Impairments in action and perception after right intraparietal damage.

We examined visually-guided reaching and perception in an individual who underwent resection of a small tumor in right intraparietal sulcus (pIPS). In the first experiment, she reached to targets presented on a touch screen. Vision was occluded from reach onset on half of the trials, whereas on the other half she had vision during the entire reach. For visually-guided reaching, she demonstrated significantly more reach errors for targets left of fixation versus right of fixation. However, there were no hemispatial differences when reaching without vision. Furthermore, her performance was consistent for reaches with either hand, providing evidence that pIPS encodes location based on an eye-centered reference frame. Second, previous studies reported that optic ataxics are more accurate when reaching to remembered versus visible target locations. We repeated the first experiment, adding a five second delay between stimulus presentation and reach initiation. In contrast to prior reports, she was less accurate in delayed versus immediate reaching. Finally, we examined whether a small pIPS resection would disrupt visuospatial processing in a simple perceptual task. We presented two small circles in succession in either the same location or offset at varying distances, and asked whether the two circles were presented in the same or different position. She was significantly more impaired left of fixation compared to right of fixation, providing evidence for a perceptual deficit after a dorsal stream lesion.
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