ABSTRACT
Abstract
Employing a combined behavioral-electrophysiological approach, we have separately assessed the effects of auditory deprivation, the late and imperfect acquisition of English, and the early acquisition of American Sign Language (ASL) on cerebral organization in congenitally deaf adults. The results from sensory studies suggest that auditory deprivation alters the anterior/posterior organization of the visual system in a bilaterally symmetrical fashion. The results from language studies suggest that the acquisition of formal (i.e., grammatical) language early in development is necessary and sufficient to stabilize a genetically biased special role of the left hemisphere in language processing: Deaf subjects who have not fully acquired the grammar of English do not show specialization of the left anterior brain regions during the reading of English, but deaf subjects who score well on tests of English grammar do display the normal pattern. Similarly, deaf and hearing subjects who acquired ASL as a first language early in development display specialization of the left anterior regions for ASL, but those who acquired ASL late and imperfectly do not. Further results from nonlanguage cognitive studies suggest that the modality through which language is first acquired significantly impacts the fundamental specializations of the two hemispheres for nonlanguage processing. Together, this pattern of results suggests that there are biological constraints on the development of language-relevant brain systems, and that the mature pattern of organization is significantly impacted by specific aspects of early language input.
