APPLIED OLFACTORY COGNITION Topic Editors Gesualdo M. Zucco, Benoist Schaal, Mats Olsson and Ilona Croy PSYCHOLOGY Frontiers in Psychology December 2014 | Applied Olfactory Cognition | 1 ABOUT FRONTIERS Frontiers is more than just an open-access publisher of scholarly articles: it is a pioneering approach to the world of academia, radically improving the way scholarly research is managed. The grand vision of Frontiers is a world where all people have an equal opportunity to seek, share and generate knowledge. Frontiers provides immediate and permanent online open access to all its publications, but this alone is not enough to realize our grand goals. FRONTIERS JOURNAL SERIES The Frontiers Journal Series is a multi-tier and interdisciplinary set of open-access, online journals, promising a paradigm shift from the current review, selection and dissemination processes in academic publishing. 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Individual articles may be downloaded and reproduced in accordance with the principles of the CC-BY licence subject to any copyright or other notices. They may not be re-sold as an e-book. As author or other contributor you grant a CC-BY licence to others to reproduce your articles, including any graphics and third-party materials supplied by you, in accordance with the Conditions for Website Use and subject to any copyright notices which you include in connection with your articles and materials. All copyright, and all rights therein, are protected by national and international copyright laws. The above represents a summary only. For the full conditions see the Conditions for Authors and the Conditions for Website Use. ISSN 1664-8714 ISBN 978-2-88919-343-1 DOI 10.3389/978-2-88919-343-1 Frontiers in Psychology December 2014 | Applied Olfactory Cognition | 2 Foreword by Richard J. Stevenson, Macquarie University (Australia). It was long thought that the human nose might be able to discriminate somewhere in the order of 10,000 different odourants. The recent finding that the human nose can discriminate something like a trillion different smells serves as yet another reminder that we have again underestimated the capacity of our sense of smell (Bushdid, Magnasco, Vosshall & Keller, 2014). This volume serves as a further corrective for anyone who should hold the view that olfaction is unimportant in human affairs. The papers presented in this ebook, carefully collated and overseen by Aldo Zucco, Benoist Schaal, Mats Olsson and Ilona Croy, showcase a large number of quite different reasons for studying the applied side of olfaction, and indeed human olfaction in general. The 23 contributions presented here cover a broad range of topics, which illustrate contemporary interests in our field. Although with a strong applied focus, a noteworthy feature of this ebook is the richness of the theoretical perspectives that are developed. These range from considerations of olfactory perception, memory, expertise, and priming right the way through to receptor genetics. These contributions, from many leading experts in the field, will surely shape much of the applied work linking olfaction to disease, which is a further focus of this ebook. In respect to health and disease, the chapters on aging, pregnancy, depression, alcohol dependency and environmental odours, present overviews and rich new data on many contemporary problems, to which the study of olfaction is now contributing. A particularly notable aspect of olfactory experience is the affective impact that odours can have on people and their lives. The ebook covers some particularly intriguing aspects of APPLIED OLFACTORY COGNITION Reference Image from: Gesualdo M. Zucco (1988), Il sistema olfattivo. Padova (I) Cleup publisher. Cover image by Christiane Wambsganss. Topic Editors: Gesualdo M. Zucco, University of Padova, Italy Benoist Schaal , Centre Européen des Sciences du Goût, CNRS, France Mats Olsson, Karolinska institutet, Sweden Ilona Croy, University of Gothenburg, Sweden Frontiers in Psychology December 2014 | Applied Olfactory Cognition | 3 work in this area, with empirical studies investigating dissociations between wanting and liking, stress reduction in the elderly, mother-infant bonding, and the emotions that different odourants can evoke. This affective line of work is nicely complemented by empirical studies