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.

Convergence of the real or virtual stereoscopic cameras is an important operation in stereoscopic display systems. For example, convergence can shift the range of portrayed depth to improve visual comfort; can adjust the disparity of targets to bring them nearer to the screen and reduce accommodation-vergence conflict; or can bring objects of interest into the binocular field-of-view. Although camera convergence is acknowledged as a useful function, there has been considerable debate over the transformation required. It is well known that rotational camera convergence or ‘toe-in’ distorts the images in the two cameras producing patterns of horizontal and vertical disparities that can cause problems with fusion of the stereoscopic imagery. Behaviourally, similar retinal vertical disparity patterns are known to correlate with viewing distance and strongly affect perception of stereoscopic shape and depth. There has been little analysis of the implications of recent findings on vertical disparity processing for the design of stereoscopic camera and display systems. We ask how such distortions caused by camera convergence affect the ability to fuse and perceive stereoscopic images.

Left and right retinal images of an object seen by the 2 eyes can occupy slightly disparate horizontal and/or vertical locations. The role of horizontal disparity (HD) in stereoscopic vision is well established, but the functional contribution of vertical disparity (VD) remains unclear. Various psychophysical studies have shown that HD and VD are used differently by the visual system depending on their location in the visual field, whether near the center of gaze or more peripheral. We show this horizontal/vertical distinction at the cellular level in monkey primary visual cortex (area V1). The range of VD encoding is reduced in central but not in the peripheral representation of the visual field. Moreover, neurons respond selectively to particular combinations of both types of disparities depending on the coded orientation as predicted by the disparity energy model. The preferred orientations of neurons near the fovea present a vertical bias that is well suited for stereopsis based on HD selectivity alone. In the periphery, instead, preferred orientations are radially biased, which allows a peripheral detector to convey the same depth signal based on either HD or VD. Such an organization has functional implications in both the perceptual and oculomotor domains.

In Li and Atick’s [1, 2] theory of efficient stereo coding, the two eyes ’ signals are transformed into uncorrelated binocular summation and difference signals, and gain control is applied to the summation and differencing channels to optimize their sensitivities. In natural vision, the optimal channel sensitivities vary from moment to moment, depending on the strengths of the summation and difference signals; these channels should therefore be separately adaptable, whereby a channel’s sensitivity is reduced following overexposure to adaptation stimuli that selectively stimulate that channel. This predicts a remarkable effect of binocular adaptation on perceived direction of a dichoptic motion stimulus [3]. For this stimulus, the summation and difference signals move in opposite directions, so perceived motion direction (upward or downward) should depend on which of the two