Disturbances of Stereopsis by Brain Damage

Abstract

It is only 16 years since the publication of the first papers in which it was shown that many binocularly activated single cells in the visual cortex of the cat have receptive fields with different visual directions in the two eyes (2, 27). In other words the receptive fields show disparity, and in such a way that different cells are maximally excited by a stimulus at different distances in front of or behind the plane of fixation and convergence. The discovery was exciting because it seemed to reveal a simple mechanisms by which the animal, without even moving its eyes, could detect the relative distance of different objects. For example, all objects in the fixation plane (more accurately, on the geometrical horopter) have zero retinal disparity, objects at increasing distances have increasing divergent disparity, and those progressively closer than the fixation plane have progressively greater convergent disparity. It is no surprise that the discovery of such cells in the cat provoked a steady stream of papers in which the existence of such cells was shown in a variety of species, in anaesthetised or conscious animals, in different areas of the cerebral cortex, and for several different kinds of disparity involving interocular differences in horizontal or vertical separation, velocity, direction of movement, and orientation of the images.