on expertise, the effect of odours on visual attention, and the relationship between particular personality traits and interest in olfaction. The gradual appropriation of methods from cognitive neuroscience into olfaction is also nicely represented in this ebook, with at least three of the chapters reporting data using neuroimaging, including a particular intriguing study looking at recognition of odours in mixtures. Finally, the close links between olfactory perception and sensory evaluation are also reflected in a chapter on wine. I hope that readers of this e-book will be struck, as I have been in reading its various chapters, how much olfaction affects our lives, and how the study of this sense can enrich it. References Bushdid, C., Magnasco, M., Vosshall, L. & Keller, A. (2014). Humans can discriminate more than 1 trillion olfactory stimuli. Science, 343, 1370-1372. Frontiers in Psychology December 2014 | Applied Olfactory Cognition | 4 Table of Contents Editorial 06 Applied Olfactory Cognition Gesualdo M. Zucco, Benoist Schaal, Mats J. Olsson and Ilona Croy Part I. Olfactory attention and memory 08 Smelly Primes – When Olfactory Primes Do or Do not Work M. A. M. Smeets and G. B. Dijksterhuis 18 Visual Attention for a Desktop Virtual Environment with Ambient Scent Alexander Toet and Martin G. van Schaik 29 A “Misfit” Theory of Spontaneous Conscious Odor Perception (MITSCOP): Reflections on the Role and Function of Odor Memory in Everyday Life Egon P . Köster, Per Møller and Jozina Mojet 41 Olfactory LOVER: Behavioral and Neural Correlates of Autobiographical Odor Memory Maria Larsson, Johan Willander, Kristina Karlsson and Artin Arshamian Part II. Olfactory expertise 46 The Impact of Expertise in Olfaction Jean-Pierre Royet, Jane Plailly, Anne-Lise Saive, Alexandra Veyrac and Chantal Delon-Martin 57 Hedonic Appreciation and Verbal Description of Pleasant and Unpleasant Odors in Untrained, Trainee Cooks, Flavorists, and Perfumers Caroline Sezille, Arnaud Fournel, Catherine Rouby, Fanny Rinck and Moustafa BensafI 65 Sensory Descriptors, Hedonic Perception and Consumer’s Attitudes to Sangiovese Red Wine Deriving From Organically and Conventionally Grown Grapes Ella Pagliarini, Monica Laureati and Davide Gaeta Part III. Chemoreception in Everyday Life 72 The Perception of Odor Objects in Everyday Life: A Review on the Processing of Odor Mixtures Thierry Thomas-Danguin, Charlotte Sinding, Sébastien Romagny, Fouzia El Mountassir,Boriana Atanasova, Elodie Le Berre, Anne-Marie Le Bon and Gerard Coureaud 90 The Influence of Health-Risk Perception and Distress on Reactions to Low-Level Chemical Exposure Linus Andersson, Anna-Sara Claeson, Lisa Ledin, Frida Wisting and Steven Nordin Frontiers in Psychology December 2014 | Applied Olfactory Cognition | 5 98 Food Neophobia and its Relation with Olfaction M. Luisa Demattè, Isabella Endrizzi and Flavia Gasperi Part IV. Odour and Emotion 104 Dynamics of Autonomic Nervous System Responses and Facial Expressions to Odors Wei He, Sanne Boesveldt, Cees de Graaf and René A. de Wijk 112 A Pleasant Familiar Odor Influences Perceived Stress and Peripheral Nervous System Activity During Normal Aging Pauline Joussain, Catherine Rouby and Moustafa Bensafi 119 How Incorporation of Scents Could Enhance Immersive Virtual Experiences Matthieu Ischer, Naëm Baron, Christophe Mermoud, Isabelle Cayeux, Christelle Porcherot, David Sander and Sylvain Delplanque 130 Relationships Between Personality Traits and Attitudes Toward the Sense of Smell Han-Seok Seo, Suji Lee and Sungeun Cho 138 Sadness Might Isolate You in a Non-Smelling World: Olfactory Perception and Depression Sylvia Schablitzky and Bettina M. Pause 158 Do Ambient Urban Odors Evoke Basic Emotions? Sandra T. Glass, Elisabeth Lingg and Eva Heuberger 169 Liking and Wanting Pleasant Odors: Different Effects of Repetitive Exposure in Men and Women Chantal Triscoli, Ilona Croy, Håkan Olausson and Uta Sailer Part V. Reproductive Life and Body Odours 177 Pregnancy and Olfaction: A Review E. Leslie Cameron 188 Maternal Status Regulates Cortical Responses to the Body Odor of Newborns Johan N Lundström, Annegret Mathe, Benoist Schaal, Johannes Frasnelli, Katharina Nitzsche,Johannes Gerber and Thomas Hummel Part VI. Olfaction in Health and Disease: from Genetic to Neuroimaging studies 194 Genetic Basis of Olfactory Cognition: