without swallowing, for approximately as long
as the food normally would be in the mouth during eating. They demonstrated
sensory-specific satiety with that procedure, showing that the sensory-specific
satiety did not depend on food reaching the stomach. Thus at least part of the
mechanism is likely to involve a change in processing in the olfactory pathways.
Banana Eaten Chicken Eaten
15 15
5 5
−5 −5
−15 −15
Change in pleasantness (mm)

Change in pleasantness (mm)
−25 −25
−35 −35
ana uma fish ke n rose ana uma fish ken rose
ban sats chic ban sats chic
Food Smelled Food Smelled
Figure 23.5. Olfactory sensory-specific satiety in humans. The pleasantness of the smell of a food became less when the
humans ate that food (banana or chicken) to satiety. A similar reduction was not found for other foods not eaten in the meal.
The changes in pleasantness were measured on a 100-mm visual-analogue rating scale. The number of subjects was 12, and
the results (as shown by the interaction term in a two-way within-subjects anova) were very significant ( p < .001).
(Adapted from Rolls and Rolls, 1997.)
It is not yet known at which of the earliest stages of olfactory processing this
modulation occurs. It is unlikely to be in the receptors, because the change in
pleasantness found was much more significant than the change in intensity (Rolls
and Rolls, 1997).
The pattern of increased consumption when a variety of foods is available, as
a result of the operation of sensory-specific satiety, may have been advantageous
during evolution to ensure that different foods with a variety of important nutri-
ents would be consumed, but for humans today, when a wide variety of foods is
readily available, it may be a factor that can lead to overeating and obesity. In a
test of that in the rat, it was found that variety itself could lead to obesity (Rolls,
Van Duijenvoorde, and Rowe, 1983b; Rolls and Hetherington, 1989).
10. Responses of Orbitofrontal Cortex Taste and Olfactory

Neurons to the Sight and Texture of Food
Many of the neurons that respond to visual stimuli in this region also show
olfactory or taste responses (Rolls and Baylis, 1994), reverse rapidly in visual-
discrimination reversal (Rolls et al., 1996b), and respond to the sight of food only
if hunger is present (Critchley and Rolls, 1996b). That part of the orbitofrontal
cortex thus seems to implement a mechanism that can flexibly alter responses
to visual stimuli depending on the reinforcement (e.g., the taste) associated with
a visual stimulus (Thorpe et al., 1983; Rolls, 1996). That facilitates prediction
of the taste that will be associated with ingestion of what is seen, thus aiding in
visual selection of foods (Rolls 1993, 1994, 1999a, 2000c).
The orbitofrontal cortex in primates is also important as an area of convergence
for somatosensory inputs, such as those related to the perceived textures of fatty
foods in the mouth. We have shown, for example, in recent recordings that single
neurons influenced by taste in that region can in some cases have their responses
modulated by the texture of the food. That was shown in experiments in which
the texture of food was manipulated by addition of methylcellulose or gelatin,
or by puréeing a semisolid food (E. T. Rolls and H. Critchley, unpublished data;
Rolls, 1997, 1999a).
11. Taste and Olfactory Responses of Primate Amygdala Neurons

The orbitofrontal cortex has rich interconnections with the amygdala, and some
amygdala neurons also show taste and olfactory responses. Sanghera, Rolls,
and Roper-Hall (1979) described taste responses in some amygdala neurons in
macaques, and Wilson and Rolls (1993, in press) found more. Nishijo, Ono, and
Nishino (1988a,b) found ingestion-related amygdala neurons, at least some of
382 Edmund T. Rolls
which probably were taste-related. Scott et al. (1993) analyzed the responses
of 35 taste neurons in the macaque amygdala. Although individual neurons
were quite broadly tuned to different tastes, the population as a whole clearly
discriminated among three tastes: sweet, salt (NaCl), and umami (monosodium
glutamate, protein taste) (Rolls, 1997; Rolls et al., 1998). To test whether or not
the representation of taste in the primate amygdala may encode its reward value,
Yan and Scott (1996) fed monkeys to satiety to determine if decreasing the reward
value of the taste to zero in that way would decrease the responses of primate
amygdala sweet-taste neurons to zero, as had been found for orbitofrontal cortex
neurons (Rolls et al., 1989). Yan and Scott found that only partial reductions of the
responses of amygdala neurons were produced by feeding to satiety (an average
of 62%). The implication is that amygdala neurons in primates can respond
differently to rewarding and punishing stimuli, but they react less extensively
than do orbitofrontal cortex neurons to the reward value when it is changed
rapidly, as during feeding to satiety, or, as described earlier for visual neurons,
in visual-discrimination reversal. Olfactory responses have also been found in
the primate amygdala (Sanghera et al., 1979), and the anterior cortical nucleus
of the amygdala and the periamygdaloid cortex receive direct connections from
the olfactory bulb (Carmichael, Clugnet, and Price, 1994).
12. Imaging Studies in Humans

In humans, it has been shown in neuroimaging studies with functional magnetic-
resonance imaging (fMRI) that taste activates an area of the anterior insula, which
probably is the primary taste cortex, and part of the orbitofrontal cortex, which
probably is the secondary taste cortex (Francis et al., 1999). The orbitofrontal
cortex taste area is distinct from areas activated by odors and by pleasant touch
(Francis et al., 1999). It has been shown that within individual subjects sepa-
rate areas of the orbitofrontal cortex are activated by sweet (pleasant) and salt
(unpleasant) tastes (O’Doherty et al., 2001). Francis et al. (1999) also found
activation of the human amygdala by the taste of glucose. Extending that study,
O’Doherty et al. (2001) showed that the human amygdala was as much acti-
vated by the affectively pleasant taste of glucose as by the affectively negative
taste of NaCl and thus provided evidence that the human amygdala is not es-
pecially involved in processing aversive stimuli as compared with rewarding
stimuli.
It is of interest that in humans there is an area of the far anterior insula that is
activated by olfactory stimuli (Francis et al., 1999; O’Doherty et al., 2000). It is
not clear whether or not that area is separate from the part of the insula activated by
taste. In macaques, the primary taste cortex (in the anterior insula and adjoining
frontal operculum) does not appear to be strongly activated by olfactory stimuli

(though further studies on this are in progress), and the human anterior insular
olfactory area may thus correspond to what in macaques is the caudal transitional
area of the orbitofrontal cortex, where it adjoins the insula, area Ofdg, where part
of the secondary taste cortex is located (Baylis et al., 1994). In humans, there
is strong and consistent activation of the right orbitofrontal cortex by olfactory
stimuli (Zatorre et al., 1992; Francis et al., 1999). In an investigation of where
the pleasantness of olfactory stimuli might be represented in humans, O’Doherty
et al. (2000) showed that activation of an area of the orbitofrontal cortex to banana
odor was decreased (relative to a control vanilla odor) after bananas were eaten
to satiety. Thus activity in a part of the human orbitofrontal cortex olfactory area
is related to sensory-specific satiety.
13. Conclusions
The primate orbitofrontal cortex is an important site for convergence of repre-
sentations of the taste, smell, sight, and mouth feel of food, and that convergence
allows the sensory properties of each food to be represented and defined in
detail. The primate orbitofrontal cortex is also the region where a short-term,
sensory-specific control of appetite and eating is implemented, in the form of
sensory-specific satiety. Moreover, it is likely that visceral and other satiety-
related signals reach the orbitofrontal cortex and there modulate the representa-
tion of food, resulting in an output that reflects the reward (or appetitive) value of
each food. Part of the evidence that the reward value (and the pleasantness of food
in humans) is represented in the orbitofrontal cortex is that macaques will work
to obtain electrical stimulation of this brain region if they are hungry, but much
less so if they are satiated (Rolls, 1999a). Further, monkeys and humans with
damage to this brain region show altered, often less selective, food preferences
(e.g., Baylis and Gaffan, 1991; Rolls, 1999b). The orbitofrontal cortex contains
not only representations of taste and olfactory stimuli but also representations of
other types of rewarding and punishing stimuli, including pleasant touch, and all
these inputs, together with the functions of the orbitofrontal cortex in stimulus–
reward and stimulus–punishment learning, provide a basis for understanding its
functions in emotional and motivational behavior (Rolls, 1999a, 2000a–d).
Acknowledgments
Some of the experiments described here were conducted in association with
Drs. A. Browning, H. Critchley, T. R. Scott, Z. J. Sienkiewicz, E. A. Wakeman,
L. L. Wiggins (L. L. Baylis), and S. Yaxley, and their collaboration is sincerely
384 Edmund T. Rolls
acknowledged. The research in our laboratory was supported by the Medical

Research Council (PG8513790).
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Section Six
Individual Variations
The final four chapters of this volume probe the theme of inter-individual vari-
ations in perceptual and cognitive performances in the chemical senses, a topic
often encountered briefly in earlier chapters. Several chapters have described how
group performances depend on previous exposure to odorants (e.g., Chapters 3,
8–10, and 21) and to tastants (Chapters 22 and 23). All those chapters have out-
lined emotional and memory processes evoked by odors and tastes that are at the
core of an individual’s functioning.
The chapters in this section more specifically address issues of chemosensory
variability linked with individual constitution and with the interactions between
individuals and given environments. Katharine Fast and colleagues (Chapter 24)
offer a survey of the relationship between taste ability and an individual’s genetic
makeup. They highlight the phenomenon of taste blindness to bitter tastants as
a window to individual variability in taste function. From that starting point
they examine how it is possible to develop standard tools for measurements of
taste intensity and hedonicity despite the considerable variability of individuals,
ranging from nontaster to supertaster status. They examine the links between
individual psychophysical data and the anatomical variations of the tongue, in-
dicating that supertasters have higher fungiform papilla counts and rate stimuli as
more intense. Similar structure–function correlates can explain sex differences.
In Chapter 25, Robyn Hudson and Hans Distel develop the argument that
we will not be able to properly account for olfactory function without paying
closer attention to the role of the conditions that have molded it in the individual-
specific environment. The multidimensionality of the odor environment makes
it difficult for the olfactory system to cope with the features of it that become
psychologically salient. Two evolved properties of olfactory cognition deal with
that difficulty, detecting a wide spectrum of molecules and developing selec-
tive responsiveness as a function of individual experience. To substantiate those
points, they compare ratings of intensity, familiarity, and pleasantness evoked by
390 Section 6: Individual Variations
a set of odorants in subjects from contrasting cultural backgrounds. Their studies

lead to the conclusion that both the qualitative and intensity ratings of odors are
fine-tuned by prior exposure.
In Chapter 26, Benoist Schaal and colleagues follow a similar line in showing
how olfaction develops from the onset of its functioning. Even at the fetal and
neonatal stages, sensory and affective responses to odor stimuli clearly are influ-
enced by previous encounters with odorants, and the adaptability and functional
malleability of olfaction can have consequences in terms of the diversity of odor
qualities that can influence behavior. It is also pointed out that, at least during
early development, preferential responses to odors may be evolutionarily or de-
velopmentally constrained: Some odor substrates appear to facilitate learning
more readily than others, and more easily in some contexts than in others. For
example, milk odors are highly attractive to newborns even when they have never
been exposed to them (i.e., formula-fed since birth). Thus prior exposure may
not always predict increased attractiveness. Olfactory predispositions whose de-
velopment precedes postnatal experience most probably combine with learned
abilities to determine stimulus salience in young organisms.
Finally, in Chapter 27, Thomas Hummel and colleagues analyze how another
variable, age, contributes to the dynamic changes in chemosensory abilities.
They develop multilevel measurements to assess (1) which performance (sensi-
tivity, discrimination, identification) is most affected by age in cross-sectional
samples ranging from young adulthood to old age, (2) which nasal subsystem is
most affected, and (3) which central locus is concerned. Age-related changes in
olfactory function are noted at all functional levels that are considered. But those
effects are heterogeneous across tasks, the decreases being more pronounced for
sensitivity than for higher-level functions. Across the different subsystems and
periods of development, trigeminal responses are more affected by age in early
adulthood, whereas olfactory responses are more reduced in old age. Finally, at
the central level, the volume and distribution of brain regions activated by odor
stimuli are reduced and different in the oldest subjects as compared with the
youngest subjects.
Taken together, these chapters provide encouragement to our efforts to improve
the existing methods and tools to assess sensory responses and use them with
subjects who bring various prior experiences from various developmental periods
in order to better understand how, why, and when individuals differ in odor and
taste perceptions and related hedonic experience and knowledge.
24
New Psychophysical Insights in Evaluating
Genetic Variation in Taste
Katharine Fast, Valerie B. Duffy, and Linda M. Bartoshuk
How awful is “awful”? And is my “awful” the same as yours? The answers to
these questions require comparing sensory or hedonic experiences across indi-
viduals, one of the most difficult tasks for psychophysicists. This chapter aims
to trace the evolution of sensory scaling techniques intended to provide such
comparisons, focusing on taste and using the discovery of taste blindness as a
starting line. The past 70 years have been exciting times in psychophysics and
have witnessed the development of methods useful for quantifying not only the
oral impact of a stimulus but also its appeal.
For several generations, psychophysicists have been concerned about our abil-
ity to scale sensory experiences. A 1,000-Hz, 98-decibel blast is a 1,000-Hz,
98-decibel blast, but we recognize that it may sound far more intense to the
department chair’s grandson than to the department chair herself. We recog-
nize this because we accept that a certain auditory deficit may accompany the
blooming of wisdom, but how do we go about quantifying perceived sound in-
tensity so that we can compare the experiences of the young and old directly?
Our scale may start in silence, but if we have assimilated the idea that a given
sound will be of different perceived intensities to different people, where do
we anchor our scale besides the bottom? The perceived strength of a cleanser’s
odor works the same way: The same concentration of scent is added to each
bottle at the factory, but the aroma may strike some as overpowering, while
being barely detectable to others. The sweetness of lemonade is similar: Sips
from the same glass will not be equally sweet to all sharing. The sense of taste,
though, is singular among its sensory siblings in that it arrives with a built-in
anatomical tool with which we can check our scales for taste. We can look
backward at our scaling procedures and see them in a new – and brighter –
light.
391
392 Katharine Fast, Valerie B. Duffy, Linda M. Bartoshuk
1. Taste Blindness
The phenomenon of taste blindness was discovered accidentally (Fox, 1931):
While Fox was transferring a quantity of phenylthiocarbamide (PTC) to a jar,
some became airborne, and a colleague remarked on its bitterness, whereas Fox
tasted nothing. Thus began a series of experiments to determine the scope of
taste blindness. Fox and Blakeslee, a geneticist, took PTC to the 1931 meeting
of the American Association for the Advancement of Science and gathered taste
responses from more than 2,500 attendees (Blakeslee and Fox, 1932). To most
(called “tasters”), Fox’s PTC crystals were bitter, but to 28% (called “nontasters”)
the crystals had essentially no taste. When the findings were published in The
Journal of Heredity, the journal included a piece of paper impregnated with PTC
crystals; that PTC paper was the ancestor of the “Prop” (6-n-propylthiouracil) pa-
per we use today (see Figure 24.4). Prop, chemically similar to PTC, is odorless,
unlike PTC, and is less toxic as well.
Family studies (e.g, Blakeslee, 1932) had suggested that taste blindness was
a simple Mendelian recessive trait. However, reliance on thresholds in gathering
information about the range of genetic sensitivity to PTC missed the breadth of
the issue. Whereas thresholds were helpful in separating nontasters from tasters,
they failed to predict, never mind capture, the range of suprathreshold experience
(e.g., Bartoshuk, 2000).
Fernberger tried tackling the question of suprathreshold experience in early
1932. He presented his subjects with PTC crystals. “They were told to swallow
the substance . . . then report the experience in terms of one of the five follow-
ing categories: tasteless, slightly bitter, bitter, very bitter, and extremely bitter.
The category of ‘tasteless’ more or less defines itself; ‘extremely bitter,’ the
other limiting category, was defined in terms of raw quinine . . .” (Fernberger,
1932, p. 323). We can agree on the importance of a zero (“tasteless”), but did
Fernberger’s “extremely bitter” (equated to the bitterness of raw quinine) mark
a reasonable top for his scale? The answer is no. We now know that raw quinine,
the taste at the top of Fernberger’s scale, is more bitter to those who can taste
PTC than to those who cannot. As will be discussed later, scaling developments
in the wake of Fernberger’s experiment gave us the tools to reveal that.
1.1. Stevens and Fechner

Stevens revolutionized psychophysics. In a paper published to mark the 100th
anniversary of Fechner’s groundbreaking Elemente der Psychophysik (Fechner,
1860), Stevens identified an error in the great scientist’s work (Stevens, 1961).
Fechner had used the JND (the amount a stimulus must be changed to produce a
“just noticeable difference”) as the unit in intensity scales. Stevens undid Fechner
by noting that if the JND did indeed mark a unit of sensation, a scale based on
Psychophysics of Genetic Variation in Taste 393
JNDs would have to have ratio properties. But Fechner’s scale did not. For
example, a tone 20 JNDs above threshold is much more than twice as loud as a
tone 10 JNDs above threshold (Stevens, 1951).
Stevens devised a method for ratio scaling called “magnitude estimation” (e.g.,
Stevens, 1969). In magnitude estimation’s earliest days, experimenters presented
subjects with the first stimulus in a series and assigned a number designating its
intensity. Subjects were instructed to rank all following stimuli on a ratio scale in
terms of that first sensation. An experimenter might first present a subject with
a 1.0-m salt solution, declare it a 20, and explain that if the next stimulus tasted
twice as strong, it should be rated a 40, and if it tasted half as strong, it should be
rated 10, and so on. Later, subjects were allowed to rate without anchors: Subjects
assigned numbers to stimuli based on their perceived intensities, without regard
to an experimenter-assigned number designation.
Though, across subjects, the numbers assigned to stimuli using magnitude
estimation can be all over the map – subject Wilma might assign 1-m sucrose
a 10, but subject Fred might call it 1,000 – they do reveal the perceived ratios
among stimuli for each subject. Normalization can help make these ratios clearer
by bringing the numbers assigned by a subject pool into line. We do this by
assigning the data from each subject a factor by which we multiply each rating:
That maintains the ratio properties of the magnitude-estimate data from each
subject, as every rating is multiplied by the same factor. We might assign a given
stimulus a certain number designation or use the average of ratings for a group
of stimuli to assign the factor. In the preceding example, we might assign 1-m
sucrose a 100. To normalize Wilma’s sucrose rating, we divide 100 by 10; to do
the same for Fred, we divide 100 by 1,000. Wilma’s factor is then 10, and Fred’s
is 0.1. The sucrose solutions Wilma called 20, 25, and 15 are now 200, 250, and
150; if Fred earlier assigned those same solutions 2,000, 2,500, and 1,500, his
numbers are now 200, 250, and 150. Although normalization helps us to better
see the sizes of ratios within subjects’ data, it cannot reveal differences among
subjects. Wilma’s rating of the 1-m sucrose solution, whether her raw 10 or her
normalized 100, does not tell us whether or not her 10 is as strong as Fred’s 1,000
(or his 100, or his 75 or 7,500). But what if we could find a stimulus that would be
equal to all? Then we could normalize magnitude-estimate data to that standard.
The trick is to find such a standard, one independent of the stimuli of in-
terest. In early studies, when there was little reason to assume that salt inten-
sity and bitterness intensity were at all linked, NaCl seemed such a standard
(Blakeslee and Salmon, 1935). For example, subjects could scale the saltiness
of NaCl and the bitterness of Prop using magnitude estimation. If we use NaCl
as our standard, we have to assume that NaCl intensity is unrelated to bitter-
ness intensity; then, on average, each of the Prop groups will perceive NaCl as
equally intense. Once we normalized our data to NaCl, we were able to identify
a group of tasters (we call them supertasters) to whom Prop was the most bitter
(Bartoshuk, 1991). We found that a variety of substances tasted most intense to
supertasters; for example, in one study (Bartoshuk, 1993), quinine was about
1.4 times as bitter to supertasters as to nontasters. We can do the same thing
by using another sense – say hearing – instead of another taste. This is mag-
nitude matching (e.g., Marks et al., 1988). We assume that if hearing and taste
are truly unrelated, and if we have a large group scaling both taste and sound,
the average hearing will be the same across any subgroups we identify. At first,
NaCl and sound appeared to be about equally good as standards (more about
this later).
1.2. Context Effects and Prop Studies

