Deficits in spatial memory and saccade targeting after left parietal injury

Purpose. Eye movements can provide a sensitive measure of cognitive strategy use (Hayhoe, Ballard, and Pelz, 1995, J Cog Neurosci, 7, 66-80) and spatial memory (Zelinsky, Hayhoe, and Ballard, 1995, Invest Ophth Vis Sci, 36(4), S373). To assess the possible role of the left parietal lobe in spatial vision and memory, the eye movements of a left parietal patient were monitored during the performance of a number of naturalistic visual tasks. Methods. A patient (43 years, male) with a localized left posterior parietal lesion showed no sign of hemineglect, hemianopia, constructional apraxia or simultanagnosia in standard neurological testing. He performed a number of visual spatial tasks while reaction times and eye movements were monitored. In a realistic visual search task, the use of spatial memory in aiding search was assessed by allowing subjects to preview the locations of objects in the search display (Zelinsky, et al.,1995). The patient also ran in a version of a blocks-copying task (Hayhoe, et al., 1995) which required the subject to inspect a partial pattern for errors before copying the rest of the pattern. Results. Both reaction times and eye movements indicate difficulty in performing complex spatial memory tasks. In the visual search task with set sizes larger than one, the distance of the landing point of the first eye movement from the target (end point error) was large for the patient compared to normal subjects. With set sizes equal to one, end point error was nearly identical for the patient and normal subjects, suggesting that the patient did not suffer from a more general targeting deficit. The patient had a greater number of eye movements within each trial, and this was reflected in slower reaction times. In the blocks-copying task the patient again showed difficulty, with more eye movements and slower reaction times. This difficulty was more pronounced during error correction, presumably because correcting errors required retaining more blocks in memory than copying. Conclusions. Results from eye movement data in this patient indicate deficits in spatial memory not apparent in standard neurological testing, suggesting a possible role of the left parietal lobe in spatial memory.