Extremely High Level of DNA Sequence Polymorphism in Promoter Regions of the Human Olfactory Receptor Genes Revealed Using the 1000 Genomes Project Dataset Elena V. Ignatieva, Victor G. Levitsky, Nikolay S. Yudin, Mikhail P . Moshkin and Nikolay A. Kolchanov 205 Brain Responses to Odor Mixtures with Sub-Threshold Components Thomas Hummel, Selda Olgun, Johannes Gerber, Uschi Huchel and Johannes Frasnelli 213 The Influences of Age on Olfaction: A Review Richard L Doty and Vidyulata Kamath 233 Olfaction in Alcohol-Dependence: A Neglected Yet Promising Research Field Pierre Maurage, Philippe Rombaux and Philippe De Timary EDITORIAL published: 12 August 2014 doi: 10.3389/fpsyg.2014.00873 Applied olfactory cognition Gesualdo M. Zucco 1 *, Benoist Schaal 2 , Mats J. Olsson 3 and Ilona Croy 4 1 Department of General Psychology, Faculty of Medicine, University of Padova, Padova, Italy 2 Centre Européen des Sciences du Goût, CNRS, Dijon, France 3 Division for Psychology, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden 4 Department of Clinical Neurophysiology, University of Gothenburg, Gothenburg, Sweden *Correspondence: zucco@unipd.it Edited and reviewed by: Eddy J. Davelaar, Birkbeck College, UK Keywords: applied olfaction, cognition, everyday life, expertise, health and disease In recent years a significant body of research has accumulated on olfaction along several lines of investigation, ranging from molec- ular mechanisms to the neural and cognitive processing of olfac- tory information, as well as to multiple influences of odors on our everyday lives. The purpose of the present Frontiers’ Research Topic is to present experimental data (run in the laboratory as well as in everyday settings), reviews and methods papers on various applied or applicable aspects of olfactory cognition along with the beneficial possibilities that olfactory cognitions make possible in ameliorating different aspects of human condition. The present Research Topic is composed of 23 articles reunited in six fields of applied olfactory cognition. The first section con- cerns basic studies on odor memory and attention. In the first article, Smeets and Dijksterhuis (2014) review the potency of odors to affect human behavior. In the second article, Toet and van Schaik (2013) focus on how such priming are dependent on the congruency between the odor prime and the behavior that is supposed to be affected. In the third article, Köster et al. (2014) reverse the typical view on memory as being triggered by cues of previously encountered objects and argue that odor memory in everyday life is about detecting novelty rather than pleasant- ness. This section ends with an overview by Larsson et al. (2014) (article fourth) on the potency of odor-cues to generate life-long autobiographical memories. The second section reunites contributions on the acquisition and consequence of olfactory expertise which remains relatively unexplored in olfaction. Royet et al. (2013), report brain imaging studies with different types of odor experts, including: perfumers, flavorists, and oenologists (article fifth). Thereafter Sezille et al. (2014) (article sixth) investigate whether experts do perceive the pleasantness of odorants differently than non-experts. Pagliarini et al. (2013) (article seventh) study the attitudes of consumers toward wine from organically grown grapes. The third section of the Research Topic addresses chemore- ception in everyday life. In the eighth article, Thomas-Danguin et al. (2014) and his colleagues survey how everyday odors such as food flavors, perfumes, and wines convey complex information which perception depends on sophisticated processing abilities at different levels of the system. Andersson et al. (2013) turn in the ninth article to the problem of health-risk perception of chem- ical exposure and its interaction with distress and the ideas the receiver has about the exposure. In the tenth article Demattè et al. (2014) review the role of olfaction in food neophobia and suggest that olfaction might work as an alerting system preventing the ingestion of potentially detrimental substances. The fourth section of the Research Topic focuses on the relationships between olfaction and emotional processes. In the eleventh article, He et al. (2014) investigates the facial expres- sions of emotion in response to odors. In the