Conflict between Stereo and Perspective in Resolving the Slant of Cyclopean Trapezoids

Abstract

Cue theory has had a resurgence in recent years as part of modular approaches to vision. Cues often seem to combine according to a weighted linear sum, although interactions may also occur. Conflict studies show that linear perspective and stereo combine to influence slant perception, with perspective weighted surprisingly heavily. We investigated the effect of conflicting linear perspective in reducing stereo slant when perspective is present as a purely cyclopean outline shape, compared with conditions when the shape is also monocularly present. In experiment 1, random line stereograms were generated with cyclopean trapezoids standing out from a background. Their outline convergence either conflicted with or supported a stereo gradient across the surface of the trapezoid. Two stereo slants and two standing disparities were used. In experiment 2, an aperture condition was included with the cyclopean trapezoids behind the surround. There was strong influence of trapezoid direction on perceived slant. This influence was only marginally increased by outlining the trapezoid. These findings demonstrate the effectiveness of cyclopean shape as perspective information. As expected, when the trapezoid was an area seen through an aperture, its direction did not significantly affect stereo slant. We conclude that stereo and perspective cannot be considered as separate modules. In binocular vision, perspective is conveyed stereoscopically.