Abstract
The effect of vertical and horizontal disparities can locally enhance or cancel each other as a function of their depth sign (Matthews et al., 2003 Vision Research 43 85–99). Can vertical disparities, suitably computed, minimize the depth effect of horizontal disparity gradient? We have already shown that thresholds of plane deformation detection, either concave or convex, induced by concentric gradient of horizontal disparity depended on disparity gradient and on its location (Devisme et al., 2004 Perception 33 Supplement 93). In this last experiment, we were interested in whether the presence of subthreshold vertical disparities would affect thresholds of deformation detection induced by disparity gradient. The stimulus consisted of a sparse random-dot display (Devisme et al., 2005 Perception 34 Supplement 114). A concentric pattern of vertical disparity gradient was applied on the stimulus between two eccentricities. Vertical disparities were computed to have opposite signs between adjacent quadrants of the visual field. However these vertical disparities had to involve no depth deformation perception. Horizontal disparity gradient, which progressively increased, was added at the same location. The observer's task consisted in detecting the deformation of the frontoparallel plane. Results suggested that the addition of vertical disparity gradient can decrease the sensitivity to horizontal disparity gradient in peripheral visual field. The processing of combined horizontal and vertical disparity gradients of opposite depth sign depend on the location in the visual field: vertical disparities, in concentric variation, seem to be differently processed according to eccentricity.