twelfth article, Joussain et al. (2014) show in a combined field and laboratory study the influence of odor exposure on emotional states. In the thirteenth article, Ischer et al. (2014) present a new approach to investigate how olfactory ambiences affect visual responses in vir- tual worlds. In the fourteen article, Seo et al. (2013) show how personality traits affect the way attitudes toward odors. Further, Schablitzky and Pause (2014) (article fifteenth) investigate the interesting link between olfactory perception and depression. Glass et al. (2014) (article sixteenth) and colleagues show how potently everyday odors can induce emotions as happiness and disgust in the perceiver, while Triscoli et al. (2014) (article sev- enteenth) find interesting gender difference in how liking and wanting of odors differ over time. The fifth section concerns aspects of human reproductive life in relation with the emission and perception of body odors. Cameron (2014) starts by reviewing how pregnancy affects the perception of environmental odors (article eighteenth). Lundström et al. (2013) (article nineteenth) show how the body odor of two day-old newborns elicits activation in reward-related cerebral areas in women, regardless of their maternal status. In the last section of the Research Topic olfaction is considered in relation with health and disease issues. Ignatieva et al. (2014) (article twentieth) hunt for a genetic explanation of interindivid- ual variability in perceptual and emotional processing of odors. Hummel et al. (2013) (article twenty-first) give us a close-up on how the brain processes odor mixtures; while Doty and Kamath (2014) (article twenty-second) review how our olfactory abilities change across the life span. Finally, Maurage et al. (2014) (article twenty-third) point to the role of olfaction in the establishment of alcohol dependence. We are grateful to all of the contributors for their commit- ment to this project and for providing new accounts of the state of the art in applied olfactory cognition. We would also like to extend our special thanks to Professor Richard J. Stevenson for writing the foreword of this book. We hope that this e-volume will help promote further research on the applied aspects of olfactory perception and cognition and attract new scientists www.frontiersin.org August 2014 | Volume 5 | Article 873 | 6 Zucco et al. Applied olfactory cognition to the field. We also hope that it will be a useful resource for colleagues and professionals dealing with the study of the chem- ical senses in relation with issues on human welfare in everyday setting. ACKNOWLEDGMENTS We are grateful to Dr. Eddy J. Davelaar, Specialty Chief Editor of Cognitive Science, a section of the Journal Frontiers in Psychology and to the members of the Editorial team of Frontiers for their competent and friendly assistance along the entire production process. REFERENCES Andersson, L., Claeson, A.-S., Ledin, L., Wisting, F., and Nordin, S. (2013). The influence of health-risk perception and distress on reactions to low- level chemical exposure. Front. Psychol 4:816. doi: 10.3389/fpsyg.2013. 00816 Cameron, E. L. (2014). Pregnancy and olfaction: a review. Front. Psychol . 5:67. doi: 10.3389/fpsyg.2014.00067 Demattè, M. L., Endrizzi, I., and Gasperi, F. (2014). Food neophobia and its relation with olfaction. Front. Psychol . 5:127. doi: 10.3389/fpsyg.2014.00127 Doty, R. 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Psychol . 5:247. doi: 10.3389/fpsyg.2014.00247 Ischer, M., Baron, N., Mermoud, C., Cayeux, I., Porcherot, C., Sander, D., et al. (2014). How incorporation of scents could enhance immersive virtual experi- ences. Front. Psychol . 5:736. doi: 10.3389/fpsyg.2014.00736 Joussain, P., Rouby, C., and Bensafi, M. (2014). A pleasant familiar odor influences perceived stress and peripheral nervous system activity during normal aging. Front. Psychol . 5:113. doi: 10.3389/fpsyg.2014.00113 Köster, E. P., Møller, P., and Mojet, J. (2014). A “Misfit” Theory of Spontaneous Conscious Odor Perception (MITSCOP): reflections on the role and function of odor memory in everyday life. Front. Psychol . 5:64. doi: 10.3389/fpsyg.2014.00064 Larsson, M., Willander, J., Karlsson, K., and Arshamian, A. (2014). Olfactory LOVER: behavioral and neural correlates of autobiographical odor memory. Front. Psychol . 