Psychophysical responses are not absolute; the context of a stimulus affects
the responses to it. See Riskey, Parducci, and Beauchamp (1979), Rankin and
Marks (1991), Schifferstein (1994), and Lawless, Horne, and Spiers (2000) for
examples concerning taste. Gescheider (1988) reviewed the matter and noted
that “context effects in psychophysical scaling . . . can be found with the use of
every psychophysical-scaling procedure. Investigators respond to this situation
in two distinct ways. On the one hand, the sensory scientist in pursuit of pure
sensory functions has attempted to eliminate context from the measurement
situation. . . . In contrast to the sensory scientist, the cognitive scientist welcomes
context effects in scaling because they supply a wealth of information about
judgment processes. . . . The stimulus contexts that are of great interest to the
sensory scientist are not those that affect judgment but those that affect sensation”
(p. 130).
In that latter category, Marks (1992) has demonstrated an assimilation con-
text effect that operates across modalities; this has particular relevance to Prop
studies. Marks found that experiencing strong stimuli in one modality can cause
a stimulus in a second modality to be perceived as stronger than normal. Thus
in a magnitude-matching study with a sound standard, if a supertaster tastes
Prop and then hears a sound, the sound will be perceived as louder than it is
perceived by a nontaster. When such data are normalized to sound, taste dif-
ferences between the supertaster and the nontaster will seem smaller than they
really are. Recognizing the impact of this context effect has changed the way we
run experiments: Prop comes last in our taste studies now, and we always begin
with our standard (tones). This methodological advance has revealed that the
differences across nontasters, medium tasters, and supertasters are larger than
we originally thought. For example, a recent study using sound as a standard
showed that quinine was about twice as bitter to supertasters as to nontasters
(Ko et al., 2000).
1.3. Prop and Tongue Anatomy

Miller and Reedy developed a simple procedure to permit the counting of fungi-
form papillae on the tongue, as well as the taste buds on those papillae (Miller
and Reedy, 1990). The surfaces of fungiform papillae do not absorb dyes, but
the taste pores (conduits to the taste buds) do. This means that a quick swab
of dye (even food coloring – we use blue, for contrast) will render the un-
stained fungiform papillae relatively easy to count on their suddenly darkened
surroundings. Fungiform papillae density can be assessed with a flashlight and
magnifying glass. Christine Bechtel, a 13-year-old working on a science project,
used a paste-on notebook-paper reinforcer, with its inner circle aligned with the
tongue tip and midline (Figure 24.3), to provide a standard template for counting
papillae; we have now adopted that procedure for our own studies. Miller and
Reedy demonstrated that Prop medium tasters have a greater density of fungi-
form papillae on their tongues than nontasters (Miller and Reedy, 1990), and
later work demonstrated that supertasters have the most fungiform papillae of
all (Bartoshuk, Duffy, and Miller, 1994). Counting taste pores is much more
difficult, because of the high magnification needed, but the numbers show the
same disparities: Supertasters have the most, and nontasters the fewest, taste
pores. Perceived taste intensities are proportional to the density of fungiform
papillae/taste pores. Anatomical measurements have supported the early obser-
vations that women were more sensitive to the bitterness of PTC/Prop; in our
most recent data, over 17% of the women had more taste pores than any of the
men (Prutkin et al., 2000).
That fungiform papillae density can be correlated with taste intensity is not the
end of this measure’s usefulness. It provides insight into the genetic variations in
perceived intensities of other oral stimuli as well. Only 25% of fungiform papillae
innervation is for taste (carried by the chorda tympani nerve); the rest is trigem-
inal innervation coding for pain and touch sensations (Whitehead, Beeman, and
Kinsella, 1985; Silver and Finger, 1991). Supertasters perceive the most burn
from oral irritants like capsaicin (chili peppers) and ethanol, just as they perceive
the most tactile sensation (e.g., oiliness, thickness) from fats in foods (Duffy et
al., 1996; Tepper and Nurse, 1997; Bartoshuk et al., 1999; Prutkin et al., 1999).
1.4. The Labeled Magnitude Scale of Green and Colleagues

Around the same time as Marks’s and Miller’s work, Green and his colleagues
devised their Labeled Magnitude Scale (LMS) (Green, Shaffer, and Gilmore,
1993; Green et al., 1996). Their motivation was to create a scale with the ra-
tio properties of magnitude estimation that would also incorporate some indi-
cation of absolute intensity through the use of adjectives. Some years earlier,
Borg (1982) had explored the placement of common intensity adjectives (e.g.,
“weak,” “moderate,” “strong,” “extremely strong,” “maximal”) on a scale to
see if he could give that scale ratio properties. That resulted in roughly log-
arithmic spacings. He believed that correct spacings of the adjectives would
have the potential to produce a universal sensory ruler that could be used in
any modality to compare sensory intensities across individuals. That belief was
based on the assumption that the range from zero to maximal perceived in-
tensity would be the same for different individuals and in different modalities
(Teghtsoonian, 1971, 1973). Green et al. (1993) had doubts that “zero to max-
imal” (Green substituted “strongest imaginable” for Borg’s “maximal”) would
have the same meaning in different modalities, and they set out to create a
scale limited to oral sensations. They took a very important step beyond Borg
by empirically determining the locations of the adjectives. Subjects were asked
to give “magnitude estimates of adjectives within the context of numerous re-
called, ‘real-life’ experiences.” The experiences were all oral sensations (e.g.,
“the bitterness of celery,” “the burn of cinnamon gum”). The distances between
the adjectives were similar to but not identical with those of Borg. In partic-
ular, the distance between “very strong” and “strongest imaginable” (Borg’s
“maximal”) was larger on Green’s LMS. Of special importance, Green’s LMS
produced functions like those produced by magnitude estimation (Green et al.,
1993, 1996).
1.5. A New Label for the Top of Green’s LMS

As Green’s LMS is portable and some subjects and patients find its use easier than
magnitude matching, we were eager to put it to use in Prop studies. Because we
knew that oral sensations were not equivalent for nontasters, medium tasters, and
supertasters, we knew that the scale as originally designed could not allow valid
comparisons across the three groups. So we instructed our subjects to consider
the top of the scale to be the “strongest imaginable sensation of any kind.” If
everyone had experienced strong sensations (e.g., sight, smell, sound, touch,
pain, thermal sensations) that were not related to their taste experiences, then
their “strongest imaginable sensation of any kind” should provide anchors for
the scale that would be equivalent, on average, for nontasters, medium tasters,
and supertasters.
We used Prop to compare Green’s LMS and magnitude matching (Bartoshuk
et al., 2000). Our 100 subjects rated the bitterness of Prop using magnitude esti-
mation with a sound standard (magnitude matching) in one session, and Green’s
LMS with our label at the top in another session (order counterbalanced). As
noted earlier, the validity of magnitude matching for comparison across groups
rests on the assumption that there is no systematic relationship between hearing

and taste, that the perceived intensities of sounds will be, on average, the same
for nontasters, medium tasters, and supertasters. On the other hand, the validity
of Green’s LMS (with our label at the top) rests on the assumption that “strongest
imaginable sensation of any kind” establishes that the domain to which the ad-
jectives apply comprises all sensations. If there is no systematic relationship
between this anchor and taste, then the anchor will reflect, on average, the same
perceived intensity for nontasters, medium tasters, and supertasters. Although
these two methods rely on very different assumptions, they produce very similar
pictures of the differences across nontasters, medium tasters, and supertasters.
That supports the conclusion that the assumptions underlying both methods are
correct; both methods appear to provide valid comparisons of sensory experi-
ences across nontasters, medium tasters, and supertasters.
1.6. Tongue Anatomy and Scaling

Figure 24.1 shows an example of the correlation between perceived taste intensity
and density of fungiform papillae using sucrose. The left panel shows the results
of a study using Green’s LMS with our label at the top. Perceived sweetness
correlates with density of fungiform papillae. The right panel shows a study
using a nine-point scale. Once we have established that a relationship exists
between perceived taste intensity and fungiform papillae density, we can compare
scales with regard to their ability to show that relation. Scales that make valid
comparisons across groups of subjects show the relation; scales invalid for such
comparisons do not. We could, of course, use taste pore density to test these scales
as well, but the measurement of taste pore density is far more labor-intensive
and requires special equipment. Measurement of fungiform papillae density is
much easier and is adequate for scale evaluation.
The nine-point scale in Figure 24.1 fails on two fronts. As is evident, su-
pertasters tend to rate the sweetness of 1-m sucrose as more intense than “very
strong”: This is a ceiling effect. Also, the absolute taste intensity reflected by
“very strong” is greatest for supertasters, less for medium tasters, and least for
nontasters.
1.7. Large Mice and Small Elephants: The Relativity

of Intensity Adjectives
As the foregoing discussion shows, intensity adjectives do not reflect the same
absolute intensities for all individuals under all conditions. Stevens made that
point more than 40 years ago: “Mice may be called large or small, and so may
strongest imaginable
sensation of any kind
very strong very strong 9

8
7
strong 6
medium 5
4
N=81
Perceived Sweetness of Sucrose

moderate 3 N=114
r=.26 2 r=.05
weak p<.05 very weak 1 N.S.
barely detectable 0
0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 120 140 160
Density of Fungiform Papillae (per cm 2)
Figure 24.1. Perceived sweetness of 1-m sucrose versus density of fungiform papillae. For the graph on the left, perceived sweetness
was measured with the Green scale (portions of the data are from Prutkin, 1997). For the graph on the right, perceived sweetness was
measured with the nine-point scale (e.g., Kveton and Bartoshuk, 1994).
elephants, and it is quite understandable when someone says it was a large mouse
that ran up the trunk of the small elephant” (Stevens, 1958, p. 633). How could
the obvious relativity of intensity adjectives have been overlooked for so long
even as they were being used to label intensity scales? The answer is, of course,
that intensity adjectives refer to a specific domain (e.g., the domain of mice or the
domain of elephants). In experiments, the domains may be specified explicitly
by the experimenter or implicitly by the setting (subjects in a taste experiment
expect to rate tastes). So in specific experiments, adjectives may have seemed
to be conveying roughly the same intensities for all subjects. But we now know
that that was not true, at least for taste.
We can illustrate the consequences of incorrectly assuming that the adjectives
mean the same to all by returning to Fernberger. We noted earlier that magnitude
matching with a tone standard shows that quinine is about twice as bitter to
supertasters as it is to nontasters. Fernberger’s scale started at “tasteless” and went
up to “extremely bitter” (the taste of raw quinine). We see, now, that Fernberger
was not using the same scale for all subjects. “Tasteless” is tasteless for everyone,
but the taste of raw quinine is not the same for everyone. Let us consider the
consequence of that for an experiment that Fernberger might have conducted.
We now know that saltiness does not vary as much across Prop groups as does
quinine, which means that the ratio of quinine to salt is largest for supertasters
and smallest for nontasters. Because Fernberger forced the ratings for quinine
to be equal for all subjects, had he asked his subjects to rate salt, he would
have seen a bizarre result: Nontasters would have rated salt as saltier than would
supertasters. Figure 24.2 illustrates this. We call this a reversal artifact.
Adjective-labeled scales – be they Fernberger’s, the nine-point, Likert, or
the visual analogue used with sensations or feelings – assume that the adjective
labels hold the same meaning for all subjects. Whenever that assumption is false,
comparisons across groups (or individuals) either can fail to show differences
that really exist or can produce reversal artifacts, as illustrated in Figure 24.2.
Many variables can contribute to systematic differences in the ways groups use
adjectives (e.g., sex, clinical status, age, ethnic status), and that is a serious issue
for any field that makes use of these scales.
Green’s LMS as originally labeled is subject to the same problem when used
for Prop studies (but not necessarily with other taste studies), because we know
that the “strongest imaginable oral sensations” are not equivalent for nontasters,
medium tasters, and supertasters. Green’s LMS does have a virtue not shared by
any of the other scales, however, and it is this: The distances between the intensity
adjectives were determined empirically. Although it has not yet been proved, we
suspect that those relative distances are invariant. One can even imagine a family
of Green LMSs of varying sizes in which the relative distances among adjectives
are always roughly the same. Assume for a moment that the strongest tea flavor
Reality
Bitterness of quinine is
weakest to nontasters
(NT) and strongest to
supertasters (ST)
Quinine Fernberger's World

NTs, MTs and STs were
forced to place the bitterness
Perceived Taste Intensity
Quinine of quinine at the top of the

scale no matter how bitter it
tasted
Quinine Quinine
NaCl
NaCl
OP
OP
PR
PR
No taste No taste
NT MT ST NT MT ST
Figure 24.2. Left: The bitterness of Prop and quinine and the saltiness of
NaCl as shown by magnitude matching and the Green scale (ratio scales).
Note that quinine, the stimulus that Fernberger used to define the top of his
scale, is not equally bitter to all. Nontasters (NT) perceived the least bitterness,
supertasters (ST) the most, and medium tasters (MT) an intermediate degree
of bitterness. The saltiness of NaCl was also associated with the ability to taste
Prop, but the effect was smaller than for quinine. Right:The distortions induced
by Fernberger’s mistake. If all subjects were forced to place the bitterness of
quinine at the top of this scale, the medium tasters and supertasters would
have to compress their ratings for NaCl proportionately. That would cause the
reversal artifact: The saltiness of NaCl would appear most intense to nontasters,
and least intense to supertasters.
is less intense than the strongest odor, which in turn is less intense than the
strongest pain. A Green LMS for tea would be smaller than that for odor, which
in turn would be smaller than that for pain. But for all of the scales, a “very
strong” sensation (tea, odor, pain) would be halfway between no sensation and
the “strongest imaginable sensation” in that domain. We also suspect that the
closest we will get to a universal sensory ruler may be the one we created earlier,
labeled “strongest imaginable sensation of any kind.” Yet we note that should we
find a good candidate for designation as an experience that we can assume to be
equally intense for all (e.g., Borg, 1990, proposed maximal perceived exertion),
such a standard would make a universal sensory ruler possible.
Incidentally, Green’s LMS can be used for magnitude matching with its origi-
nal label (“strongest imaginable oral sensation”) at the top. Including a standard
permits the responses to be normalized to the standard. For example, including

tones would permit taste data to be normalized to the tones, allowing comparisons
across nontasters, medium tasters, and supertasters.
2. Valid Taste Comparisons across Groups:

What Have We Learned?
Data collected from control subjects have allowed us to assess the effects of
various abnormalities on taste and oral somatosensation. When a patient’s per-
ceived intensity ratings for taste or tactile stimuli are well below those we would
expect for someone with a similar array of fungiform papillae, the presence
nontaster supertaster supertaster

with viral
damage
strongest imaginable
sensation of any kind
Perceived Bitterness of Quinine
placement of
reinforcement
on tongue tip
(Fungiform Papillae)
supertaster
very strong with viral
damage
supertaster
strong
nontaster
moderate
weak
barely detectable
20 40 60 80 100 120 140 160 180
Density of Fungiform Papillae (per cm2 )
Figure 24.3. The three circles at the top of the figure are sketches of the fungi-
form papillae in a circular area (6 mm in diameter) inside a paper reinforcement
placed at the tip of the tongue next to the midline (see sketch of tongue on graph).
The graph shows the regression line for the perceived bitterness (Green scale)
of quinine hydrochloride (0.001 m) swabbed onto fungiform papillae on the
anterior tongue. The filled circles indicate the bitterness ratings by the subjects
whose fungiform papillae densities are illustrated above.
strongest imaginable Females Males
pleasent sensation
very strong
strong
Pleasant
moderate
neutral weak
weak
moderate
strong
very strong Figure 24.4. Hedonic ratings (Green
Unpleasant
r = -.19 r = .20 scale) for grapefruit juice and whole
Hedonic Rating of Grapefruit Juice

strongest imaginable p < .01 p < .01 milk plotted against the bitterness of
unpleasant sensation
Prop paper (3-cm circles of filter pa-
strongest imaginable per impregnated with 1.6 mg Prop).
pleasent sensation
Subjects were 20–53 years old, with
BMIs < 35. Correlation coefficients
very strong
are shown on each panel. The hedonic
strong
Pleasant
scale was derived from the Green sen-
moderate sory scale as described in the text. Note
weak
neutral weak that the labels “barely detectable” were
moderate omitted because of lack of space on the
strong ordinate.
very strong
Unpleasant
Hedonic Rating of Whole Milk

r = -.15 r=0
strongest imaginable p=.01 N.S.
unpleasant sensation
ba we m str ve a s i m st b w m
ar ea o s tr ve an se im str
re ak od on ry ny en a ro on ry y nsa ag on
ly er g st ki sati gin nge ely k dera g str ki t in ge
de at
e ro nd on ab st d te o nd ion a st
b
te ng l
of e
et
ec ng of le
ct ta
ab b
le le
Bitterness of PROP Paper

of pathologic conditions often can explain the dissociation. The integrity of

fungiform papillae appears to be controlled by the trigeminal nerve in humans.
We know that in extreme cases, such as when the chorda tympani nerve is
cut during surgery, fungiform papillae remain on the tongue even though their
service as a first stop for taste is meaningless (T. Janjua and S. R. Schwartz, un-
published data). Thus damage to the sense of taste produced by head trauma, ear
infections, and upper respiratory tract infections (Solomon et al., 1991; Bartoshuk
et al., 1996) and cyclical changes in taste due to hormonal changes (e.g.,
Glanville and Kaplan, 1965; Prutkin et al., 2000), which occur in the absence
of damage to the trigeminal nerve, affect taste, but not the density of fungiform
papillae.
Figure 24.3 shows the correlation between bitterness and fungiform papillae
density on the anterior tongue for normal subjects. Three circles are pictured;
they show the fungiform papillae in a 6-mm circle near the tip of the tongue
(the diameter of the hole in a paper reinforcement). The left-hand circle is from
a normal nontaster tongue, and the middle circle is from a normal supertaster
tongue. The right-hand circle is from the tongue of a supertaster who has suffered
viral damage; her tongue shows fungiform papillae density analogous to that of
the other supertaster, though her bitterness perception is less than the nontaster’s.
Taste pathologic states and hormonal variation will alter taste experience, but
not the density of fungiform papillae. The effects of such taste alterations on the
density of taste pores are still unknown.
2.1. Valid Hedonic Scaling

