Contributed Article

Previous Inodels £if stereopsis have concentrated on the task of binocularly matching left and right eye primith'es uniquely. A disparity smoothness constraint is often invoked to limit the number of possible matches. These approaches neglect the fact that surface discontinuities are both abundant in natural eve! )'day scenes, and provide a useful cue for scene segmentation. da Vinci stereopsis refers to the more general problern of dealing Ivith surface discontinuities and their associated unmatched monocular regions }vithin binocular scenes. This study develops a mathematical realization of a neural netlvork theory of biological vision, called FACADE theo! )', that sholvs holY early cortical stereopsis processes are related to later cortical processes of three-dimensional surface representation. The mathematical model demonstrates through computer simulation holY the visual cortex Inay generate threedilnensional boundary segmentations and use them to control filling-in of three-dimensional surface properties in response to visual scenes. Model mechanisms correctly match disparate binocular regions while filling-in monocular regions Ivith the correct depth within a binocularly viewed scene. This achievelnent required the introduction of a new multiscale binocular filter for ;\'tereo matching }vhich clarifies holv cortical complex cells match image contours of like contrast polarity, while pooling signals from opposite contrast polarities. The filter also suggests how false binocular matches and unmatched monocular cues are automatically handled across multiple spatial scales. Pooling of signals froln evenand odd-S)'lnmetric simple cells at complex cells helps to eliminate spurious activity peaks in matchable signals. Later stages of cortical processing by the blob and interblob streams, including refined models of cooperative boundary grouping and reciprocal stream interactions betlveen boundary and surface representations, are modeled to provide a complete silnulation of the da Vinci stereopsis percept. @ 1997 Elsevier Science Ltd. All rights reserved. Keywords-Binocular vision, Boundary contour system, da Vinci stereopsis, Depth perception, FACADE theory, Feature contour system, Neur21l network, Stereopsis, Visual cortex. (Brewster, 1856). Until recently, most computational models of this binocular combination process have concentrated on solving the correspondence problem (Marr, 1980). This is the problem of binocularly matching identical regions from each eye's view into a single cyclopean percept. Typical approaches employ a variety of constraints to simplify this problem even further, one example being the uniqueness principle of Marr (1980). However, because the eyes are horizontally displaced within the head and therefore receive different twodimensional images of the world, each eye typically sees regions that are not registered by the other eye. In pursuing the correspondence problem, many researchers have neglected the fact that these unmatched monocular regions are common. For example, when we view a partially occluded surface, one eye typically registers more of the farther surface than the other does. Our percept of the farther surface is derived from an integration of the