What is it about?
Detecting social and emotional signals helps us to quickly estimate others' feelings and intentions. In humans, previous work has shown that already at the early stages of processing the immediate environment, attentional priority is given to emotional signals over neutral signals. To date, however, this attention bias for emotions has mainly been studied using pictures of unfamiliar others. How is this biased influenced by seeing familiar people that are close to us? Furthermore, previous research has shown that an attention bias for emotions is likely shared with some other animals, particularly other primates like bonobos. How do bonobos attend to emotional pictures of familiar group mates and strangers? Bonobos are one of our closest living relatives and are known for their relatively high tolerance toward strangers. They have been observed sharing food with bonobos from other groups and adopting their infants. As humans, we can also empathize with strangers, but at the same time, we can also be highly intolerant of them. In this study, we aimed to study whether these other-regarding tendencies in bonobos and humans affect early attention to emotions. Specifically, we presented bonobos and humans with emotional and neutral pictures of familiar individuals (e.g., family members, friends, other group mates) and strangers and measured which pictures caught their attention. We currently do fully understand what kind of emotions are important to bonobos, and therefore we used pictures of bonobos engaged in certain behaviors that we know are important to them and that may underly a positive or negative emotional state. As positive signals, we used pictures of bonobos engaged in sex, grooming, and play. As negative signals, we used self-scratching and yawning, because these behaviors are often seen when individuals are stressed. For humans, we know that emotional faces capture attention and therefore used facial expressions of happiness, sadness, anger, and fear. To test whether attention to emotions is affected by familiarity, we used a dot-probe task. In this task, participants saw two pictures side by side for a very brief duration (only 300 milliseconds): one emotional and one neutral picture. Furthermore, these pictures were of either familiar individuals or strangers. After the pictures disappeared, a dot was shown in one of the two locations. Participants had to touch this dot as soon as it appeared, and here we measured their response time. The idea behind this task is that participants are faster at touching dots that appear behind a picture that caught their initial attention. We found that for bonobos, emotional pictures of strangers capture attention faster than neutral pictures of those same individuals. For humans, we found the reverse: attention was drawn to emotional pictures of familiar others rather than neutral pictures. A possible explanation for this difference is that bonobos evolved in a relatively stable environment with less competition over resources, reducing the need for intergroup aggression and therefore enabling bonobos to socialize with strangers. On the other hand, humans had to adapt to various, sometimes arduous environments, increasing competition over valuable resources and therefore also increasing the need to protect the “in-group” (e.g., family, friends) against others. Nevertheless, it should be noted we did not directly test how emotional pictures of familiar and unfamiliar others compete for attention when they are presented together. Therefore, we need more studies looking into how emotional attention is affected by familiarity with the expressor(s) of these emotions.
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Why is it important?
As far as we know, this is the first study examining how attention toward emotions is affected by seeing close others and strangers taking a comparative approach. In a world in which inequality, discrimination, intolerance, and war are still ubiquitous, we need to continue to improve our understanding of why these phenomena are so difficult to abolish. Some of these behaviors may have deep evolutionary roots and we think that a comparative and evolutionary perspective can complement research on how we perceive others. Here, bonobos are an interesting model species due to their more xenophilic tendencies, which can also occur in humans. By learning about what drives intolerance on the one hand and empathy on the other, we can eventually find ways to effectively induce positive and long-lasting behavioral changes. Of course, for this to happen, much more work is needed. Furthermore, in comparison to literature on humans, the work on attention toward emotions in non-human animals is extremely limited. Although the field of animal affective science is growing, we still know so little about how other animals experience their (social) world. It is important we continue to minimize this knowledge gap so that we can better understand the evolutionary history of social cognition across different animal species. Furthermore, as animals often play an important role in our daily lives, understanding their (emotional) experiences is crucial in order for us to take good care of them.
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This page is a summary of: Attention toward emotions is modulated by familiarity with the expressor: A comparison between bonobos and humans., Emotion, January 2023, American Psychological Association (APA), DOI: 10.1037/emo0000882.
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Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions
In social animals, the fast detection of group members’ emotional expressions promotes swift and adequate responses, which is crucial for the maintenance of social bonds and ultimately for group survival. The dot-probe task is a well-established paradigm in psychology, measuring emotional attention through reaction times. Humans tend to be biased toward emotional images, especially when the emotion is of a threatening nature. Bonobos have rich, social emotional lives and are known for their soft and friendly character. In the present study, we investigated (i) whether bonobos, similar to humans, have an attentional bias toward emotional scenes compared with conspecifics showing a neutral expression, and (ii) which emotional behaviors attract their attention the most. As predicted, results consistently showed that bonobos’ attention was biased toward the location of the emotional versus neutral scene. Interestingly, their attention was grabbed most by images showing conspecifics such as sexual behavior, yawning, or grooming, and not as much—as is often observed in humans—by signs of distress or aggression. The results suggest that protective and affiliative behaviors are pivotal in bonobo society and therefore attract immediate attention in this species.
Attentional Bias in Humans Toward Human and Bonobo Expressions of Emotion
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.
No Evidence for Biased Attention Towards Emotional Scenes in Bornean Orangutans (Pongo pygmaeus)
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.
Emotion processing across and within species: A comparison between humans (Homo sapiens) and chimpanzees (Pan troglodytes).
For social species, recognizing and adequately yet quickly responding to the emotions of others is crucial for their survival. The current study investigates attentional biases toward emotions in two closely related species, humans and chimpanzees. Prior research has demonstrated that humans typically show an attentional bias toward emotions. We here build on that literature by studying the underlying unconscious mechanisms within and across humans and chimpanzees and aim to gain insight into the evolutionary continuity of expressions. Experiment 1 tested whether chimpanzees show an attentional bias toward the expressions of conspecifics and whether this putative bias is modulated by the stimulus presentation duration, being 33 ms or 300 ms. The stimuli were followed by a visual mask in the form of a neutral body image. This backward-masking procedure eliminated the visibility of the stimuli that were presented for 33 ms, rendering their presentation subliminal. In contrast to our prediction, no attentional bias toward emotions was observed in chimpanzees. The goal of Experiment 2 was to verify this finding and to investigate chimpanzees’ reaction to human stimuli. Replicating Experiment 1, no evidence of an attentional bias toward emotions was observed in chimpanzees. In Experiment 3 we used the same chimpanzee and human expressions in 711 museum visitors and confirmed that humans do have an attentional bias toward emotions. Interestingly, this bias was independent of the stimulus presentation duration and most strikingly, independent of the species that was observed. Implications for theorizing about species differences in attentional mechanisms in processing emotions are discussed, as well as directions for future research, to investigate our preliminary findings and this potential species difference further.
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