DEVELOPMENT OF CEREBRAL SPECIALIZATIONS

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The long-term objectives of this application are to assess the roles of sensory and language experience in the development of functionally specialized neural systems. Different conceptions of the functional organization of the visual system and the language system will be tested in studies of normal adults and the effects of altered input on the development of these systems will be determined through the study of groups of individuals with specific alterations in the nature and timing of sensory and/or language experience. Event-related brain potentials (ERPs) will be recorded from over several brain regions as monolingual and bilingual hearing subjects whose first exposure to English occurred at different ages, and congenitally deaf and hearing individuals whose first exposure to ASL occurred at different ages, perform tasks designed to activate specific aspects of sensory and language functions. The specific aims of each of the six series of proposed experiments are: I. To test the hypothesis that the dorsal and ventral processing streams within the visual system are differentially affected by auditory deprivation since birth. II. To assess the hypothesis that the temporal coincidence between grammatical information and facial expression in ASL results in greater left hemisphere representation of faces in deaf and hearing native signers. III. To explore the hypothesis that the processing of semantic and grammatical information in English is mediated by different neural systems with different critical periods and to further differentiate rules and constraints within the grammatical subsystem. IV. To explore the hypothesis that (a) there is overlap in the neural systems that mediate ASL and English, (b) similar subsystems can be identified within each that are independent of modality and (c) modality constraints produce differences in the neural systems that mediate grammatical processing in English and ASL. V. To explore the hypothesis that similar neural systems with similar critical periods mediate the processing of phonological information in English and ASL. VI. To utilize masking paradigms to contrast automatic and controlled processing of language and non-language material and to test the hypothesis that automatic functions are more vulnerable to altered early experience than are controlled aspects of processing. In the long run these studies should contribute information of practical significance for developing, refining and evaluating rehabilitative and educational programs for deaf and language impaired individuals. Since these studies will evaluate the periods in development when altered experience has its greatest impact, the results will also have implications for when specific educational programs would optimize development in normal hearing children.