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The effects of valenced odors on facial perception
Stockholm University, Faculty of Social Sciences, Department of Psychology, Perception and psychophysics.ORCID iD: 0000-0001-5999-2196
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We use our senses to navigate in the world. An important property of olfaction, the sense of smell, is to enable us to approach beneficial things, and to avoid what might be toxic or otherwise harmful in our environment. Other peoples’ behaviors are also paramount for our survival. Thus, we use our vision to decode their internal states from their facial expressions. For many modalities, multiple senses are integrated to enhance sensory percepts. In this thesis, I investigated how valenced odors affect the perception of facial expressions. Specifically, using a multi-method approach, I studied the integration of unpleasant and pleasant odor contexts on odor-congruent and incongruent facial expressions, disgusted, and happy faces.

The effects I am interested in are those that valenced odors have on face perception, attention to faces, and the cortical processing of faces. To answer these questions, I used questionnaires, ratings, EEG, and behavioral measures such as reaction times. Across studies, ratings of face valence are affected in the direction of the odor valence (e.g., faces are rated more negatively in the context of an unpleasant odor). Also, overall, the results in my studies indicate that faces are perceived as more arousing in valenced odor contexts; however, these effects occur regardless of facial expression.

In study 1, I found that valenced odors and facial expressions are integrated at an earlier time-frame than previously thought. Specifically, I found that the N170 event-related potential component (ERP) to disgusted facial expressions was lower in amplitude in the unpleasant odor condition than in the pleasant odor condition. This effect was not present for happy faces in the N170 component. An unpleasant odor might thus facilitate the processing of threat-related information.

In study 2, I found evidence that odors, in general, did not affect the recognition speed of facial expressions that changed from neutral to disgusted or happy over 3 seconds. Also, I found robust evidence against congruency effects in facial expression recognition reaction times (RTs). The results indicated that faces overall were recognized faster in the unpleasant odor condition. Further, these results were not qualified by individual differences in body odor disgust. Thus, unpleasant odors might facilitate the recognition of facial expressions regardless of trait body odor disgust.

In study 3, I studied whether valenced odors directed spatial attention toward odor-congruent facial expressions in a “dot-probe” task. I found decisive evidence that odors do not affect attention towards disgusted and happy facial expressions, casting doubt on the dot-probe experiment. However, I found that probes were detected faster as a function of time-on-task in the unpleasant odor condition. I hypothesized that this effect might be due to maintained vigilance in the presence of an unpleasant odor and task fluency effects.

In summary, the results indicate that valenced odors affect facial perception. Generally, faces are perceived as more valenced and arousing in odor contexts. Further, an unpleasant odor may decrease RTs; however, this effect seems to be irrespective of the target type. Also, odor face integration may happen earlier than thought; yet, evidence in the literature is mixed, and more research is needed. The methods I have used may increase transparency and robustness of published results, and help accelerate knowledge development in this field of research.

Place, publisher, year, edition, pages
Stockholm: Department of Psychology, Stockholm University , 2020. , p. 98
Keywords [en]
Valenced odors, Facial expressions, Disgust, Happiness, Olfaction, Emotion, Reaction Times, Evaluation, Ratings, EEG, ERP, N170
National Category
Psychology
Research subject
Psychology
Identifiers
URN: urn:nbn:se:su:diva-179663ISBN: 978-91-7911-040-6 (print)ISBN: 978-91-7911-041-3 (electronic)OAI: oai:DiVA.org:su-179663DiVA, id: diva2:1413702
Public defence
2020-04-24, digitally via conference (Zoom), public link https://stockholmuniversity.zoom.us/j/61510779105, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2020-04-01 Created: 2020-03-11 Last updated: 2022-02-26Bibliographically approved
List of papers
1. Background Odors Modulate N170 ERP Component and Perception of Emotional Facial Stimuli
Open this publication in new window or tab >>Background Odors Modulate N170 ERP Component and Perception of Emotional Facial Stimuli
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2018 (English)In: Frontiers in Psychology, E-ISSN 1664-1078, Vol. 9, article id 1000Article in journal (Refereed) Published
Abstract [en]

Successful social interaction relies on the accurate decoding of other peoples' emotional signals, and their contextual integration. However, little is known about how contextual odors may lead to modulation of cortical processing in response to facial expressions. We investigated how unpleasant and pleasant contextual background odors affected emotion perception and cortical event-related potential (ERP) responses to pictures of faces expressing happy, neutral and disgusted facial expressions. Faces were, regardless of expression, rated more positively in the pleasant odor condition and more negatively in the unpleasant odor condition. Faces were overall rated as more emotionally arousing in the presence of an odor, irrespective of its valence. Contextual odors also interacted with facial expressions, such that happy faces were rated as especially non-arousing in the unpleasant odor condition. The early, face-sensitive N170 ERP component also displayed an interaction effect. Here, disgusted faces were affected by the odor context such that the N170 revealed a relatively larger negativity in the context of a pleasant odor compared with an unpleasant odor. There were no odor effects on the responses to faces in other measured ERP components (P1, VPP, P2, and LPP). These results suggest that odors bias socioemotional perception early stages of the visual processing stream. However, effects may vary across emotional expressions and measurements.

