A common mechanism for illusory and occluded object completion.

Abstract

New phenomena and results are reported that implicate a common contour interpolation mechanism in illusory and occluded (modal and amodal) object completion.In 3 experiments, a speeded classification task was used to study novel quasimodal displays in which occluded and illusory contours join.Results showed the same advantages in speed and accuracy over control displays for quasimodal, illusory, and occluded displays.The implications of quasimodal displays, along with another new display type in which contour linkages must precede determination of modal or amodal appearance, are considered.These logical considerations and empirical results suggest that amodal and modal completion depend on a common underlying mechanism that connects edges across gaps.A number of visual phenomena share the property that boundaries and shape are perceived in locations where no local information is present.These gaps in the projected boundaries and surfaces of objects often go unnoticed because of visual completion processes that deliver representations of complete boundaries, whole objects, and continuous surfaces.Some examples are partly occluded objects, illusory objects, some cases of apparent transparency, and spontaneously splitting objects (SSOs).For the central figure seen in each example in Figure 1, the four displays are equivalent in terms of the contours and gaps given in the stimulus.These visual phenomena have often been considered to be manifestations of different processes.Michotte, Thines, and Crabbe (1964), emphasizing differences in their phenomenology, divided completion processes into two types.Objects that are completed modally have a sensory presence in the areas that lack local specification.In the illusory figure in Figure Ib, for example, one can note the apparent lightness of the completed surface or answer a question about whether that surface has a small blue spot on it.(It does not.)In cases of amodal completion, one perceives or registers unspecified parts of objects, but these do not have a sensory presence.In Figure la, the black parts are perceived as connecting behind the occluder, but this connection is hidden.