Horizontal disparity gradient with vertical disparity in different depth planes

Abstract

Vertical and horizontal disparities can locally enhance or cancel each other depending on their depth sign (Matthews et al., 2003 Vision Research 43 85–99). The presence of vertical disparities modifies the sensitivity to horizontal disparity gradient in the peripheral visual field, relative to the depth sign of vertical disparity (Devisme et al., 2006 Journal of Vision 6 (6) 656a). In the present experiment, vertical disparities were computed to be always congruent in shape with concentric horizontal disparity gradients applied between 7 and 14 degrees of eccentricity. The stimulus consisted of a sparse random-dot display. The horizontal disparity gradients, crossed or uncrossed, produced respectively concave or convex shapes. However, whereas for horizontal disparities, the central disc (7° radius) of the shape was in the fixation plane, the central disc for vertical disparities could be in front of, behind or in the fixation plane. Horizontal and vertical disparities increased together from their fixation plane disparity, between the two eccentricities. The observers' task consisted in detecting the deformation of the frontoparallel plane. Results highlighted that the modifications of the sensitivity to horizontal disparity gradient, induced by vertical disparities, depended on the depth sign of the vertical disparities relative to both the fixation plane and the depth sign of horizontal disparities. Horizontal disparity allows to perceive the shape, concave or convex, and vertical disparity fixes the depth relative to the fixation plane.