Dependence of reaction time on visual fields in patients with unilateral hemispheric lesions.

Reaction times (RTs) to light stimuli which appeared at central and lateral positions were measured in 13 normal subjects and 34 patients with unilateral lesions in the left or the right hemisphere. The normal subjects showed slowing of RTs to both lateral stimuli compared to the central stimulus, the extent of which was equal between the left and right hands. The patients with left hemispheric lesions had slower RTs to the stimulus contralaterally to the lesion than ipsilaterally and centrally. The patients with right hemispheric lesions had slower RTs both to the contralateral and central stimuli than to the ipsilateral. The results are discussed in relation to functional differentiation of the left and right hemispheres for visual processing.