Page 108 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 4
complexity of the stimuli, therefore making the interpretation of the stimuli more ambiguous (Tottenham et al., 2013). A combination of these two interpretations may explain our bonobo results in that our stimuli may underrepresent the interest bonobos have in emotionally-salient information. Nevertheless, it is important to note that humans do show an emotional bias across all the categories of emotions even with a similarly prepared stimulus set. Moreover, in a follow-up experiment where we zoomed in on facial expressions rather than scenes (as well as investigating effects of expression channels such as face vs. body), an emotional bias was not observed (in prep, (Kim et al., 2021)). At the moment, It is difficult to know how bonobos interpret emotional images and whether emotional scenes are better at providing more salience than isolated faces. Future research could use dynamic emotional cues using videos or a combination of images with sound, as this has previously proved to be successful in uncovering an emotion bias in for instance chimpanzees (Kano & Tomonaga, 2010a).
Another limitation of our study is the small sample size. Moreover, we were only able to test female bonobos. The reason for this is that bonobos are rarely found in zoos and face a high risk of extinction (Fruth et al., 2016), and even fewer are accessible for research purposes. As such, we cannot extrapolate our findings to the entire species. Nevertheless, our results convergence with a small, but growing body of experimental studies indicating that bonobos and other apes are sensitive to the emotional cues of others (Kano et al., 2016; Kret et al., 2016; Laméris et al., 2022; Pritsch et al., 2017; Van Berlo et al., 2020a), and showing that bonobos have remarkably well-developed brain structures that are important for emotion processing (Issa et al., 2019; Stimpson et al., 2016).
Perceiving emotions in others is at the foundation of more complex socio-cognitive abilities such as cooperation and empathy (Levine et al., 2018). Our findings show that bonobos, like humans, voluntarily look longer at emotionally salient signals such as distress and sex. Our findings converge with previous studies, suggesting that the groundwork for higher social cognition is likely shared with our closest living relatives.
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