Page 181 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

(e.g., covert attention) are recruited but also when emotional scenes are presented for a longer duration (Chapter 4). Bonobos and humans were presented with emotional and neutral scenes of conspecifics and heterospecifics (Figure 1i, a, c). Each emotional and neutral stimulus combination was shown for three seconds, thereby recruiting not only initial, more reflexive attentional mechanisms, but also more voluntarily controlled attention. We found that humans overall showed a more pronounced emotion bias than bonobos, i.e., humans looked longer to emotional scenes of different categories (play, grooming and embracing, sex, distress, and yawning), whereas bonobos only looked longer to scenes of distressed bonobos or bonobos having sex. For both species, distress was the most salient emotional category, holding attention the longest. Moreover, we extended our previous findings (Chapter 2) indicating a lack of attentional bias to human emotional expressions in bonobos. Conversely, humans looked longer at grooming and playing bonobos: two categories also rated most positively in the study of Chapter 3. In general, humans and bonobos appeared to be most sensitive to the emotions of individuals of their own species. Additionally, humans appeared sensitive to the emotions of bonobos, but bonobos not to the emotions of humans.
In Chapter 5, I moved away from attention and focused on another unconscious
process at stake during social interactions: spontaneous mimicry (Figure 1ii).
Specifically, we investigated contagious yawning and self-scratching in relation
to social closeness and context in orangutans: our most distantly related relatives
within the great ape family (Figure 1a-c). Nine orangutans were observed for a
period of four months, and all occurrences of yawning and self-scratching and the
context within which they occurred were recorded. There was only sufficient data
on self-scratching, as yawn occurrences are generally rarer. The results showed that
in orangutans, self-scratching was indeed contagious, and most strongly so during 8 situations where there was tension, and between individuals with a relatively weak
social bond. The novelty of the findings is that this study presents a potential case
of negative emotion contagion, rather than the more typically presented positive
emotion contagion.
In Chapter 6, I reported on an experiment on contagious yawning in orangutans (Figure 1ii). Orangutans were presented with videos of real, unfamiliar orangutans, familiar orangutans (conspecifics that were also housed in Apenheul), and a 3D avatar orangutan (Figure 1a, b). The orangutans in the videos either yawned or showed a neutral expression, allowing us to investigate whether yawns occur more frequently in response to other yawns compared to neutral videos. For the first time,
General discussion
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