Page 105 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotions hold the attention of bonobos and humans
Conclusion
In general, humans attended longer to emotional scenes compared to neutral scenes. This general emotion bias was also present for scenes of bonobos, although it was less pronounced. Humans tended to look longer at all types of emotional scenes involving humans, although evidence for a bias towards yawning was not robust.
Discussion
Emotions and their perception in non-human animals are intriguing, yet elusive
(Anderson & Adolphs, 2014). To progress our understanding of when and how the 4 brain evolved to efficiently process emotionally salient cues, we set out to study
attention for emotions in our closest relatives, bonobos, and in humans. We found
that both species preferentially attended to conspecific over heterospecific emotional
scenes. Moreover, attention appeared to be strongly tuned to conspecifics in distress.
Furthermore, bonobos showed an (albeit weak) attentional bias towards sex stimuli,
while humans tended to look longer at emotional scenes across all categories. Below,
we first discuss the findings in experiment 1, followed by a comparison between the
results of humans (experiment 2) and bonobos.
In the first experiment, we partially confirmed our expectation that bonobos preferentially look at emotional scenes over neutral scenes of other bonobos and humans. Seeing distressed others can be a very salient cue, for instance, because detecting potential social or environmental threats can be crucial to survival (Öhman et al., 2001a). Similarly, in bonobos, socio-sexual interactions play a major role in preserving stability in the group (for instance to ameliorate tension) (Genty et al., 2015), and sexual stimuli may therefore receive enhanced attention. Bonobos showed no pronounced attention bias towards playful, grooming, or yawning scenes. These results are somewhat surprising, as a previous study found an implicit attentional bias towards scenes depicting yawning and grooming (in addition to sexual scenes) (Kret et al., 2016), and one study found that playful scenes interfered with bonobos’ attention in an emotional Stroop task (Laméris et al., 2022). However, this could be explained by the results capturing different attentional processes, with reaction time paradigms possibly tapping into bottom-up attention, and eye-tracking paradigms having the potential to also measure top-down attention
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