Innate sensitivity to face-to-face biological motion

Sensitivity to face-to-face stimuli configurations, which likely indicates interaction, seems to appear early in infants' development, and recently a preference for face-to-face (vs. other spatial configurations) has been shown to occur in macaque monkeys. It is unknown, however, whether such a preference is acquired through experience or as an evolutionary-given biological predisposition. Here, we exploited a precocial social animal, the domestic chick, as a model system to address this question. Visually naive chicks were tested for their spontaneous preferences for face-to-face vs. back-to-back hen dyads of point-light displays depicting biological motion. We found that female chicks have a spontaneous preference for the facing interactive configuration. Males showed no preference, as expected due to the well-known low social motivation of males in this highly polygynous species. These findings support the idea of an innate and sex-dependent predisposition toward social and interacting stimuli in a vertebrate brain such as that of chicks.