Page 91 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotions hold the attention of bonobos and humans
(Wilson & Tomonaga, 2018)) contributed to the null-results. Moreover, two recent
studies showed that in apes, emotional cues such as the play face (Laméris et al., 2022)
or snakes and food items (Hopper et al., 2021a) impact reaction time on an emotional
Stroop task. Finally, eye-tracking studies with chimpanzees and orangutans revealed
spontaneous gazing at negatively valenced emotional signals (Kano & Tomonaga,
2010a; Pritsch et al., 2017). Combined, these findings suggest that like in humans,
apes’ attention is tuned to emotionally salient information. However, different methodologies may tap into different attentional processes (with e.g., Stroop tasks
measuring interference in attention, and dot-probes and eye-tracking likely measuring
bottom-up or top-down attention), and few studies have directly compared how
humans and great apes view emotional expressions or emotionally salient scenes.
The aim of the current study is to further examine how apes, specifically bonobos, 4 compare to humans in their allocation of attention to emotionally valent stimuli using
eye-tracking. Compared to other apes, bonobos show marked differences in brain areas involved in social cognition, with a higher degree of connectivity and volume in the amygdala (regulating emotions, attention, memory, and social decision-making) and subgenual anterior cingulate cortex (regulating positive affect and arousal) (Issa et al., 2019; Stimpson et al., 2016). This makes them an interesting referential model to reconstruct the evolution of emotional capacities (Gruber & Clay, 2016). At the same time, bonobos are underrepresented in socio-cognitive studies due to their rarity and zoos and their endangered conservation status (Fruth et al., 2016). As such, bonobos’ unique socio-emotional characteristics warrant a closer look at how this species perceives emotions.
To this end, we used a preferential looking paradigm with eye-tracking to investigate whether attention of bonobos (experiment 1) and humans (experiment 2) is preferentially sustained to emotionally-laden scenes of conspecifics or heterospecifics (i.e., the other species). Previous findings show that emotionally salient signals modulate the early stages of processing social signals (Hopper et al., 2021a; Kret et al., 2016; Laméris et al., 2022; Van Berlo et al., 2020a). Building on this, we expect that if emotions hold relevance to bonobos beyond an initial attentional bias, they will show a longer looking duration to emotional compared to neutral scenes, similar to humans. Moreover, we expect that bonobos and humans also attend longer to emotional scenes of heterospecifics, as there is some continuity between emotional expressions of great apes and humans (Kret et al., 2018).
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