Can Green’s LMS be used to scale hedonic measures? A valid scale for measuring
the hedonic properties of food would have great benefit, as what we eat has
significant impact on our health. Popeye’s preference for spinach may have
reduced his risk for cancer, whereas Wimpy’s love of burgers may have added
to his girth and placed him on the road to cardiovascular disease.
Given the lessons of sensory scaling, we might pursue magnitude matching as
a means of gathering hedonic data by looking for a standard experience, sensory
or hedonic, against which to measure subjects’ responses. We could also try the
Green LMS, with the assumption that the “strongest imaginable pleasant” and
“strongest imaginable unpleasant” experiences will have some universal mean-
ing. Figure 24.4 shows data collected in such fashion (Duffy et al., 1999). Two
mirror-image Green LMSs were presented to participants: “strongest imaginable
dislike” lay at the left end of the line, “strongest imaginable like” lay on the right,
and “neutral” marked where the zeros aligned. Because the liking and disliking
of any food are subject to many factors – past experience, culture, geography –
it makes sense to limit our search for links between sensory intensity and pref-
erence to homogeneous groups. The subjects in Figure 24.4 all had body mass
indexes (BMIs) below 35; as BMI is a measure of obesity, that level excluded the
morbidly obese, who might have exhibited distinct food preferences. The sub-
jects were between the ages of 20 and 53; that excluded postmenopausal women.
Data from men and women are shown separately, as we know that sex is a vari-
able in perceived taste intensity. Despite the remaining diversity, there is some
order in the data. For example, female supertasters in our sample liked grapefruit
juice less than female nontasters, confirming the observations of Drewnowski,
Henderson, and Shore (1997), and male supertasters liked it more than male non-
tasters. Female supertasters also liked whole milk less than female nontasters,
confirming the data of Duffy and Bartoshuk (1996); no effect was seen for males.
The category scales so commonly used in sensory studies are also being used
as hedonic scales. Is the Green LMS superior to them in this context as well? We
suspect so, given that many of the logical problems inherent in category scales
also apply to their hedonic incarnations (e.g., lack of ratio properties, ceiling
effects, reversal artifacts).
3. Perspectives
Taste offers a unique tool for evaluation of psychophysical scales. Counts of
fungiform papillae and perceived taste intensities are linked, and we can evaluate
the power of a psychophysical scale to capture differences across subjects by how
well that scale captures this linkage. Hedonic scales pose additional challenges,
but the prize may be worth the effort. Valid measures of the intensity of affective
experiences may reveal new phenomena as well as challenge long-held views.
The impact of what we have learned about taste may have implications that will
reach far beyond this one sensory modality. Now that we have identified the
serious consequences of the current use of adjective-labeled scales in taste, we
must be prepared to look for similar examples in other fields.
Acknowledgments
We thank the National Institutes of Health, grant DC00283, The Donaghue
Women’s Health Investigator Program at Yale, and the U.S. Department of
Agriculture, grant 9603745 NRICG, for financial support for these studies.
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25
The Individuality of Odor Perception
Robyn Hudson and Hans Distel
1. Odors Are Cognitive Constructs

The central argument of this chapter is that odors are the products of plastic ner-
vous systems and that to adequately understand how olfactory stimuli influence
physiology and behavior it is necessary to understand how experience shapes the
way odorants are received and processed. Fundamental to the argument is the
conceptual distinction between odorants and odors (Hudson, 1999). Odorants
are molecules, entities of the external world objectively definable in terms of
physicochemical characteristics and capable of being interpreted by particular
nervous systems to yield the perceptions we call odors. Odors are the subjec-
tive products – constructs, if you like – of individual nervous systems and thus
potentially are open to the many modulating influences of what might broadly
be thought of as “mind.” They are among the phenomena that drive behavioral,
physiological, and psychological functioning and thus are phenomena that we
need to understand.
Following from that, we shall not be able to provide a proper account of
olfactory function without considering the role of individual experience in shap-
ing it. Indeed, increasing numbers of studies are suggesting that learning sig-
nificantly influences aspects of olfactory function as diverse as the evocation
of memories and associations, hedonic judgment, the early acquisition of pref-
erences, and the ability to perceive and discriminate odors (Engen, 1991), as
reviewed by Ayabe-Kanamura et al. (1998); see also the chapters in Sections 2
and 3 of this volume.
This experience-dependent, subjective aspect of odor perception helps explain
one of the central puzzles of olfaction: the inability to provide an objective clas-
sification of the odor world, as reviewed by Hudson (1999). Despite persistent
and imaginative attempts to identify the true relationships that determine the way
we perceive and respond to odors, it has thus far not proved possible to order
408
The Individuality of Odor Perception 409
the odor world according to a limited number of objective, physicochemical pa-

rameters, nor to identify populations of receptor cells consistent with any such
order. Recent breakthroughs in identifying ligands for specific olfactory recep-
tors (Krautwurst, Yau, and Reed, 1998; Zhao et al., 1998) and identifying zones
of the sensory epithelium that express particular receptor populations (Ressler,
Sullivan, and Buck, 1993; Strotmann, Konzelmann, and Breer, 1996), as well
as demonstration that these project to form epitope maps in the olfactory bulb
(Ressler, Sullivan, and Buck, 1994; Vassar, Ngai, and Axel, 1994; Mori, 1995),
are undoubtedly of major importance in advancing our understanding of odorant
reception. And yet, given that most receptor neurons appear capable of respond-
ing to a variety of odorants (Sicard and Holley, 1984; Sicard, 1986; Sato et al.,
1994; Bozza and Kauer, 1998; Duchamp-Viret, Chaput, and Duchamp, 1999;
Sicard, Chapter 18, this volume), that most natural odorants consist of many,
even hundreds, of volatiles (Laing et al., 1989; Maarse, 1991), and that lesioning
of large and arbitrarily selected areas of the olfactory bulb has shown few mea-
surable effects on behavioral responses to odor stimuli (Hudson and Distel, 1987;
Lu and Slotnick, 1998), it is difficult to see how those advances alone can account
for odor coding. Adding to this complexity are reports of extensive polymorphism
in human olfactory receptors (Lancet et al., 1993; Glusman et al., 1996).
2. An Evolutionary Perspective
The failure of olfactory research to provide a satisfactory objective classification
of odor quality or an account of odor coding at the primary receptor level is
understandable when we consider the task with which the olfactory system is
confronted. Under natural conditions the olfactory system faces a particular
problem not encountered in other sensory modalities, namely, the large numbers
and inherent unpredictability of the potentially relevant stimuli. The problem
lies not only in the wide range of potential molecular effects but also in their
seemingly endless possibilities for combining. That makes it extremely difficult
to try to reduce the chemical world to a few primary features and to map them
onto the receptor surface. In an evolutionary sense, that has also made it difficult
for the system to anticipate which features of the chemical environment are going
to be of particular relevance and to construct neural filters accordingly. In only
a few specific contexts – for example, the development of pheromonal signals
involved in reproduction (Vandenberg, 1983; Hudson and Distel, 1995) – are
odorants reliable predictors of events and resources that will promote survival
and reproductive fitness.
Olfactory systems appear to have evolved several means for coping with the
problem of such vast numbers of stimuli. One has been to develop receptor
410 Robyn Hudson and Hans Distel
surfaces capable of responding to a wide range of molecular features. That is

reflected by the large number of receptor proteins – perhaps as many as 1,000 in
mammals (Buck and Axel, 1991) – now believed to exist and by the presence of
some broadly tuned receptor neurons capable of responding in distinctive ways to
a spectrum of odorants (Sicard and Holley, 1984; Sicard, 1986; Duchamp-Viret
et al., 1999; Sicard, Chapter 18, this volume).
A second means for coping is by learning. Learning permits flexibility and
selectivity, enabling individuals to acquire or enhance their neural representations
of the most appropriate information in a particular environment (Hudson et al.,
1998). Thus, early in the chain of perception, within the olfactory bulb, learning
processes appear to play an important part in selecting, defining, amplifying, and
storing patterns of activation that are of particular significance and in helping to
distinguish those patterns from the continually shifting patterns of background
“noise” impinging on receptors, as reviewed by Brennan and Keverne (1997).
A third means for coping with the wide range of stimuli is to alter the receptive
properties of the system according to local conditions and individual experience
so as to enhance sensitivity at the receptor surface to those molecules that are of
potential or actual relevance. Again, there is a growing body of evidence support-
ing the existence of such phenomena (Wang, Wysocki, and Gold, 1993; Nevitt
et al., 1994; Semke Distel, and Hudson, 1995), as reviewed by Hudson and Distel
(1998).
3. Empirical Evidence
We shall now discuss three examples from our recent work in human olfaction
illustrating how individual experience can influence various aspects of olfactory
function. Consistent with our belief in the importance of using natural stimuli and
natural routes of stimulus delivery, those studies had two methodological features
in common: Subjects were exposed to multimolecular, complex odorants drawn
from everyday life (cf. Laing et al., 1989; Maarse, 1991), and the odorants were
presented in squeeze bottles, with the subjects being encouraged to use their
own natural sniffing techniques when sampling them (cf. Laing, 1982, 1983,
1985).
3.1. Cross-Cultural Comparisons

Obviously in humans it is difficult to define or control ecologically relevant ol-
factory experience – an essential requirement for investigating the relationship
between naturally occurring individual learning and olfactory function. A pos-
sible solution is to make use of presumed geographical differences in olfactory
experiences and compare responses to everyday odors across cultures. Because

the findings from our first application of that strategy have been published else-
where (Ayabe-Kanamura et al., 1998; Distel et al., 1999), we report them only
briefly here.
We compared the responses of 40 Japanese subjects and 44 age-matched
German subjects to 18 everyday odorants (Ayabe-Kanamura et al., 1998). Sub-
jects were asked to rate the stimuli on intensity, familiarity, pleasantness, and
edibility, to describe associations elicited by them, and, if possible, to name
them. One-third of the odorants were presumed to be familiar to the Japanese,
one-third to the Germans, and one-third to both populations. Better performances
by the Japanese in providing appropriate descriptors for “Japanese” odorants,
and by the Germans for “European” odorants, supported our pre-selection of the
stimuli as culture-typical. Particularly clear differences between the two popula-
tions were found in pleasantness ratings. In general, a positive relationship was
found between the pleasantness rating and judgment of a stimulus as edible, sug-
gesting that culture-specific experiences – particularly of foods – significantly
influence odor perception. More surprising, there were significant differences
between the two populations in regard to intensity ratings for some odorants.
Those differences did not seem to be artifacts of the test situation and raised the
possibility that experience might influence such basic aspects of odor perception
as subjective perception of stimulus strength.
That was examined by extending the original Japanese-German sample to
include a group of 39 age-matched Mexican subjects tested using the same
substances and in the same way (Distel et al., 1999). Despite large individual
differences in the responses to a given odorant among the subjects in the three
populations, significant positive correlations were found between rating scores
for three measures: intensity, pleasantness, and familiarity. Most notable were
the consistent positive correlations between perceived intensity and the ratings
of familiarity and pleasantness. That suggested that the subjective perceptions of
the intensities of odors may depend not only on stimulus concentration but also
on aspects of an individual’s experiences of odorants in the context of everyday
life.
It would seem to make sense that odors that have acquired meaning for an
individual should be perceived and attended to more readily than stimuli of
little relevance, and that should result in stronger subjective impressions of
their strengths. However, that is not the way we are accustomed to thinking
about stimuli in classic psychophysical research, where it has long been as-
sumed that there are close and invariant relationships between our subjective
perceptions and the objectively measurable physical properties of the external
world.
3.2. Intra-cultural Comparisons

Given the clear results (and, in the case of perceived intensity, the surprising
results) of our cross-cultural comparisons, we were interested in examining the
generality of those findings by seeing if they could be replicated in culturally
more homogeneous populations. Because the more surprising and potentially
most controversial finding in our studies concerned the relationship between
experience or knowledge of an odor and its perceived intensity, that aspect has
been particularly emphasized.
Influence of prior knowledge. A first, preliminary study involved test-

ing the responses of a northern European, mainly Scandinavian, population of
nine women and four men (mean age 26.5 ± 2.3 years) to 30 everyday odorants,
some of which are listed in Figure 25.1. The method of stimulus presentation was
Odorant Identification Intensity Judgement

no yes 1 2 3 4 5
Vanilla 1 2
Soil 6 5
Anis 1 2
Arrak* 3 3
Cat food 5 1
Coconut 4 2
Peanut butter 2 4
Cheese 4 8
Pine wood 4 3
Banana 2 4
Cinnamon 4 3
Coffee 2 11
Pipe tobacco 3 6
Whiskey 2 2
*Arrak is a Swedish liquor 1 2 3 4 5
Figure 25.1. Median rating scores for intensity judgments when subjects could
identify the odorant (open circles) or could not (filled circles).
the same as in our cross-cultural study. In a first trial, subjects sampled each sniff
bottle and responded “certainly know,” “certainly don’t know,” or “uncertain.”
Of the 30 odorants, 20 were then selected as being well known to some sub-
jects and unknown to others. In a second trial on the same day, subjects were
presented with 4 of the odorants, 2 they had claimed to recognize and 2 they
did not know, and, in addition, the odor of coffee, which all subjects claimed to
know. An attempt was made to select odorants in such a way as to have equal
numbers of subjects knowing and not knowing a given odor, in order to control
for possible intrinsic effects of odorants on perception.
Subjects first rated the intensities of the five odors on a 5-point scale that
included intermediate values (e.g., 4.6). In a second round they were asked
to rate the odors for pleasantness and familiarity on similar 5-point scales, to
indicate whether or not the odors represented edible substances and whether
or not they would be willing to eat those substances, and finally to name each
odorant or provide an association.
The responses to the odorants were divided into two groups, on the basis of the
apparent certainty of subjects’ odor knowledge inferred from accurate naming or
provision of an appropriate association. Because several of the knowledge ratings
from the first trial with 20 odorants appeared inaccurate, the final groups were
not equal in number, and 6 odorants had to be dropped from the final analysis. So
14 odorants were judged by subjects with different levels of odor knowledge – on
average, by four subjects knowing the odor and by three not knowing it. Median
scores for the two groups were calculated for each substance.
Subjects who knew an odor gave higher intensity ratings, on average, than did
those not knowing it (3.8 vs. 2.9) (Figure 25.1), as well as higher pleasantness
ratings (3.5 vs. 2.7) and higher familiarity ratings (3.7 vs. 3.0). Those differ-
ences were significant when compared across all odor pairs combined (Wilcoxon
signed-ranks test, p < .006, p < .02, p < .01, respectively).
The findings basically confirmed those in our cross-cultural study. We found
the same pattern of positive association between subjects’ familiarity with or
knowledge of an odor and their judgments of its intensity and pleasantness.
Thus, although it was based on a very small sample, the study suggested
that such relationships may exist even within culturally more homogeneous
groups and do not depend on the marked differences in experience of partic-
ular odorants presumed to exist in different cultures – differences that would
have been further enhanced by our selection of culture-typical stimuli in the
cross-cultural study. The similarity between the findings in the Scandinavian
study and the cross-cultural study also reduces the probability that the differ-
ences between national groups found in the cross-cultural study were genetically
based.
Prior knowledge versus context. Encouraged by such results, we con-

ducted a larger study (Distel and Hudson, 2001) along similar lines with German
subjects, but with one modification. In addition to assessing the relationships be-
tween subjects’ prior knowledge of a set of everyday odors and their ratings of
intensity, pleasantness, and familiarity, we evaluated the association between the
subjects’ judgments of the goodness of fit between (1) their perceptions of the
odors and (2) information about the odor sources provided by the experimenter.
The responses of 76 medical students (mean age 24.2 ± 5.2 years) of both
sexes (47% women) to the 24 everyday odorants listed in Figure 25.3 were
tested under two conditions: (A) without information about the odor source;
(B) together with the veridical name of the odorant. In both conditions we asked
the subjects to rate the intensity, pleasantness, and familiarity of the odors on a
scale from 1 to 10. In condition A we also asked them to identify the source,
whereas in condition B we asked them to rate how well the odor corresponded
to the name provided (on a scale from 1 to 5). Subjects were randomly assigned
to one of the two groups, with 38 subjects in each. Each group rated half of the
odorants using condition A, and the other half using condition B, so that each
odorant was rated the same number of times under the two conditions.
No significant differences were found between men and women, and so their
scores have been combined. Again, the findings have basically confirmed those
of our earlier studies. As summarized in Figure 25.2, for the three parameters
0 1 2 3 4 5 6 7 8 9 10
INTENSITY with name
without name
PLEASANTNESS with name
without name
FAMILIARITY with name
without name
0 1 2 3 4 5 6 7 8 9 10
Figure 25.2. Median rating scores for everyday odorants presented with and
without veridical names: filled circles, odor not identified; open circles, odor
identified; filled squares, name inappropriate for odor; open squares, name
appropriate for odor.
of intensity, pleasantness, and familiarity, knowledge of the odor, either be-

cause of a subject’s ability to identify the source or because the veridical name
was provided by the experimenter, was associated with higher ratings for all
three parameters. Knowledge of the veridical name was associated with in-
creases of 0.7, 1.3, and 1.0 points for intensity, pleasantness, and familiar-
ity, respectively, and the effect was significant (Wilcoxon signed-ranks test,
p < .025 across all odorants combined). If subjects were able to identify the
odor sources unaided (37% of presentations under condition A), the increase in
rating scores (compared with inability to identify) was significant for intensity
( p < .001) and was even more pronounced for pleasantness and familiarity (both
p < .0001).
However, when subjects believed that the names provided did not fit the odors
(59% of presentations under condition B), they were judged to be less intense,
less pleasant, and less familiar than when names and odors were perceived to
coincide (Figure 25.2; 5 vs. 6.75, 6 vs. 7.5, and 5 vs. 8.75 points, respectively;
Wilcoxon signed-ranks test, p < .0001).
Figure 25.3 shows ratings of intensity for all of the odorants to illustrate
in more detail the influence of subjects’ prior knowledge on their judgments
of intensity. The pattern in the left panel (condition A) confirms the positive
association between subjects’ knowledge of an odor (correct identification of its
source) and their perceptions of its intensity, and the right panel (condition B)
shows a clear association between the perceived intensity of an odor and subjects’
judgments of the goodness of fit between the veridical name provided and their
own perceptions of the odor.
In addition to confirming our earlier findings, the study just described suggests
that odor perception can be strongly influenced by the goodness of fit between
subjects’ expectations or imagination of how a particular odorant should smell
and their external contextual information (in this case, provision of the veridical
name). If the fit between internal expectations and external information is good,
ratings of intensity, pleasantness, and familiarity will be higher. If the fit is poor,
the resulting dissonance will lead to lower ratings for those parameters.
But how can we account for such variability in responding? There surely are
as many answers to that as there are individual lives and olfactory experiences,
but there is one general factor that may well be important: Most of the stimuli
used were foods or beverages and thus would normally have been experienced
in the context of ingestion. In our study, the absence of taste input and of the
aromas released by chewing and mixing with saliva – that is, the sensory com-
plex of flavor – may have contributed to the dissonance between the subjects’
expectations generated by provision of the veridical name and their perceptions
arising from smell alone.
Odorant without Name Odorant with Name
IDENTIFIED FITTING
vs. NOT IDENTIFIED vs. NOT FITTING
0 2 4 6 8 10 0 2 4 6 8 10
Honey
***
Soil
***
Cumin
* **
Cinnamon
* **
Tea
*
Chocolate
*
Olive oil
* *
Rosmary
*
Hazel nut
* *
Sawdust
* **
Vanilla
Pipe tobacco
**
Marzipan
***
Cider
***
Mayonnaise
***
Coconut
***
Oregano
*
Banana
Stale bread
***
Rum
*
Parmesan
**
Orange
Sherry
Whiskey
0 2 4 6 8 10 0 2 4 6 8 10
Figure 25.3. Median scores for intensity judgments for everyday odorants
presented with and without veridical names: filled circles, odor not identi-
fied; open circles, odor identified; filled squares, name inappropriate for odor;
open squares, name appropriate for odor; *p < .05; **p < .01; ***p < .001;
Wilcoxon-Mann-Whitney test for independent samples.
And what might these results tell us about the nature of odor representation
in the brain? It has often been debated whether or not we can truly remember
or imagine odors, and thus to what extent we possess accurate, detailed, and
behaviorally relevant odor images (Crowder and Schab, 1995). The findings
here suggest that we do indeed possess such internal representations and that
they are of sufficient definition and force to shape our perceptions of odors,
depending on the goodness of fit among our images, the actual olfactory stimuli,
and the information available from our immediate environment.
4. Implications for Future Research

