Interocularly unpaired zones escape local binocular matching

When a closer surface partially occludes a more distant surface, there exist image zones adjacent to the occluding edge on the rear surface which are visible to one eye and not the other. These half-occluded or interocularly unpaired zones do not carry explicit disparity information, yet their depth is perceived as a stable and continuous extension of the rear surface. Moreover, such zones escape binocular rivalry. In addition to these properties, we now report another special characteristic of this unpaired zone in comparison to normally paired regions. An unpaired probe dot added here escapes non-unique local Panum matching which would otherwise bestow it with a depth outside the surface. Thus paradoxically, depth of the probe is most stable in the unpaired zone. This finding indicates that what is considered to be one of the most fundamental processes for binocular depth perception, namely local matching, is subject to more global surface occlusion constraints.