Keywords
ERP, facial expressions, emotion, odors, N170, LPP
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-158235 (URN)10.3389/fpsyg.2018.01000 (DOI)000436327500001 ()29997539 (PubMedID)
Note

This work was supported by the Swedish Foundation for Humanities and Social Sciences (M14-0375:1); and Marianne and Marcus Wallenberg Foundation (MMW 2014:0178) to JO.

Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2022-03-23Bibliographically approved
2. Do Valenced Odors and Trait Body Odor Disgust Affect Evaluation of Emotion in Dynamic Faces?
Open this publication in new window or tab >>Do Valenced Odors and Trait Body Odor Disgust Affect Evaluation of Emotion in Dynamic Faces?
2017 (English)In: Perception, ISSN 0301-0066, E-ISSN 1468-4233, Vol. 46, no 12, p. 1412-1426Article in journal (Refereed) Published
Abstract [en]

Disgust is a core emotion evolved to detect and avoid the ingestion of poisonous food as well as the contact with pathogens and other harmful agents. Previous research has shown that multisensory presentation of olfactory and visual information may strengthen the processing of disgust-relevant information. However, it is not known whether these findings extend to dynamic facial stimuli that changes from neutral to emotionally expressive, or if individual differences in trait body odor disgust may influence the processing of disgust-related information. In this preregistered study, we tested whether a classification of dynamic facial expressions as happy or disgusted, and an emotional evaluation of these facial expressions, would be affected by individual differences in body odor disgust sensitivity, and by exposure to a sweat-like, negatively valenced odor (valeric acid), as compared with a soap-like, positively valenced odor (lilac essence) or a no-odor control. Using Bayesian hypothesis testing, we found evidence that odors do not affect recognition of emotion in dynamic faces even when body odor disgust sensitivity was used as moderator. However, an exploratory analysis suggested that an unpleasant odor context may cause faster RTs for faces, independent of their emotional expression. Our results further our understanding of the scope and limits of odor effects on facial perception affect and suggest further studies should focus on reproducibility, specifying experimental circumstances where odor effects on facial expressions may be present versus absent.

Keywords
disgust, olfaction, odors, facial expression, emotion, reaction time, evaluation
National Category
Psychology (excluding Applied Psychology)
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-147328 (URN)10.1177/0301006617720831 (DOI)000418611600005 ()
Available from: 2017-09-22 Created: 2017-09-22 Last updated: 2022-02-28Bibliographically approved
3. Background odors affect behavior in a dot-probe task with emotionally expressive faces
Open this publication in new window or tab >>Background odors affect behavior in a dot-probe task with emotionally expressive faces
2019 (English)In: Physiology and Behavior, ISSN 0031-9384, E-ISSN 1873-507X, Vol. 210, article id 112540Article in journal (Refereed) Published
Abstract [en]

Odors affect perception of social cues in visual environments. Although often underestimated, people use their sense of smell to guide approach or avoidance behavior in social contexts. However, underlying psychological mechanisms are not well known. Prior work suggested olfactory effects are due to increased attention or arousal, or depend on the congruency between olfactory and visual cues. Our aim was to assess how odors influence attentional processes using a dot-probe task with odor-congruent and odor-incongruent facial expressions (happy, disgusted and neutral expressions paired with pleasant odor, unpleasant odor and no-odor). In a pre-registered analysis plan, we hypothesized either faster reaction times attributed to arousal from odors in general, or to faces that were emotionally congruent with the odors. We also hypothesized time-on-task effects specific to the odor compared to the control condition. Using Bayesian linear models, we found strong evidence that the faces were rated as more arousing and emotional in odor contexts. However, the dot-probe task did in fact not provide an effective cue to selective visual attention, and odors did not modulate overall attention to the faces. However, we found a time-on-task effect such that in the unpleasant odor condition, response times decreased over time, whereas in the no-odor and pleasant condition there was a slight increase in response times. We conclude that time-on-task effects is an interesting venue for odor-visual interaction research, and such effects might explain inconsistent findings in the prior research literature.

Keywords
affective odors, facial expression, emotion, reaction time
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-175739 (URN)10.1016/j.physbeh.2019.05.001 (DOI)000488654900026 ()31104855 (PubMedID)
Available from: 2019-11-11 Created: 2019-11-11 Last updated: 2022-02-26Bibliographically approved

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