Page 107 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotions hold the attention of bonobos and humans
positive emotional expressions also occurs (Becker et al., 2011). In a previous study, we found an implicit attentional bias towards stressful scenes in a heterogeneous human population, as well as to scenes involving sex and yawning (Kret & Van Berlo, 2021). Here, we add to the existing literature by showing that emotional scenes also spontaneously hold attention for longer durations in a task without a clear goal to the participants, and even when a competing social, but emotionally-neutral stimulus is present.
Interestingly, the attentional pattern of humans for human emotional scenes
differed from that for bonobo emotional scenes. Humans looked longer at bonobos
engaged in grooming and play compared to neutral scenes, but not at sex or yawning
scenes, even though we found an effect for these two categories within the human
scenes. Furthermore, we found weak evidence that humans looked longer at neutral 4 scenes rather than bonobo distress scenes; the opposite from what we found for
distress scenes of humans. In a previous study, adults rated distress scenes of bonobos
as negative and highly arousing (similar to ratings of distress scenes of chimpanzees
(Kret et al., 2018)), possibly due to canine visibility (Kret & Van Berlo, 2021). In our
study, participants may have looked away from the distress scenes because they
are intense in terms of emotional arousal, but this remains speculative. To date,
very little work has examined how humans view (other) emotional expressions of
primates (see e.g., Kret & Van Berlo (2021); Maréchal et al. (2017)). As such, future
work on attentional biases could benefit from including questionnaires that measure
participants’ interpretation of and feelings towards the stimuli.
Compared to our bonobo sample, humans appear to preferentially sustain attention to emotional scenes across all categories. A possible explanation for this difference is that humans have evolved exceptionally distinctive and exaggerated communicative faces in order to communicate more effectively (Kret et al., 2020), and therefore also have a sensitivity to a wider range of expressions. Nevertheless, alternative explanations, particularly relating to our methodology, must be considered.
We report several limitations to our study. First, we used static images of emotional expressions instead of dynamic scenes. Studies have suggested that the dynamic facial expressions of emotion provide richer information than static expressions, causing stronger activation in brain regions associated with emotion recognition (Arsalidou et al., 2011). Second, we made use of more complex social and emotional scenes rather than isolated facial expressions, potentially providing more contextual information. However, it is possible that by providing this context, we increase the
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