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Baoxia Liu, Clifton M. Schor; The effect of occlusion on amodal completion and surface slant perception. Journal of Vision 2005;5(8):576. doi: https://doi.org/10.1167/5.8.576.
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© ARVO (1962-2015); The Authors (2016-present)
In natural environments, occlusion of objects occurs because of the unique viewpoint of an observer and the three-dimensional geometry of the scene. When one object partially occludes another, we perceive the visible portions of the occluded object as part of a single object. The perceptual completion of the visible features is called amodal completion (Michotte, Thines, & Grabbe, 1964/1991). In the present study, we investigated the role of occlusion in amodal completion for surface slant estimates based on stereoscopic cues. We used three surfaces composed of random dots. Two large half ellipses with the same slant were aligned vertically and a small elliptical patch was centered between them. Subjects estimated the slant difference between the small central patch and the two large surrounding patches. In the first condition, the three random-dot surface patches were presented unoccluded. In the second condition, a fourth rectangular surface with a center aperture was added to occlude the space between the three random-dot surfaces. Under this condition, the three random-dot patterns were seen as a single partially occluded surface (i.e. amodal completion). The perceived slant difference between the center surface patch and surrounding patches was smaller when an occluder was present in the second condition than in the first unoccluded condition. The effect of amodal completion was independent of the depth and the slant of the occluder when varied independently of the surrounding patches. The results show that slant estimation of the center small surface is biased towards the slant of the outside surfaces and this amodal completion was enhanced by partial occlusion.
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