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Despite the tight link between the visibility of the iris and pupil, the perceived effects of these two have been studied largely in isolation. We demonstrate, across two experimental studies, that the effects of perceived pupil size are dependent on the visibility of the iris. In a first study, our participants donated more and had more positive impressions of portraits of non-human primates when these were manipulated to appear having larger pupils. Post-hoc inspection of our data suggested that the difference was greater for species with more conspicuous irises. In a second study, we concomitantly manipulated iris brightness and pupil size. Brighter irises and larger pupils elicited greater donations. Participants rated photographs with brighter irises as cuter, more attractive and friendlier, but only when they had dilated pupils. Our results have methodological implications for studies manipulating eye appearance, and help interpret results from previous studies.

Children's ability to accurately recognize the external emotional signals produced by those around them represents a milestone in their socioemotional development and is associated with a number of important psychosocial outcomes. A plethora of individual studies have examined when, and in which order, children acquire emotion knowledge over the course of their development. Yet, very few attempts have been made to summarize this body of work quantitatively. To address this, the present meta-analysis examined the age-related trajectories of emotion recognition across childhood and the extent to which typically developing children's recognition of external emotional cues (in the face, voice, and body) is influenced by a host of participant-, task-, and stimulus-related factors. We analyzed children's emotion recognition overall (independent of specific emotion categories) and for specific basic emotions. In total, k = 129 individual studies, investigating a total of N = 31,101 2-12-year-old children's emotion recognition abilities were included in our analyses. Children's recognition accuracy across all emotion categories was significantly above chance and improved with age in the same manner for all emotions. Emotion recognition accuracy was also moderated by region of study and task type. The order in which children became proficient at identifying specific emotions was consistent with previous qualitative reviews: Happiness was the easiest emotion to recognize, and disgust and fear were the most difficult to recognize across age. Task- and stimulus-related moderator variables also influenced specific emotion categories in different ways. We contextualize these results with regard to children's socioemotional development more broadly, and we discuss how our findings can be used to guide researchers and practitioners interested in children's social skills. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

In a number of species, including humans, perceived outgroup threat can promote ingroup cohesion. However, the distribution and selection history of this association across species with varied intergroup relations remains unclear. Using a sample of 8 captive groups (N = 43 individuals), we here tested whether bonobos, like chimpanzees, show more affiliative ingroup behaviour following perception of outgroup cues (unfamiliar male long-distance vocalisations). We used comparable methods to our previous study of captive chimpanzees, and found that, although weaker, there was an association for more frequent social grooming in response to the outgroup condition than the control condition, alongside more alert posture and increased self-directed behaviour. This provides preliminary evidence for an ancestral origin to the proximate association between outgroup cues and ingroup cohesion, at least prior to the Pan-Homo split, and suggests the presence of intergroup competition in our last common ancestor., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Brooks et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

While alterations in both physiological responses to others' emotions as well as interoceptive abilities have been identified in autism, their relevance in altered emotion recognition is largely unknown. We here examined the role of interoceptive ability, facial mimicry, and autistic traits in facial emotion processing in non-autistic individuals. In an online Experiment 1, participants (N = 99) performed a facial emotion recognition task, including ratings of perceived emotional intensity and confidence in emotion recognition, and reported on trait interoceptive accuracy, interoceptive sensibility and autistic traits. In a follow-up lab Experiment 2 involving 100 participants, we replicated the online experiment and additionally investigated the relationship between facial mimicry (measured through electromyography), cardiac interoceptive accuracy (evaluated using a heartbeat discrimination task), and autistic traits in relation to emotion processing. Across experiments, neither interoception measures nor facial mimicry accounted for a reduced recognition of specific expressions with higher autistic traits. Higher trait interoceptive accuracy was rather associated with more confidence in correct recognition of some expressions, as well as with higher ratings of their perceived emotional intensity. Exploratory analyses indicated that those higher intensity ratings might result from a stronger integration of instant facial muscle activations, which seem to be less integrated in intensity ratings with higher autistic traits. Future studies should test whether facial muscle activity, and physiological signals in general, are correspondingly less predictive of perceiving emotionality in others in individuals on the autism spectrum, and whether training interoceptive abilities might facilitate the interpretation of emotional expressions., (© 2024. The Author(s).)

Humans flexibly adapt expressions of emotional messages when interacting with others. However, detailed information on how specific parts of the face and hands move in socio-emotional contexts is missing. We identified individual gesture and facial movements (through automated face tracking) of N  = 80 participants in the UK, produced while watching amusing, fearful, or neutral movie scenes either alone or with a social partner. Amusing and fearful scenes, more so than neutral scenes, led to an overall increase in facial and gesture movements, confirming emotional responding. Furthermore, social context facilitated movements in the lower instead of upper facial areas, as well as gesture use. These findings highlight emotional signaling components that likely underwent selection for communication, a result we discuss in comparison with the nonhuman primate literature. To facilitate ecologically valid and cross-cultural comparisons on human emotion communication, we additionally offer a new stimuli database of the recorded naturalistic facial expressions., Competing Interests: The authors declare no competing interests., (© 2024 The Authors.)

