Amodal representation depends on the object seen before partial occlusion

We demonstrate history-dependent effects in the amodal representation of pa rtially occluded objects. The experience of seeing the fully visible object s before partial occlusion is shown to be influential in the way the object s are represented after occlusion has occurred. Using the method of ambiguo us apparent motion correspondence to probe the extent of amodal continuatio n, bars of variable length were partly occluded by a moving rectangle. Afte r a variable delay period, the part of the bars that remained visible under went an apparent motion sequence. Subjects reported whether the perceived m otion was horizontal or vertical. With a 1-s delay after occlusion, each of the five subjects tested showed a bias favoring motion in the direction of the elongated bars. These results indicate greater amodal continuation in the case of long bars after they have been occluded for an appreciable peri od of time. A control experiment varying the stereoscopic disparity of the occluder ruled out explanations based on two-dimensional effects, reinforci ng the conclusion that the past history has a specific effect on amodal rep resentations. With a delay of 2 s following occlusion, four of six subjects tested showed the history effect, indicating potentially longer durations for the effect, with individual differences in the duration. We conclude th at the amodal representation of an object depends on the object seen before partial occlusion. (C) 1998 Elsevier Science Ltd. All rights reserved.