Manual, blowing, and verbal simple reactions to lateralized flashes of light in commissurotomized patients.

Abstract

Interhemispheric transfer of information was examined in two complete commissurotomy patients with the simple reaction-time paradigm. The patients had to produce a finger, blowing, or verbal response to a light appearing in either the right or the left visual field, and a control subject was tested in exactly the same conditions. The three subjects displayed qualitatively similar patterns of results overall. The finger task yielded a highly significant interaction between visual field and responding hand, and the reaction-time difference between the ipsilateral and contralateral responses was of the order of 30 and 50 msec for each patient, respectively, suggesting that subcortical transfer of information is highly inefficient in the manual task as compared with a callosal route. By contrast, the blowing and the verbal tasks resulted in no visual-field difference, even though the latter require the specialized mechanisms of the left hemisphere for speech production. The results suggest that, before being organized within the left hemisphere, a verbal response may be initiated in subcortical structures to which both hemispheres have equally efficient access.