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

Combining electrodermal activity analysis and dynamic causal modeling to investigate the visual-odor multimodal integration during face perception

Objective. This study presents a novel methodological approach for incorporating information related to the peripheral sympathetic response into the investigation of neural dynamics. Particularly, we explore how hedonic contextual olfactory stimuli influence the processing of neutral faces in terms of sympathetic response, event-related potentials and effective connectivity analysis. The objective is to investigate how the emotional valence of odors influences the cortical connectivity underlying face processing and the role of face-induced sympathetic arousal in this visual-olfactory multimodal integration.Approach. To this aim, we combine electrodermal activity (EDA) analysis and dynamic causal modeling to examine changes in cortico-cortical interactions.Results. The results reveal that stimuli arising sympathetic EDA responses are associated with a more negative N170 amplitude, which may be a marker of heightened arousal in response to faces. Hedonic odors, on the other hand, lead to a more negative N1 component and a reduced the vertex positive potential when they are unpleasant or pleasant. Concerning connectivity, unpleasant odors strengthen the forward connection from the inferior temporal gyrus (ITG) to the middle temporal gyrus, which is involved in processing changeable facial features. Conversely, the occurrence of sympathetic responses after a stimulus is correlated with an inhibition of this same connection and an enhancement of the backward connection from ITG to the fusiform face gyrus.Significance. These findings suggest that unpleasant odors may enhance the interpretation of emotional expressions and mental states, while faces capable of eliciting sympathetic arousal prioritize identity processing.

Body odor disgust sensitivity (BODS) is related to extreme odor valence perception

Odors are important disease cues, and disgust sensitivity to body odors reflects individual differences in disease avoidance. The body odor disgust sensitivity (BODS) scale provides a rapid and valid assessment of individual differences. Nevertheless, little is known about how individual differences in BODS might correlate with overall odor perception or how it is related to other differences in emotional reactivity (e.g., affect intensity). We investigated how BODS relates to perceptual ratings of pleasant and unpleasant odors. We aggregated data from 4 experiments (total N = 190) that were conducted in our laboratory, and where valence and intensity ratings were collected. Unpleasant odors were body-like (e.g., sweat-like valeric acid), which may provide disease cues. The pleasant odors were, in contrast, often found in soap and cleaning products (e.g., lilac, lemon). Across experiments, we show that individuals with higher BODS levels perceived smells as more highly valenced overall: unpleasant smells were rated as more unpleasant, and pleasant smells were rated as more pleasant. These results suggest that body odor disgust sensitivity is associated with a broader pattern of affect intensity which causes stronger emotional responses to both negative and positive odors. In contrast, BODS levels were not associated with odor intensity perception. Furthermore, disgust sensitivity to odors coming from external sources (e.g., someone else's sweat) was the best predictor of odor valence ratings. The effects were modest in size. The results validate the BODS scale as it is explicitly associated with experimental ratings of odor valence.

Positive and negative facial valence perception are modulated differently by eccentricity in the parafovea

Understanding whether people around us are in a good, bad or neutral mood can be critical to our behavior, both when looking directly at them or when they are in our peripheral visual field. However, facial expressions of emotions are often investigated at central visual field or at locations right or left of fixation. Here we assumed that perception of facial emotional valence (the emotion's pleasantness) changes with distance from central visual field (eccentricity) and that different emotions may be influenced differently by eccentricity. Participants (n = 58) judged the valence of emotional faces across the parafovea (≤ 4°, positive (happy), negative (fearful), or neutral)) while their eyes were being tracked. As expected, performance decreased with eccentricity. Positive valence perception was least affected by eccentricity (accuracy reduction of 10-19% at 4°) and negative the most (accuracy reduction of 35-38% at 4°), and this was not a result of speed-accuracy trade-off or response biases. Within-valence (but not across-valence) performance was associated across eccentricities suggesting perception of different valences is supported by different mechanisms. While our results may not generalize to all positive and negative emotions, they indicate that beyond-foveal investigations can reveal additional characteristics of the mechanisms that underlie facial expression processing and perception.

A Review of the Effects of Valenced Odors on Face Perception and Evaluation

How do valenced odors affect the perception and evaluation of facial expressions? We reviewed 25 studies published from 1989 to 2020 on cross-modal behavioral effects of odors on the perception of faces. The results indicate that odors may influence facial evaluations and classifications in several ways. Faces are rated as more arousing during simultaneous odor exposure, and the rated valence of faces is affected in the direction of the odor valence. For facial classification tasks, in general, valenced odors, whether pleasant or unpleasant, decrease facial emotion classification speed. The evidence for valence congruency effects was inconsistent. Some studies found that exposure to a valenced odor facilitates the processing of a similarly valenced facial expression. The results for facial evaluation were mirrored in classical conditioning studies, as faces conditioned with valenced odors were rated in the direction of the odor valence. However, the evidence of odor effects was inconsistent when the task was to classify faces. Furthermore, using a z-curve analysis, we found clear evidence for publication bias. Our recommendations for future research include greater consideration of individual differences in sensation and cognition, individual differences (e.g., differences in odor sensitivity related to age, gender, or culture), establishing standardized experimental assessments and stimuli, larger study samples, and embracing open research practices.

Negative Bias During Early Attentional Engagement in Major Depressive Disorder as Examined Using a Two-Stage Model: High Sensitivity to Sad but Bluntness to Happy Cues

Negative attentional bias has been well established in depression. However, there is very limited knowledge about whether this depression-relevant negative bias exits during initial attentional allocation, as compared with the converging evidence for the negative bias during sustained attention engagement. This study used both behavioral and electrophysiological measures to examine the initial attention engagement in depressed patients influenced by mood-congruent and mood-incongruent emotions. The dot-probe task was performed with a 100-ms exposure time of the emotional cues (emotional and neutral face pairs). The behavioral results showed that the patients responded faster following valid compared with invalid sad facial cues. Electrophysiological indexes in the frame of the two-stage model of attentional modulation by emotions provided cognitive mechanisms in distinct attention engagement stages: (1) the patients exhibited reduced P1 amplitudes following validly than invalidly happy cues than did the healthy controls, indicating a positive attenuation at an early stage of automatic attention orientation; and (2) the patients exhibited enhanced whereas the controls showed reduced P3 amplitudes following validly than invalidly sad cues, suggesting a mood-congruent negative potentiation in depression at the later stage of top-down voluntary control of attention. Depressed patients show a negative bias in early attentional allocation, reflected by preferred engagement with mood-congruent and diminished engagement with positive emotional cues/stimuli.

An Overprotective Nose? Implicit Bias Is Positively Related to Individual Differences in Body Odor Disgust Sensitivity

Body odors are universal elicitors of disgust, a core emotion that plays a key role in the behavioral immune system (BIS) - a set of psychological functions working to avoid disease. Recent studies showed that body odor disgust sensitivity (BODS) is associated with explicit xenophobia and authoritarianism. In the current experimental pre-registered study (https://osf.io/6jkp2/), we investigated the association between olfactory pathogen cues, BODS and implicit bias toward an outgroup (tested by an implicit association test). Results show that BODS is positively related to implicit bias toward an outgroup, suggesting that social attitudes may be linked to basic chemosensory processes. These attitudes were not influenced by background odors. Additionally, BODS was related to social, but not economic conservatism. This study extends the BIS framework to an experimental context by focusing on the role of disgust and body odors in shaping implicit bias.