Cortical Dynamics of 3-D Figure-Ground Perception of 2-D Pictures
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This article develops the FACADE theory of 3-D vision and figure-ground separation to explain data concerning how 2-D pictures give rise to 3-D percepts of occluding and occluded objects. These percepts include pop-out of occluding figures and amodal completion of occluded figures in response to line drawings, to Bregman-Kanizsa displays in which the relative contrasts of occluding and occluded surfaces are reversed, to White displays from which either transparent or opaque occlusion percepts can obtain, to Egusa and Kanizsa square displays in which brighter regions look closer, and to Kanizsa stratification displays in which bistable reversals of occluding and occluded surfaces occurs, and in which real contours and illusory contours compete to alter the reversal percept. The model describes how changes in contrast can alter a percept without a change in geometry, and conversely. More generally it shows how geometrical and contrastive properties of a picture can either cooperate or compete when forming the boundaries and surface representations that subserve conscious percepts. Spatially long-range cooperation and spatially short-range competition work together to separate the boundaries of occluding figures from their occluded neighbors. This boundary ownership process is sensitive to image T-junctions at which occluded figures contact occluding figures, but there are no explicit T-junction detectors in the network. Rather, the contextual balance of boundary cooperation and competition strengthens some boundaries while breaking others. These boundaries control the filling-in of color within multiple, depth-sensitive surface respresentations. Feedback between surface and boundary representations strengthens consistent boundaries while inhibiting inconsistent ones. It is suggested how both the boundary and the surface representations of occluded objects may be amodally completed, even while the surface representations of unocclucled objects become visible through modal completion. Distinct functional roles for conscious modal and amodal representations in object recognition, spatial attention, and reaching behaviors are discussed. Model interactions are interpreted in terms of visual, temporal, and parietal cortex. Model concepts provide a mechanistic neural explanation and revision of such Gestalt principles as good continuation, stratification, and non-accidental solution.