Occlusion junctions do not improve stereoacuity

Occlusion geometry gives rise to interocular shifts in the positions of binocularly viewed contour junctions. Since these shifts do not give rise to normal binocular disparities, they have been called 'pseudodisparities'. Previous work has shown that the unmatched contour segments of a partially occluded contour at occlusion junctions can be used to recover the geometry of the occluding surface through the construction of 'illusory' contours. Here, experiments were performed to determine whether such junction shifts could enhance stereoscopic depth detection when the relative disparity between the contours was below threshold. Our results showed that stereoscopic depth detection does not improve when pseudodisparity is present. We conclude that the visual system is less sensitive to pseudodisparity than to conventional disparity information. We suggest that the primary role of pseudodisparity is to overcome conditions of camouflage.