5:312. doi: 10.3389/fpsyg.2014.00312 Lundström, J. N., Mathe, A., Schaal, B., Frasnelli, J., Nitzsche, K., Gerber, J., et al. (2013). Maternal status regulates cortical responses to the body odor of newborns. Front. Psychol 4:597. doi: 10.3389/fpsyg.2013. 00597 Maurage, P., Rombaux, P., and de Timary, P. (2014). Olfaction in alcohol- dependence: a neglected yet promising research field. Front. Psychol . 4:1007. doi: 10.3389/fpsyg.2013.01007 Pagliarini, E., Laureati, M., and Gaeta, D. (2013). Sensory descriptors, hedo- nic perception and consumer’s attitudes to Sangiovese red wine deriving from organically and conventionally grown grapes. Front. Psychol . 4:896. doi: 10.3389/fpsyg.2013.00896 Royet, J.-P., Plailly, J., Saive, A.-L., Veyrac, A., and Delon-Martin, C. (2013). The impact of expertise in olfaction. Front. Psychol . 4:928. doi: 10.3389/fpsyg.2013.00928 Schablitzky, S., and Pause, B. M. (2014). Sadness might isolate you in a non- smelling world: olfactory perception and depression. Front. 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Visual attention for a desk- top virtual environment with ambient scent. Front. Psychol 4:883. doi: 10.3389/fpsyg.2013.00883 Triscoli, C., Croy, I., Olausson, H., and Sailer, U. (2014). Liking and wanting pleasant odors: different effects of repetitive exposure in men and women. Front. Psychol. 5:526. doi: 10.3389/fpsyg.2014.00526 Conflict of Interest Statement: The authors declare that the research was con- ducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received: 02 July 2014; accepted: 22 July 2014; published online: 12 August 2014. Citation: Zucco GM, Schaal B, Olsson MJ and Croy I (2014) Applied olfactory cognition. Front. Psychol. 5 :873. doi: 10.3389/fpsyg.2014.00873 This article was submitted to Cognitive Science, a section of the journal Frontiers in Psychology. Copyright © 2014 Zucco, Schaal, Olsson and Croy. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Frontiers in Psychology | Cognitive Science August 2014 | Volume 5 | Article 873 | 7 REVIEW ARTICLE published: 12 February 2014 doi: 10.3389/fpsyg.2014.00096 Smelly primes – when olfactory primes do or do not work M. A. M. Smeets 1,2 * and G. B. Dijksterhuis 1,3 1 Unilever R&D, Vlaardingen, Netherlands 2 Faculty of Social and Behavioural Sciences, Utrecht University, Utrecht, Netherlands 3 Section for Sensory and Consumer Science, Faculty of Science (FOOD), University of Copenhagen, Copenhagen, Denmark Edited by: Mats Olsson, Karolinska Institutet Stockholm, Sweden Reviewed by: Adrian Von Muhlenen, University of Warwick, UK Egon Peter Koster, Helmholtz Institute at Utrecht University, Netherlands *Correspondence: M. A. M. Smeets, Faculty of Social and Behavioural Sciences, Utrecht University, Heidelberglaan 1, 3584 Cs Utrecht, Netherlands e-mail: m.a.m.smeets@uu.nl In applied olfactory cognition the effects that olfactory stimulation can have on (human) behavior are investigated. To enable an efficient application of olfactory stimuli a model of how they may lead to a change in behavior is proposed. To this end we use the concept of olfactory priming. Olfactory priming may prompt a special view on priming as the olfactory sense has some unique properties which make odors special types of primes. Examples of such properties are the ability of odors to influence our behavior outside of awareness, to lead to strong affective evaluations, to evoke specific memories, and to associate easily and quickly to other environmental stimuli. Opportunities and limitations for using odors as primes are related to these properties, and alternative explanations for reported findings are offered. Implications for olfactory semantic, construal, behavior and goal priming are given based on a brief overview of the priming literature from social psychology and from olfactory perception science. We end by formulating recommendations and ideas for a future research agenda and applications for olfactory priming. Keywords: olfaction, priming, cognition and emotion, behavior, valence INTRODUCTION There is a substantial literature from social cognition on priming, demonstrating the sometimes substantial and unexpected effects that environmental stimuli can have on information processing and behavior. Due to the traditional emphasis in psychological science on visual and auditory perception and language, only few