Page 33 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotional attention is modulated by familiarity
al., 2008). Likely, the environments that both species evolved in contributed to how
they interact with others. For bonobos, intergroup tolerance may have resulted
from specific ecological conditions, as they live and evolved in a demarcated area
in the Democratic Republic of the Congo. Here, reduced feeding competition and 2 environmental stability lead to the formation of stable social parties that prevent
extreme territorial encounters with other groups (Hare et al., 2012; Wrangham, 1999). The picture for human evolution is different: ancestral humans migrated great distances across the globe as a result of the extraordinarily volatile climate that caused scarcities in resources for substantial periods of time. This paved the way for intergroup conflicts among our hunter-gatherer ancestors (Ember & Ember, 1992). In turn, these aggressive interactions have fostered a strong focus on the in-group (e.g., family and friends) on the one hand, and xenophobia on the other (Bowles, 2009). Therefore, although humans and bonobos are both highly social animals, their different other-regarding tendencies warrant a closer look at how the two species process emotions of family, friends, and strangers. Specifically, we ask how familiarity impacts early attentional mechanisms that help distinguish between emotionally relevant signals from group members or other, unfamiliar individuals.
To make inter-species comparisons of selective attention for emotions possible, the emotional dot-probe paradigm has been proven useful (MacLeod et al., 1986; Van Rooijen et al., 2017). In the task, individuals have to press a central dot, followed by a short presentation of an emotional and a neutral stimulus. Another dot (the probe) then replaces either the emotional or neutral stimulus. Individuals are generally faster at tapping the probe that replaces the stimulus that biased their attention towards it (usually the emotional stimulus) compared to a probe replacing the other stimulus (the neutral stimulus. See e.g., Belopolsky et al., 2011; Koster et al., 2004 for in-depth discussions on the dot-probe and attentional capture or disengagement). As such, the emotional dot-probe task provides an easy way to tap into the underlying attentional mechanisms that guide emotion perception.
In the current study, we investigate how bonobos and humans attend to expressions of emotion of familiar and unfamiliar individuals. Here, we define familiarity by the social and familial relationship between the observer and the expressor of emotions on the one hand, and unfamiliar others on the other. Further, there is an ongoing debate on the definition of emotions and their expressions (Adolphs et al., 2019; Crivelli & Fridlund, 2018; James, 1884; LeDoux, 2021; Russell & Barrett, 1999; Waller et al., 2020). We here define emotions as adaptive brain states that produce a range of behavioral patterns (expressions) (De Waal, 2011).
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