Perceiving emotions in others is at the foundation of higher-order social cognition. The importance of emotions is evidenced by the fact that they receive prioritized attention at early stages of processing the environment in humans and some other primates. Nevertheless, we do not fully understand how emotion modulates attention over longer durations in primates, particularly in great apes. Bonobos, one of our closest relatives, stand out in emotion processing and regulation among great apes. This makes them an interesting comparison species and a valuable model for studying the evolution of emotion perception in hominids. We investigated how bonobos and humans spontaneously attend to emotionally valent scenes in a preferential looking task using eye-tracking. With Bayesian mixed modelling, we found that bonobos and humans generally looked longer at emotional scenes, mainly of conspecifics. Moreover, while bonobos did not have a bias toward emotional human scenes, humans sustained their attention toward bonobos playing, grooming and having sex. Furthermore, when exploring an immediate bias for emotions, humans showed a bias toward affiliative human scenes, and bonobos showed a bias away from bonobos-in-distress scenes. These findings suggest that emotions modulate attention at early and later attentional stages in bonobos, similar to humans.

Robotics, using social mechanisms like hormonal modulation, may accelerate our understanding of core sociality principles.

External eye appearance in avian taxa has been proposed to be driven by social and ecological functions. Recent research in primates suggests, instead, that, photoprotective functions are important drivers of external eye appearance. Using similar methods, we examined the variation in external eye appearance of 132 parrot species (Psittaciformes) in relation to their ecology and sociality. Breeding systems, flock size and sexual dimorphism, as well as species' latitude and maximum living altitude, and estimated UV-B incidence in species' ranges were used to explore the contribution of social and ecological factors in driving external eye appearance. We measured the hue and brightness of visible parts of the eye and the difference in measurements of brightness between adjacent parts of the eye. We found no link between social variables and our measurements. We did, however, find a negative association between the brightness of the inner part of the iris and latitude and altitude. Darker inner irises were more prevalent farther away from the equator and for those species living at higher altitudes. We found no link between UV-B and brightness measurements of the iris, or tissue surrounding the eye. We speculate that these results are consistent with an adaptation for visual functions. While preliminary, these results suggest that external eye appearance in parrots is influenced by ecological, but not social factors., (© 2024. The Author(s).)

Primate faces provide information about a range of variant and invariant traits, including some that are relevant for mate choice. For example, faces of males may convey information about their health or genetic quality through symmetry or facial masculinity. Because perceiving and processing such information may have bearing on the reproductive success of an individual, cognitive systems are expected to be sensitive to facial cues of mate quality. However, few studies have investigated this topic in non-human primate species. Orang-utans are an interesting species to test mate-relevant cognitive biases, because they are characterised by male bimaturism: some adult males are fully developed and bear conspicuous flanges on the side of their face, while other males look relatively similar to females. Here, we describe two non-invasive computerised experiments with Bornean orang-utans (Pongo pygmaeus), testing (i) immediate attention towards large flanges and symmetrical faces using a dot-probe task (N = 3 individuals; 2F) and (ii) choice bias for pictures of flanged males over unflanged males using a preference test (N = 6 individuals; 4F). In contrast with our expectations, we found no immediate attentional bias towards either large flanges or symmetrical faces. In addition, individuals did not show a choice bias for stimuli of flanged males. We did find exploratory evidence for a colour bias and energy efficiency trade-offs in the preference task. We discuss our null results and exploratory results in the context of the evolutionary history of Bornean orang-utans, and provide suggestions for a more biocentric approach to the study of orang-utan cognition., (© 2024. The Author(s).)

Over the last decades, theoretical perspectives in the interdisciplinary field of the affective sciences have proliferated rather than converged due to differing assumptions about what human affective phenomena are and how they work. These metaphysical and mechanistic assumptions, shaped by academic context and values, have dictated affective constructs and operationalizations. However, an assumption about the purpose of affective phenomena can guide us to a common set of metaphysical and mechanistic assumptions. In this capstone paper, we home in on a nested teleological principle for human affective phenomena in order to synthesize metaphysical and mechanistic assumptions. Under this framework, human affective phenomena can collectively be considered algorithms that either adjust based on the human comfort zone (affective concerns) or monitor those adaptive processes (affective features). This teleologically-grounded framework offers a principled agenda and launchpad for both organizing existing perspectives and generating new ones. Ultimately, we hope the Human Affectome brings us a step closer to not only an integrated understanding of human affective phenomena, but an integrated field for affective research., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

For highly visual species like primates, facial and bodily emotion expressions play a crucial role in emotion perception. However, most research focuses on facial expressions, while the perception of bodily cues is still poorly understood. Using a novel comparative priming eye-tracking design, we examined whether our close primate relatives, the chimpanzees ( Pan troglodytes ), and humans infer emotions from bodily cues through subsequent perceptual integration with facial expressions. In experiment 1, we primed chimpanzees with videos of bodily movements of unfamiliar conspecifics engaged in social activities of opposite valence ( play and fear ) against neutral control scenes to examine attentional bias toward succeeding congruent or incongruent facial expressions. In experiment 2, we assessed the same attentional bias in humans yet using stimuli showing unfamiliar humans. In experiment 3, humans watched the chimpanzee stimuli of experiment 1, to examine cross-species emotion perception. Chimpanzees exhibited a persistent fear-related attention bias but did not associate bodily with congruent facial cues. In contrast, humans prioritized conspecifics' congruent facial expressions (matching bodily scenes) over incongruent ones (mismatching). Nevertheless, humans exhibited no congruency effect when viewing chimpanzee stimuli, suggesting difficulty in cross-species emotion perception. These results highlight differences in emotion perception, with humans being greatly affected by fearful and playful bodily cues and chimpanzees being strongly drawn toward fearful expressions, regardless of the preceding bodily priming cue. These data advance our understanding of the evolution of emotion signaling and the presence of distinct perceptual patterns in hominids., (© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences.)

