Biological motion facilitates filial imprinting

Abstract

To study the functional role of the predisposed preference for Johansson's biological motion (BM) at an early stage of life, newly hatched domestic chicks, Gallus gallus domesticus, were exposed to a variety of motion pictures composed of light points (in red or yellow), and then tested for their learned colour preference. Point-light animations depicting the BM of a walking hen successfully facilitated both the approach activity during imprinting and the learned preference in the test, although significant positive correlations did not appear between these at the individual level. Furthermore, scrambling the light points did not significantly reduce the effects, whereas linear motion of a hen-shaped set of points had no effect. If pretreated with the linear motion, those chicks primed with a high BM preference score showed a high learning score in subsequent imprinting. We conclude that the local movement feature of the BM animation is critical in making chicks approach and learn the associated colour. We propose a scenario wherein naive chicks have an innate preference for BM, which arises prior to imprinting through nonspecific visual experience in the early posthatch period. The induced BM preference then allows chicks to form a learned colour preference for the associated colour more effectively, leading to the development of tighter social attachment.