At least three broad implications emerge from the studies described here.
4.1. Importance of Experience

The findings from all four of our studies point to the importance of individual
experience or knowledge in shaping responses to odors and thus in influencing
odor-guided behavior. In doing so, the findings underscore the individuality of
olfactory perception. Therefore we should not expect to be able to identify finely
graded psychophysical universals – at least not with respect to behaviorally
relevant, everyday odorants – and in assessing olfactory function we will need
to take into account the individual amounts and types of experience with the
particular test stimuli used.
That raises the question to what extent the ages of subjects and the particular
contexts in which their olfactory learning occurred can influence the intensity
and longevity of memory for odors. For example, the widespread phenomenon of
odors evoking vivid memories from early childhood (Engen, 1991), combined
with reports of early olfactory imprinting in animals, as reviewed by Hudson
(1993), would suggest that early experience may be particularly salient. Certainly
there is now ample evidence that human newborns possess a good sense of smell
and rapidly learn olfactory features of their environment from birth and probably
even in utero (Schaal et al., Chapter 26, this volume).
4.2. Influence of Context

It follows from all the foregoing evidence and discussion that odors are expe-
rienced and learned in individual contexts that are culturally specific. Not only
can a particular odor signify or predict a particular context or event (a bottom-up
process, if you will), but also a particular context can activate expectations of the
odors to be encountered (a top-down process), and depending on the goodness
of fit between those two processes, one’s behavioral responses and decisions are
made either for good or ill. That is particularly clear in the context of eating,
the basic biological function in which the chemical senses still play the critical
and dominant role: We order from a menu and then judge the dish or the wine,
to a considerable extent, on the basis of the degree of congruence between our
experience-based expectations and our immediate chemosensory perceptions.
Of course, there are some lucky surprises, occasional positive mismatches be-
tween expectation and actuality, but as many newlyweds and market researchers
know, those tend to be the exceptions.
4.3. Explanatory Limits of Peripheral Coding

As we review our findings and those from other studies, we see that perhaps
their most far-reaching consequences, and thus the ones that have to be thought
through most carefully, are the implications for our efforts to understand what we
generally refer to as olfactory coding. Initially based on chemistry-inspired psy-
chophysics, and more recently advanced by spectacular achievements in molec-
ular biology, olfactory research has long been guided by the reductionist dream
of being able to identify neural and perceptual universals and to understand the
whole as the sum of its parts.
Without doubt, reductionist approaches have provided and will continue to
provide essential information and perhaps breakthroughs of the kind mentioned
in Section 2 of this chapter. At the same time, for reasons outlined in that same sec-
tion and supported by many examples in this volume (e.g., Sicard, Chapter 18),
we need to recognize the limitations imposed on reductionist levels of expla-
nation by the increasingly well-documented operation of cognitive processes.
Recognition of that necessity should not lead to annoyance or despair. Rather, it
should increase our appreciation of a sensory system that allows such individual,
ecologically appropriate fine tuning to an infinitely complex chemical world.
Acknowledgments
The data for the Scandinavian study were collected during a practical class at the
1998 International Course in Sensory Ecology, Lund University, Sweden. We
thank the director of the course, Bill Hansson, for making this possible.
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26
Olfactory Cognition at the Start of Life:
The Perinatal Shaping of Selective
Odor Responsiveness
Benoist Schaal, Robert Soussignan, and Luc Marlier
In the days following birth, human newborns are swept into a whirlwind of
stimuli that are both complex and unpredictable in terms of space, time, and
multimodal contingencies. In their very first excursion into the postnatal world,
newborns can respond to only a limited array of those stimuli, but their brains
possess effective perceptive and integrative capacities that soon will allow them to
organize differential perceptions and directional actions in what might otherwise
be a “blooming, buzzing confusion.” Our current knowledge of the initial states
of perceptual and cognitive functions and their development has been derived
almost exclusively from studies of unimodal and cross-modal visual and auditory
perceptions (e.g., Gottlieb and Krasnegor, 1985; Lewkowicz and Lickliter, 1994;
Kellman and Arterberry, 1998; Slater, 1998; Rochat, 1999). However, evidence
that nonvisual, nonaural cues are involved in the partitioning of the neonatal
Umwelt has begun to accumulate, both for animals and for humans. Studies have
demonstrated, for example, that some newborn animals rely so profoundly and
pervasively on olfactory cues that “we cannot appreciate their behavior without
understanding the roles of olfaction” (Alberts, 1981, p. 352). Compared with the
findings in animal studies, the evidence for olfactory modulation of behavior in
our own species remains narrow and shallow, although the body of data is steadily
growing. Accordingly, our current knowledge of human cognitive development
does not encompass the psychological facets of the chemical senses, a situation
that may distort our understanding of the world and mind of the infant (Turkewitz,
1979).
This chapter deals with the initial state of olfactory functioning in the human
infant and its changes during early development. We shall first survey some recent
research on sensory and hedonic discrimination of odors at the very beginning
of cognition. Then we shall address such issues as whether or not olfactory com-
petence is predisposed to process certain kinds of stimuli during early develop-
ment. By which experience-dependent or experience-independent mechanisms is
421
422 Benoist Schaal, Robert Soussignan, and Luc Marlier
olfactory cognition shaped? How variable are individuals’ trajectories of olfac-

tory development as functions of the early odor environment?
1. Discriminative, “Categorical,” and Hedonic Processing

of Odors by Newborns
Two basic processes have been investigated in attempts to describe infant percep-
tion: discrimination and categorization. Success in discrimination is generally
considered to indicate an ability to process a given stimulus in a given con-
text. The most straightforward measure of early discrimination ability relies
on expression of differential responses to distinct odors presented in succes-
sion. The frequency with which subjects will respond and the magnitude and
latency of their motor or autonomic reactions clearly will vary for different odor
stimuli (e.g., Engen, Lipsitt, and Kaye, 1963; Self, Horowitz, and Paden, 1972;
Yasumatsu et al., 1994; Soussignan et al., 1997).
Simultaneous presentation of odor stimuli can provide even stronger evidence
for discrimination. Thus, paired odor-choice paradigms (Macfarlane, 1975) have
been used in a number of studies of infants’ ability to actively show odor discrim-
ination, recognition, and preference. Some of those studies will be summarized
later.
Infants readily detect and differentiate odors, but little is known about the
“dimensions” they use in discriminative processing. It is generally assumed that
the differential stimulative power of odorants results both from sensory attributes
(quality, intensity, irritation) and from psychological attributes (hedonic value,
familiarity). There is empirical evidence that newborns treat some of those di-
mensions discriminatively, such as quality (Engen and Lipsitt, 1965), intensity
(Rovee, 1969), and familiarity (Schleidt and Genzel, 1990). Most such studies
have relied on the notion that hedonic responses are basic in early development
(Schneirla, 1965). Hence, they have made use of the dichotomous nature of
neonatal behavior, that is, use of the two response tendencies termed, in vari-
ous theoretical contexts, positive versus negative, approach versus withdrawal,
attraction versus aversion, orientation versus defense, or low versus high arousal.
The use of behavioral markers of opposite response tendencies allowed some
interesting insights into the early ability to differentiate odor stimuli. Early
experiments suggested that “naive” newborns (i.e., tested right after birth, with
minimal postnatal chemosensory experience) showed different facial expres-
sions when exposed to odorants that had opposite hedonic valences. Steiner
(1979) took advantage of that observation to try to assess empirically the he-
donic responses of newborns exposed to odorants categorized a priori, by adults,
as hedonically positive or negative: The photographs of infants’ facial expressions
Olfactory Cognition in Newborns 423
elicited by putatively pleasant odors (e.g., banana, vanilla, milk) were rated by
a panel, blind to the stimuli presented, as indicating attraction or indifference.
In contrast, the infants’ facial responses to unpleasant odors (having fishy or
rotten qualities) were consistently rated as indicating rejection. On the basis of
the precocity indicated by those differential responses, as well as similar data
from an anencephalic newborn, Steiner concluded that “their innate, possibly
inherited character is demonstrated” (Steiner, 1979, p. 278). He speculated on
the existence of a “hedonical monitor” that would release the facial responses in
a stereotyped, reflexive way. However, it was not clear whether infants were re-
sponding to stimulus differences in intensity, quality, or familiarity. In addition,
the newborns’ facial responses to the odors were judged from single photographs
of each expression taken at some undefined time after stimulus administration and
assessed by a rather coarse judgment method. Despite those concerns, Steiner’s
observations remain important in that they raised the issue of whether newborns
respond selectively to specific odors or to categories of odors when smelling
stimuli for the first time.
In a reinvestigation of neonatal ability to discriminate hedonically between
odors, we attempted to control for several of the shortcomings in the Steiner study
(Soussignan et al., 1997): Three-day-old infants were presented with odorants
from their perinatal environment or with pure, reagent-grade odorants. All bi-
ological odorants were unfamiliar and were either of human origin (amniotic
fluid, breast milk, but not from the infant’s own mother) or of commercial origin
(cow’s-milk-based formula and protein hydrolysate formula, but not the brand
usually consumed by the infant); pure vanilla and butyric acid were diluted
to match, in intensity and trigeminal potency, each of the biological odorants.
Subjects were thus presented with 12 odor stimuli (plus a wet control) while
their respiratory rates and facial responses were recorded. Changes in respira-
tory rates (relative to control) demonstrated that all odors had been detected.
Facial behaviors (in terms of proportion of responding infants, and numbers and
durations of facial actions) also differentiated between the odor stimuli and the
control. However, a fine-grained quantification of facial movements, using the
infant version of Ekman and Friesen’s Facial Action Coding System (Oster and
Rosenstein, 1993), did not confirm that odorants classified by adults as pleasant
(vanillin) and unpleasant (butyric acid) triggered facial expressions reflecting
attraction and aversion, respectively. In fact, the topographies and combinations
of facial actions were extremely variable across subjects (Figure 26.1). Thus
the olfacto-facial responses were far from having the stereotyped character of
a reflex. Nevertheless, butyric acid was significantly more effective in evok-
ing facial markers of disgust than was vanillin, whereas vanillin did not trigger
more smiling or mouthing movements than did butyric acid. Thus, reliable facial
70 B
60
*
Vanilla
50 Butyric acid
% Subjects
40
30
20
10
0
Smiling Disgust
Figure 26.1. A: Samples of the facial expressions of newborns in response to
odors: (upper left) formula milk (age 82 hours, latency from stimulus onset
5.12 sec); (upper right) butyric acid (age 115 hours, latency 2.88 sec, concen-
tration 0.0078%); (lower left) butyric acid (age 124 hours, latency 2.76 sec,
concentration 0.125%); (lower right) vanillin (age 68 hours, latency 3.56 sec,
concentration 0.0078%). B: Proportions of infants displaying smiling (FACS
action unit 12) and disgust (FACS action units 9–10) to successive presentations
of the odors of vanillin and butyric acid (rated by an adult panel as pleasant and
unpleasant, respectively); *p < .05. (Adapted from Soussignan et al., 1997.)
responses of human newborns seemed to be more easily elicited by an un-

pleasant (to adults) stimulus than by an iso-intense pleasant stimulus. Among
the biological odorants, only the odor of unfamiliar amniotic fluid increased the
numbers of negative facial actions, as compared with the control stimulus. The
odor of the unfamiliar formula did not provoke increased expressions of disgust,
although it was rated slightly unpleasant to very unpleasant by adults. Thus
infants’ facial responses may, by far, not correspond to adults’ hedonic ratings
of odorants.
Two points from our study pertaining to the early development of olfactory
cognition should be highlighted. First, positive and negative behavioral ten-
dencies, as demonstrated by the infants’ facial responses to odors, seem to be
relatively independent. Thus, pleasantness and unpleasantness may constitute
independent perceptual dimensions, and the opposite repertoires of responses
may emerge at different rates during development. It has been suggested that
a general positive emotional responsiveness develops earlier than negative re-
sponsiveness (Schneirla, 1965; Izard, 1977). That rule, however, may not apply
equally to all modalities: Although the data on neonatal olfaction are limited,
they suggest that olfacto-facial systems for responding may be better integrated
on the negative pole than on the positive pole of hedonic space.
Second, in our experiment described earlier (Soussignan et al., 1997), the au-
tonomic measure revealed an influence of odor familiarity on responsiveness:
Whereas bottle-fed infants responded with their highest increases in respiratory
rates to the unfamiliar formula milk, breast-fed infants showed the highest in-
creases in their respiratory activity to unfamiliar breast milk. Such differential
responsiveness can be interpreted as reflecting abilities (1) to extract information
from complex, unfamiliar chemical stimuli, (2) to compare variations of such
information to previously stored information, and (3) to respond discriminatively
to a stimulus that fits (or does not fit) to an already encoded odor image.
Deriving a single psychological category from different versions of a stimu-
lus has been termed, in the realm of vision, “extraction of invariants” (Antell,
Caron, and Myers, 1985) or “perceptual equivalence categorization” (Bornstein,
1984). With the use of a habituation paradigm, similar abilities for invariance
extraction from olfactory stimuli have been shown in newborns by Engen and
Lipsitt (1965). They found that 3-day-old newborns were able to discriminate
the odor of a mixture and the odors of its components. Following a habituation
of respiratory disruption produced by an anise/asafetida mixture, dishabituation
was obtained with asafetida alone, but not with the anise component. Judgments
of similarity by adults indicated that the odor of the mixture was dominated
by the anise note, suggesting that newborns had difficulty in discriminating be-
tween pure anise and the mixture. When the procedure was repeated with a more
balanced odorant mixture of isoamyl acetate and heptanal, both odorants effi-
ciently dishabituated the respiratory disruption; in addition, the dishabituation
efficacy of each compound was proportional to its dissimilarity from the mixture
(as judged by adults). That approach not only confirmed that the newborns were
able to make fine qualitative discriminations but also suggested that they may
have perceived the qualitative distance between those odors much as did adults.
Neonatal ability to extract invariants from salient odor stimuli was further as-
sessed by using the phenomenon of negative alliesthesia. “Alliesthesia” refers to a
shift in one’s hedonic evaluation of food that has been eaten to satiation (Cabanac
and Duclaux, 1973). It is called “negative” (“positive”) when the change in one’s
internal state is a decrease (increase) in the perceived pleasantness of a given
stimulus. That model would predict that motivation-dependent fluctuations in
hedonic responsiveness would pertain only to the odor of a familiar food or to
odors resembling that of the familiar food. Accordingly, we set out to determine
if infants would show hedonic discrimination for milk odors as a function of their
prandial state (Soussignan, Schaal, and Marlier, 1999). Taking advantage of the
qualitative variety and stability of the brands of milk formulas, we tested only
bottle-fed newborns. Their facial responses were recorded as they were exposed
to five odorants: familiar (regular formula); unfamiliar but qualitatively similar
(unfamiliar regular formula); unfamiliar and dissimilar to the familiar formula
(protein hydrolysate formula and vanillin); neutral control (the similarities had
been assessed by an adult panel). Measurements of facial movements revealed
that, after feeding, infants displayed more hedonically negative expressions to
their familiar formula and, to a lesser extent, to the unfamiliar but qualitatively
similar formula than they had before feeding (Figure 26.2). In contrast, their
prandial state had no effect on hedonic facial expressions when responding to
the odors of the protein hydrolysate formula and the vanillin. In brief, newborns
showed post-ingestive increases in aversive facial expressions to odorants that
shared quality or intensity features with their habitual food, but not to odorants
with unfamilar features (vanillin, protein hydrolysate formula).
Those data can be interpreted as evidence that newborns are able to generalize
the sensory features of a familiar odorant to a similar, but qualitatively different,
odorant they have never encountered. Interestingly, such transfers were seen
across substantial variations in stimulation contexts and behavioral states. Infants
were able to encode qualitative features of their milk perceived retronasally while
being fed and to transfer their responses into a testing situation in which the
stimulus was presented orthonasally, quite independent of oral chemoreception.
In addition, they were asleep during the olfactory tests, but were awake during
the acquisition phase (i.e., the feeding episodes), which suggests that low-level
cognitive processes were involved in the sensory encoding.
80
Preprandial
70 Postprandial
60
% Subjects
50 +
*
40
30
20
10
0
FRF URF HPF VAN CON
Stimuli
Figure 26.2. Proportions of newborns (n = 22) displaying aversive facial
responses to the odors of familiar and unfamiliar regular formulas (FRF and
URF, respectively), an unfamiliar protein hydrolysate formula (HPF), vanillin
(VAN), and a control stimulus (CON, water) as functions of the prandial state;
*p < .01; +p = .07. (Adapted from Soussignan et al., 1999.)
In sum, human infants, from the very beginning of extrauterine life, are compe-
tent to extract qualitative information from environmental odors and to translate
that into hedonic responsiveness. To a great extent, the hedonic direction of an
infant’s response to a given odor is dependent on previous exposure. Some of
the mechanisms mediating such experiential effects will be surveyed next.
2. Shaping of Olfactory Preferences in Early Ontogeny