Competing Interests: Competing interests statement:The author declares no competing interest.

The ongoing debate between basic emotion theories (BETs) and the theory of constructed emotion (TCE) hampers progress in the field of emotion research. Providing a new perspective, here we aim to bring the theories closer together by dissecting them according to Tinbergen's four questions to clarify a focus on their evolutionary basis. On the basis of our review of the literature, we conclude that whereas BETs focus on the evolution question of Tinbergen, the TCE is more concerned with the causation of emotion. On the survival value of emotions both theories largely agree: to provide the best reaction in specific situations. Evidence is converging on the evolutionary history of emotions but is still limited for both theories-research within both frameworks focuses heavily on the causation. We conclude that BETs and the TCE explain two different phenomena: emotion and feeling. Therefore, they seem irreconcilable but possibly supplementary for explaining and investigating the evolution of emotion-especially considering their similar answer to the question of survival value. Last, this article further highlights the importance of carefully describing what aspect of emotion is being discussed or studied. Only then can evidence be interpreted to converge toward explaining emotion.

Why can humans be intolerant of, yet also be empathic toward strangers? This cardinal question can be tackled by studying emotions in our closest living relatives, bonobos. Their striking xenophilic tendencies make them an interesting model for reconstructing the socioemotional capacities of the last common ancestor of hominids. Within two dot-probe studies, we compared bonobos' and humans' attention toward scenes depicting familiar (kith and kin) or unfamiliar individuals with emotional or neutral expressions. Results show that the attention of bonobos is biased toward emotional scenes depicting unfamiliar bonobos, but not toward emotional groupmates (Study 1). In contrast, Study 2 shows that human attention is biased toward emotional rather than neutral expressions of family and friends, but not toward unfamiliar others. On the one hand, our results show that an attentional bias toward emotions is a shared phenomenon between humans and bonobos, but on the other, both species have their own unique evolutionarily informed biases. These findings support previously proposed adaptive explanations for xenophilia in bonobos that potentially biases them toward emotional expressions of unfamiliar conspecifics, and parochialism in humans, which makes them sensitive to the emotional expressions of close others. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Facial mimicry as well as the accurate assessment of one's performance when judging others' emotional expressions have been suggested to inform successful emotion recognition. Differences in the integration of these two information sources might explain alterations in the perception of others' emotions in individuals with Social Anxiety Disorder and individuals on the autism spectrum. Using a non-clinical sample (N = 57), we examined the role of social anxiety and autistic traits in the link between facial mimicry, or confidence in one's performance, and emotion recognition. While participants were presented with videos of spontaneous emotional facial expressions, we measured their facial muscle activity, asked them to label the expressions and indicate their confidence in accurately labelling the expressions. Our results showed that confidence in emotion recognition was lower with higher social anxiety traits even though actual recognition was not related to social anxiety traits. Higher autistic traits, in contrast, were associated with worse recognition, and a weakened link between facial mimicry and performance. Consequently, high social anxiety traits might not affect emotion recognition itself, but the top-down evaluation of own abilities in emotion recognition contexts. High autistic traits, in contrast, may be related to lower integration of sensorimotor simulations, which promote emotion recognition., (© 2023. The Author(s).)

Many social species, humans included, mimic emotional expressions, with important consequences for social bonding. Although humans increasingly interact via video calls, little is known about the effect of these online interactions on the mimicry of scratching and yawning, and their linkage with trust. The current study investigated whether mimicry and trust are affected by these new communication media. Using participant-confederate dyads ( n = 27), we tested the mimicry of four behaviours across three different conditions: watching a pre-recorded video, online video call, and face-to-face. We measured mimicry of target behaviours frequently observed in emotional situations, yawn and scratch and control behaviours, lip-bite and face-touch. In addition, trust in the confederate was assessed via a trust game. Our study revealed that (i) mimicry and trust did not differ between face-to-face and video calls, but were significantly lower in the pre-recorded condition; and (ii) target behaviours were significantly more mimicked than the control behaviours. This negative relationship can possibly be explained by the negative connotation usually associated with the behaviours included in this study. Overall, this study showed that video calls might provide enough interaction cues for mimicry to occur in our student population and during interactions between strangers. This article is part of a discussion meeting issue 'Face2face: advancing the science of social interaction'.

Physical attractiveness plays a crucial role in mate choice for both men and women. This is reflected in visual attention: people immediately attend towards and look longer at attractive faces, especially when they are motivated to find a partner. However, previous studies did not incorporate real-life dating decisions. Here, we aimed to combine attentional tasks with individual attractiveness ratings and a real-life mate choice context, namely a speed-dating paradigm. We investigated whether heterosexual non-committed young adults showed biases in immediate and voluntary attention towards attractive faces and preferred dating partners. In line with previous research, we found considerable individual differences in individual attractiveness preferences. Furthermore, our results showed that men had a bias towards attractive faces and preferred dating partners in the immediate attention task, while results for women were mixed. In the voluntary attention task, however, both men and women had an attentional bias towards attractive faces and preferred dating partners. Our results suggest that individual attractiveness preferences are good predictors of especially voluntary attention. We discuss these findings from an evolutionary perspective and suggest directions for future research., (© 2023. The Author(s).)

