PERCEPTION OF PARTLY OCCLUDED OBJECTS BY YOUNG CHICKS

Completion of partly occluded objects is a ubiquitous phenomenon in hu man visual perception. It is unclear, however, whether it occurs at al l in other species: Studies on visual discrimination learning have rev ealed that animals usually attend to parts and features of the discrim inative stimuli rather than to global object properties. We provide he re the first demonstration of recognition of partly occluded objects i n a bird species, the domestic chick Gallus gallus, using the naturali stic setting made available by filial imprinting, a process whereby yo ung birds form attachments to their mothers or some artificial substit ute. In Experiment 1, newborn chicks were reared singly with a red car dboard triangle, to which they rapidly imprinted and therefore treated as a social partner. On Day 3 of life, the chicks were presented with pairs of objects composed of either isolated fragments or occluded pa rts of the imprinting stimulus. Chicks consistently chose to associate with complete or with partly occluded ver sions of the imprinting obj ect rather than with separate fragments of it. Similarly, in Experimen t 2, chicks reared with a partly occluded triangle chose to associate with a complete triangle rather than with a fragmented one, whereas ch icks reared with a fragmented triangle chose to associate with a fragm ented triangle and not with a complete one. Newborn chicks thus appear to behave as if they could experience amodal completion.