Background Odors Modulate N170 ERP Component and Perception of Emotional Facial Stimuli

Abstract

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.

Background odors affect behavior in a dot-probe task with emotionally expressive faces

“…Faces, independently of their expressions, were rated as more negative in the unpleasant odor condition and more positive in the pleasant odor condition, replicating results of previous studies (Cook et al, 2015;Cook et al, 2018;Syrjänen et al, 2018). Similar to previous research, faces were also rated as more arousing during odor exposure compared to the no-odor control condition (Cook et al, 2015;Syrjänen et al, 2018). Manipulation checks confirmed that the ratings of odor valence and intensity confirmed our expectations.…”

“…Cook et al (2017) showed that the rated valence of faces is affected by congruent odors; disgusted faces were rated as more negative in an unpleasant odor context and happy faces were rated as more positive in a pleasant odor context. However, this specific interaction has not been found in other studies (Cook et al, 2015;Cook et al, 2018;Syrjänen et al, 2018). In general, results indicate that affective odors affect valence ratings of faces regardless of their expression (e.g.…”

“…unpleasant odors cause all facial expressions to be perceived more negatively). Arousal ratings show similar general effects, as faces are rated as more arousing in both pleasant and unpleasant odor conditions regardless of expression (Cook et al, 2015;Syrjänen et al, 2018), although in our prior work (Syrjänen et al (2018) happy faces perceived during exposure to an unpleasant odor (incongruent condition) were rated as less arousing. These results indicate that odors might affect subjective evaluations of faces either by stimulus congruence-specific effects, or by unspecific effects in the valence and arousal dimensions.…”

“…The unpleasant (valeric acid) and pleasant (lilac essence) odors were carefully diluted with a nearly odorless solution (Propylene glycol, 1,2-propanediol 99%, Sigma-Aldrich). Based on previous psychophysical investigations, we used a concentration of 30% for both odors, which represents moderate intensity (Syrjänen et al, 2018). In the present study, odor exposure was achieved through placing odorized cotton pads in an elastic cotton tube that was attached under the nose of participants, as in our previous studies (Syrjänen et al, 2017;Syrjänen et al, 2018).…”

Effects of unpleasant odors on emotion recognition: The right hemisphere and valence-specific hypotheses

“…Odors can modulate the recognition of disgust (Seubert et al, 2010), or happiness (Leppänen & Hietanen, 2003), while in the ambient odor conditions Reaction Times (RTs) in simple visual or auditory tasks significantly decrease (Millot, Brand, & Morand, 2002). Background odors may modulate the perception of emotional facial stimuli (Syrjänen et al, 2018) or attention may be modulated due to the effects of ambient odors (Michael et., 2003;Seigneuric et al, 2010). This indicates that olfactory stimuli may affect the modalities of perception and attention.…”