Binocular Disparity and the Perception of Depth Physiological Computation of Binocular Disparity the Correspondence Problem Disparity Attraction and Repulsion Binocular Receptive Field Models and Characteristic Disparity Motion-stereo Integration Pulfrich Depth Illusions

Binocular Disparity and the Perception of Depth 1 We perceive the world in three-dimensions even though the input to our visual system, the images projected onto our two retinas, has only two spatial dimensions. How is this accomplished? It is well known that the visual system is able to infer the third dimension, depth, from a variety of visual cues present in the retinal images. One such cue is binocular disparity, the positional diierence between the two retinal projections of a given point in space (Fig. 1). This positional diierence results from the fact that the two eyes are laterally separated and therefore see the world from two slightly diierent vantage points. The idea that retinal disparity contributes critically to depth perception derives from the invention of the stereoscope by Wheatstone in the 19th century, with which he showed conclusively that the brain uses horizontal disparity to estimate the relative depths of objects in the world with respect to the xation point, a process known as stereoscopic depth perception or stereopsis. Because simple geometry provides relative depth given retinal disparity , the problem of understanding stereo vision reduces to the question: How does the brain measure disparity from the two retinal images in the rst place? Since Wheatstone's discovery, students of vision science have used psychophysical, physiological , and computational methods to unravel the brain's mechanisms of disparity computation. In 1960, Julez made the important contribution that stereo vision does not require monocular depth cues such as shading and perspective (see Julesz (1971)). This was demonstrated through his invention of random dot stereograms. A typical stereogram consists of two images of randomly distributed dots that are identical in all aspects except that a central square region of one image is shifted horizontally by a small distance with respect to the other image (see Fig. 6a for an example). When each image is viewed individually, it appears as nothing more than a at eld of random dots. However, when the two images are viewed dichoptically (i.e., the left and right images are presented to the left and right eyes respectively at the same time) the shifted central square region \jumps" out vividly at a diierent depth. This nding demonstrates that the brain can compute binocular disparity without much help from other visual modalities. The rst direct evidence of disparity coding in the brain was obtained in the late 1960s, when Pettigrew …