Historically, there has been a great deal of confusion in the literature regarding cross-cultural differences in attitudes towards artificial agents and preferences for their physical appearance. Previous studies have almost exclusively assessed attitudes using self-report measures (i.e., questionnaires). In the present study, we sought to expand our knowledge on the influence of cultural background on explicit and implicit attitudes towards robots and avatars. Using the Negative Attitudes Towards Robots Scale and the Implicit Association Test in a Japanese and Dutch sample, we investigated the effect of culture and robots' body types on explicit and implicit attitudes across two experiments (total n  = 669). Partly overlapping with our hypothesis, we found that Japanese individuals had a more positive explicit attitude towards robots compared to Dutch individuals, but no evidence of such a difference was found at the implicit level. As predicted, the implicit preference towards humans was moderate in both cultural groups, but in contrast to what we expected, neither culture nor robot embodiment influenced this preference. These results suggest that only at the explicit but not implicit level, cultural differences appear in attitudes towards robots., Supplementary Information: The online version contains supplementary material available at 10.1007/s12369-022-00917-7., Competing Interests: Conflict of interestNo potential conflict of interest was reported by the authors., (© The Author(s) 2022.)

Attention may be swiftly and automatically tuned to emotional expressions in social primates, as has been demonstrated in humans, bonobos, and macaques, and with mixed evidence in chimpanzees, where rapid detection of emotional expressions is thought to aid in navigating their social environment. Compared to the other great apes, orangutans are considered semi-solitary, but still form temporary social parties in which sensitivity to others' emotional expressions may be beneficial. The current study investigated whether implicit emotion-biased attention is also present in orangutans ( Pongo pygmaeus ). We trained six orangutans on the dot-probe paradigm: an established paradigm used in comparative studies which measures reaction time in response to a probe replacing emotional and neutral stimuli. Emotional stimuli consisted of scenes depicting conspecifics having sex, playing, grooming, yawning, or displaying aggression. These scenes were contrasted with neutral scenes showing conspecifics with a neutral face and body posture. Using Bayesian mixed modeling, we found no evidence for an overall emotion bias in this species. When looking at emotion categories separately, we also did not find substantial biases. We discuss the absence of an implicit attention bias for emotional expressions in orangutans in relation to the existing primate literature, and the methodological limitations of the task. Furthermore, we reconsider the emotional stimuli used in this study and their biological relevance., Supplementary Information: The online version contains supplementary material available at 10.1007/s42761-022-00158-x., Competing Interests: Competing InterestsThe authors declare no competing interests., (© The Author(s) 2022.)

Previous work has established that humans have an attentional bias towards emotional signals, and there is some evidence that this phenomenon is shared with bonobos, our closest relatives. Although many emotional signals are explicit and overt, implicit cues such as pupil size also contain emotional information for observers. Pupil size can impact social judgment and foster trust and social support, and is automatically mimicked, suggesting a communicative role. While an attentional bias towards more obvious emotional expressions has been shown, it is unclear whether this also extends to a more subtle implicit cue, like changes in pupil size. Therefore, the current study investigated whether attention is biased towards pupils of differing sizes in humans and bonobos. A total of 150 human participants (141 female), with a mean age of 19.13 (ranging from 18 to 32 years old), completed an online dot-probe task. Four female bonobos (6 to 17 years old) completed the dot-probe task presented via a touch screen. We used linear mixed multilevel models to examine the effect of pupil size on reaction times. In humans, our analysis showed a small but significant attentional bias towards dilated pupils compared to intermediate-sized pupils and intermediate-sized pupils when compared to small pupils. Our analysis did not show a significant effect in bonobos. These results suggest that the attentional bias towards emotions in humans can be extended to a subtle unconsciously produced signal, namely changes in pupil size. Due to methodological differences between the two experiments, more research is needed before drawing a conclusion regarding bonobos., Supplementary Information: The online version contains supplementary material available at 10.1007/s42761-022-00146-1., Competing Interests: Conflict of InterestThe authors declare no competing interests., (© The Author(s) 2022.)

People make rapid inferences about others' thoughts and intentions. For example, they observe facial movements and pupil size of others and unwittingly make use of this information when deciding whether to trust someone or not. However, whether spontaneous mimicry depends on visual awareness of the stimulus and whether these processes underlie trust decisions is still unknown. To investigate whether visual awareness modulates the relationship between emotional expressions, mimicry and trust, participants played a series of trust games and saw either their partners' faces with a neutral, happy or fearful expression, or their partners' eyes in which the pupil size was large, medium or small. Subjects' trust investments, facial movements and pupil responses were measured. In half of the trials, the stimuli were rendered invisible by continuous flash suppression. Results showed that facial expressions were mimicked and influenced trust decisions during the conscious condition, but not during the unconscious (suppressed) condition. The opposite was found for pupil size, which influenced trust decisions during states of unawareness. These results suggest that the neurobiological pathway linking the observation of facial expressions to mimicry and trust is predominantly conscious, whereas partner pupil size influences trust primarily when presented unconsciously. This article is part of the theme issue 'Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience'.

External eye appearance across primate species is diverse in shape and colouration, yet we still lack an explanation for the drivers of such diversity. Here we quantify substantial interspecific variation in eye shape and colouration across 77 primate species representing all extant genera of anthropoid primates. We reassess a series of hypotheses aiming to explain ocular variation in horizontal elongation and in colouration across species. Heavier body weight and terrestrial locomotion are associated with elongated eye outlines. Species living closer to the equator present more pigmented conjunctivae, suggesting photoprotective functions. Irises become bluer in species living further away from the equator, adding to existing literature supporting a circadian clock function for bluer irises. These results shift the current focus from communicative, to ecological factors in driving variation in external eye appearance in anthropoid primates. They also highlight the possibility that similar ecological factors contributed to selection for blue eyes in ancestral human populations living in northern latitudes., (© 2022. The Author(s).)

