Page 67 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Attention towards humans’ and bonobos’ emotion
all demographic information. After indicating interest in participating in one of the experiments, participants gave informed consent. The study was approved by the Ethics Committee of Leiden University (CEP17-0213/74 for adults, CEP17-0604/222 for children). All participants were debriefed after the completion of the study.
Table 1. Demographic information of the participants.
Type of task Species on Participants Gender Age
stimulus Female Male Mean SD Min Max 3
Emotion Human Adult 53 47 36.28 15.61
perception
18 75 Child 13 13 8.41 2 5 12
Bonobo
Bonobo keeper Adult Child
9.62 26 50 13.54 18 84 3.05 4 17 13.08 18 74 2.67 3 17 16.13 18 78 51 69 9.28 2.9 4 17
Dot-probe Human Adult Child Bonobo Adult Child
Stimuli
84 68 33.94 69 80 9.36 153 135 37.45
4 1 37.88 201 157 30.5 48 53 9.93
The stimulus materials have been used in two previous studies with bonobo subjects. In the first study, Kret et al. (2016) showed bonobos emotional pictures including sex, grooming, yawning, panthoot, interactions with food, play, and distress (Figure 1). The authors observed that bonobos’ attention was immediately captured by emotional scenes. In a subsequent study, Van Berlo et al. (2021) used all new, but similar stimulus materials. In their study, the scenes showing food and panthoots were dropped as these showed hardly any effect in the first study. In addition, based on behavioral observations that were made during the first study, they decided to include scenes where individuals were self-scratching, which occurs under arousal (Maestripieri et al., 1992). The findings of van Berlo replicated the effect observed in Kret et al. (2016), suggesting that bonobos recognize the emotional expressions of conspecifics and that these are thus readable and distinctive from the neutral scenes.
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