Neural responses in the retinotopic representation of the blind spot in the macaque V1 to stimuli for perceptual filling-in

When visual stimuli that cover the entire blind spot are presented monocula rly, the color and brightness of the surrounding field are seen within the blind spot, although it receives no retinal input. Important questions abou t such perceptual filling-in are whether neurons in the visual system repre senting visual field locations within the blind spot are activated when fil ling-in occurs and, if so, what the properties of these neurons are. To add ress these questions, we recorded the activities of single neurons in the p rimary visual cortex (V1) of the awake monkey. We first identified the area of V1 representing the region of the blind spot and then assessed neural r esponses to stationary visual stimuli of various size. We found that there are neurons in layer 4 and deeper laminae, particularly layer 6, that respo nd to large stimuli covering the blind spot which induces perceptual fillin g-in. Most of these neurons had very large binocular receptive fields that extended outside the blind spot. These neurons also preferred relatively la rge stimuli and exhibited color selectivity. These results indicate that wh en a large uniform surface is presented on the blind spot, neurons at the V 1 region representing the blind spot transmit signals essential for filling -in that inform of the presence of a large surface as well as the absence o f smaller stimuli at the blind spot.