DIRECTIONAL HYPERACUITY IN GANGLION-CELLS OF THE RABBIT RETINA

Biological visual systems can detect positional changes that are finer than these systems' acuity to sine-wave gratings, a property known as hyperacuity. Some systems can even detect changes finer that the phot oreceptor spacing. We report here that rabbit's directionally selectiv e ganglion cells not only detect positional changes in the hyperacuity range, but also discriminate the direction of their motion. Our exper iments show that directional selectivity occurs for edges of light mov ing as little as 1.1 mu m (26'' of visual angle) across the retina. Th is distance corresponds to a hyperacuity, since the acuity to sine-wav e gratings of rabbit's On-Off DS ganglion cells is about 125 mu m (50' ). In addition, this distance is smaller than the minimal spacing betw een rabbit photoreceptors (1.9 mu m or 46''), as estimated from cell-d ensity studies (Young and Vaney, 1991). Such a hyperacuity suggests lo w-noise high-gain signal transmission from photoreceptors to ganglion cells and that directional selectivity can arise in small portions of retinal dendritic processes.