Human chemosignals modulate emotional perception of biological motion in a sex-specific manner

Construction and validation of the Dalian emotional movement open-source set (DEMOS)

Human body movements are important for emotion recognition and social communication and have received extensive attention from researchers. In this field, emotional biological motion stimuli, as depicted by point-light displays, are widely used. However, the number of stimuli in the existing material library is small, and there is a lack of standardized indicators, which subsequently limits experimental design and conduction. Therefore, based on our prior kinematic dataset, we constructed the Dalian Emotional Movement Open-source Set (DEMOS) using computational modeling. The DEMOS has three views (i.e., frontal 0°, left 45°, and left 90°) and in total comprises 2664 high-quality videos of emotional biological motion, each displaying happiness, sadness, anger, fear, disgust, and neutral. All stimuli were validated in terms of recognition accuracy, emotional intensity, and subjective movement. The objective movement for each expression was also calculated. The DEMOS can be downloaded for free from https://osf.io/83fst/ . To our knowledge, this is the largest multi-view emotional biological motion set based on the whole body. The DEMOS can be applied in many fields, including affective computing, social cognition, and psychiatry.

Sex-specific effects of human chemosignal on perception of angry but not fearful faces

Androsta-4,16,-dien-3-one (androstadienone), a steroids implicated as a human social chemosignal, has been reported to impact one's emotional perception along the valence axis. The current study takes a step further to examine whether it modulates the perception of angry and fearful faces, two negative emotions that are similar with respect to valence and arousal, but signal different social values. Systematic comparisons of psychophysical data collected from 40 heterosexual men and 45 heterosexual women revealed that androstadienone subconsciously biased heterosexual men toward perceiving the male faces as less angry, while it biased the heterosexual women toward perceiving the female faces as angrier. Meanwhile, androstadienone did not affect the perception of fearful faces in either men or women. These findings indicate that the modulation of androstadienone on negative emotional perceptions is not uniform, suggesting that it alters the perception of specific rather than general negative emotions. In particular, it impacts one's perception of anger, which signals impending aggression, and hence could further impact an individual's social interaction in a sex-specific manner.

Different armpits under my new nose: Olfactory sex but not gender affects implicit measures of embodiment

Conflicting multisensory signals may alter embodiment to produce self-identification with a foreign body, but the role of olfaction in this process has been overlooked. We studied in healthy participants how sex (male and female sweat odors) and gender (male and female cosmetic scents) olfactory stimuli contribute to embodiment. Participants saw, on a head mounted display, the first-person perspective of a sex mismatching person. Synchronous visuotactile stimulation was applied to enhance illusory embodiment. Simultaneously, they smelled either sex- or gender- congruent or incongruent stimuli. We assessed implicit (skin conductance responses to visual threats) and explicit (questionnaire) measures of embodiment. Stronger responses to threat were found when participants smelled the sex-congruent compared to the sex-incongruent odor, while no such differences were found for the cosmetic scents. According to the questionnaire, embodiment did not differ between conditions. Post-experimental assessment of the presented cues, suggest that while both sweat odors were considered generally male, cosmetic scents were not. The presented scents were generally not associated with the embodied body. Our results suggest that sex-related body odors influence implicit but not explicit aspects of embodiment and are in line with unique characteristics of olfaction in other aspects of cognition.

Estratetraenol increases preference for large sexual reward but not impulsivity among heterosexual males

There is increasing evidence suggesting that estratetraenol, a human chemosignal deemed a putative sex pheromone, affects social cognition and sexual behavior. The present study investigates the effects of estratetraenol on preference for sexual rewards in heterosexual males. Seventy-six male participants received either estratetraenol or a control carrier in a double-blind, placebo-controlled, within-participant design. Participants underwent a sexual delay discounting task, in which they were asked to make a choice between a variable larger-later option (i.e., waiting longer to view a sexual picture for a longer duration) and a smaller-sooner option (i.e., waiting for a fixed shorter period of time to view the same picture for a shorter duration). Results revealed that, compared to the control solution, estratetraenol selectively increases preference for larger-later sexual rewards. Computational modelling showed that estratetraenol has no observable influence on impulsivity, as indexed by the discounting rate. These findings suggest that estratetraenol could increase men's sexual motivation, possibly facilitating behavioral processes associated with the pursuit of a sexual partner.

