Page 55 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotional attention is modulated by familiarity
General discussion
Emotional expressions are pivotal to understanding the internal state of others and
predicting their future behavior, and as such, receive privileged access to attention 2 (Adolphs, 2008; LeDoux, 1998; Öhman et al., 2001b). Crucially, emotions can arise
in social situations involving close others, yet are rarely studied in this context. In
this study we investigated the potential link between emotional attention and
familiarity with the expressor in two closely related species: humans and bonobos.
In Experiment 1, attention of bonobos appeared to be attuned to emotional scenes
depicting unfamiliar others, but not to emotional scenes depicting familiar others. This
emotion bias did not extend to emotional facial expressions of familiar and unfamiliar
humans (Experiment 2). For our zoo-visitor sample in Experiment 3, we found that
emotional expressions of familiar companions (family, friends, or colleagues), but not
unfamiliar others, grab attention. Below we discuss these results within a comparative
framework, and consider the study’s limitations.
Humans and bonobos seem to share an immediate bias for emotional scenes and expressions (Kret et al., 2016; Kret & Van Berlo, 2021) and we here show that this bias is modulated by familiarity. At least for bonobos, this modulation occurs only when viewing conspecifics, not humans. Interestingly, studies with chimpanzees (Kret et al., 2018; Wilson & Tomonaga, 2018) and our own study with orangutans (Pongo pygmaeus) (Laméris et al., 2021, under review) did not find a general bias for emotions using the dot-probe paradigm. No data exist on gorillas (Gorilla gorilla). It is possible that, compared to other apes, bonobos are more sensitive to emotions of conspecifics, evidenced by their strongly connected brain pathways involved in emotion processing (Issa et al., 2019; Stimpson et al., 2016). However, three dot-probe studies involving monkeys did find an attentional bias towards threatening faces of conspecifics (King et al., 2012; Lacreuse et al., 2013; Parr et al., 2013). Moreover, looking time paradigms have shown that, chimpanzees, orangutans, and rhesus macaques (Macaca mulatta) looked longer to (negative) emotional expressions than to neutral expressions (Bethell et al., 2012; Howarth et al., 2021; Kano & Tomonaga, 2010a; Pritsch et al., 2017). Overall, these findings suggest that an attentional bias towards emotional signals is shared at least within the primate order (and potentially also in other animals, although results are mixed (Kremer et al., 2021; Lee et al., 2018; Luo et al., 2019)).
The brain is proficient at distinguishing between faces of familiar, socially close others and strangers, evidenced by the prioritized and highly optimized processing of
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