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.


For a long time, it was taboo to speak about emotions in non-human animals (hereafter: animals), but fortunately, new work comes out every day showing that capacities once solely ascribed to humans are shared with other animals. With the advancement of technologies such as touchscreens, eye-tracking, and non-invasive devices to measure physiological responses, we are now at an age where we can gain unique insights into the minds of animals. In this publication, we take a step in this direction by zooming in on attention, because attention can function as a proxy for what is interesting to our non-human participants. Furthermore, by focusing on emotions in bonobos and comparing their psychology to humans, I hope we can learn more about what drives empathy and intolerance towards individuals that are not immediately part of our “in-group” (like family, friends, and colleagues). Finally, with our results, I hope to contribute to the growing field of animal affective science from the perspective of the bonobo: one of the four remaining great-apes (the others being chimpanzees, gorillas, and orangutans) that give us a glimpse into our evolutionary past. It is difficult to directly study emotions and social cognition in our extinct human cousins. Therefore, bonobos and their other great-ape counterparts are the closest living links we have to our past. Moreover, understanding how they experience the world will help us to accommodate great apes living in zoos and sanctuaries and to protect them in the wild. I feel a high sense of urgency to learn what we can from these beautiful animals because great apes – like so many animals – are critically endangered and our environments are rapidly changing due to climate change. In my opinion, we must cherish the opportunities we have to study them for as long as this remains possible.

Evy van Berlo
University of Amsterdam

Read the Original

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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