Androstadienone influences women's perception of happiness and anger on same-sex faces: Preliminary findings

This study investigated whether androstadienone (AND) influences women's emotional perception of potential mates and rivals in a manner that promotes women's reproductive success. Sixty participants (29 in the fertile phase and 31 in the luteal phase) rated their perception of happiness, sadness, anger and sexual arousal from male and female neutral faces during exposure to AND or control solution on two consecutive days. The results showed that AND led women to perceive neutral female faces as unhappier, regardless of their menstrual cycle phase. In addition, AND led women in the fertile phase (i.e., periovulatory phase) to perceive more anger from neutral female faces. Further, no AND-effects were found on the emotional perception of male faces, nor were there perceptions of the sadness or sexual arousal in female faces. These findings may suggest that AND influences women's cognitive processing that can benefit women from staying away from potential threats or preparing to reduce the costs of intrasexual competition.

Neural circuits of anxiolytic and antidepressant pherine molecules

In this review, we describe proposed circuits mediating the mechanism of action of pherines, a new class of synthetic neuroactive steroids with demonstrated antianxiety and antidepressant properties, that engage nasal chemosensory receptors. We hypothesize that afferent signals triggered by activation of these peripheral receptors could reach subgroups of olfactory bulb neurons broadcasting information to gamma-aminobutyric acid (GABAergic) and corticotropin-releasing hormone (CRH) neurons in the limbic amygdala. We propose that chemosensory inputs triggered by pherines project to centrolateral (CeL) and centromedial (CeM) amygdala neurons, with downstream effects mediating behavioral actions. Anxiolytic pherines could activate the forward inhibitory GABAergic neurons that facilitate the release of neuropeptide S (NPS) in the locus coeruleus (LC) and GABA in the bed nucleus of the stria terminalis (BNST) and inhibit catecholamine release in the LC and ventral tegmental area (VTA) leading to rapid anxiolytic effect. Alternatively, antidepressant pherines could facilitate the CRH and GABAergic neurons that inhibit the release of NPS from the LC, increase glutamate release from the BNST, and increase norepinephrine (NE), dopamine (DA), and serotonin release from the LC, VTA, and raphe nucleus, respectively. Activation of these neural circuits leads to rapid antidepressant effect. The information provided is consistent with this model, but it should be noted that some steps on these pathways have not been demonstrated conclusively in the human brain.

Contextualising courtship: Exploring male body odour effects on vocal modulation

Voice characteristics are important to communicate socially relevant information. Recent research has shown that individuals alter their voices depending on the context of social interactions and perceived characteristics of the audience, and this affects how they are perceived. Numerous studies have also shown that the presence of bodily odours can elicit psychological changes in people. Here, we tested whether the presence of male axillary odour would influence vocal modulations in courtship contexts. We analysed differences in vocal parameters and attractiveness ratings across 950 recordings from 80 participants as they responded to opposite-sex target stimuli. Using these, we tested whether men's and women's vocal parameters and perceived stimuli attractiveness differed in the presence or absence of the odour. We expected women to speak with increased voice F₀, and men to lower their pitch, when exposed to male body odour, especially if it were of high quality. However, neither the presence of male odour, its quality, nor the addition of androstadienone produced any consistent changes in vocal parameters. Nevertheless, rated stimulus attractiveness was predicted by F₀ and especially F₀ variability, suggesting that this is a key parameter in signalling attraction during human courtship, and supporting the idea that vocal modulations are context-sensitive.

Olfaction in the Multisensory Processing of Faces: A Narrative Review of the Influence of Human Body Odors

A recent body of research has emerged regarding the interactions between olfaction and other sensory channels to process social information. The current review examines the influence of body odors on face perception, a core component of human social cognition. First, we review studies reporting how body odors interact with the perception of invariant facial information (i.e., identity, sex, attractiveness, trustworthiness, and dominance). Although we mainly focus on the influence of body odors based on axillary odor, we also review findings about specific steroids present in axillary sweat (i.e., androstenone, androstenol, androstadienone, and estratetraenol). We next survey the literature showing body odor influences on the perception of transient face properties, notably in discussing the role of body odors in facilitating or hindering the perception of emotional facial expression, in relation to competing frameworks of emotions. Finally, we discuss the developmental origins of these olfaction-to-vision influences, as an emerging literature indicates that odor cues strongly influence face perception in infants. Body odors with a high social relevance such as the odor emanating from the mother have a widespread influence on various aspects of face perception in infancy, including categorization of faces among other objects, face scanning behavior, or facial expression perception. We conclude by suggesting that the weight of olfaction might be especially strong in infancy, shaping social perception, especially in slow-maturing senses such as vision, and that this early tutoring function of olfaction spans all developmental stages to disambiguate a complex social environment by conveying key information for social interactions until adulthood.