Mammalian newborns have a general ability to associate distinct odors with
different contexts and later to exhibit differential behavior patterns to those odors.
Early acquisition of olfactory competence thus is characterized by high degrees of
plasticity and specificity of odor–response associations; for reviews, see Alberts
(1987), Johanson and Terry (1986), Wilson and Sullivan (1994), and Hudson,
Schaal, and Bilko (1999). Human newborns are equally adept olfactory learners,
though much less studied. They not only can detect and discriminate odorants but
also will behave in ways indicating that they can use olfactory “representations”
derived from previous experience.
Some of the processes by which odor-mediated preferences are acquired by
human newborns have been uncovered in social contexts. The first empirical
evidence that responses to social odors could be highly selective came from
choice tests using the odor of the mother’s breast (Macfarlane, 1975; Russell,
1976; Schaal et al., 1980). The response to breast odor apparently is related to
both postnatal age and the amount of direct exposure to the mother’s body
(Macfarlane, 1975; Russell, 1976). That has been confirmed by comparing
2-week-old breast- and bottle-fed infants: Whereas the former were differen-
tially attracted to the axillary odors of their mothers (as compared with axillary
odors from unfamiliar lactating women), the latter did not differentiate their
mothers’ axillary odors from the axillary odors of other bottle-feeding mothers.
The absence of a differential response from bottle-fed infants was believed to be
related to their less extensive prior exposure to their mothers’ skin odors (Cernoch
and Porter, 1985). In a further study, we sought to assess the ability of 4-day-old
breast- and bottle-fed newborns to discriminate the odor of their familiar milk
and the odor of an unfamiliar milk (Marlier and Schaal, 1997). When presented
with the odors of their own mothers’ milk and the odor of another mother’s milk
simultaneously, breast-fed newborns responded selectively in favor of their own
milk by longer-duration head turns and appetitive mouthing. In contrast, bottle-
fed newborns did not exhibit clear differential responses when presented with
their familiar formula and an unfamiliar, qualitatively different formula. The
amount of exposure to milk odor may not necessarily be causal to the differen-
tial effects of breast feeding and bottle feeding, because factors such as the daily
chemical environment obviously can have an impact, in at least two respects:
(1) breast- and bottle-fed infants are exposed to distinct arrays of milk-borne
substances, possibly affecting olfactory performance differentially (Marlier,
Schaal, and Soussignan, 1998b); (2) they are exposed to different chemosensory
contexts: somewhat variable for breast-fed infants versus monotonous for bottle-
fed infants (Jiang et al., 1998). Although, it has not yet been shown that early
variability in food-related odors will later lead to discriminative keenness in
human infants, empirical evidence for a functional consequences from early
food variability (i.e., reduced neophobia toward unfamiliar foods) has been
obtained in young rats (Capretta, Petersik, and Steward, 1975).
The effectiveness of early odor learning has been further substantiated by
experiments that have examined to what extent artificial odorants can become
preferred in different reinforcing contexts, such as mother–infant contact outside
the feeding situation (Schaal, 1986), breast feeding per se (Schleidt and Genzel,
1990), and tactile stimulation (Sullivan et al., 1991b). In Schleidt and Genzel’s
study, mothers perfumed their breasts for 2 weeks after birth. At the ages of 1
and 2 weeks, their infants were given a choice test between the familiar perfume
and a novel odor. At both times, the infants oriented longer to their mothers’
perfume than to the control. After the test at 2 weeks, the breast-odor association
was discontinued for some of the infants, while their peers remainded exposed
Mean relative duration of orientation (%)

70
** ** **
60
50
40
30
20
10
0
1 2 >3 (A) >3 (B)
Age (Weeks)
Figure 26.3. Mean relative durations of head (nose) orientations toward the
odor of a perfume associated with the mother’s breast (solid bars) and toward
a novel control odor (empty bars) by newborns aged 1 week (n = 17), 2 weeks
(n = 18), and more than 3 weeks (subgroup A, n = 6; subgroup B, n = 10).
Infants were exposed to the perfume in conjunction with breast feeding during
weeks 1 and 2; odorization of the mother’s breast was continued after week
2 for subgroup A, but was discontinued for subgroup B; choice tests lasted
4 minutes; **p < .01. (Adapted from Schleidt and Genzel, 1990.)
to it. In a third paired-choice test, at 3–6 weeks, the preference for the mothers’
perfume had disappeared in the former subgroup of infants, but it was maintained
in the latter subgroup (Figure 26.3). Thus, an artificial odor can acquire a positive
value after repeated association with the mother’s breast or with suckling; but its
positive value apparently can rapidly reverse to neutrality when it is no longer
reinforced. In the study by Sullivan et al. (1991b), 1-day-old newborns were
assigned to four treatment conditions: odor paired with massage of the newborn,
odor and massage applied successively, odor only, and massage only – each
for 10 periods of only 30 sec each. On the following day, general activity and
head-turning responses were recorded in the presence of the odor. Only those
infants who had been given odor and massage concomitantly exhibited “general
arousal” and positive head turns toward the odorant. Thus the variability in
hedonic valence for such artificial odor stimuli revealed by the use of various
reinforcements shows the considerable plasticity of neonatal odor preferences.
However, there is some empirical evidence to suggest that the early malleabil-
ity of odor hedonics may be developmentally or evolutionarily constrained:
Certain odors seem to be learned more easily than others. Some studies have
suggested that there is something special about the breast odor of lactating
women (Makin and Porter, 1989), as well as about the odor of human milk
itself. Colostrum or milk that is collected without any contamination by areo-
lar skin secretions can elicit positive head orientation and appetitive mouthing
responses in 2- and 4-day-old breast-fed newborns (Marlier and Schaal, 1997;
Marlier, Schaal, and Soussignan, 1997, 1998a). Furthermore, 4-day-olds who
had been fed milk formula exclusively since birth responded more strongly to
the odor of breast milk taken from an unfamiliar woman than to the odor of their
own familiar formula (Marlier and Schaal, 1999). Thus, it appears that infants
have a stronger attraction toward milk-related odors they have never directly
experienced than toward an odor repeatedly experienced in the feeding context.
In other words, the amount of previous exposure, even in the highly reinforcing
contexts of comfort contact with the mother and of intake and satiation, does not
explain all cases of positive responses to odors.
Several mechanisms might account for such odor-elicited positive orientations
at first whiff that are not mitigated by postnatal feeding experience. It cannot
be excluded that to bottle-fed infants, the unfamiliar odor of human milk might
be reminiscent of their own mothers’ body odor. It is also possible that infants
may react to an intensity contrast, with breast or milk odors being weaker than
formula odors (Jiang et al., 1998). Recent data, however, indicate that after
the two stimuli were matched in intensity, the greater arousing power of human
milk remained unchanged (Marlier and Schaal, 1999). Alternatively, the power of
human milk odor may derive from (1) an inborn attraction to odors bearing special
psychobiological properties, (2) rapid postnatal odor learning, (3) prenatal odor
learning, or (4) the combined actions of those mechanisms. Those hypothetical
possibilities will be briefly surveyed:
First, the potential action of special substances with pheromone-like proper-
ties, contained in mammary secretions and minimally dependent on prior expo-
sure, has been mentioned for the human species (Russell, 1976), but thus far never
seriously investigated. However, studies of other mammals have offered sugges-
tive evidence for the existence of such pheromonal cues present around the nipple
and/or in milk (e.g., Hudson and Distel, 1995; Coureaud et al., 1999, 2001).
Second, states of calm arousal can promote very rapid engagement of odor
learning in both animal and human newborns (Wilson and Sullivan, 1994;
Sullivan et al., 1991b). Thus the salience of maternal odors might become rapidly
established through internal and external events related to the birth process. For
example, uterine contractions induce a generalized arousal state that leads to
immediate olfactory learning in rat pups (Ronca, Abel, and Alberts, 1996). In
the first hours after birth, human infants are in a prolonged state of calm arousal
(McLaughlin, O’Connor, and Denni, 1981), during which they demonstrate coor-
dinated motor activity (head orientation, rooting movements, and sucking). That
state of relative “sensory receptiveness” after birth correlates with neurochemi-
cal states (e.g., high concentrations of norepinephrine) (Lagerkrantz, 1996) that
favor rapid odor learning (Sullivan, McGaugh, and Leon, 1991a).
Third, neonatal attraction to the odor of human milk might be traceable back to
the olfactory experience of the fetus. That possibility was examined in a recent
series of experiments that consisted in exposing newborns simultaneously to
salient prenatal and postnatal odorants. When facing a choice between the odor
of their mothers’ colostrum and the odor of their own amniotic fluids, 2-day-old
breast-fed newborns did not orient toward either stimulus (Marlier et al., 1997,
1998a). That equal treatment for the odors of amniotic fluid and colostrum waned,
however, at 4 days of age, when the infants were more (i.e., longer) attracted by
their mothers’ breast milk than by amniotic fluid (Figure 26.4). That develop-
mental shift in relative orientation to a prenatal odor and a postnatal odor was
interpreted as reflecting (1) chemosensory continuity of the substrates that con-
tact the chemosensors of the fetus/newborn before and after birth (the odors of
both being influenced by the mother’s diet) (Schaal, Orgeur, and Rognon, 1995b)
and (2) the possibility that with lactogenesis, around postpartum day 3, the odor
of the lacteal secretions departs from the odor of colostrum and amniotic fluid
and thus becomes increasingly distinguishable.
3. Odor Learning in the Fetus, Newborn, and Infant

Obviously the hypothesis of transnatal continuity in chemosensory substrates
depends on the functioning of odor perception and learning in the fetus and on the
use of that sensory information by the newborn. We therefore sought to examine
the responsiveness to odors encountered in utero by exposing newborns at day 3
to samples of their own amniotic fluid (Schaal, Marlier, and Soussignan, 1995a)
and to unfamiliar amniotic fluid (Schaal, Marlier, and Soussignan, 1998). Both
breast- and bottle-fed groups responded selectively in favor of the odor of their
own familiar amniotic fluid. Findings in a subgroup of cesarean-born, bottle-fed
infants strengthened the case for prenatal acquisition of amniotic odor, because
they had their breathing pathways cleared of amniotic remnants immediately after
birth, were thoroughly washed, and were not reexposed to any amniotic-like cues
that might have been transferred into their mothers’ milk. Thus, those newborns
seemed to have the ability to retrieve the unique amniotic odor signature acquired
3 days earlier in the aquatic conditions of the womb.
To further test the ability of fetuses to learn an isolated odor note, we com-
pared the olfactory responses of infants born to mothers who had consumed anise
4 4
3 3
A 2 2
1 1
Mean relative duration of orientation (%)
60 B
Amniotic fluid **
50 Colostrum or milk
**
40
30
20
10
0
1 2 3 4 5
Age (Days)
Figure 26.4. A: Device used for simultaneous, symmetrical presentation of
paired odor pads (hatched zones). B: Mean relative durations of head orienta-
tions for five groups of breast-fed infants of different ages exposed to choice
tests contrasting the odor of their own amniotic fluid with the odor of their
mother’s lacteal secretion of the day: group 1 (n = 9, mean age 9.7 hours);
group 2 (n = 20, age 33.6 hours); group 3 (n = 12, age 55.4 hours); group 4
(n = 16, age 85.1 hours); group 5 (n = 9, age 114.2 hours). The choice tests
lasted 2 minutes; **p < .01 (Adapted from Marlier et al., 1997.)
during pregnancy and infants born to mothers who had never ingested anise dur-
ing pregnancy (Schaal, Marlier, and Soussignan, 2000). Both groups of infants
were tested at 3 hours and at 4 days of age for behavioral markers of attraction
(positive head-turning, appetitive mouthing responses) and markers of aversion
(negative facial actions) when presented with pure, diluted anise. Infants born
to anise-consuming mothers showed stable preference for anise at both times.
In contrast, the newborns from non-anise-consuming mothers displayed aver-
sion responses at the 3-hour testing, and neutral responses at the 4-day testing.
That finding clearly demonstrates that pregnant women influence, partly through
diet, the olfactory preferences of their offspring. Furthermore, infants are able
to extract an olfactory component from the highly noisy chemical environment

of the amniotic fluid.
The odor knowledge of fetuses at birth is further enriched by their ability as
infants to learn rapidly from early interactions with their odor world. Without
going into the question of which subtype of memory is involved, we can say
that several studies have shown that olfactory memory is well developed in the
newborn. The first evidence came from habituation experiments indicating that
newborns (aged 2–3 days) showed short-term retention of odor information (i.e.,
over several minutes within a single test session) (Engen et al., 1963; Engen and
Lipsitt, 1965). Much longer retention capacity of the immature brain has been
reported with conditioning or exposure paradigms. In an experiment cited earlier
(Sullivan et al., 1991b), the pairing of citrus odor with massage for infants aged
4–16 hours resulted, the next day, in differential arousal and preferential head
orientation toward the citrus odor, as compared with a novel floral odor; see
Hermans and Baeyens (Chapter 8, this volume) for a similar effect in adults. That
approximately 24-hour recall ability was corroborated in a study that consisted
in “merely” odorizing the newborns’ crib atmosphere over a period beginning,
on average, 12 hours after birth and lasting for 23 hours (Balogh and Porter,
1986). The next day (on average, 42 minutes after the exposure had ended),
subjects’ head-turning was examined in a test comparing the familiar odor and
a novel odor. Infants oriented longer to the familiar stimulus, but that effect
reached significance only for females. Using the same familiarization procedure
(beginning 20 hours after birth and lasting for 22 hours) and the same testing
paradigm, Davis and Porter (1991) found that even after a 2-week delay, without
reexposure to the familiarization odor, the infants spent longer periods oriented
toward the familiar odor than toward a novel odor. In that case, no sex difference
was noted.
To sum up, these data indicate that from the earliest stages of ontogeny, the
human mind can acquire and store olfactory information and demonstrate selec-
tive recall not only of perceptions imprinted during the postnatal period but also
of those acquired during the prenatal period. Thus far, the postnatal stability of
prenatal odor learning has been shown to last for at least 3 to 4 days, and neonatal
odor memory can still be shown after a 2-week delay.
One may wonder if there are sensitive periods for odor learning. Although
that has not yet been investigated in ad hoc experiments in humans, animal data
clearly suggest developmental windows more favorable for olfactory acquisi-
tion. For example, the one-trial odor-learning ability of newborn rabbits follows
a steep decline over postnatal days 1–5 (Kindermann, Hudson, and Distel, 1994).
Likewise, 3-month-old rats will respond preferentially to an odor presented
during the first week (but not later) in association with tactile stimulation
(Leon et al., 1987). More recently, rodents have been shown to be highly
sensitive to odor exposure following eye-opening, around postnatal day 10
(Voznessenskaya, Feoktistova, and Wysocki, 1999). Thus the first postnatal days
may correspond to a state of neural plasticity, correlated with specific endocrine
levels and neurochemical states. Particular reinforcing events, such as mother-
initiated contacts, arousal, suckling, and gastrointestinal stimulation, may act
synergistically to facilitate odor learning in mammalian neonates. Whether or
not such facilitating circumstances for odor learning also apply to the human
newborn needs further investigation.
Finally, whereas it is known that odor memories are especially resistant to
decay over time in adult subjects (Herz and Engen, 1996), the longevity of
infantile odor and flavor associations has not been studied systematically over
the life span. Although there is some clear evidence of very long-term retention
of early chemosensory experience in mice and dogs (e.g., Mainardi, Marsan,
and Pasquali, 1965; Hepper, 1994), the human data are thus far only suggestive
of similar processes in the functional context of ingestion. For example, in a
retrospective study of self-reported food aversions among adults, the origins of
many aversive responses could be traced back to events that had occurred before
the age of 5 years (Garb and Stunkart, 1974). A stronger indication of the long-
term consequences of early chemosensory experience was provided by a study
(Mennella and Beauchamp, 1996) on infants’ acceptance of formula milks –
especially protein hydrolysates that often are reported to have an aversive smell
(to adults). Only those infants who had been fed such formulas during their first
2 months were willing to ingest them at age 7 months; infants who had never
tasted such formulas prior to the ingestion test at age 7 months refused them.
Finally, a quasi-experimental survey has contributed to our speculations about
long-term impact of early flavor exposure. Haller et al. (1999) took advantage of
the fact that before 1992, when the European Community policy changed, many
brands of formula milk had been vanilla-flavored. When testing preferences for
a regular ketchup versus vanillin-added ketchup in persons aged 12 to 59 years
(mean 28.8 years), they noted that 60% of subjects who had been bottle-fed
before 1992 preferred the vanilla-added ketchup, but the reverse was noted for
breast-fed subjects who had not been exposed to vanilla in the nursing context
(71% preferring regular ketchup).
4. Conclusions and Prospects

The results discussed here paint a picture of olfaction as a sophisticated means
for information extraction and perceptual elaboration operating from the earli-
est stages of cognitive development. The best-established fact of early olfactory
cognition is that infantile responsiveness to odors is strongly affected by experi-

ence. Both discriminative and hedonic responses to odors are clearly influenced
by previous encounters with odorants, and such adaptability has far-reaching
consequences in terms of the diversity of stimuli that can influence behavior, as
well as the multiplicity of contexts (with or without reinforcers) that can pro-
mote learning. The high plasticity of odor learning presumably has evolved to
ensure optimal adaptive responses in the unpredictible postnatal environment.
The immediate registration of novel odors by newborns in social and inges-
tive situations probably helps them to rapidly deploy such learning for selective
social interaction and energy conservation responses, leading to normal species-
specific development.
Our interaction with environmental odors does not begin at birth. Newborns
emerge from the amniotic niche with their responses biased in favor of cues
that they encountered therein. That selective responsiveness supports the no-
tion of a multilevel continuity in the sensory processing of odor stimuli before
and after birth: (1) Peripheral chemoreceptive mechanisms capture odorants in
either aqueous and aerial media. (2) The fetal brain is mature enough to encode
complex mixtures as well as isolated olfactory cues. (3) Odor experience in the
amnion induces differential attention and behavior in the newborn. The fetal odor
memory is durable enough to help activate adaptive responses (e.g., orientation,
searching, soothing, mouthing) to prenatal odors in the postnatal environment
(e.g., amniotic fluid spread on the mother’s body by the newly born infant) or
to odors encountered in both environments (e.g., aromas present in utero and
in colostrum). The progressive disappearance of odor cues from the original
(prenatal) acquisition context leads to a declining probability of reactivation of
memory traces. However, at the same time, memory stores are further enriched
and elaborated through encounters with new odors in new contexts provided
by the current developmental niche. Olfaction thus serves to track continuity
against a background of continual change that constitutes the normal course of
development.
The exact delineations of such acquisition and memory processes, as well as
their resistance to decay over time, are directions for future research. The data
discussed here suggest that both associative and nonassociative mechanisms are
involved and that early memory can remain accessible to later activation, rather
than being superseded or simply erased by later learning. Research on very young
animals, and also humans, should prove especially useful in further delineating
the basis of early olfactory plasticity, such as the time scale (sensitive periods) and
neural mechanisms involved, the development of perceptual processes, short- and
long-term memory, and cognitive top-down mechanisms (e.g., priming, olfactory
lexicon).
The early integrative functions in olfaction most probably favor the devel-
opment of expectancies and categorizations that engage more general cognitive
competence. Whether or not newborns can use olfactory cues to build cross-
modal relationships has not yet been addressed, but older infants are able to
associate and recall the pairing of an odor with an object. For example, 4-month-
olds who had been exposed to an object A paired with cherry odor and to an
odor-free object B looked longer toward object A (as compared with the scent-
less object B) when the cherry odor was subsequently diffused in the test room
(Fernandez and Bahrick, 1994). Similarly, in an everyday setting, previous expo-
sure to vanilla (via mother’s milk or the home environment) was correlated posi-
tively with the patterns of exploration of a vanilla-scented toy by 6–13-month-old
infants (Mennella and Beauchamp, 1998). Reardon and Bushnell (1988) have
speculated that chemosensory–visual pairings might be easier for young infants
to learn than somatosensory–visual or visual–visual relationships, because the
hedonic values of chemical signals are more salient and hence more easily mon-
itored as cues to the reinforcing event. That proposal marks chemosensation, by
virtue of its tight connections with affective processes, as an important starting
point for understanding the organization of cognitive development (e.g., Van
Toller and Kendal-Reed, 1995). Thus, one solution to Bruner’s developmental
riddle (If we must already know something in order to learn anything, how do we
get started learning at all?) may well be to learn about odors, flavors, and tastes!
Acknowledgments
The reseach reported in this chapter was partially funded by the Direction
Générale de l’Alimentation (programme “Aliment Demain”), Ministères de la
Recherche et de la Technologie, et de l’Agriculture. Dr. Tao Jiang is acknowl-
edged for her help.
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27
Age-related Changes in Chemosensory
Functions
Thomas Hummel, Stefan Heilmann, and Claire Murphy
Early in this century it was shown that aging is accompanied by a decrease in

intranasal chemosensory sensitivity to camphor (Vaschide, 1904). Numerous
studies have confirmed such findings for various odorants (Venstrom and
Amoore, 1968; Schiffman, Moss, and Erickson, 1976; Stevens and Cain, 1987).
Others have reported decreased ability to identify odorants with increasing age
(Doty et al., 1984; Wood and Harkins, 1987; Cain and Gent, 1991), as well as
greater tendencies for olfactory adaptation and slower recovery of threshold sen-
sitivity (Stevens et al., 1989). In contrast, few investigators have reported stable
olfactory function over a life span (e.g., Rovee, Cohen, and Shlapack, 1975).
1. What Is the Anatomical Substrate for Age-related Loss

of Chemosensory Function?
The olfactory system is part of a living organism that undergoes significant
changes related to aging. Both peripheral sensory and central processing units
are affected in that process. In the following we shall try to summarize some of
those effects concerning the aging olfactory epithelium, as well as changes in
the central nervous system that may contribute to the deterioration of the aging
sense of smell.
1.1. Central Nervous System and Olfactory Bulb

