Reversal in stereo discrimination by contrast reversal.

ABSTRACT When bars are flashed to appear nearer or farther than the plane of fixation, some observers are unable to localize the bar correctly in depth. For example, with light bars presented against a darker background, convergent disparities may be confused with similar stimuli presented monocularly to only one eye, whereas divergent disparities may be identified correctly. If now the contrast of the bars is reversed, so that they appear dark against a lighter background, then the stereo discrimination will reverse: convergent disparities will be identified correctly, whereas the divergent disparities previously discriminated now will be confused with the monocular stimuli. Such reversals in depth may be the result of interactions between center and surround components of disparity mechanisms.