Further evidence for focal effect of right hemisphere damage on simple reaction time

Changes of simple visual reaction time were analyzed in two groups of unilateral brain damaged patients in order to evaluate to what extent intrahemispheric localization of lesions affects performance. Possible interactions with size were avoided by selecting a localization criterion, i.e. the median section of lesion, uncorrelated with size of damage. By preliminarly establishing that the distribution of lesions in our hemispheric groups did not differ, we were enabled to confirm that intrahemispheric localization of damage has a different bearing on performance depending on side of lesion. In the right hemisphere group slower performances were generally associated with frontal damage whereas in the left hemisphere group localization did not influence the performance. The use of independent indexes for size and locus of lesion proved the existence of an interaction between these parameters in the right hemisphere group.