Page 51 - Emotions through the eyes of our closest living relatives- Exploring attentional and behavioral mechanisms

Emotional attention is modulated by familiarity
while a dot-probe study with bonobos found an attentional bias for emotional
scenes (Kret et al., 2016), other studies found that isolated facial expressions can also
modulate attention in apes (Laméris et al., 2022; Pritsch et al., 2017). As such, we
did not expect the discrepancy between the bonobo stimuli and human stimuli to 2 significantly impact outcomes of both experiments.
Stimuli consisted of pictures of the face showing either an emotional (angry, fearful, happy, sad) or neutral expression presented against a neutral background, similar to the expressions depicted in Figure 5. Each stimulus showed either a familiar companion (a family member, a close friend, or a colleague), or an unfamiliar individual (a companion of a previous, unfamiliar participant). For practical reasons, we only used four out of the six basic emotions (Ekman, 1999), as the task would become undesirably long given that our participants were voluntarily taking part in our study. Pictures were sized 400x300 pixels.
Each participant completed 40 trials. In 20 trials, the probe appeared behind an emotional stimulus, and in the other 20 trials it appeared behind a neutral stimulus. For each of these 20 trials, 10 trials depicted a familiar individual, and 10 trials an unfamiliar individual. Since we only had eight unique photos of a familiar other as well as eight unique photos of a stranger, we repeated two stimulus pairs within each condition to reach the maximum of 40 trials. The number of stimuli per emotional category was counter-balanced across participants (including the repetitions), and stimulus combinations (emotional plus neutral) were presented in a semi-randomized order. A total of 4040 pictures were split into three sets and rated on intensity, emotionality (whether a stimulus depicts an emotional or neutral expression), and authenticity by 18 university graduates and PhD candidates, and on average there was good agreement (ICCintensity = .80, ICCemotion = .80, and ICCauthenticity = .68, see Tables S10.1 and S10.2).
Procedure
Visitors passing by the bonobo enclosure with at least one other person were approached by test leaders. Visitors were told about the ongoing research with the bonobos, and were asked if they wanted to perform in a similar task. If they wanted to participate, the experimenter decided which participant was going to perform the dot-probe task (‘dot-probe participant’) and who was going to be on the photos that subsequently served as stimulus material (‘photo participant’). Individuals could only participate in the study once (and either as dot-probe or photo participant). After reading the information sheet and signing a consent form, photos were made
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