Olfactory receptor neurons (ORNs) may be subject to alterations similar to those
seen in neurons in the aging brain. Alterations in the aging central nervous sys-
tem (CNS) include, for example, deficits in the regulation of intracellular cal-
cium levels, increased leakage of synaptic transmitters, and changes in neuronal
arborization (Smith, 1988). Calcium potentials in neurons from older individu-
als also exhibit decreased amplitude and prolonged excitation (Verkhratsky and
441
442 Thomas Hummel, Stefan Heilmann, and Claire Murphy
Toescu, 1998). In addition, there is a decrease in glucose metabolism that is

associated with changes in transmitter release and an increase in free-radical
production, as reviewed by Busciglio et al. (1998), and aging mitochondria
are thought to be potential sources of oxidative lesions (Ames, Shigenaga, and
Hagen, 1995). As endogenously produced oxidants add to cellular aging, sus-
ceptibility to toxic stress is increased (Verkhratsky and Toescu, 1998). Higher
centers of the olfactory pathway are reported to undergo histological changes, as
described in the mouse (Machado-Salas, Scheibel, and Scheibel, 1977). There is
also evidence suggesting that there is a loss of plasticity of the aging CNS (Mori,
1993; Verkhratsky and Toescu, 1998) that might affect the perception of odors.
In 1941, Smith reported atrophy of the olfactory bulb (OB) with increasing age
(Smith, 1941). He believed the OB to contain approximately 10,000 glomeruli,
their number decreasing with age, leading to a reduced overall size of the OB.
Atrophy of the OB and olfactory tract seems to be part of the aging process of
the olfactory system (Bhatnagar et al., 1987b; Jones and Rog, 1998). Meisami
et al. (1998) reported that the numbers of both glomeruli and mitral cells (MCs)
in the human OB decline with age. These findings were consistent with those of
Bhatnagar et al. (1987b), who reported the MCs declined in number and size with
aging, and the thickness of the glomerular layer decreased. In contrast, the total
numbers and densities of granule cells in the OB increase in aging rats (Kaplan,
1985). It was shown by Hinds and McNelly (1981) that the MC volume in the
OB declines in aged animals, with a delay of 3.5 months following loss of ORNs,
suggesting that such changes occur as a consequence of the loss of ORNs in the
mucosa. In the study of Hinds and McNelly (1981), the number of MCs remained
constant, which was not consistent with the findings in a different strain of rats
(Kaplan, 1985) or findings in humans (Bhatnagar et al., 1987b; Meisami et al.,
1998). Changes also occur in the number of glomerular dendrites: Their number
peaks at the beginning of the last third of the average life span in experimental
animals.
Gap-43 is a protein expressed mostly by immature ORNs; it is presumed to be
a marker for differentiating cells. Its expression declines significantly in the OB
in older rats (Casoli et al., 1996), although MCs maintain the ability to express
Gap-43 (Weiler and Farbman, 1997); the reduced Gap-43 level may eventually
lead to a decrease in neuronal plasticity.
Declining sensory functions in audition, balance, and olfaction have been
explained by bone apposition at places where the respective nerves pass through
the skull. Krmpotic-Nemancic (1969) described a narrowing of the holes of the
cribriform plate and the bony passage of the acoustic and vestibular nerves with
increasing age. Thus, in some individuals, functional loss may simply be due to
nerve compression (Kalmey, Thewissen, and Dluzen, 1998).
Age-related Changes in Function 443
1.2. Olfactory Epithelium

A patchy appearance of the olfactory epithelium (OE) has frequently been re-
ported (von Brunn, 1892; Morrison and Costanzo, 1990). Early investigators
assumed that replacement of OE by respiratory mucosa might be due to inflam-
matory processes (Kolmer, 1927). The fetal OE is described as thick and highly
cellular, covering the upper part of the nasal cavity in a continuous fashion. In
contrast, the adult OE is thinner than the respiratory mucosa and has lost that
structure. It appears to be degenerated, with an inconsistent distribution sur-
rounded by respiratory tissue (Naessen, 1971; Paik et al., 1992). According to
Weiler and Farbman (1997), the higher number of proliferating cells in younger
animals (rat) is due to the growth-associated increase in the area of the OE. In
rats, the number of ORNs increases considerably between months 3 and 24, and
it decreases after month 29 (Hinds and McNelly, 1981). The adult epithelium
shows changes especially in the zonal distribution of the supporting cell and sen-
sory cell nuclei. Supporting cells were shown to accumulate pigment granules
with age (Naessen, 1971). Intraepithelial capillaries are not present in adult OE
(Naessen, 1971; Nakashima, Kimmelman, and Snow, 1984, 1985).
Continuous neural cell death in the OE is a phenomenon well described in
rats (Carr and Farbman, 1993). It occurs during the entire life of the individual
among immature olfactory neurons; it is not limited to receptors reaching the
end of their life spans. Both environmental and genetic factors may influence
the regeneration of the OE. The rostral part of the OE shows more signs of
deterioration than the caudal part (Farbman, 1990; Loo et al., 1996). It is not
clear whether infection, air flow, or loss of regeneration potential is responsible
for those changes; however, the pattern suggests environmental influences, as
deterioration is found predominantly in the anterior part of the nasal cavity (Loo
et al., 1996).
In contrast to fetal and neonatal OE, tissue obtained from adult humans has
been reported to contain dystrophic neurites. Dystrophic neurites show neuro-
filament expression, which is not observed in normal ORNs. Those dystrophic
neurites appeared to originate from morphologically altered ORNs in deeper
layers of the OE (Trojanowski et al., 1991). The changes were present even in
one young adult (age 16 years). Thus, if degeneration was the reason for that
observations, then those alterations may begin in childhood.
The histological changes in ORNs mentioned earlier are accompanied by
molecular changes within the cells. Specifically, it has been reported that intracel-
lular localization of neuron-specific tubulin in immature ORNs differs between
young and old animals, suggesting differences in the regeneration of ORNs at
different ages (Lee and Pixley, 1994). Decreased adrenergic innervation of the
OE (in mice) may also contribute to changes in olfactory sensitivity (Chen et al.,
1993). In addition, reduced P-450 expression in the aging human nasal mucosa
may contribute to olfactory loss. This may be the basis for facilitated access
of harmful substances to ORNs, which in turn may produce a higher degree of
damage because of reduced detoxification abilities (Getchell et al., 1993).
ORNs from older humans, however, retain their ability to respond to odorants.
They even seem to be capable of responding to more substances than ORNs from
younger subjects (Rawson et al., 1998). This may represent a compensatory
mechanism at a peripheral level for the overall loss of ORNs.
2. Age-related Loss of Olfactory Function Documented

with Different Approaches
2.1. Psychophysical Studies
As indicated earlier, numerous investigations (e.g., Venstrom and Amoore, 1968;
Schiffman, 1979; Doty et al., 1984; Murphy et al., 1985; Wysocki and Gilbert,
1989) have indicated age-related decreases in olfactory function. This has been
shown for odor thresholds [e.g., coffee, citral (Megighian, 1958), n-butanol
(Kimbrell and Furchtgott, 1963), domestic gas (Chalke and Dewhurst, 1957),
commercial food odors (Schiffman et al., 1976), musk odor (Schiffman and
Pasternak, 1979), 10 normal fatty acids from formic to caproic (Venstrom and
Amoore, 1968), dibutylamine, spray thinner, isoamyl alcohol, acrylic acid methyl
ester, hydrogen sulfide (Bahnmüller, 1984), phenol (Fordyce, 1961; Joyner,
1963), d-limonene, isoamyl butyrate, benzaldehyde (Stevens and Cain, 1987),
1-butanol, isoamyl butyrate, phenyl ethylmethyl ethylcarbinol, and pyridine
(Cain and Gent, 1991)], suprathreshold odor intensity perception (e.g., Stevens
and Cain, 1987; Wysocki and Gilbert, 1989), odor discrimination (e.g., Schiffman
and Pasternak, 1979), odor identification (e.g., Schiffman et al., 1976; Schemper,
Voss, and Cain, 1981; Doty et al., 1984; Stevens and Cain, 1987; Wood and
Harkins, 1987; Cain, 1989; Wysocki and Gilbert, 1989; Cain, Reid, and Stevens,
1990; Ship and Weiffenbach, 1993), and odor memory (e.g., Nordin and Murphy,
1998; Lehrner, Gluck, and Laska, 1999; Lehrner and Walla, Chapter 17, this
volume).
Few studies have directly compared multiple olfactory functions in different
tests. One of our investigations (Hummel et al., 1998) focusing on olfactory
event-related potentials (discussed later) found only an age-related decrease in
the subjects’ ability to discriminate odors; similar changes were present, but non-
significant, for odor thresholds (odorants: phenylethyl alcohol, pyridine; method
of ascending limits) and odor identification (identification of eight odorants).
Whereas the psychophysical methods used in that study may have been somewhat
inadequate (cf. Stevens and Dardawala, 1993; Doty et al., 1995), a much more
sophisticated technique used by Cain et al. (1995) showed age-related reduc-
tions in thresholds that actually preceded reductions in ability to identify odors.
Similar findings emerged when recalculating data from a study (Hummel et al.,
1997) in which olfactory testing was performed using “Sniffin’ Sticks” (Kobal
et al., 1996). That procedure combines tests for odor discrimination (16 triplets
of odorants, forced choice), odor identification (16 odorants, multiple forced
choice), and assessment of n-butanol odor thresholds (single staircase, seven
reversals, triple forced choice). A total of 104 caucasian subjects participated
(52 male and 52 female); for details, see Hummel et al. (1997). For statistical
analyses, 12 groups (n = 8–11; age 18–84 years) were defined based on the
subjects’ ages. After normalization of the data with regard to average results in
the youngest subjects (age 18–22 years), results were investigated using anal-
ysis of variance for repeated measures with the factors “age group” and “test.”
For all measurements, performances decreased with increasing age (Figure 27.1)
[F(184/2) = 12.00; p < .001; power = 0.995]; the decreases were most pro-
nounced in subjects older than 65 years. However, they did not appear to be uni-
form for all olfactory tests, but were found to be relatively more pronounced for
odor thresholds [interaction “test” × “age group”: F(184/22) = 2.61; p < .001;
Age related changes for odor identification,

odor discrimination, and odor thresholds
[score in %, related to youngest group]
120
B
J J J F B threshold
100 JF F B
B F FB
FJ J
JF JF F F
BJ BB discrimination
BB J JF F
80 BJ J F identification
60 B
B
40
20
0
10 20 30 40 50 60 70 80
[age]
Figure 27.1. Mean scores for odor identification, odor discrimination, and odor
thresholds (n = 8–11) in relation to the subjects’ ages. Mean scores were nor-
malized to the average score for the youngest group tested. A significant effect
of the factor “age” was observed. Decreases in sensitivity were found to be most
pronounced for threshold measurements in the oldest subjects investigated.
power = 0.999]. Thus, assuming that threshold measurements may reflect the
function of the peripheral olfactory system to a larger degree than other olfac-
tory tests (e.g., Jones-Gotman and Zatorre, 1988; Hornung et al., 1998; Moberg
et al., 1999), those findings might indicate that age-related changes in olfactory
function are largely due to damage of the OE (cf. Nakashima et al., 1984; Rosli,
Breckenridge, and Smith, 1999). They also appear to indicate that changes in ol-
factory threshold may not immediately affect other, presumably more complex
olfactory functions like odor discrimination and odor identification. In other
words, it may be that the subjects’ ability to discriminate odorants is partly in-
dependent of olfactory thresholds, especially in view of the data from Rawson
et al. (1997), who reported an age-related, broader “tuning” of ORNs. In fact,
Cain and co-workers recently presented evidence that odor discrimination ap-
pears to be independent of absolute sensitivity (Cain et al., in press; cf. Hummel
et al., 1998).
2.2. Studies Using Chemosensory Event-related Potentials

Chemosensory event-related potentials (ERPs) have become important tools
not only in olfactory research (Livermore, Hummel, and Kobal, 1992; Lorig
et al., 1996) but also for diagnosis of olfactory disorders (Kobal and Hummel,
1994, 1998). Chemosensory ERPs reflect the intensity of a stimulus (Kobal and
Hummel, 1988) and can discriminate between the excitation of trigeminal nerves
and olfactory nerves (Hummel and Kobal, 1992).
Age-related decreases in chemosensory function are also indicated by ERP
measures. Specifically, the ERP’s P2 amplitude and the composite N1P2 am-
plitudes decreased with increasing age, but a prolongation of N1 peak latencies
was observed. Using amyl acetate, Evans, Cui, and Starr (1995) reported de-
creases in peak-to-peak N1P2 amplitudes in relation to the subjects’ ages. They
also reported a significant life-span prolongation of the P2 latency, accompa-
nied by a trend for mean N1 latencies to increase with age. In addition, Hawkes
and co-workers (personal communication) found both an age-related decrease
in ERP amplitudes and an increase of latencies for the stimulant H2 S (n = 60).
As that has been confirmed by numerous other studies (e.g., Murphy et al.,
1994; Hummel et al., 1998; Covington et al., 1999), it can be assumed that es-
pecially the earlier ERP components (e.g., N1) reliably reflect loss of olfactory
function.
Olfactory ERP data indicate that changes in the processing of olfactory infor-
mation may appear relatively early in life. Specifically, data from Murphy et al.
(1998) and Hummel et al. (1998) suggest that ERP amplitudes already exhibit
decreases in middle age (Figure 27.2). In elderly individuals, that may, at least
Age related changes of olfactory and

trigeminal ERP amplitudes N1P2
60
F CO2
[␮V]
F
J Vanillin
40 H H2S
F F
H
J J
20 H
JH
0
15-34 35-54 55-74
[years]
Figure 27.2. Mean ERP amplitudes N1P2 at recording position Cz in response

to stimulation with CO2 , vanillin, and H2 S for three different age groups of
subjects (data from Hummel et al., 1998). The age-related decrease in N1P2
amplitudes was different for the trigeminal stimulant (CO2 ) compared with the
two olfactory stimulants. Specifically, for CO2 the decrease was found to be
most pronounced between the youngest group and the middle-aged group. In
contrast, responses to olfactory stimulation decreased between the middle-aged
group and the oldest group.
in part, be due to increased adaptation to repetitive olfactory stimuli (Stevens

et al., 1989; Morgan et al., 1997).
In a series of studies, Murphy and co-workers investigated age-related changes
in ERPs with a special focus on the late component of the potential, the P3
component (Murphy et al., 1996). That component has been demonstrated to
be related to endogenous processes (Pause et al., 1996), such as whether or
not a stimulus contains new and relevant information compared with previous
stimuli (e.g., Sutton, Braren, and Zubin, 1965). Findings have indicated that
the age-related decrease in the P3 amplitude is related to overall reduction of
neuropsychological performance (Geisler et al., 1999; Morgan et al., 1999).
Thus, the olfactory P3 may serve as a reliable indicator of attentional resources
related to olfactory cognitive processing (Murphy et al., 1998). However, the
question remains in what specific way the changes indicated by the olfactory P3
differ from age-related changes seen in the visual and auditory systems (Ford
and Pfefferbaum, 1985; Knight, 1987; Tachibana, Toda, and Sugita, 1992).
Murphy et al. (1994) investigated chemosensory ERPs to amyl acetate in the
elderly (mean age 66 years, n = 7) and in young adults (mean age 27 years,
n = 7). They found differences in amplitudes at central and parietal record-

ing positions, but not at the frontal site Fz. That agrees with data provided by
Hummel et al. (1998), who described a leveling of the topographical differences
between ERP amplitudes: Differences between groups were largest at the central
site Cz, and were smaller at frontal (Fz) and parietal (Pz) sites. That may indicate
changes in the cortical processing of olfactory sensations. In younger subjects,
olfactory stimulation seems to activate areas in the temporal and insular cortices
(Kettenmann et al., 1996; Ayabe-Kanamura et al., 1997), which in turn produces
the specific surface pattern of the topographical distribution of olfactory ERP
amplitudes (Hummel and Kobal, 1992; Hummel et al., 1992; Kobal, Hummel,
and Van Toller, 1992; Livermore et al., 1992; Murphy et al., 1994; Evans et al.,
1995). The change in that topographical distribution of olfactory ERPs in older
subjects may be due to central nervous plasticity. There the processing of ol-
factory information may be reorganized, possibly as a consequence of loss of
neurons both in the periphery (e.g., Nakashima et al., 1985; Rosli et al., 1999)
and at central sites (e.g., Bhatnagar et al., 1987a; Yousem et al., 1998).
Electrophysiological studies have also indicated differences in age-related
changes in responses to trigeminal or olfactory stimuli. Specifically, responses
to trigeminal and olfactory stimulation may follow different courses across a life
span (Figure 27.2). However, more research is needed to investigate the behav-
ioral correlates of such changes in trigeminal responsiveness, as discussed later.
2.3. Imaging Studies