Humans use smiles - widely observed emotional expressions - in a variety of social situations, of which the meaning varies depending on social relationship and the context in which it is displayed. The homologue of the human smile in non-human primates - both due to morphological and functional similarities - is the bared-teeth display (BT). According to the power asymmetry hypothesis (PAH), species with strict linear dominance hierarchies are predicted to produce distinct communicative signals to avoid escalations of social conflicts. Hence, while the BT in a despotic species is predicted to be expressed from low- to high-ranking individuals, signaling submission, the BT in a tolerant species is predicted to be expressed in multiple contexts, regardless of rank. We tested this hypothesis in a group of 8 captive chimpanzees ( Pan troglodytes ), a species commonly characterized as rather despotic. An investigation of 11,774 dyadic social interactions revealed this chimpanzee group to have a linear dominance hierarchy, with moderate steepness. A Bayesian GLMM - used to test the effects of social contexts and rank relationships of dyads on the use of the BT display - indicated multi-contextual use of the BT which is contingent on the rank relationship. We also found that slight morphological and/or acoustic variants (i.e., silent bared-teeth and vocalized bared-teeth) of the BT display may have different communicative meanings. Our findings are in line with the prediction derived from the PAH for a moderately despotic species, and the view that the human smile originated from the primate BT display., Supplementary Information: The online version contains supplementary material available at 10.1007/s42761-022-00138-1., Competing Interests: Conflicts of InterestThe authors declare no competing interests., (© The Author(s) 2022.)

Reading emotions from other people's facial expressions is an important skill that guides social interactions. With limited auditory input and atypical emotion socialization, deaf and hard-of-hearing (DHH) children may develop atypical processing patterns when reading emotional faces. The current study aimed at understanding whether and how DHH and typically hearing (TH) children differed at 3 emotion processing levels: gaze patterns, physiological arousal, and interpretation. Fifty-five DHH children and 72 TH children completed an emotional face matching task in which they were presented with happy, angry, fearful, and emotionally neutral faces. During the task participants' eye gazes and pupil diameter were measured by an eye-tracking device. The DHH and TH children both paid most attention to the eye region when reading emotional faces. Yet, a contrast between happy faces and nonhappy faces was observed in physiological arousal and interpretation tendency in the DHH children only: Nonhappy facial expressions were more arousing and were confused more often than happy expressions, which may reflect the DHH children being less experienced in processing nonhappy expressions due to limited access to the social environment. The results highlighted the importance of looking into the qualitative differences between typical and atypical development. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Facial expressions are key to navigating social group life. The Power Asymmetry Hypothesis of Motivational Emancipation predicts that the type of social organization shapes the meaning of communicative displays in relation to an individual's dominance rank. The bared-teeth (BT) display represents one of the most widely observed communicative signals across primate species. Studies in macaques indicate that the BT display in despotic species is often performed unidirectionally, from low- to high-ranking individuals (signaling submission), whereas the BT display in egalitarian species is usually produced irrespective of dominance (mainly signaling affiliation and appeasement). Despite its widespread presence, research connecting BT displays to the power asymmetry hypothesis outside the Macaca genus remains scarce. To extend this knowledge, we investigated the production of BT in relation to social dominance in dyadic interactions (N = 11,377 events) of 11 captive bonobos (Pan paniscus). Although adult bonobos were more despotic than previously suggested in the literature, BT displays were produced irrespective of dominance rank. Moreover, while adults produced the BT exclusively during socio-sexual interactions, especially during periods of social tension, immature bonobos produced the BT in a wider number of contexts. As such, the results indicate that the communicative meaning of the BT display is consistent with signaling appeasement, especially in periods of social tension. Moreover, the BT display does not seem to signal social status, supporting the prediction for species with a high degree of social tolerance. These results advance our understanding of the origins of communicative signals and their relation to species' social systems., (© 2022 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.)

In their "social contextual view" of emotional mimicry, authors Hess and Fischer (2022) put forward emotional mimicry as a social regulator, considering it a social act, bound to certain affiliative contexts or goals. In this commentary, we argue that the core function of mimicry is to ease predicting conspecifics' behaviours and the environment, and that as a consequence, this often smoothens social interactions. Accordingly, we make three main points. First, we argue that there is no good reason to believe that the mimicry of negative expressions is fundamentally different than the mimicry of positive or ambiguous or autonomic expressions. Second, we give examples of empirical evidence that mimicry is not always a social act. Third, we show that mimicry has primary benefits for the mimicker. As such, we will briefly summarise and elaborate on the relevant findings in these respects, and propose a comparative, multi-method and ecologically valid approach which can explain the multifaceted character of the phenomenon.

In a series of three studies, we examined whether third-party observers can detect attraction in others based on subtle nonverbal cues. We employed video segments of dates collected from a speed-dating experiment, in which daters went on a brief (approx. 4 min) blind-date and indicated whether they would like to go on another date with their brief interaction partner or not. We asked participants to view these stimuli and indicate whether or not each couple member is attracted to their partner. Our results show that participants could not reliably detect attraction, and this ability was not influenced by the age of the observer, video segment location (beginning or middle of the date), video duration, or general emotion recognition capacity. Contrary to previous research findings, our findings suggest that third-party observers cannot reliably detect attraction in others. However, there was one exception: Recognition rose above chance level when the daters were both interested in their partners compared to when they were not interested., Supplementary Information: The online version contains supplementary material available at 10.1007/s12144-022-02927-0., Competing Interests: Conflict of interestThe authors declare no conflict of interest., (© The Author(s) 2022.)

