Page 31 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms
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                                Emotional attention is modulated by familiarity
Introduction
Emotional expressions are a major force in navigating the social world; they provide
valuable insights into the emotional states of others and help to predict others’ 2 behaviors (Cosmides & Tooby, 2000). The expression of emotions is not uniquely
human and is shared with other animals (Darwin, 1872; Zych & Gogolla, 2021). Yet, we
still understand little about how animals perceive and understand others’ emotions
(Nieuwburg et al., 2021; Paul & Mendl, 2018). Here, taking a comparative perspective
will be crucial in elucidating how socio-emotional capacities evolved over time, in
ancestral humans as well as other animals. One way to move forward is to compare the
emotional processing capacities of humans with those of closely related species.
Within the primate order, bonobos (Pan paniscus) are humans’ closest living relatives, together with chimpanzees (Pan troglodytes). Compared to chimpanzees and other apes, bonobos have strongly developed emotional pathways in the brain (Issa et al., 2019; Stimpson et al., 2016). Behaviorally, bonobos are more tolerant of others and show reduced aggression (Furuichi, 2011; Gruber & Clay, 2016; Hare et al., 2012; Tan & Hare, 2017; Tokuyama et al., 2021). Because of their xenophilic tendencies, bonobos form an interesting comparison species for gaining evolutionary insights into humans’ emotional capacities (Gruber & Clay, 2016; Kret et al., 2016; Stimpson et al., 2016). We currently have limited knowledge about how bonobos perceive emotional expressions, and this is a pressing issue given that they are an endangered species (Fruth et al., 2016). Scientific progress is further hampered by bonobos being rare in zoos and sanctuaries (the worldwide zoo-managed population consists of only 225 individuals, managed by the EAZA in Europe and the SPP in the US; Stevens, 2020). Thus, to elucidate the socio-emotional capacities of our shared common ancestor, more comparative studies are needed that include bonobos. We make a step in this direction by investigating selective visual attention for emotions in a comparative framework including bonobos and humans. Specifically, we test whether the identity of the expressor (i.e., a familiar or unfamiliar conspecific) modulates early attention for emotions.
Expressions of emotions facilitate the communication of emotions and intentions between individuals, and are therefore integral to social animals (Prochazkova & Kret, 2017; Zych & Gogolla, 2021). The importance of emotional expressions is reflected in the fact that, over evolutionary time, selective pressures gave rise to brains that are able to quickly attend to and understand emotional expressions (LeDoux, 1998). Research in humans has demonstrated that already during the earliest stages of
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