No Evidence of Attentional Bias Toward Threatening Conspecific and Allospecific Faces in Capuchin Monkeys (Sapajus [Cebus] apella) Using a Dot-Probe Task

The ability to quickly perceive and interpret threatening facial expressions from others is critical for successfully maintaining group cohesion in social nonhuman primate species. Rapid detection of threatening or negative stimuli in the environment compared to neutral stimuli, referred to as an attentional bias toward threat, is adaptive in that faster threat detection can lead to greater survival outcomes. However, the evolutionary roots of attentional bias formation toward social threat are not well understood. The present study investigated attentional biases toward social threat and the factors associated with them, including underlying hormonal mechanisms, in socially housed capuchin monkeys. Attentional biases were assessed using a dot-probe task that measured capuchins' latency to respond to a target using a joystick after viewing threatening or neutral conspecific or allospecific faces or nonface stimuli. In our first study, we examined how age, dominance status, sex, and cortisol level related to attentional biases. In our second study, we examined how manipulated oxytocin (OT) influenced attentional biases. Capuchin monkeys did not show attentional biases toward threatening faces or objects, but they showed attentional avoidance of scrambled familiar conspecific face stimuli. Cortisol and social rank were associated with attentional bias toward threat in the capuchin monkeys that participated in this study, which suggests that stress and dominance relate to attentional bias toward social threat. Manipulated OT increased attentional avoidance of scrambled familiar and unfamiliar face images, but not unscrambled faces or objects. Overall, we did not find compelling evidence of attentional biases toward social threat in capuchin monkeys.