Do nonhuman animals (henceforth, animals) have emotions, and if so, are these similar to ours? This opinion piece aims to add to the recent debate about this question and provides a critical re-evaluation of what can be concluded about animal and human emotions. Emotions, and their cognitive interpretation, i.e., feelings, serve important survival functions. Emotions, we believe, can exist without feelings and are unconsciously influencing our behavior more than we think, and possibly more so than feelings do. Given that emotions are expressed in body and brain, they can be inferred from these measures. We view feelings primarily as private states, which may be similar across closely related species but remain mostly inaccessible to science. Still, combining data acquired through behavioral observation with data obtained from noninvasive techniques (e.g., eyetracking, thermography, hormonal samples) and from cognitive tasks (e.g., decision-making paradigms, cognitive bias, attentional bias) provides new information about the inner states of animals, and possibly about their feelings as well. Given that many other species show behavioral, neurophysiological, hormonal, and cognitive responses to valenced stimuli equivalent to human responses, it seems logical to speak of animal emotions and sometimes even of animal feelings. At the very least, the contemporary multi-method approach allows us to get closer than ever before. We conclude with recommendations on how the field should move forward., Competing Interests: Conflict of InterestThe authors declare no competing interests., (© The Author(s) 2022.)

Parent-to-child transmission of information processing biases to threat is a potential causal mechanism in the family aggregation of anxiety symptoms and traits. This study is the first to investigate the link between infants' and parents' attention bias to dynamic threat-relevant (versus happy) emotional expressions. Moreover, the associations between infant attention and anxiety dispositions in infants and parents were explored. Using a cross-sectional design, we tested 211 infants in three age groups: 5-to-7-month-olds (n = 71), 11-to-13-month-olds (n = 73), and 17-to-19-month-olds (n = 67), and 216 parents (153 mothers). Infant and parental dwell times to angry and fearful versus happy facial expressions were measured via eye-tracking. The parents also reported on their anxiety and stress. Ratings of infant temperamental fear and distress were averaged across both parents. Parents and infants tended to show an attention bias for fearful faces with marginally longer dwell times to fearful versus happy faces. Parents dwelled longer on angry versus happy faces, whereas infants showed an avoidant pattern with longer dwell times to happy versus angry expressions. There was a significant positive association between infant and parent attention to emotional expressions. Parental anxiety dispositions were not related to their own or their infant's attention bias. No significant link emerged between infants' temperament and attention bias. We conclude that an association between parental and infant attention may already be evident in the early years of life, whereas a link between anxiety dispositions and attention biases may not hold in community samples., (© 2021. The Author(s).)

Humans are social animals whose well-being is shaped by the ability to attract and connect with one another, often through brief interactions. In addition to physical features, a choreography of movements, physical reactions and subtle expressions may help promote attraction. Here, we measured the physiological dynamics between pairs of participants during real-life dating interactions outside the laboratory. Participants wore eye-tracking glasses with embedded cameras and devices to measure physiological signals including heart rate and skin conductance. We found that overt signals such as smiles, laughter, eye gaze or the mimicry of those signals were not significantly associated with attraction. Instead, attraction was predicted by synchrony in heart rate and skin conductance between partners, which are covert, unconscious and difficult to regulate. Our findings suggest that interacting partners' attraction increases and decreases as their subconscious arousal levels rise and fall in synchrony., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Affective states are expressed in an individual's physical appearance, ranging from facial expressions and body postures, to indicators of physiological arousal (e.g., a blush). Confirming the claimed communicative function of these markers, humans are capable of distinguishing between a variety of discrete emotion displays. In an attempt to explain the underlying mechanism, characteristic bodily changes within the observer, including physiological arousal and mimicry, have been suggested to facilitate the interpretation of an expression. The current study aims to create a holistic picture of emotion perception by (1) using three different sources of emotional information (prototypical facial expressions, bodily expressions, and subtle facial cues) and (2) measuring changes in multiple physiological signals (facial electromyography, skin conductance level, skin temperature, and pupil size). While participants clearly discriminated between perceived emotional expressions, there was no overall 1-1 correspondence with their physiological responses. Some specific but robust effects were observed. Angry facial expressions were consistently responded to with a peak in skin conductance level. Furthermore, sad body expressions were associated with a drop in skin temperature. In addition to being the best recognized expression, viewing happy faces elicited congruent facial muscle responses, which supports the potential role of embodied simulation in emotion recognition. Lastly, tears were not only rated as highly emotional intense but also evoked a peak in skin conductance level in the observer. The absence of distinct physiological responses to other expressions could be explained by the lacking functionality of affect sharing in a non-interactive experimental context. Consequentially, emotional alignment in body and mind might especially take place in real social situations, which should be considered in future research., Supplementary Information: The online version contains supplementary material available at 10.1007/s42761-021-00083-5., Competing Interests: Conflict of interestThe authors declare no conflict of interest., (© The Society for Affective Science 2022.)

