The Effect of Frontal and Parietal Lesions on Saccadic Reaction Time

Abstract

The effect of unilateral circumscribed lesions in different areas of the frontal and parietal cortex on the distribution of saccadic reaction times (SRT) is investigated in 32 neurological patients and 17 normal controls. Among frontal patients only those with a lesion in the FEF region showed an increased percentage of express saccades, especially with saccades towards the side ipsilateral to the lesion. This applied to conditions in which fixation was interrupted prior to target appearance (‘gap paradigm’). With fixation point ‘overlap’ express saccades were largely suppressed, as in normals. All patients with a frontal lesion showed a decreased percentage of contralateral anticipatory saccades. In contrast, the percentages of direction and time errors of these patients were in the normal range. Patients with dorsolateral parietal lesions showed decomposed SRT patterns (high SRT variability, increased percentages of time and direction errors, decreased percentages of express and anticipatory saccades). The decomposition had a contralateral preponderance and increased if more than one stimulus was visible beside the saccade target. The findings are compatible with the notion that the frontal cortex is involved in the voluntary control of visually triggered saccades, and that the parietal cortex mainly deals with visual target selection.