Infants' perception of object unity in translating and rotating displays.

In 3 experiments, the authors examined the sensitivity of infants to the unity of a partly occluded moving rod undergoing translation, rotation, or oscillation. Four-month-old infants were sensitive to the unity of the partly occluded rod when it translated, but not when it rotated, behind an occluder. Six-month-old infants perceived the rotating rod as continuing behind the occluder, but they did not perceive the unity of a rod that oscillated back and forth behind the occluder. Finally, 6-month-old infants showed an ambiguous response to a rotating rod when the shape of the occluder was changed from rectangular to round. These findings suggest that all types of common motion are not equivalent for specifying infants' perceptions of occluded objects. Additional factors should be considered that take into account the information specified by different types of motion and by different conditions at the intersection of the occluder and the object.