Spatiotemporal continuity, smoothness of motion and object identity in infancy

A preferential looking method served to investigate 4-month-old infants' apprehension of the identity of objects over successive encounters. In Expts 1 and 2, infants were familiarized with events in which objects moved either continuously or discontinuously behind two narrow screens. Subsequent looking times to one- vs. two-object displays provided evidence that infants apprehend object identity in accord with the principle that objects move continuously. In Expts 3 and 4, infants were familiarized with events in which objects moved behind one wide screen with an occlusion time either appropriate or inappropriate to their visible speed. Subsequent looking times to one- vs. two-object displays provided no evidence that infants apprehend object identity in accord with the principle that objects move smoothly. The findings are contrasted with those of studies of infants' search for objects. Continuity may be an early-developing, core principle by which humans individuate objects, but this principle may not guide all early-developing actions on objects.