To our knowledge there has been only one study that has investigated age effects
on olfaction using functional magnetic-resonance imaging (Yousem et al., 1999).
The 10 participating subjects underwent olfactory testing using the University
of Pennsylvania Smell Identification Test (UPSIT) (Doty, 1995). Five subjects
(3 women, 2 men; age 62–80 years) were compared to five younger subjects
(3 women, 2 men; age 18–27 years). The older group had an UPSIT score of 33.0;
the younger group had a mean UPSIT score of 38.0. Each task paradigm con-
sisted of alternating rest–stimulus cycles (30 sec each) over 6 minutes. Eugenol,
phenylethyl alcohol, and hydrogen sulfide were used for olfactory stimulation;
they were delivered using a continuous-flow olfactometer (OM4-B; Burghart,
Wedel, Germany). Stimuli were delivered intranasally to both sides (4 liters/min;
stimulus duration 1 sec) every 4 sec during the 30-sec “on period.” During the
30-sec “off period” the patient received room air; for details, see Yousem et al.
(1999).
On group maps, the older subjects showed the largest number of activated
voxels in the right perisylvian region, followed by the right superior frontal
region. Single voxels of activation were noted in the right inferior frontal and
left superior frontal zones. Most individual maps demonstrated activation in the
right perisylvian, right and left superior frontal, and right and left inferior frontal
regions. In general, right-side activation was greater than left-side activation. The
younger subjects showed greater volumes of activation. The sites of activation
identified in the older group were also activated to the greatest degree in the
younger group, namely, the right perisylvian, right superior frontal, right inferior
frontal, and left superior frontal regions. In addition, the group maps for the
younger subjects showed activation in the left superior frontal and left perisylvian
zones and both cingulate regions. All younger subjects showed activation in the
right inferior frontal and left perisylvian regions.
Thus the major finding of that study was that there was a decreased volume
of activation after the age of 60. In general, the same areas that were found to be
activated in older subjects were also found to be activated in younger subjects.
However, with regard to group maps, younger subjects exhibited activation in
the left and right cingulate regions, and they exhibited left-side activity in the
superior frontal and perisylvian regions. That was not seen in group maps for
older subjects. Those differences in activated brain areas may, at least in part,
explain the age-related changes observed in the topographical distribution of
olfactory ERPs discussed earlier.
3. Trigeminal Sensitivity Also Appears to Decrease

in an Age-related Manner
Compared with the data for the olfactory system, considerably fewer data are
available regarding age-related changes in trigeminal chemoreception. Elevated
thresholds to trigeminal stimuli (e.g., menthol) were reported in elderly subjects
(Minz, 1968; Murphy, 1983); in addition, a steeper slope of the intensity function
was found for younger adults. Stevens, Plantinga, and Cain (1982) found an age-
related decrease in the perceived intensity of CO2 (a trigeminal stimulus with
minimal or no odor qualities), and Stevens and Cain (1986) reported a strong
age-related elevation of the threshold for transitory apnea in response to CO2 .
As mentioned earlier, that age-related loss of trigeminal function is also seen
in ERP studies (Hummel et al., 1998). Interestingly, the cross-sectional results
were also confirmed, at least in part, by data obtained from a single subject,
where trigeminal ERPs were recorded over a period of 10 years. There an intra-
individual decrease in response amplitudes to CO2 stimuli occurred between the
ages of 28 and 38 years.
Similar age-related changes have been reported for other nociceptive, pain-
related processes. Specifically, responsiveness of Adelta-fibers to nociceptive
heat stimuli appears to decrease in relation to age, but C-fiber function seems to
be largely unaffected (Harkins, Price, and Martelli, 1986; Chakour et al., 1996;
Harkins et al., 1996). Those functional observations have been confirmed on a
histological level, where the number of myelinated fibers (A-fibers) appears to
decrease with increasing age (Ochoa and Mair, 1969; Kenshalo, 1986). Translat-
ing that into terms of intranasal trigeminal function of chemosensors, it should
result in decreased stinging sensations (Adelta-fibers), and the perception of
burning sensations (C-fibers) should remain mostly unchanged. Those obser-
vations correlate closely with changes found for ERPs to intranasal trigeminal
stimuli that mostly were due to the activation of Adelta-fibers (Harkins, Price,
and Katz, 1983; Hummel et al., 1994). Overall, the indication is that the trigem-
inal chemoreceptive system exhibits an age-related functional decrease, aspects
of which appear to be similar to those of the olfactory system.
4. Perspectives
The aging process in the olfactory system cannot be reduced to a single phe-
nomenon. It involves all levels, from anatomical to molecular changes. It seems
to be a process influenced by genetic and environmental factors, involving the
olfactory system itself and the higher centers of information processing. Age-
related changes in olfactory function are observed at all levels of information
processing. However, they do not appear to be the inevitable fate of each indi-
vidual (Rowe and Kahn, 1987; Almkvist, Berglund, and Nordin, 1992). Thus,
especially when considering potential therapeutic interventions, further studies
are needed to determine in more detail which parts of the olfactory system are
most relevant to the decreases in olfactory function and to find out what can be
done to prevent or delay the age-related changes.
Acknowledgments
Part of the work reported here was based on research performed in collaboration
with G. Kobal, S. Barz, B. Sekinger, E. Pauli, S. R. Wolf (all at Universität
Erlangen-Nürnberg, Germany), D. M. Yousem, J. A. Maldjian, D. C. Alsop,
R. J. Geckle, and R. L. Doty (all at the University of Pennsylvania, USA). It was
supported by the Marohn-Stiftung, Germany, and by grant P01 DC 00161 from
the National Institute on Deafness and Other Communication Disorders, USA.
The help of Dragoco and Harmann & Reimer (both Holzminden, Germany)
and Givaudan (Hannover, Germany) in some of the studies is also appreciated.
In addition, we are indebted to Dr. W. S. Cain for helpful comments on this
manuscript.
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Index
accessory olfactory bulb, 179 aromatherapy, 165, 167

acetone, 167 arousal, 76, 126, 152, 183, 184, 197, 422, 429, 430,
acetylcholine, 336, 337 433, 434
acute rhinitis, 7 artistic creation, 5, 24
adaptation, 17, 31, 32, 117, 167, 246, 304, 362, 375, association, 32, 69, 74, 120, 123, 127, 128, 146,
441, 447 162, 169, 171, 189, 190, 218, 225, 227, 233,
aesthetics, 3, 9, 24 234, 248, 261, 263, 281, 283, 313, 330, 377,
affective, 4, 16–18, 101, 117, 119–137, 140–155, 383, 413, 414, 415, 428, 429, 433
165, 172, 173, 210, 225, 235, 252, 317, associative learning, 119, 121, 127, 134, 165, 172,
324–332, 390, 404, 436. See also emotion 233, 291, 292, 337. See also learning
affective, affective cognition, 117, 165, 173 associative olfactory learning, 339 emotional
affective congruence, 133, 135 association, 37, 164. See also learning
affective dimension, 16. See also hedonic attention, 17, 21, 22, 30, 31, 36, 89, 120, 129, 131,
affective habituation, 252 140, 184, 190, 226, 227, 247, 291, 303,
age, 17, 27, 76, 136, 150, 160, 168, 212, 222, 236, 311–314, 317, 435
238, 255, 262, 279–285, 316–318, 390, 399, infra-attention, 2
412, 414, 417, 428–434, 441–450 selective attention, 22, 303, 311, 312, 317
age-related changes, 441, 444, 446–449 autobiographical memory, 168, 169, 225, 251. See
aging, 232, 236, 441, 442, 444, 450 also episodic memory
alcohol, 134, 167, 265, 444, 448 autonomic nervous system, 150, 155, 183
aliphatic acid, 182 aversion, 30, 32, 67, 233, 352, 422, 423, 432
alliesthesia, 379, 426 aversive conditioning, 153, 292, 350, 360, 362
Alzheimer’s disease, 209, 261–272, 357. See also awareness, 4–11, 22, 30–33, 64, 117, 122–136,
dementia 163, 178, 182, 209, 212–227, 231, 250, 268,
ammonia, 161 353
amniotic fluid, 160, 161, 423, 425, 431, 433, 435 axillary compounds, 181–183
amygdala, 203, 381
amyl acetate, 30, 49, 144, 160, 235, 302, 446, 447 baby powder, 51, 163, 168
androstadienone, 183–190. See also hormone balsam, see isobornyl acetate
androstenone, 180, 318, 319. See also hormone banana, 49, 56, 106, 160, 383, 423
anethole, 141 basal ganglia, 231
anger, 10, 146, 152, 197, 198, 234 bed nucleus of the strial terminalis, 350
anise, 106, 425, 431, 432 beer, 38, 162
anosmia, 30, 105, 111, 318 behavior, 18, 20, 31, 37–40, 48, 79, 117, 131, 136,
specific anosmia, 30, 35, 105, 111, 318 150, 160–172, 178–189, 226, 279, 303, 337,
anterior olfactory nucleus, 202, 262, 263, 269, 272 378, 390, 408, 417, 421–435
anthropology, 45, 67, 68, 74, 141 consumer behavior, 37–39
anxiety, 128, 129, 163, 164, 262 eating behavior, 40
apocrine glands, 180 emotionally conditioned behavior, 131, 160
apolipoprotein E, 268, 270 neonatal behavior, 422, 426, 435
appetite, 153, 183, 378, 383, 426 odor-guided behavior, 417
apple, 33, 47, 55, 56, 58, 59, 61, 221 sexual behavior, 182
aroma, 77, 391, 432 beta oscillation, 344
457
458 Index
beverage, 27, 415 246, 278, 279, 292, 336, 339, 350, 352, 360,
binding theory, 339 361, 433
bitterness, 30, 32, 38, 369, 371, 373, 389, 392–396, appetitive conditioning, 153
399, 403 aversive conditioning, 153, 292, 350, 360
body odor, 77, 78, 149, 150, 316, 318, 319, 430 conditioned stimulus, 120–126, 128, 134–136,
body temperature, 183 226
bombykol, 178, 179 emotionally conditioned behavior, 160
bottled milk, 161, 225. See chapter 26 evaluative conditioning, 117, 120–123, 125, 127,
brain imaging, 145, 292, 335, 336, 346, 360 134–136
butyric acid, 160, 423 fear conditioning, 152, 201, 234. See also fear
Pavlovian learning, 120, 122, 123
cadaver, 30 unconditioned stimulus, 120–128, 131, 136, 153,
camphor, 4, 106, 111, 441 161, 162, 201, 226
candy, 56, 57, 59, 60, 64, 162 unconscious odor conditioning, 22
caprylic, 102, 105, 147 consciousness, 7, 69, 79, 232, 237
capsaicin, 395 consumer, 36–39, 110
carvone, 28, 300 cortex
carnation, 169 cortical taste area, 350, 352, 356, 360, 362, 367,
categorization, 5, 17, 47, 54, 55, 58, 60, 61, 64, 67, 371
68, 75, 76, 95, 104, 155, 179, 221, 255 entorhinal cortex, 202, 263, 269–272, 292,
cerebellum, 200, 240, 326 335–340
cerebral blood flow, 240, 329 frontal operculum, 240, 357, 367, 383
cerebral damage, 239 insular cortex, 199, 200–204, 240, 241, 326, 357,
cheese, 30 358, 367, 371, 375, 376, 382, 383, 448
chemical communication, 179, 182, 190 isocortex, 263, 271
chemoreceptor, 360 olfactory cortex, 179, 263, 272, 292, 329
chemosensory event-related potentials, 309, opercular cortex, 371, 375, 376
311–319, 446, 447 orbitofrontal cortex, 151, 152, 171, 198–200,
cherry oil, 161 202–204, 240, 269, 272, 325, 326, 329, 330,
children, 9, 36, 76, 90, 120, 149, 160, 161, 170, 171, 332, 333, 367, 371, 373, 375, 376–379,
197, 222, 225, 226, 235, 267, 278–286, 381–383
422–436 parietal cortex, 241
chocolate, 142, 163, 168 piriform cortex, 202, 241, 269, 270, 272, 292,
chorda tympani nerve, 360, 361, 395, 403 325, 326, 329, 330, 335–343, 346
cingulate gyrus, 199, 200, 203, 240, 358, 449. See prefrontal cortex, 200, 240
also limbic system retrosplenial cortex, 198
cinnamon, 76, 256, 396 taste cortex, 367, 371, 375–377, 382, 383
citrus, 55, 56, 58, 104, 106, 109, 318, 433 temporal cortex, 202. See also temporal lobe
civet, 31, 134, 150 cosmetics, 58, 60, 61, 76, 92
cleaning products, 60, 255 cosmology, 45, 71, 74, 78, 79
clove oil, 162–164, 184 cribriform plate, 202, 442
cluster analysis, 106, 107, 130, 371 crosscultural comparisons, 410–412
cocaine, 7, 164 German, 141, 225, 411, 414
coffee, 4, 29, 31, 37, 38, 162, 166, 168, 169, 254, Japanese, 141, 411
256, 413, 444 Mexican, 141, 411
cognitive development, 278, 421, 434, 436 cross-adaptational relationships, 35
cognitive task, 22, 143, 190, 336 crosscultural psychology, 74
color, 4, 30, 36, 49, 64, 68, 74–78, 82, 88–91, 100, culture
122, 132, 134, 264, 284, 379 culinary culture, 119
color lexicon, 68, 74 culture dependency, 35
color terms, 49, 74, 75 Kwoma (New Guinea), 76–79
combinatorial coding, 295 Ongee, 45, 71–79
comestibility, 154, 251, 254, 255, 258, 411 Western culture, 45, 68, 70, 165
communication, 9, 11, 12, 27, 52, 53, 164, 165, 171, cyclodecanone, 144
179, 180, 182, 190, 446
chemical communication, 180, 182, 190 2-deoxyglucose studies, 301
chemosensory communication, 179 dementia, 232, 262, 263, 265–267, 272, 273. See
pheromonal communication, 179, 180. See also also Alzheimer’ s disease
pheromone dentistry, 131, 162, 234
conditioning, 22, 117, 120–128, 134–136, 152, depression, 129, 232, 262, 317, 345
153, 161, 170–172, 201, 226, 227, 231–234, detection threshold, 248, 295, 352
Index 459
development, see children functional imaging studies, 50, 150, 152, 198,
displeasure, 4. See also hedonic 201, 202, 204, 324–328, 350, 352, 353,
D-methyl mannopyranoside, 354 356–360, 371, 382, 448. See also brain
D-threonine, 353–356, 361 imaging
fungiform papillae, 389, 395, 397, 401, 403, 404
eccrine glands, 180
echo-planar imaging, 356. See also brain imaging Gap-43, 442
electroencephalography, 153, 164, 335, 336, 338 gas, 5, 86, 88, 224, 264, 444
emotion, 1, 17, 24, 27, 32, 36, 79, 117, 119, 132, gas, domestic gas, 444
146–160, 164, 171, 172, 184, 196–204, 212, gender, 77, 79, 133, 135, 166, 212. See also sex
227, 234. See also affective difference
enantiomer, 112 genes, 180, 181, 293, 294, 295, 362
entorhinal cortex, see cortex genetic factor, 316, 443
epilepsia, 32, 203, 240 genetic risk factor, 268
essential oil, 108, 109, 134 genetic sensitivity, 392
estratetraenol, 183–190. See also hormone genetic variation, 395
etheric oil, 125 geraniol, 141
eugenol, 103, 141, 162, 164, 234, 317 glomerulus, 297, 299. See also olfactory bulb
evoked field potentials, 150, 338. See also glutamic acid, 371
electroencephalography glycyrrhizic acid, 353, 354, 356
exhalation, 82, 85, 314 G-protein-coupled receptor, 294, 362
expertise, 1, 20–22, 36, 45, 52, 89, 91, 100, 102, 107, guanosine 5 -monophosphate, 353, 354
109, 212, 222, 223, 344, 345. See also perfumer gustation, 68, 70, 75, 78, 352. See also taste
face, 62, 89, 121, 201, 211, 212, 217, 220, 221, habituation, 31, 32, 201, 233, 252, 291, 312, 313,
223, 224 336, 337, 342, 343, 346, 425, 433. See also
face memory, 211, 220, 223 familiarization
facial recognition, 199, 220 health, 32, 117, 160, 165–168, 171, 172, 212, 232,
familiarity, 52, 59, 102, 141–154, 165, 217, 221, 239, 403
235–239, 249, 266–272, 278–285, 326, 389, health condition, 212
411– 415, 422–425 health perception, 27, 166, 183
familiarity judgment, 153, 154, 217, 271, 326 hedonic, 18, 24, 61, 108, 117, 119, 140–155,
familiarization, 20, 292, 350–356, 358, 359, 160–172, 181, 210, 226, 227, 235, 292, 314,
360–363, 433. See also habituation 324–328, 353–360, 378, 390, 391, 403–408,
fatty acid, 373, 444 421, 422, 425–427, 429, 435, 436
fear, 146, 152, 153, 162, 164, 172, 196–199, 201, acquisition of odor hedonics, 22, 120, 136
202, 234 disgust, 8, 12, 118, 146, 152, 196–202, 234,
fecal odor, 9, 11, 30, 160, 235 423, 425
flavor, 37, 40, 57, 60, 76, 78, 95, 121–123, 161, hedonic valence, 18, 148, 168, 422
201, 204, 225, 226, 376, 377, 379, 399, 415, hedonic values, 436
434 unpleasant odor, 9, 10, 16, 117, 140, 146,
flavor representation, 377 150–154, 162, 163, 166, 172, 201, 202, 252,
food flavor, 40, 119 326, 423
flower, 11, 16, 56, 59, 60, 73, 79, 89, 96, 163 heptanal, 295, 426
food, 11, 28–40, 56–61, 119, 141, 142, 161, 171, herb, 163
225–227, 233, 234, 264, 286, 292, 336, 342, hierarchical structure, 108, 109
343, 352, 353, 373–383, 395, 403, 404, 426, hippocampus, 171, 202, 263, 269, 271, 335, 336,
428, 434, 444 337, 346. See also limbic system
acceptance of food, 376 hormone, 178, 319
evaluation of foods, 27 hormonal status, 185, 353
familiar foods, 141 hormonal variation, 403
food-deprived condition, 342, 343 luteinizing hormone, 180, 253, 254
food-intake questionnaire, 353 household odors, 265, 280
food poisoning, 233 human leukocyte antigen, 181, 316, 318
food preference, 161, 225, 227, 286, 383, 404 hunger, 36, 72, 185, 226, 367, 373, 375, 376, 378,
textural properties of food, 29, 381 381, 383
fragrance, 18, 19, 21, 22, 76, 82, 85–87, 90, 92, 94, Huntington’s disease, 272
95, 104, 110, 120, 123, 163 hydrogen disulfide, 151
frontal operculum, see cortex hyposmia, 35, 295, 298
fruit, 16, 30, 55–61, 76, 90, 107, 163, 221, 376, hypothalamus, 145, 155, 179, 183, 326, 329, 330,
377, 378 332, 350, 351, 373, 376, 379
460 Index
in utero, 160, 417, 431, 435 implicit learning, 246

