Disease avoidance is one of the main roles of olfaction. In particular, body odors are universal elicitors of disgust, a core emotion that plays a key role in disease avoidance. The disease avoidance theoretical framework emphasizes psychological mechanisms – attitudes and behaviors – aiming to recognize and evade pathogen threats. Thus, it focuses on behavioral immune defenses and disgust, which often evokes such attitudes and behaviors. Importantly, the quality of body odors changes with sickness, and thus olfactory disease detection is possible. Body odor disgust sensitivity (BODS) might reflect a behavioral disposition to avoid pathogens, and it may also involve social attitudes that prefer limited contact with strangers. The general aim of this thesis was to investigate the connection between olfaction, (body) odor disgust, and social attitudes from the perspective of disease avoidance.

In Study I, I investigated the relationship between disgust sensitivity to body odors and prejudice. Using an online survey, I found that high levels of BODS were associated with stronger prejudice towards a fictitious refugee group and that this relationship was partially explained by perceiving the group as different in terms of food, hygiene, and sanitary practices. In Study II, I looked at the association between olfactory stimulation, BODS, and implicit bias toward an outgroup. BODS levels were positively related to implicit bias towards an outgroup; however, this bias was not affected by olfactory cues. In Study III, I aimed to see if the relationship between BODS and prejudice generalizes across different cultures and locations. I found that higher BODS levels were associated with more prejudiced attitudes towards a fictitious refugee group across nine countries on all continents. As in Study I, this relationship was partially explained by perceived dissimilarities of the refugees’ norms regarding hygiene and food preparation, and general attitudes toward immigration. In Study IV, I investigated the relationship between the self-reported body odor disgust and perception of real odors, showing 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.

Overall, the research presented in this thesis supports the idea that there is a link between olfactory disgust and prejudice, which can be explained by disease avoidance behaviors.

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 (), 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.

Objective: This study investigated age-dependent and subtype-related alterations in electroencephalography (EEG) power spectra and current source densities (CSD) in children with attention deficit and hyperactivity disorder (ADHD).

Methods: We performed spectral and cortical source (exact low-resolution electromagnetic tomography, eLORETA) analyses using resting state EEG recordings from 40 children (8-16 years) with combined and inattentive subtypes of ADHD and 41 age-matched healthy controls (HC). Group differences in EEG spectra and CSD were investigated at each scalp location, voxel and cortical region in delta, theta, alpha and beta bands. We also explored associations between topographic changes in EEG power and CSD and age.

Results: Compared to healthy controls, combined ADHD subtype was characterized with significantly increased diffuse theta/beta power ratios (TBR) with a widespread decrease in beta CSD. Inattentive ADHD subtype presented increased TBR in all brain regions except in posterior areas with a global increase in theta source power. In both ADHD and HC, older age groups showed significantly lower delta source power and TBR and higher alpha and beta source power than younger age groups. Compared to HC, ADHD was characterized with increases in theta fronto-central and temporal source power with increasing age.

Conclusions: Our results confirm that TBR can be used as a neurophysiological biomarker to differentiate ADHD from healthy children at both the source and sensor levels.

Significance: Our findings emphasize the importance of performing the source imaging analysis in order to better characterize age-related changes in resting-state EEG activity in ADHD and controls.

Body odors provide important social and health-related cues in many species. While human body odor perception often triggers feelings of disgust, few studies have investigated body odor disgust in a systematic way. We have developed the body odor disgust scale (BODS), a brief 12-item scale to assess the extent to which individuals are disgusted by common body odors such as sweat and urine. The scale development included both internal and external validation tests. We used the BODS in conjunction with scales measuring social attitudes and biases, and found consistent associations between high body odor disgust and stronger authoritarian attitudes, as well as more pronounced outgroup biases. Our work is consistent with the “behavioral immune system” framework, wherein social attitudes and political ideologies are shaped by perceived pathogen risk and disease avoidance via feelings of disgust. Body odor perception may thus not only be important for personal interactions, but may also be linked to social attitudes and political ideologies.