Perception of Social Odor and Gender-Related Differences Investigated Through the Use of Transfer Entropy and Embodied Medium

The perception of putative pheromones or social odors (PPSO) in humans is a widely debated topic because the published results seem ambiguous. Our research aimed to evaluate how cross-modal processing of PPSO and gender voice can affect the behavioral and psychophysiological states of the subject during a listening task with a bodily contact medium, and how these effects could be gender related. Before the experimental session, three embodied media, were exposed to volatilized estratetraenol (Estr), 5α-androst-16-en-3 α-ol (Andr), and Vaseline oil. The experimental session consisted in listening to a story that were transmitted, with a male or female voice, by the communicative medium via a Bluetooth system during a listening task, recorded through 64-active channel electroencephalography (EEG). The sense of co-presence and social presence, elicited by the medium, showed how the established relationship with the medium was gender dependent and modulated by the PPSO. In particular, Andr induced greater responses related to co-presence. The gender of the participants was related to the co-presence desire, where women imagined higher medium co-presence than men. EEG findings seemed to be more responsive to the PPSO–gender voice interaction, than behavioral results. The mismatch between female PPSO and male voice elicited the greatest cortical flow of information. In the case of the Andr–male voice condition, the trained model appeared to assign more relevance to the flow of information to the right frontotemporal regions (involved in odor recognition memory and social behavior). The Estr–male voice condition showed activation of the bilateral frontoparietal network, which is linked to cognitive control, cognitive flexibility, and auditory consciousness. The model appears to distinguish the dissonance condition linked to Andr matched with a female voice: it highlights a flow of information to the right occipital lobe and to the frontal pole. The PPSO could influence the co-presence judgements and EEG response. The results seem suggest that could be an implicit pattern linked to PPSO-related gender differences and gender voice.

Oxytocin modulates human chemosensory decoding of sex in a dose-dependent manner

There has been accumulating evidence of human social chemo-signaling, but the underlying mechanisms remain poorly understood. Considering the evolutionarily conserved roles of oxytocin and vasopressin in reproductive and social behaviors, we examined whether the two neuropeptides are involved in the subconscious processing of androsta-4,16,-dien-3-one and estra-1,3,5 (10),16-tetraen-3-ol, two human chemosignals that convey masculinity and femininity to the targeted recipients, respectively. Psychophysical data collected from 216 heterosexual and homosexual men across five experiments totaling 1056 testing sessions consistently showed that such chemosensory communications of masculinity and femininity were blocked by a competitive antagonist of both oxytocin and vasopressin receptors called atosiban, administered nasally. On the other hand, intranasal oxytocin, but not vasopressin, modulated the decoding of androstadienone and estratetraenol in manners that were dose-dependent, nonmonotonic, and contingent upon the recipients’ social proficiency. Taken together, these findings establish a causal link between neuroendocrine factors and subconscious chemosensory communications of sex-specific information in humans.

Pheromone effects on the human hypothalamus in relation to sexual orientation and gender

Pheromones are chemicals that serve communicational purposes within a species. In most terrestrial mammals, pheromones are detected by either the olfactory epithelium or the vomeronasal organ and processed by various downstream structures including the medial amygdala and the hypothalamus to regulate motivated behaviors and endocrine responses. The search for human pheromones began in the 1970s. Whereas bioactive ligands are yet to be identified, there has been accumulating evidence that human body odors exert a range of pheromone-like effects on the recipients, including triggering innate behavioral responses, modulating endocrine levels, signaling social information, and affecting mood and cognition. In parallel, results from recent brain imaging studies suggest that body odors evoke distinct neural responses from those observed with common nonsocial odors. Two endogenous steroids androsta-4,16,- dien-3-one and estra-1,3,5(10),16-tetraen-3-ol are considered by some as candidates for human sex pheromones. The two substances produce sexually dimorphic effects on human perception, mood, and physiological arousal. Moreover, they reportedly elicit different hypothalamic response patterns in manners contingent on the recipients' sex and sexual orientation. Neuroendocrine mechanisms underlying the effects of human chemosignals are not yet clear and await future detailed analyses.