innate, 29, 30, 32, 118, 119, 146, 160, 423, 430 incidental learning, 209, 219, 220
inosine 5 -monophosphate, 371 learning-induced changes, 341
intensity, 18, 20, 22, 28–35, 78, 101–112, 127, learning-induced plasticity, 340
129, 140–155, 167, 199, 213, 240, 241, learning processes within the olfactory bulb, 410
249, 292, 311, 324–333, 350–362, 379, 381, odor learning, 120, 161, 164, 211, 227, 428,
389, 391–404, 411–415, 422–430, 430–435
444–449 Pavlovian learning, 120, 122, 123
intensity adjectives, 396, 397, 399 perceptual learning, 212
intensity along time, 18, 357 postnatal odor learning, 430
intensity discrimination, 28, 240, 241 prenatal odor learning, 430, 433
intensity judgment, 143, 144, 145, 154, 328 unintentional learning, 225
intensity parameters, 101, 110, 112 lemon, 55–59, 61, 76, 108, 134
intensity/pleasantness relationship, 141, 142, 145, lexicon, 49, 53, 74–75, 82
153, 326, 327, 413 lexical meaning, 53
perceived intensity, 110, 141, 142, 145, 249, 357, life-span, 232, 236, 434, 441, 446, 448. See also age
359, 360, 362, 391, 395–397, 401, 411, 412, ligands, 299
415, 449 limbic system, 119, 172, 179, 190, 200, 326, 345
taste intensity, 213, 350, 352, 360, 389, 395, 397, limonene, 28, 55, 142, 300, 441
404 linguistics, 19, 45, 48–64, 82–97, 101, 145–150. See
intentional learning, 209, 211, 219, 220. See also also lexicon, lexical meaning, semantic
declarative memory linguistic resources, 45, 52
intentional retrieval, 211. See also declarative local field potentials, 338
memory long-term potentiation, 337
isoamyl acetate, 302, 311, 426 L-valine, 354
isobornyl acetate, 167
isovaleric acid, 144, 301 magnetic-resonance imagery, 118. See also brain
imaging
jasmine oil, 165 major histocompatibility complex, 181
memory, 2, 8, 10, 17, 20–23, 33–40, 47–61, 82, 90,
ketchup, 225, 434 117, 132, 140, 142, 160–171, 189, 202, 209,
211–227, 231–241, 246–258, 261–272,
label, 45, 48–51, 54, 55, 59, 61, 76, 85, 209, 214, 278–286, 291, 294, 303, 309–314, 325, 328,
218, 221, 225, 236, 248, 280, 281, 285, 396, 336–343, 433, 435, 444
397, 399, 400 declarative memory, 171, 231
labeled categories, 62 emotional memory, 160, 171, 181
Labeled Magnitude Scale, 395 episodic memory, 36, 231, 232, 235, 237–239,
language 241, 252, 264–266
Bororo of Brazil, 75 explicit memory, 211, 213, 214, 246, 247, 252,
English, 19, 45, 48, 52, 53, 55, 63, 64, 69, 70, 75, 258, 264, 279, 281, 283, 285
78, 83, 95, 285 implicit memory, 33, 209, 211, 213, 217–219,
French, 19, 45, 48, 51, 52, 54, 62, and Chapter 4 223, 246–248, 250, 257, 258, 279, 283
Japanese, 75 long-term memory, 171, 227, 238, 265, 278, 309,
Kapsiki of Cameroon, 75 336, 337, 341, 435
Kwoma, 77, 79 metamemory, 235, 237
Latin, 69, 146 mnemonic strategies, 223, 278
Ongee, 72 neonatal odor memory, 433
Seerer Ndut of Senegal, 75 procedural memory, 231, 234
Wewéya of Sumba, 75 short-term memory, 237, 238, 278, 291, 313, 314,
lateralization, 203, 258, 326 337, 342, 343
lavender, 104, 124, 163, 165 verbal memory, 33, 211, 213, 214
learning, 17, 22, 31–36, 111, 117, 119–134, working memory, 171, 231, 237–240, 256, 271,
160–172, 179, 190, 201, 204, 209, 211–227, 328
231–239, 246, 264, 279–286, 291, 292, 303, mental imagery, 17, 22, 23, 24
314–319, 337–346, 352–362, 371, 383, 390, methyl methacrylate, 152
408, 410, 417, 428–436 methyl salicylate, 162
associative learning, 119, 121, 127, 134, 165, 172, mitral cell, 301, 302, 336, 442
233, 291, 292, 337 mixture, 18, 19, 20–22, 24, 30, 32, 89, 92, 93, 95,
behavioral learning, 337, 338 119, 425, 426
effect on synaptic transmission, 346 complex odorants, 410
effect of learning on taste, 352 multimolecular odorants, 410
evaluative learning, 119, 121–125 mono-rhinal smelling, 218, 253, 257
Index 461
mood, 31, 36, 117, 118, 120, 127–130, 155, olfactory receptor family, 294, 299
160–173, 181–190, 212 olfactory receptor mRNA, 297
motivation, 113, 184, 317, 342, 367, 375, 395 olfactory space, 72, 106, 108, 109, 113, 145, 146,
multidimensional analysis, 108, 109 148
multidimensional methods, 105–109, 112 olfactory transduction, 299, 311
multidimensional scaling technique, 35, 108, 140, olfactory tubercle, 202
264, 371 Ongee, see Chapter 5
multi-unit activity, 336, 338 opercular cortex see cortex
mushroom, 30 oral sensation, 367, 396, 399, 400
musk, 48, 90, 102, 444 orange, 47, 55, 56, 58, 59, 64, 108, 142, 169, 215,
musty, 31 254
orbitofrontal cortex, see cortex
naringin, 354 orthonasal, 119, 426. See also retronasal
neophobia, 141, 352, 353, 356, 359, 428 ovulation, 181, 318. See also hormone
Neroli, 20, 21 ozone, 5
neural coding, 350, 363
neural representation, 291, 295, 303, 304, 339, parabrachial nuclei, 350, 351
410 Parkinson’s disease, 272
neural networks, 105, 111, 117, 141, 145, 154, 189, parosmia, 298
201, 231, 233, 239 periamygdaloid nucleus, 263
noradrenaline, 336 peri-insular area, 357–360. See also cortex, insular
nucleus of the solitary tract, 350, 351, 367, 368, 371, perfume, 16–25, 31, 57, 62, 82–97, 109–111, 120,
375, 376 123, 137, 161, 182, 225, 428, 429
perfumer, 16–25, 36, 71, 101–111, 184, 213, 224
odor pheromone, 178–180, 183, 184, 189, 190, 318. See
odor classification, 34, 35, 100, 105, 146, 147, also vomeronasal organ
155, and Chapter 7 modulating pheromone, 179, 190
odor coding, 21, 297, 303, 325, 409 pheromonal communication, 179, 180. See also
odor concentration, 28, 311 communication
odor detection, 9, 33, 71, 145, 189, 234, 248, 263, priming pheromone, 179, 180
265, 270, 279, 280, 291, 295, 298, 314–318, releaser pheromone, 179, 182
444 philosophy, 1, 53, 68, and Chapter 1
odor identification, 36, 133, 218, 223, 224, pine, 90, 124, 169, 256
234–237, 240, 248, 249, 251, 253, 254, 265, piriform cortex, see cortex
267–271, 280, 444–446, 448 pleasantness, 16, 18, 24, 102, 103, 117, 140–154,
odor naming, 19, 21, 45, 51, 224, 278–280, 284, 162, 168, 217, 220, 248–251, 326–328, 332,
285. See also odor identification 333, 376, 378, 379, 381, 383, 389, 411–415,
odor quality, 34, 35, 101, 103, 107, 109, 240, 255, 425, 426. See also hedonic
256, 311, 312, 324, 326, 409 pleasure, 4, 27, 33, 36, 67, 378, 379. See also
odor recognition, 28, 221, 223, 225, 239, 240, hedonic
283, 284. See also recognition pontine taste relay, 350, 351, 367
odor/taste aversion, 233 popcorn, 169
odor terms, 45, 62, 75, 85, 86, 88, 91, 95, 150 positron-emission tomography, 50, 145, 150, 198,
body odor, 77, 78, 149, 150, 316, 318, 319, 430 202, 240, 326, 329. See also brain imaging
malodor, 12, 13, 146, 147, 165 preference, 32, 119, 148, 161, 221, 225–227, 235,
maternal odors, 428, 430 252, 278, 352, 356, 360, 362, 403, 404, 422,
noxious odor, 329. See also health 429, 432, 434
source of, 16, 19, 255, 293, 414, 415 acquisition of preference, 408
olfactory bulb, 40, 179, 202, 263, 269, 291, 293, priming, 28, 131–137, 179, 180, 209, 210, 213, 217,
297, 298, 301–303, 318, 325, 332, 335–340, 218, 227, 231, 232, 234, 246–258, 279, 286,
342– 346, 382, 409, 410, 441, 442 319, 435
atrophy of the olfactory bulb, 442 affective priming, 131–137
olfactory cortex, see cortex cross-modal priming, 246
olfactory epithelium, 179, 184, 187, 202, 263, 269, perceptual priming, 210, 255, 257, 258
293, 295–297, 302, 441, 443, 444, 446 repetition priming, 209, 213, 218, 246, 247, 249,
receptor cells, 294, 296, 297–303, 409, 410, 441, 251–258
446 semantic priming, 213
olfactory nerve, 63, 171, 297, 446 verbal priming, 209, 251
olfactory paranoia, 12 Prop, 392–396, 399
olfactory plasticity, 318, 319, 435 propionic acid, 152
olfactory receptor proteins, 293. See also receptor psychoanalysis, see Chapter 1
proteins pyridine, 30, 144, 168, 444
462 Index
quinine, 339, 353, 369, 371, 392, 394, 399 taste

bitterness, 30, 32, 38, 369, 371, 373, 389,
receptor proteins, 189, 293, 297, 410. See also 392–396, 399, 403
olfactory receptor proteins saltiness, 371, 393, 399
recognition, 21, 22, 28, 33, 51, 52, 71, 101, 107, sour, 38, 56, 57, 369, 371, 373
126, 141, 143, 179, 198, 199, 212–214, 216, sweet, 32, 55–57, 93, 106, 108, 146, 371, 373,
217, 220–225, 231, 238–240, 247, 264–272, 377, 382, 391
281–285, 291, 304, 341, 422 taste-aversion conditioning, 352
impaired recognition, 222 taste blindness, 389, 391, 392
recognition memory, 52, 220, 238, 239, 264–266, taste buds, 395
270, 271, 283–285. See also memory taste cortex, see cortex
recognition performance, 143, 216, 221, 222 taste intensity, 213, 350, 352, 360, 389, 395, 397,
retronasal, 119, 426. See also orthonasal 404
Roudnitska Edmond, 1, 17–20, 23, 71, 89, 100, 104 taste nerves, 352
taste pore, 395, 397, 403
saltiness, 371, 393, 399 taste quality, 350
San Diego Odor Identification Test, 267, 269, 272 taste receptors, 353, 362, 373
sarsaparilla, 162 taste sensitivity, 350, 356, 363
scopolamine, 337 taste terms, 75
semantic umami, 371, 373, 382
semantic knowledge, 21, 23, 236, 265, 280, 284, taster
285. See also semantic memory medium taster, 394, 396, 397, 399, 401
semantic memory, 222, 231, 232, 235, 237, 239, nontaster, 394, 403
264, 266, 267, 270 supertaster, 389, 394, 403
semantic odor memory, 270 taurine, 353–356
semantic processing, 21, 143, 148, 209, 257, 264, temporal coding, 312
284, 285 temporal lobe, 202, 240, 264, 272, 325, 357
semantic processing in Alzheimer’s disease, 264 thalamus, 200, 202, 203, 240, 325, 326, 335, 350,
semantic properties, 23, 24, 84, 85, 90 351, 358, 367, 369
semantic relation, 92 thymol, 144
sensitization, 167, 233 time intensity profile, 357
sensory-specific satiety, 40, 373, 378–381, 383 tip-of-the-nose (effect), 212, 235, 236,
septal area, 332 237
serotonin, 336 tobacco, 169
sex difference, 316, 389, 433. See also gender tomato, 58, 142
male/female, 33, 48, 77–79, 128–135, 163, 165, trigeminal innervation, 395
180–187, 202, 255, 257, 316, 317–319, 353, trigeminal nerve, 29, 161, 312, 403
395, 404, 412, 414, 445, 448 trigeminal stimulation, 161, 235
shoe polish, 256 trimethylundecylenic aldehyde, 127, 163
sick-building syndrome, 166 tufted cell, 297, 301, 302
skunk, 48, 161
smoke, 72, 77, 90, 161, 264 umami taste, 371, 373, 382
smoker, 255 universals, 68, 74, 149, 150, 417, 418
social chemosignal, 178, 182, 184, 189. See also University of Pennsylvania Smell Identification
communication Test, 267–269, 272, 280, 448
social communication, 9. See also communication unpleasantness, 16, 117, 145, 150, 152, 332, 425.
sour, 38, 56, 57, 369, 371, 373 See also hedonic
steroid, 179, 180, 183–187, 189, 190. See also
hormone vanilla, 47, 57, 86, 90, 92, 96, 153, 161, 203, 225,
strawberry, 31, 56, 57, 61 286, 383, 423, 436
structure-odor relationships, 100, 106, 110–112 vanillin, 29, 151, 164, 225, 423, 426
subiculum, 240, 241, 269 veridical label, 45, 47–51, 54, 55, 59–61, 221,
substantia innominata, 373 281
suckling, 161, 429, 434 vigilance, 31, 162, 166, 309
sucrose, 339, 353, 361, 393, 397 vomeronasal organ, 179, 180, 184, 186, 187
sugar, 76, 226
superior frontal gyrus, 326 wine, 39, 90, 222–224, 417
sweat, 160, 180, 183, 235, 318 wintergreen, 76, 162, 167
sweet, 32, 55–57, 93, 106, 108, 146, 371, 373, 377,
382, 391 yeast (fermented), 153

Catherine Rouby, Benoist Schaal, Danièle Dubois, Rémi Gervais, A. Holley - Olfaction, Taste, and Cognition-Cambridge University Press (2002)

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Catherine Rouby, Benoist Schaal, Danièle Dubois, Rémi Gervais, A. Holley - Olfaction, Taste, and Cognition-Cambridge University Press (2002)

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OLFACTION, TASTE, AND COGNITION

Catherine Rouby is an associate professor of neuroscience at Université Claude

Danièle Dubois is a research director at the CNRS, Institut National de la Langue

A. Holley is a professor of neuroscience at Université Claude Bernard and

Cambridge University Press

© Cambridge University Press 2002

This book is in copyright. Subject to statutory exception and to the provision of

First published in print format 2002

Cambridge University Press has no responsibility for the persistence or accuracy of

Section 1: A Speciﬁc Type of Cognition 1

Section 2: Knowledge and Languages 45

Section 3: Emotion 117

Section 4: Memory 209

Section 5: Neural Bases 291

20 Processing of Olfactory Affective Information: Contribution

Section 6: Individual Variations 389

Baeyens, Frank, Department of Psychology, University of Leuven, Tiensest-

07, France; CNRS, 69622 Villeurbanne, France, Tel: +33 4 37 28 74 91,

David, Sophie, Modèles, Dynamiques, Corpus, CNRS, Université Paris X –

Degel, Joachim, Allmendring 12, 75203 K önigsbach-Stein, Germany, Tel:

Distel, Hans, Institut für Medizinische Psychologie, Ludwig-Maximilians-

Dubois, Danièle, Laboratoire Languages, Cognitions, Pratiques, Ergonomie,

Duffy, Valerie B., Department of Surgery (Otolaryngology), Yale University

Fast, Katharine, Department of Surgery (Otolaryngology), Yale University

Faurion, Annick, Laboratoire de Neurobiologie Sensorielle, École Pratique

Faxbrink, Maria, Department of Psychology, Uppsala University, Box 1225,

Gervais, Rémi, Institut des Sciences Cognitives, CNRS/Université Claude

Hayreh, Davinder J. S., Department of Psychology, University of Chicago,

Heilmann, Stefan, Department of Otorhinolaryngology, University of Dresden

Pause, Bettina M., Institute of Psychology, Christian-Albrechts-Universität zu

Valentin, Dominique, École Nationale Supérieure de Biologie Appliquée à la

We acknowledge the support of a number of people without whom this book

This book is dedicated to Edmond Roudnitska, who was an artist, a creator of

also a generous man. Through creation of the Fondation Roudnitska he enabled

Olfactory experience is difﬁcult to deﬁne: From ineffable to unmentionable, it

Why Such Negativity?

That failed operation was to play a fundamental role in psychoanalytic theory,

Diderot D (1955). Lettre à Mademoiselle de la Chaux. In: Correspondance

Pradines M (1958). Traité de psychologie générale (1943–1950). Paris: Presses

It is currently recognized that odor attributes can be grouped in three main

3. Perceptual Analysis and Description of Perfumes

for a magazine, what I understand by the expression olfactory form. Here is my

4. Learning and Memory

worked out by Nature. . . . What then is my problem? It is precisely to try and

6. Olfactory Mental Imagery

unfamiliar odors would have minimal semantic properties. Finally, additional

the relationship between perfumery and scientiﬁc knowledge has featured

2. Characteristics of the Sense of Smell

2.1. The Sense of Smell Is a “Nominal” Sense

2.2. The Sense of Smell Is a “Near” Sense

2.3. The Sense of Smell Is a “Hidden” Sense

2.4. The Sense of Smell Is an “Associative” and “Emotional” Sense

2.5. The Sense of Smell Has a “Special Memory”

Consequences for olfactory

subgroupings of observers and reanalysis of the data based on differences be-

sensations and feelings attached to it that are extremely difﬁcult to describe.

1. Odors and Their Names

(2) the corresponding psychological conception of “lexical access,” which supposes

We shall therefore examine the conceptual frameworks that attempt to account

2. The Veridical Label: An Odor Name?

2.1. The Stimuli

C A’1, A’2 actually presented

differences in odor-naming performances depending on the mode of presentation

2.2. The Names

(the “object-source”), or a term or wording referring to the substance (vertex A,

2.3. The Mental Representations

1. The sensory representations of the presented stimuli (C 1 or C 2 as a represen-

3. Odors and Their Wording in Identiﬁcation Tests

1. an adequate semantic theory of lexical meaning (domain of linguistics), de-

Citron (Lemon) Orange (Orange) Pomme (Apple)

property of the “smell of X .” It is consistent with the hypothesis that odor

Type 2: Generic terms for sources

lemon orange apple Total

Types of answers N % N % N % N % cumulated%

1. expected basic-level source (e.g., 28 36 20 24 10 10 58 22 22

Total 78 100 84 100 98 100 260 100 100