Existence and implications of a tilted binocular disparity space.

The existence of a tilted binocular disparity space was experimentally established. The results of the experiment showed that a texture surface which under binocular viewing appears to be oriented vertically and perpendicular to the line of sight in fact is tilted such that the portions of the texture surface above and below fixation incline toward and away from the observer, respectively. Under monocular viewing such a discrepancy between apparent and objective vertical tilt is not observed. This suggests that under binocular viewing the cortical representations of the upper and lower visual hemifields are biased toward uncrossed and crossed disparities, respectively. The tilted binocular disparity space is explained in terms of an experientially induced disparity gradient effected during development of the binocular system.