Considerable variation exists in the contagiousness of yawning, and numerous studies have been conducted to investigate the proximate mechanisms involved in this response. Yet, findings within the psychological literature are mixed, with many studies conducted on relatively small and homogeneous samples. Here, we aimed to replicate and extend upon research suggesting a negative relationship between psychopathic traits and yawn contagion in community samples. In the largest study of contagious yawning to date (N = 458), which included both university students and community members from across 50 nationalities, participants completed an online study in which they self-reported on their yawn contagion to a video stimulus and completed four measures of psychopathy: the primary and secondary psychopathy scales from the Levenson Self-Report Psychopathy Scale (LSRPS), the psychopathy construct from the Dirty Dozen, and the Psychopathic Personality Traits Scale (PPTS). Results support previous findings in that participants that yawned contagiously tended to score lower on the combined and primary measures of psychopathy. That said, tiredness was the strongest predictor across all models. These findings align with functional accounts of spontaneous and contagious yawning and a generalized impairment in overall patterns of behavioral contagion and biobehavioral synchrony among people high in psychopathic traits., (© 2021. The Author(s).)

Observing others' emotions triggers physiological arousal in infants as well as in adults, reflected in dilated pupil sizes. This study is the first to examine parents' and infants' pupil responses to dynamic negative emotional facial expressions. Moreover, the links between pupil responses and negative emotional dispositions were explored among infants and parents. Infants' and one of their parent's pupil responses to negative versus neutral faces were measured via eye tracking in 222 infants (5- to 7-month-olds, n = 77, 11- to 13-month-olds, n = 78, and 17- to 19-month-olds, n = 67) and 229 parents. One parent contributed to the pupil data, whereas both parents were invited to fill in questionnaires on their own and their infant's negative emotional dispositions. Infants did not differentially respond to negative expressions, while parents showed stronger pupil responses to negative versus neutral expressions. There was a positive association between infants' and their parent's mean pupil responses and significant links between mothers' and fathers' stress levels and their infants' pupil responses. We conclude that a direct association between pupil responses in parents and offspring is observable already in infancy in typical development. Stress in parents is related to their infants' pupillary arousal to negative emotions., (© 2021 The Authors. Developmental Psychobiology published by Wiley Periodicals LLC.)

Human adult laughter is characterized by vocal bursts produced predominantly during exhalation, yet apes laugh while exhaling and inhaling. The current study investigated our hypothesis that laughter of human infants changes from laughter similar to that of apes to increasingly resemble that of human adults over early development. We further hypothesized that the more laughter is produced on the exhale, the more positively it is perceived. To test these predictions, novice ( n = 102) and expert (phonetician, n = 15) listeners judged the extent to which human infant laughter ( n = 44) was produced during inhalation or exhalation, and the extent to which they found the laughs pleasant and contagious. Support was found for both hypotheses, which were further confirmed in two pre-registered replication studies. Likely through social learning and the anatomical development of the vocal production system, infants' initial ape-like laughter transforms into laughter similar to that of adult humans over the course of ontogeny.

A consistent finding in the literature is that men overperceive sexual interest in women (i.e., sexual overperception bias). Several potential mechanisms have been proposed for this bias, including projecting one's own interest onto a given partner, sexual desire, and self-rated attractiveness. Here, we examined the influence of these factors in attraction detection accuracy during speed-dates. Sixty-seven participants (34 women) split in four groups went on a total of 10 speed-dates with all opposite-sex members of their group, resulting in 277 dates. The results showed that attraction detection accuracy was reliably predicted by projection of own interest in combination with participant sex. Specifically, men were more accurate than women in detecting attraction when they were not interested in their partner compared to when they were interested. These results are discussed in the wider context of arousal influencing detection of partner attraction., (© 2021. The Author(s).)

Objectives: For children to understand the emotional behavior of others, the first two steps involve emotion encoding and emotion interpreting, according to the Social Information Processing model. Access to daily social interactions is prerequisite to a child acquiring these skills, and barriers to communication such as hearing loss impede this access. Therefore, it could be challenging for children with hearing loss to develop these two skills. The present study aimed to understand the effect of prelingual hearing loss on children's emotion understanding, by examining how they encode and interpret nonverbal emotional cues in dynamic social situations., Design: Sixty deaf or hard-of-hearing (DHH) children and 71 typically hearing (TH) children (3-10 years old, mean age 6.2 years, 54% girls) watched videos of prototypical social interactions between a target person and an interaction partner. At the end of each video, the target person did not face the camera, rendering their facial expressions out of view to participants. Afterward, participants were asked to interpret the emotion they thought the target person felt at the end of the video. As participants watched the videos, their encoding patterns were examined by an eye tracker, which measured the amount of time participants spent looking at the target person's head and body and at the interaction partner's head and body. These regions were preselected for analyses because they had been found to provide cues for interpreting people's emotions and intentions., Results: When encoding emotional cues, both the DHH and TH children spent more time looking at the head of the target person and at the head of the interaction partner than they spent looking at the body or actions of either person. Yet, compared with the TH children, the DHH children looked at the target person's head for a shorter time (b = -0.03, p = 0.030), and at the target person's body (b = 0.04, p = 0.006) and at the interaction partner's head (b = 0.03, p = 0.048) for a longer time. The DHH children were also less accurate when interpreting emotions than their TH peers (b = -0.13, p = 0.005), and their lower scores were associated with their distinctive encoding pattern., Conclusions: The findings suggest that children with limited auditory access to the social environment tend to collect visually observable information to compensate for ambiguous emotional cues in social situations. These children may have developed this strategy to support their daily communication. Yet, to fully benefit from such a strategy, these children may need extra support for gaining better social-emotional knowledge., Competing Interests: This work was supported by The Royal Netherlands Academy of Arts and Sciences under Grant 530-5CDP17; the Taiwan Ministry of Education under Grant GSSA1071007013. No potential conflict of interest was reported by the authors., (Copyright © 2020 The Authors. Ear & Hearing is published on behalf of the American Auditory Society, by Wolters Kluwer Health, Inc.)