priming studies employ olfactory primes. In contrast, there is a bountiful literature from the chemical senses community on the effects of olfactory stimuli on perceptual and cognitive pro- cessing that could be conceived of as priming research, but is not always discussed within a priming framework. These liter- atures seem somehow disconnected. In this review we intend to forge a connection between the two in order to explore how conceiving of odors as primes can help us make better sense of their potential for influencing human information processing and behavior. Secondly, we propose guidelines for how odors are best used as primes based on the intrinsic and sometimes unique properties of the olfactory system that can be seen as opportunities but also as limitations. More systematic research on odor priming could be envisioned to realize its full potential for applications if both properties and limitations are taken into account. We will formulate a possible research agenda for such research. We will start by addressing what we actually mean by priming and primes. PRIMING IN THE SOCIAL SCIENCES Priming refers to the phenomenon that incidental stimuli have been shown to influence higher-order cognitive and behavioral outcomes without the individual’s awareness or appreciation of this influence (Bargh et al., 2010). Interestingly, such “incidental” priming stimuli can be manipulated in the context of experimental studies to achieve effects in participants in a mere passive, inactive manner. This is opposite to earlier (social) cognitive approaches in which experimental manipulations used to be brought to the conscious attention of participants to study how they affected decision-making (Bargh, 2006). To illustrate the former, Bargh (2006) gives the example of how polite behavior can be studied in an experiment in which the concept of politeness is passively manipulated by embedding adjectives related to politeness in a scrambled word test disguised as a language test, which is then fol- lowed by an opportunity to behave politely. Thus, priming research allows us to investigate how higher mental processes such as judg- ment and social behavior can be triggered and then operate in the absence of conscious awareness (Bargh and Morsella, 2008). The notion that environmental stimuli can prime behavior is interesting, as it implies that there is a bridge between perception of the stimulus (e.g., a word related to politeness) and motor behav- ior (the polite behavior of waiting for someone to finish speaking instead of interrupting) possibly in the form of an activated mental concept of politeness. Specifically, by presenting words or images, the underlying related concept becomes accessible – an associa- tive process – for further information processing (cf. Loersch and Payne, 2011). The mental content that has thus become available is now likely to be used as a source of information in subsequent information processing and behavior. Loersch and Payne (2011) distinguish between four types of priming: semantic priming (category identification), construal priming (judgment), behav- ior priming (action), and goal priming (motivation). Whichever type of priming occurs depends on whether the current situa- tion invites, e.g., judgment rather than behavior or vice versa, and on other attributes such as a person’s attitudes toward a primed category, personal goals and interests or constraints of the situ- ation. A good example of the latter is an experiment by Cesario et al. (2010) in which participants who were in a enclosed booth when primed with a social stereotype of aggression, chose for a www.frontiersin.org February 2014 | Volume 5 | Article 96 | 8 Smeets and Dijksterhuis Olfactory priming fight-like behavioral response, whereas those who were seated in an open field chose for a flight-like behavioral response. An important consequence of Loersch and Payne’s situated inference model of priming is that single primes can have mul- tiple effects (i.e., as either one or more types of priming), but also that these effects are not the same for everybody or in all situations. This has special relevance for applications of priming in the real world, where individuals and situations will differ greatly. In addition to the four types of priming that are central to the Loersch and Payne framework, we can