Direction of motion discrimination after early lesions of striate cortex (V1) of the macaque monkey

Abstract

Previous studies have established that humans and monkeys with damage to striate cortex are able to detect and localize bright targets within the resultant scotoma. Electrophysiological evidence in monkeys suggests that residual vision also might include sensitivity to direction of visual motion. We tested whether macaque monkeys with longstanding lesions of striate cortex (V1), sustained in infancy, could discriminate visual stimuli on the basis of direction of motion. Three monkeys with unilateral striate cortex lesions sustained in infancy were tested 2-5 years postlesion on a direction of motion discrimination task. Each monkey was trained to make saccadic eye movements to a field of moving dots or to withhold such eye movements, depending on the direction of motion in a coherent random dot display. With smaller motion displays, monkeys were unable to detect or discriminate motion within the scotoma, although they could discriminate moving from static stimuli. Yet, each monkey was able to discriminate direction of motion when the motion stimulus was larger, but still confined to the scotoma. The results demonstrate that the recovery after infant damage to striate cortex includes some sensitivity to direction of visual motion.motion perception ͉ recovery of function ͉ blindsight ͉ saccadic eye movements H umans and monkeys with damage to V1 retain or recover the ability to detect and localize visual targets within the scotoma (1-6). In both species, the vision that survives V1 damage often depends on the mode of testing, typically requiring forced-choice or similar paradigms (6-8), and there is considerable variability in the extent and nature of the residual vision, particularly in humans. One factor that may contribute to the variability in the extent of residual vision observed across subjects with V1 damage is the age at which the lesion is sustained (9). We previously have shown that monkeys with lesions of V1 in infancy demonstrate greater residual vision than their adult-lesion counterparts, as measured by their ability to detect and localize visual stimuli within the scotoma (10). The residual vision after lesions in infancy is robust and does not depend on the type of testing paradigm as it does after adult lesions (11). Other studies in this laboratory have found that many neurons within extrastriate area MT retain their selectivity for the direction of a moving bar in the absence of V1 input (12), suggesting that destriate vision might include some residual motion sensitivity. In the present study, we trained monkeys with longstanding unilateral lesions of V1 on a direction of motion discrimination task and then tested them both inside and outside of the scotoma. Our results indicate that some ability to discriminate direction of motion survives lesions of V1 in monkeys, at least when the damage is sustained early in life. MethodsSubjects. Three female Macaca fascicularis monkeys, weighing between 2 and 5 kg, were used as subjects. Each monkey had received large or total unilateral lesions of stria...

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