Why are certain individuals persistent in opposing immigration? The behavioral immune system framework implies that a psychological mechanism, which adapted to detect and avoid pathogen threats, is also reflected in contemporary social attitudes. Moreover, prejudice towards outgroups might be partially driven by implicit pathogen concerns related to the perceived dissimilarity with these groups' hygiene and food preparation practices. Disgust, a universal core emotion supposedly evolved to avoid pathogen threats, as well as olfaction, both play a pivotal role in evoking disgust. In an online study (N = 800), we investigated whether individual differences in body odor disgust sensitivity (BODS) correlate with negative attitudes towards a fictive refugee group. The data analysis plan and hypotheses were preregistered. Results show that body odor disgust sensitivity is associated with xenophobia: BODS was positively associated with negative attitudes towards the fictive group. This relationship was partially mediated by perceived dissimilarities of the group in terms of hygiene and food preparation. Our finding suggests prejudice might be rooted in sensory mechanisms.

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.

Numerous studies indicate that attention deficit/hyperactivity disorder (ADHD) is related to some developmental trends, as its symptoms change widely over time. Nevertheless, the etiology of this phenomenon remains ambiguous. There is a disagreement whether ADHD is related to deviations in brain development or to a delay in brain maturation. The model of deviated brain development suggests that the ADHD brain matures in a fundamentally different way, and does not reach normal maturity at any developmental stage. On the contrary, the delayed brain maturation model assumes that the ADHD brain indeed matures in a different, delayed way in comparison to healthy age-matched controls, yet eventually reaches proper maturation. We investigated age-related changes in resting-state EEG activity to find evidence to support one of the alternative models. A total of 141 children and teenagers participated in the study; 67 diagnosed with ADHD and 74 healthy controls. The absolute power of delta, theta, alpha, and beta frequency bands was analyzed. We observed a significant developmental pattern of decreasing absolute EEG power in both groups. Nonetheless, ADHD was characterized by consistently lower absolute EGG power, mostly in the theta frequency band, in comparison to healthy controls. Our results are in line with the deviant brain maturation theory of ADHD, as the observed effects of age-related changes in EEG power are parallel but different in the two groups.

Research Problem: The purpose of this research synthesis is to identify new opportunities for smell-enabled games based upon current olfactory research, and to present early game concepts that have emerged from our empirical assessments.

Literature Review: We briefly summarize key projects in the history of scent technologies for film and media. Human-Computer Interaction researchers have also explored a number of uses for scent delivery in interactive digital media. Recent developments in olfactory psychology and neuroscience research suggest that a fruitful avenue for exploration is to develop learning games that expand olfactory capacity.

Methodology: We have conducted two studies of computer-based perceptual and cognitive olfactory tasks. 

1. Mixture perception experiment: We designed a perceptual experiment where the task was to correctly estimate the intensity of odor components in a blend of coffee and tea. Blended odors were presented to 10 healthy adults by means of a computer-controlled olfactometer. Following each stimulation, the participant used a computer interface to estimate the intensity of components of the blend.

2. Event-based memory experiment: We have developed a digital olfactory version of the children’s game “Memory.” The game interface consists of 32 white squares that are presented in a grid pattern on the screen and that, when participants click on them, triggers the release of one of eight possible smells from the olfactometer. Fifteen healthy adult participants were tested in 10 laboratory sessions distributed over three weeks.

Results and Conclusions: Our empirical results suggest that smell training through learning games holds promise as a means of improving cognitive function. The results of our event-based memory experiment suggest that both olfactory and visual memory capacities might have benefitted from olfactory game training. The results of our mixture perception experiment indicate that binary odor mixtures might provide a suitable starting point for perceptual training, and we suggest that a smell-enabled game might include adaptive difficulty by progressively introducing more complex mixtures. We have used event-based memory and mixture perception as “olfactory targets” for game mechanic development, and present early design concepts for “Smelly Genes” and “Scenter.” Finally, we discuss future directions and challenges for this new, interdisciplinary research topic.

Body odor disgust sensitivity (BODS) reflects a behavioral disposition to avoid pathogens, and it may also involve social attitudes. Among participants in the USA, high levels of BODS were associated with stronger xenophobia towards a fictitious refugee group. To test the generalizability of this finding, we analyzed data from 9 countries across five continents (N = 6836). Using structural equation modeling, we found support for our preregistered hypotheses: higher BODS levels were associated with more xenophobic attitudes; this relationship was partially explained by perceived dissimilarities of the refugees’ norms regarding hygiene and food preparation, and general attitudes toward immigration. Our results support a theoretical notion of how pathogen avoidance is associated with social attitudes: “traditional norms” often involve behaviors that limit inter-group contact, social mobility and situations that might lead to pathogen exposure. Our results also indicate that the positive relationship between BODS and xenophobia is robust across cultures.