The neurobiology of sign language and its implications for the neural basis of language.

The left cerebral hemisphere is dominant for language, and many aspects of language use are more impaired by damage to the left than the right hemisphere. The basis for this asymmetry, however, is a matter of debate; the left hemisphere may be specialized for processing linguistic information or for some more general function on which language depends, such as the processing of rapidly changing temporal information or execution of complex motor patterns. To investigate these possibilities, we examined the linguistic abilities of 23 sign-language users with unilateral brain lesions. Despite the fact that sign language relies on visuospatial rather than rapid temporal information, the same left-hemispheric dominance emerged. Correlation analyses of the production of sign language versus non-linguistic hand gestures suggest that these processes are largely independent. Our findings support the view that the left-hemisphere dominance for language is not reducible solely to more general sensory or motor processes.