From retinal images to perceived shapes

Vision is based on spatial correspondences between physically different structures - in environment, retina, brain, and perception. We first examine the correspondence between environmental surfaces and their retinal images, and show that this consists of two-dimensional second-order differential structure associated with local surface shape, suggesting that this might be a primitive form of spatial information. Next, experiments on hyperacuities for detecting relative motion and binocular disparity among separated image features found that spatial positions are visually specified by the surrounding optical pattern rather than by retinal coordinates, minimally affected by random image perturbations produced by 3D object motions. The primitive spatial information represented at the retina, therefore, involves the differential structure associated with local surface shape.