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Anushree Karnik, Barbara Heider, Ralph M. Siegel; Inferior parietal recordings and behavioral effects of shifting prisms on visually guided reaching. Journal of Vision 2007;7(9):294. doi: 10.1167/7.9.294.
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The relationship between motor and visual representations in area 7a and the dorsal prelunate (DP) is explored by perceptually shifting the visual field. The monkey was required to fixate a point at one of nine positions on a touch screen while a visual stimulus (expansion optic flow, diameter 8°) appeared behind the fixation point. This phase of the task was considered ‘perceptual.’ The change from structured to unstructured motion cued the monkey to make a ballistic hand movement towards the target. The monkey held his hand on the touch screen (reach phase). Three dimensional hand position was monitored in some experiments. Neural activity was recorded contralateral to the reaching arm. For neurons with spatial tuning properties, Fresnel prisms with a 10° shift opposite to the preferred location were placed in front of the monkey's eyes. Under this condition, the visual input was distorted whereas the motor output had to be maintained by the monkey; the monkey was required to reach to the physical, not perceived, location of the target. With the prism the animal correctly reached to the target within a few trials, although the kinematics remained affected. The shifting prisms significantly altered the neural representation in areas 7a and DP. The gain field and the reach field tuning thus far appears the same even with the prisms. This is surprising given the sensorimotor mismatch introduced by the prisms. This suggests that in posterior parietal cortex, visual and reach responses might represent separate inputs and do not affect each other.
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