Correctly recognizing and efficiently attending to emotional situations are highly valuable skills for social species such as humans and bonobos, humans' closest living relatives. In the current study, we investigated whether humans perceive a range of emotional situations differently when these involved other humans compared to bonobos. A large group of children and adults participated in an emotion perception task and rated scenes showing either bonobos or humans in situations depicting distressed or aggressive behavior, yawning, scratching, grooming, playing, sex scenes or neutral situations. A new group of people performed a dot-probe task to assess attentional biases toward these materials. The main finding is that humans perceive emotional scenes showing people similarly as emotional scenes of bonobos, a result reflecting a shared evolutionary origin of emotional expressions. Other results show that children interpreted bonobos' bared teeth displays as a positive signal. This signal is related to the human smile, but is frequently seen in distressed situations, as was the case in the current experiment. Children may still need to learn to use contextual cues when judging an ambiguous expression as positive or negative. Further, the sex scenes were rated very positively, especially by male participants. Even though they rated these more positively than women, their attention was captured similarly, surpassing all other emotion categories. Finally, humans' attention was captured more by human yawns than by bonobo yawns, which may be related to the highly contagious nature of yawns, especially when shown by close others. The current research adds to earlier work showing morphological, behavioral and genetic parallels between humans and bonobos by showing that their emotional expressions have a common origin too.

While new regulations obligate or recommend people to wear medical masks at public places to prevent further spread of the Covid-19 virus, there are still open questions as to what face coverage does to social emotional communication. Previous research on the effects of wearing veils or face-covering niqabs showed that covering of the mouth led to the attribution of negative emotions and to the perception of less intense positive emotions. The current study compares a sample from the Netherlands with a sample from the United Arab Emirates on their perception of emotions from faces covered by a niqab, censoring black bars, or uncovered faces. The results show that covering the mouth area leads to greater anxiety in participants in both countries. Furthermore, although participants did not report greater decoding difficulties for faces that were covered as compared to fully visible, results show that face coverage did influence emotion perception. Specifically, happiness and anger were perceived as being less intense. Further, face coverage by a niqab, as compared to black bars, yielded lower emotional intensity ratings. We conclude that face coverage in particular can modulate the perception of emotions, but that affective contextual cues may play a role as well., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Kret, Maitner and Fischer.)

Recognising conspecifics' emotional expressions is important for nonhuman primates to navigate their physical and social environment. We address two possible mechanisms underlying emotion recognition: emotional contagion, the automatic matching of the observer's emotions to the emotional state of the observed individual, and cognitive empathy, the ability to understand the meaning and cause of emotional expressions while maintaining a distinction between own and others' emotions. We review experimental research in nonhuman primates to gain insight into the evolution of emotion recognition. Importantly, we focus on how emotional contagion and cognitive empathy can be studied experimentally. Evidence for aspects of cognitive empathy in different nonhuman primate lineages suggests that a wider range of primates than commonly assumed can infer emotional meaning from emotional expressions. Possibly, analogous rather than homologous evolution underlies emotion recognition. However, conclusions regarding its exact evolutionary course require more research in different modalities and species., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Yawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood. Scholars have suggested a link between contagious yawning (CY) and sociality due to its appearance in mostly social species. Nevertheless, as findings are inconsistent, CY's function and evolution remains heavily debated. One way to understand the evolution of CY is by studying it in hominids. Although CY has been found in chimpanzees and bonobos, but is absent in gorillas, data on orangutans are missing despite them being the least social hominid. Orangutans are thus interesting for understanding CY's phylogeny. Here, we experimentally tested whether orangutans yawn contagiously in response to videos of conspecifics yawning. Furthermore, we investigated whether CY was affected by familiarity with the yawning individual (i.e. a familiar or unfamiliar conspecific and a 3D orangutan avatar). In 700 trials across 8 individuals, we found that orangutans are more likely to yawn in response to yawn videos compared to control videos of conspecifics, but not to yawn videos of the avatar. Interestingly, CY occurred regardless of whether a conspecific was familiar or unfamiliar. We conclude that CY was likely already present in the last common ancestor of humans and great apes, though more converging evidence is needed.

Cooperation is pivotal for society to flourish. To foster cooperation, humans express and read intentions via explicit signals and subtle reflections of arousal visible in the face. Evidence is accumulating that humans synchronize these nonverbal expressions and the physiological mechanisms underlying them, potentially influencing cooperation. The current study is designed to verify this putative linkage between synchrony and cooperation. To that end, 152 participants played the Prisoner's Dilemma game in a dyadic interaction setting, sometimes facing each other and sometimes not. Results showed that synchrony in both heart rate and skin conductance level emerged during face-to-face contact. However, only synchrony in skin conductance levels predicted cooperative success of dyads. Crucially, this positive linkage was strengthened when participants could see each other. These findings show the strong relationship between our bodily responses and social behavior, and emphasize the importance of studying social processes between rather than within individuals in real-life interactions.