HAPTIC PROCESSING BY THE LEFT-HEMISPHERE IN A SPLIT-BRAIN PATIENT

We report the case of a patient who suffered an ischemic accident resu lting in damage to the anterior part of the corpus callosum and to the white matter in the posterior right hemisphere. Recognition of two-di mensional haptic stimuli explored with the right hand was severely imp aired. The deficit was not specific to the type of stimuli, since lett ers, digits and geometrical shapes were not correctly recognized. Poor performance was not due to a specific mode of haptic exploration, sin ce deficits were also observed without active manipulation of the stim uli. In contrast, the patient correctly named visual letters presented in the right visual hemifield (left hemisphere), and recognized three -dimensional common objects palpated with the right hand. Comparable r esults were observed in a surgical split-brain patient tested as a con trol. We conclude that (i) the construction of spatial representations of haptic stimuli, such as two-dimensional stimuli or three-dimension al block letters, cannot be fully realized in the intact left hemisphe re, this ability requiring the contribution of both hemispheres, and ( ii) tests for correct naming of common objects do not provide sufficie nt evidence to establish the integrity of the system involved in the i dentification of haptic information processed by the right hand of spl it-brain patients. (C) 1997 Elsevier Science Ltd.