Search asymmetries for threatening faces in chimpanzees (Pan troglodytes)

For primates, the ability to efficiently detect threatening faces is highly adaptive; however, it is not clear exactly how faces are detected. This study investigated whether chimpanzees show search asymmetries for conspecific threatening faces featuring scream and bared teeth expressions. Five adult female chimpanzees participated in a series of touchscreen matching-to-sample visual search tasks. In Experiment 1, search advantages for scream versus neutral targets and scream versus bared teeth targets were found. A serial search strategy indicated greater difficulty in disengaging attention from scream versus neutral distractors. In Experiments 2a and 2b, search advantages for scream versus neutral targets remained when the mouth was darkened, suggesting that the brightness contrast of the mouth was not critical for the efficient detection of scream targets. In Experiments 3a and 3b, search advantages for inverted scream versus neutral targets disappeared, indicating configural processing. Together, exclusion of the brightness contrast of the mouth as a low-level perceptual confound, and evidence of configural processing, suggested the scream faces may have been perceived as threatening. However, the search advantage for scream faces is most likely explained by the presence of teeth, independently of threat. The study provides further support that an attentional bias toward threatening faces is a homologous trait, which can be traced back to at least the last common ancestor of Old World monkeys and apes. (PsycInfo Database Record (c) 2022 APA, all rights reserved).