UBC Theses and Dissertations
Completion of occluded objects in early vision : an exploration of spatial limits Shore, David I.
Our visual experience is of complete objects despite the fact that the retina is often given only partial views of these objects. Objective support for this perceptual completion of partly occluded objects was generated in Experiment 1 in which same-different response time (RT) was measured for objects that were either complete, partly occluded, or notched. Complete and partly occluded objects yielded similar RTs, while notched objects took much longer to match. For larger amounts of overlap the occluded condition took longer than the whole condition. This suggested that rapid completion is limited to relatively small gap sizes. In Experiment 2, we varied the amount of occlusion systematically in order to find the limit of rapid completion. With 25%object occlusion or less, we again found evidence for rapid completion; beyond this point subjects appeared to use a strategy that was similar to that used in the notch condition. The separability of completion from other cognitive processes was investigated using two strategies. First, in Experiment 3 the task demands were varied from an identification task to a categorization task. Similar spatial limitations were found for both of these tasks. Second, in Experiment 4 the target was a moving object and it was again found that completion was separable from other later processes such that moving targets were easier to complete but no easier to classify. These results support the proposal of a preattentive completion process that is spatially limited.
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