Page 90 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Chapter 4
et al., 2013; Pinsk et al., 2009; Tsao et al., 2008). Great apes are known to automatically mimic facial expressions of others (Davila-Ross et al., 2008; Laméris et al., 2020; Palagi et al., 2019b; Van Berlo et al., 2020b), which is often linked to emotion contagion, or the convergence of emotional experiences (Pérez‐Manrique & Gomila, 2022) (also see (Adriaense et al., 2020) for a critical review). Furthermore, great apes console conspecifics in distress (Clay et al., 2018). Work on physiological determinants of emotion perception indicates that in chimpanzees (Pan troglodytes), seeing or hearing conspecifics fight creates changes in cortisol level, heart rate variability, skin temperature (Dezecache et al., 2017; Kano et al., 2016), and temperature in the inner ear (Parr & Hopkins, 2000). Finally, there is some evidence that great apes can discriminate between emotional faces of conspecifics (Buttelmann et al., 2009; Parr, 2001), and that memory is enhanced for emotional stimuli (Kano et al., 2008). This converging evidence, therefore, suggests that great apes share our sensitivity to emotional cues.
Some work has looked into the continuity of emotional expressions and their perception and recognition across different species. All mammals likely share homologous brain structures underlying emotional networks (Panksepp, 2011), and already over a century ago, Darwin theorized that expressions of emotions are universally shared among certain animals. Indeed, within the primate lineage, there is some overlap between human expressions of emotions and that of other primates (Kret et al., 2020). Moreover, one study showed that orangutans (Pongo pygmaeus) and human children looked longer at fearful human expressions, and the silent bared-teeth display of orangutans (Pritsch et al., 2017). These results suggests that emotional faces that carry a similar meaning in the two species (i.e., fear) are relevant enough to attend to. While this work is promising, it is clear that more research is needed to understand the phylogenetic continuity of emotional expressions and their perception across species. There is still a great deal to explore in terms of the mechanisms underlying emotion perception in great apes, and specifically, very little work has examined the attentional processes underlying emotion perception in these animals.
Two studies looking into implicit attention using a dot-probe paradigm found that bonobos attend faster to emotionally-laden scenes of others compared to neutral scenes (Kret et al., 2016), and especially of unfamiliar conspecifics (Van Berlo et al., 2020a). This effect has not been found in chimpanzees (Kret et al., 2018; Wilson & Tomonaga, 2018), but it is not yet clear whether methodological considerations (e.g., ecological validity of stimuli (Kret et al., 2018), or stimulus presentation duration
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