distinguish between perceptual priming, repetition priming, and affective priming which bear relevance to odor priming. We speak of percep- tual priming when prime and target share perceptual attributes. This is not the same as semantic priming. For example, Koenig et al. (2000) found that while odors presented during a learning phase acted as perceptual primes when participants were pre- sented with these odors again during a test phase, there was no such priming effect when odor names – rather than odors themselves – had been used during the learning phase. The explanation for the difference may lie in the fact that percep- tual priming involves modality-specific subsystems in memory, whereas semantic priming involves associative (amodal) sub- systems in memory (Koenig et al., 2000). Repetition priming refers to the phenomenon that a stimulus can act as its own prime. When presented again, an odor is processed faster because its representation in memory was activated just before, and there is still a memory trace available. For odors, this was dis- cussed by Olsson et al. (2002). They conclude that in some of the older repetition priming literature it is hard to disentan- gle purely olfactory priming from semantic priming – which is related to the previously mentioned distinction between per- ceptual priming and semantic priming. In Olsson (1999) even negative priming occurred when odors that were correctly iden- tified were proven to be processed more slowly than odors that had not been identified. Identification of odors allowed for verbal labeling and may have led to semantic overshadowing (cf. Melcher and Schooler, 1996). Finally, in affective priming there is an unintentional influence of a first evaluative (affec- tive) response, acting as a prime, on the subsequent processing of a target stimulus. For example, the positive affective tone of primes (often words) may activate affectively congruent mate- rial in memory (Klauer, 1997). Explanations have been sought in affective congruency between prime and target (both “posi- tive” or “negative”), but also in congruency in response tendency. Consequently, positive affective primes would facilitate (congru- ent) approach responses, and negative affective primes would facilitate (congruent) avoidance responses to affectively congru- ent targets (Förster and Liberman, 2007). Odors may be potent affective primes as will be highlighted later in Section “Priming via valence”. Central to many explanations of how activated concepts can prime behaviors is William James’ ideo-motor action principle which holds that activation of a cognitive representation of an action increases the likelihood of that action being carried out, via the triggering of active behavior representations, which cause movement of relevant muscles (Schröder and Thagard, 2013). Deliberate choice or motivation is not considered to be necessary. Priming effects, then, occur as a result of the spread- ing of activation , by which activation of one node in memory automatically spreads to another. Thus, priming effects are effort- less and uncontrollable. For a more detailed account of how this might work involving computational modeling and neu- ral networks, the reader is referred to Schröder and Thagard (2013). Priming effects are supposed to take place outside of aware- ness. Social and cognitive psychologists have somewhat different perspectives on this. In cognitive psychology, awareness in this context would be equated with ability to perceive. For example, individuals could only be presumed to be unaware of a stimulus if stimulus intensity or duration would be below perceptual thresh- old (hence, at subliminal levels). According to Bargh (1992), it does not matter much from a social psychologist perspective whether someone is aware of the stimulus event, as long as the individual remains unaware of the ways in which the stimulus is interpreted and of the influence of this awareness on subsequent processing. Both subliminal as well as supraliminal primes have been proven to be effective primes (Bargh and Morsella, 2008). Goal or need state play an important role: for example Karremans et al. (2006) demonstrated that subliminal priming with a brand drink name such as Lipton Ice Tea positively affected participants’ choice for and intention to drink the primed drink, but only for those