Effects of stimulus degradation on letter-matching performance of left and right hemispheric stroke patients

Performance on a letter-matching task involving conditions of perceptual degradation was tested on 18 Right CVA patients, 18 Left CVA patients and 18 control subjects. Letter stimuli were presented in three conditions: Clear, Line-Masked, and Blurred. Subjects judged whether two letters of a pair were the same in name or different in name. Right CVA patients performed significantly less accurately than did Left CVA patients and control subjects when letters were perceptually degraded with a line mask overlay or by blurring. No significant differences were found between the two patients groups when the letters were presented without perceptual degradation (the Clear condition), but both patient groups were significantly less accurate than control subjects. The results are similar to findings reported in visual half-field studies with neurologically normal subjects and indicate right-hemisphere superiority for the processing of perceptually degraded visual information.