ABSTRACT
Abstract
The left cerebral hemisphere provides the neural substrate for language in hearing-speaking individuals. The underlying basis of the specialization of the left hemisphere for language, however, has not been clearly understood. The study of sign languages of deaf individuals provides a unique opportunity for investigating brain function for language, because sign language displays complex linguistic structures by manipulating spatial relations. It, thus, exhibits properties for which each of the hemispheres of hearing individuals shows a differing specialization. Understanding brain organization for sign languages is allowing us to uncover basic principles underlying hemispheric specialization.
We have been investigating the language, visual-spatial, and motor abilities of profoundly deaf signers who have acquired lesions of either the left or the right cerebral hemisphere. Remarkably, the signers with right hemisphere lesions were not aphasic for sign language. This preserved signing stood in the face of marked deficits the right-hemisphere damaged signers showed in processing nonlanguage spatial relations. In contrast, the signers with left-hemisphere damage showed frank sign language aphasias (and relatively preserved nonlanguage spatial functions). Importantly, the sign language impairments were not uniform, but rather cleaved along lines of linguistically relevant components. Taken together, the data indicate that the left hemisphere has an innate predisposition for language. 146Furthermore, the underlying basis of the specialization of the left hemisphere for language seems related to linguistic functions and the processing operations required, rather than to properties of the signal itself.
