Abstract

The effects of differences in contrast between test and reference stimuli on stereopsis were investigated. Stereoscopic stimuli that were limited in their spatial-frequency composition were presented on a single video monitor and were viewed through synchronized liquid-crystal shutters. The test stimulus was presented in the middle of the screen with reference stimuli above and below. Binocular disparity of the test stimulus was produced by programmable delay of the horizontal sweep for the video image of one eye. The first experiment measured stereoscopic thresholds for test and reference stimuli with identical spatial-frequency composition but with variable contrast. In agreement with previous reports, stereo thresholds decreased as contrast was increased. In a second experiment, the contrast of the test stimulus was fixed, and the contrast of the reference varied from zero to twice the contrast of the test. Stereo thresholds decreased until the contrast of the reference equalled that of the test, and then they became constant. In a third experiment, the binocular disparity of the reference stimuli was varied. Stereo thresholds decreased with contrast in the same way as in the first two experiments. Our results emphasize the dependence of stereoscopic vision on contrast for stimuli on or off the horopter.

© 1990 Optical Society of America