Abstract
A moving object is temporarily invisible as it passes behind an occluding surface, but people perceive it as moving continuously behind the occluder, suggesting that the representation of the moving object is amodally maintained during its disappearance. In this study, we investigated whether amodal representation of a moving object can persist when relative surface depths do not favor occlusion, in a situation where an occluding surface has an aperture in it. We manipulated the binocular disparity depth of the surface seen through the aperture in 3D displays, ranging from the depth of the occluder to that of background. In Experiment 1, subjects viewed apparent motion displays of two alternately presented tokens abutting each side of an occluder, and indicated in a yes/no task whether they saw the motion tokens passing behind the surface within the aperture. In Experiment 2, subjects viewed continuous motion displays of a moving object which was invisible as it passed behind an occluder, and indicated whether they saw one object or two. When the surface in the aperture was close in depth to the background, observers were less likely to perceive the motion occluded by this surface, but reported two distinct object motions separated by the aperture. But given sufficient depth difference between the surface in the aperture and the background, they reported occlusion of a moving object by this surface, even though the object was slightly in front of it (so that occlusion of the whole path was geometrically impossible). These findings suggest that the motion signal produced by dynamic occlusion is strong enough that even when surface depths do not support occlusion of an object, the impression of a continuously moving object does not cease, but its amodal representation persists so that the object's disappearance is attributed to occlusion by a more distant surface.
NIH (NEI) EY15888, IGERT (DGE) 0549115.