Facial expressions play a central role in primate social communication, but in cognitive experiments, they are typically presented out of context and directed at the subject. In natural settings, however, primates often see facial expressions as part of social interactions between others. In this study, we investigated how the direction and expressivity of faces affect the social attention of rhesus macaques, Macaca mulatta . We presented 81 semi-freeranging rhesus macaques with still images depicting two male (avatar) conspecifics either facing each other (suggesting a third-party social interaction) or facing away (suggesting no interaction), and with either neutral or expressive faces (a threat and a silent bared-teeth display). We measured total looking time and the number of gaze shifts between the faces. Macaques looked significantly longer at expressive faces in interactions compared with neutral, noninteracting faces. Gaze shifts did not differ between conditions, but there was a trend towards greater frequency for expressive trials. These results, based on male avatars, suggested that the expressivity and the social context of a face impact how much attention it receives, highlighted the importance of context in primate facial expression processing and the adaptive significance of third-party observation in primates. • Faces embedded in social interaction draw more attention than noninteracting faces. • Expressivity and social context of a face impact how much attention it receives. • Third-party facial expressions can provide adaptive social information.
O’Callaghan et al. (Thu,) studied this question.