We measured the ability to fuse dichoptic images of a horizontal line alone or in the presence of a textured background with different vertical disparity. Nonius-line measurements of vertical vergence were also obtained. Diplopia thresholds and vertical vergence gains were much higher in response to an isolated vertically disparate line than to one with a zero vertical-disparity background. The effect of the background was maximum when it was coplanar with the target and decreased with increasing relative horizontal disparity. We conclude that vertical disparities are integrated over a restricted range of horizontal disparities to drive vertical vergence. 2000 Elsevier Science Ltd. All rights reserved.

With normal binocular vision, maximal stereoacuity requires an extended viewing duration, but the relationship between the critical viewing duration for stereopsis and other variables affecting stereoacuity is unknown. The purposes of the study were to investigate the properties of normal temporal integration for stereoscopic vision with respect to the effects of contrast and spatial frequency of the stimuli and to determine whether the temporal summation of disparity is affected in deficient stereopsis caused by abnormal binocular vision during infancy. Psychophysical methods were used to measure stereothresholds in human and monkey subjects with either normal binocular vision or abnormal binocular vision. The results showed that the critical viewing duration for stereoscopic depth discrimination was independent of variations in basic stimulus parameters and/or the subjectÕs stereoacuity. A critical duration of approximately 100 ms was found for both local (narrowband Gabor and broadband line targets) and global (dynamic random dots) stimuli. Although stereothresholds increased with decreasing stimulus contrast, the properties of temporal integration did not. Stereothresholds were substantially elevated for monkeys and humans with abnormal binocular vision, but the critical durations for these subjects were not significantly different from those of subjects with normal binocular vision. Overall, the results demonstrate that the general properties of temporal integration for stereopsis are similar to other detection and discrimination tasks that do not require binocular processing. In addition, increased integration time does not account for the elevated stereothresholds of subjects with abnormal binocular vision.