The Interaction of Stereopsis and Perspective in the Perception of Depth

Abstract

When only stereoscopic information is available, the slant of a single isolated surface around a vertical axis is often greatly underestimated. If two small objects (probes), separated horizontally by several degrees, are displayed in front of such a surface, the depth of the probes is perceived relative to the perceived slant of the background surface, leading to systematic misperception of the point of subjective equality (PSE) of the distances of the probes from the observer (Mitchison and Westheimer, 1984 Vision Research24 1063 – 1073; Gillam et al, 1993 Perception22 Supplement, 35). In the present study we found that when we added global perspective information to the background surface, thus increasing its perceived slant, this substantially improved the PSE of the probes. Alternatively, when we added frontal stereoscopic surfaces above and below the background surface, thus providing gradients of disparity discontinuities across the surface boundaries, this also produced an improvement in the perceived slant of the background surface, but produced an even greater improvement in the PSE of the probes. These results imply that the local stereoscopic information specifying the depth of each probe relative to the background surface is integrated with the perceived slant of the background surface, whether specified by global stereoscopic information or by global perspective information, to determine the relative depth of the probes. This integration of local stereoscopic information with global slant information appears to be more complete, however, when the global information is provided by stereopsis rather than by perspective.