who were thirsty. To conclude, subliminality of stimulation could be important but only because if the individual is unaware of the stimulus event we can be sure they are unaware of the potential influence it has on their behavior. And, even when people are able of perceiving a priming stimulus, we might still conclude its subsequent effects on behavior take place outside of awareness. So far we have seen that priming refers to the ability of “inci- dental” environmental stimuli to influence higher order cognitive processing and behavioral outcomes, and that these influences occur outside of awareness, effortlessly, and automatically. Mental representation of concepts play an important role, as activation of such a concept by a prime can lead to the simultaneous trigger- ing of other cognitive, motivational, and behavioral processes by spreading of activation in memory. Both supraliminal as well as subliminal stimuli have been shown to be effective primes. Before we continue to look at the suitability and effectivity of odors as primes, we will first explore the unique properties of the sense of smell. UNIQUE PROPERTIES OF OLFACTION We are about to make claims about the suitability of contextual odors as primes. We start by introducing an important distinc- tion: that between odor and odorant . The term odorant refers to the volatile chemical substance that is capable of eliciting the expe- rience of an odor – it can be a single compound as well as a mixture consisting of a large number of compounds. The odor exclusively refers to an individual’s experience, it is a percept. The olfactory experience (an “odor”) is in all likelihood elicited by an odorant , but there have been occasions in which odor experiences have been reported even in the absence of an odorant. In a study by Knasko et al. (1990) the presence of an odor was strongly sug- gested by the context. Participants who were given the suggestion Frontiers in Psychology | Cognitive Science February 2014 | Volume 5 | Article 96 | 9 Smeets and Dijksterhuis Olfactory priming of a pleasant odor being in the room reported a more positive mood. A more extreme example is reported by O’Mahony (1978) who told a compelling story on TV which resulted in people call- ing the TV station stating that they had indeed smelled an odor emanating from their TV set. Furthermore, it is possible that a cer- tain odor, experienced as resulting from a specific odorant, is not experienced by 100% of the subjects. Some subjects may perceive another odor, based on, for example, prior (lack of) experience with the odor. Odors in memory are also referred to as odor objects , that, even when consisting of ten or hundreds of volatile components (the odorant ) are perceived as unitary perceptual events (the odors ) against a continually shifting olfactory background (Stevenson and Wilson, 2007). This goes to illustrate that there is not a necessary relation between the chemical properties, or even the presence, of an odorant, and the odor perceived as resulting from it (cf. Wilson and Stevenson, 2006). A focus on the so called “stimulus problem” (Stevenson and Boakes, 2003) will likely lead to incomplete theo- ries and remain insufficient to understand olfactory perception in its entirety. SENSE OF SMELL IS AN IMPLICIT SENSE The sense of smell has also been alluded to as a hidden or implicit sense (Köster, 2002). Because vision is usually in the center of our attention, it is presumed to be the dominant sense, followed by the senses of hearing and touch. As a result, people tend to be less aware of odorants in their environment. Odorants, after all, cannot be seen or heard, and they can only be felt if they are at high enough concentrations to stimulate the trigeminal nerve innervating the nose, throat, mouth, and eyes, which induces sen- sations of tingling, prickling, burning, or even pain (Doty et al., 2004). There are large individual differences in the tendency to be aware of odors such that some people never seem to notice any, and would go to sleep without problem on a mattress on which the cat had just peed, whereas others are quick to notice any unpleasant or pleasant odors and would avoid them or seek them out purposefully (Smeets et al., 2008). Regardless, odorants –and their odors – are in general unlikely to draw attention unless they are especially pleasant