Abstract
Concepts of objects as enduring and complete across space and time rely on perceptual filling-in of gaps imposed by occlusion. Rudimentary object concepts have been documented in infants within several months after birth, but little is known how such concepts arise. We examined development of existence constancy by presenting 4- and 6-month-old infants with a display consisting of a ball moving back and forth, the center of its trajectory occluded by a box (the experimental condition). We recorded eye movements with a corneal reflection eye tracker. We reasoned that a representation of the continuity of the object across occlusion would be revealed by a consistent pattern of anticipatory eye movements. We tested a second group of 4- and 6-month-olds in a training condition; these infants were first exposed to an unoccluded trajectory for 2 minutes prior to viewing the occluded-trajectory display. As expected, 6-month-olds in the experimental condition produced reliably more anticipations than did the 4-month-olds, implying a more robust representation of the object under occlusion. We found also that there were no age differences in anticipation in the training condition, and that 4-month-olds who received training produced a similar proportion of anticipations in response to the occlusion display relative to 6-month-olds in the experimental condition. Simple oculomotor maturation between 4 and 6 months, therefore, is unlikely to be responsible for the improvement in performance from training in the younger infants. In sum, 2 minutes of training with a moving, unoccluded object leads to knowledge of continuity across occlusion in 4-month-old infants. Older infants received no additional benefit from training, implying a more complete object representation prior to testing. These results suggest a strong role for learning in acquisition of initial object concepts and perceptual filling-in.