The measurement of eye movements has proven to be a powerful tool for the study of the components of complex visuo-motor behaviors. As described above, we have developed a computational theory to describe aspects of the task, including visual search and saccade targetting. At this point the evidence suggests that parietal cortex is involved in selection of targets in goal-directed behavior such a saccade targetting, so we were anxious to get evidence of the neural basis of the proposed computational structures. Consequently we are examining the behavior of patients with localized parietal lesions on our block-copying task. Tests done by Merigan and Shimosaki show that patients who pass standard neuropsychological tests may show up as very abnormal on our eye-movement tasks. Although the task can be performed by the subject, eye movement monitoring reveals unusual eye movement patterns which we speculate might reflect difficulties in saccade targeting. We also extended the testing of patients with parietal lobe lesions to a spatial memory task developed within the resource by post-doctoral stu-dent Greg Zelinski. Patients with parietal lobe lesions appear unable to use the spatial location information that is provided immediately prior to the search task. Control experiments indicate that this inability is not due to any deficits in object recognition, general memory, or the ability to locate named objects. Rather, it appears to be a defect specific to the processing of visual-spatial information.
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