Page 65 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Attention towards humans’ and bonobos’ emotion
related stimuli than to neutral stimuli and this effect was stronger in children with high anxiety, a difference that further increased with age (Dudeney et al., 2015).
In typical emotion perception tasks it is impossible to pull apart effects of emotion
as an isolated construct from effects of emotions expressed by a specific species.
The latter is commonly assumed, but whether effects are specific to the emotional
expressions of other humans can only be investigated by directly comparing biases
toward emotional expressions of other species. On the one hand, one could argue
that it is easier to embody the emotional expressions from conspecifics than from 3 other species with very different bodies. On the other hand, as Darwin (1872) already
noted, the similarities in the expression of emotion across species are high and may
render the former argument trivial. An earlier preliminary study gives some insight
into this question (Kret et al., 2018). In the study, participants performed a dot-probe
task with threatening or neutral expressions expressed only by adult male humans and
chimpanzees. The results showed a significant bias toward threat, but no interaction
between threat and species; suggesting that processing emotional expressions may
not rely on the species of the expressor. This finding further supports the evolutionary
argument.
An alternative explanation is that attentional capture from threat is also functional: humans benefit from quickly detecting and responding to threatening stimuli irrespective of whether it is displayed from a human or chimpanzee. Nevertheless, whether the same principle holds for positive expressions remains uncertain. Positive emotions, child or female models were not included so the generalizability of the findings is uncertain. For instance, humans would likely perceive expressions of sexual arousal as more relevant or interesting when expressed by a human compared to a chimpanzee. In contrast, the image of two playing apes expressing joy might attract human attention. Indeed, it is common in zoos for apes to end up tangled in a play of tag or peek-a-boo with human children. In the current study, we aim to disentangle the effect of sender species on emotional attentional biases. To that extent, the bonobo provides an excellent model. Not only is it our closest living relative (together with the chimpanzee we shared a common ancestor that lived roughly 6 million years ago) and shows very similar musculature of the face and body (Diogo, 2018), it also is a very rare species that people do not get to see often. There are only two zoos in the Netherlands that house a group of bonobos, so except for frequent visitors of these zoos, people in general have had few or no learning experiences with these animals.
An important factor that might account for discrepancies in attentional biases toward emotions is individual differences, such as age and gender. As humans age,
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