Untangling the Ties Between Social Cognition and Body Motion: Gender Impact

We proved the viability of the general hypothesis that biological motion (BM) processing serves as a hallmark of social cognition. We assumed that BM processing and inferring emotions through BM (body language reading) are firmly linked and examined whether this tie is gender-specific. Healthy females and males completed two tasks with the same set of point-light BM displays portraying angry and neutral locomotion of female and male actors. For one task, perceivers had to indicate actor gender, while for the other, they had to infer the emotional content of locomotion. Thus, with identical visual input, we directed task demands either to BM processing or inferring of emotion. This design allows straight comparison between sensitivity to BM and recognition of emotions conveyed by the same BM. In addition, perceivers were administered a set of photographs from the Reading the Mind in the Eyes Test (RMET), with which they identified either emotional state or actor gender. Although there were no gender differences in performance on BM tasks, a tight link occurred between recognition accuracy of emotions and gender through BM in males. In females only, body language reading (both accuracy and response time) was associated with performance on the RMET. The outcome underscores gender-specific modes in visual social cognition and triggers investigation of body language reading in a wide range of neuropsychiatric disorders.

Sex differences in main olfactory system pathways involved in psychosexual function

We summarize literature from animal and human studies assessing sex differences in the ability of the main olfactory system to detect and process sex-specific olfactory signals ("pheromones") that control the expression of psychosexual functions in males and females. A case is made in non primate mammals for an obligatory role of pheromonal signaling via the main olfactory system (in addition to the vomeronasal-accessory olfactory system) in mate recognition and sexual arousal, with male-specific as well as female-specific pheromones subserving these functions in the opposite sex. Although the case for an obligatory role of pheromones in mate recognition and mating among old world primates, including humans, is weaker, we review the current literature assessing the role of putative human pheromones (eg, AND, EST, "copulin"), detected by the main olfactory system, in promoting mate choice and mating in men and women. Based on animal studies, we hypothesize that sexually dimorphic effects of putative human pheromones are mediated via main olfactory inputs to the medial amygdala which, in turn, transmits olfactory information to sites in the hypothalamus that regulate reproduction.

The Subtle Signaling Strength of Smells: A Masked Odor Enhances Interpersonal Trust

Most everyday smells, from lavender to body odors, are complex odorant mixtures that “host” particular compounds that guide (social) behavior and motivation (biomarkers). A key element of social behavior is interpersonal trust, and building on previous research showing that (i) lavender odor can enhance trust, and that (ii) certain compounds in body odor can reduce stress in mice and humans (called “social buffering”), we examined whether a grassy-smelling compound found in both body odors and lavender, hexanal, would enhance interpersonal trust. Notably, we applied odor masking to explore whether trust could be influenced subconsciously by masked (i.e., undetectable) hexanal. In Study 1 (between-subjects), 90 females played a Trust Game while they either smelled hexanal (0.01% v/v), clove odor (eugenol: 10% v/v), or hexanal masked by clove odor (a mix of the former). As a sign of higher trust, participants gave more money to a trustee while exposed to masked hexanal (vs. the mask: eugenol). In Study 2 (within-subjects, double-blind), another sample of 35 females smelled the same three odors, while they rated the trustworthiness of a spectrum of faces that varied on trustworthiness. Controlling for subjective odor intensity and pleasantness and substantiating that masked hexanal could not be distinguished from the mask, faces were perceived as more trustworthy during exposure to masked hexanal (vs. the mask: eugenol). Whereas non-masked hexanal also increased face trustworthiness ratings, these effects disappeared after controlling for the odor’s subjective intensity and pleasantness. The combined results bring new evidence that trust can be enhanced implicitly via undetected smells.

A scent of romance: human putative pheromone affects men's sexual cognition

Previous studies suggest that the putative human pheromone estratetraenol affects several systems underlying human functioning and appears to activate neural systems that are known to affect sexual behavior. In this study, we investigated whether exposure to estratetraenol affects men's social cognition abilities. In the first experiment, men performed the Interpersonal Perception task while being exposed to estratetraenol and to a control solution. Men performed the task with better accuracy while being exposed to estratetraenol. This improvement was evident especially in the Intimacy category where participants evaluated romantic relationships. In a second experiment, we exposed a different sample of men to estratetraenol and to a control solution while performing a task that implicitly measured their emotional reaction to photos depicting two humans either romantically touching or not, with a control condition of two inanimate objects either touching or not. We found that the participants' emotional reaction to touch was stronger under exposure to estratetraenol. Together, these results suggest that exposure to estratetraenol may trigger a change in men's social cognition, especially in sexually related situations.