The research proposed here is directed toward determining which neural systems and related functions are most dependent on and modified by experience during human development. We will characterize the sensitive periods when particular perceptual and language systems display experience-dependent changes and contrast these systems with those that retain the ability to change throughout life. We will acquire event-related brain potentials (ERPs) and structural and functional magnetic resonance images (MRI) of the brain to precisely characterize both the timing and the location of neural activations as subjects perform tasks designed to activate specific aspects of sensory and language functions. We will assess the hypotheses that (1) congenitally deaf subjects (Ss) are more sensitive to and display more extensive neural activation than hearing Ss to motion (but not color), especially in the far periphery of the visual fields and that these differences occur in classical visual areas, multi modal areas and in primary and secondary auditory cortices, (2) deaf Ss are more sensitive to change within the periphery of a visual scene than are normally hearing Ss, (3) subjects blind since birth are more accurate and display greater activation of classical auditory, multi modal and visual areas when processing the location (but not the pitch) of sounds presented in the far auditory periphery. In addition, we will (4) characterize the identity and time-course of operation of the neural subsystems important in processing phonological, morphological, syntactic and semantic processing in normal adults, (5) determine the effects of delays in language acquisition on these same subsystems by studying bilinguals who acquired 12 at different ages, and (6) assess the hypotheses that neural systems active when native signers process semantic information and non-spatial syntax in ASL overlap extensively with those observed when native speakers process English, but that processing spatial syntax in ASL selectively engages areas of the right hemisphere that are not typically active in grammatical processing of English. We will assess the hypothesis that this pattern of cerebral specialization is dependent on early exposure to ASL but is independent of auditory deprivation. Since the proposed research will determine which perceptual and language systems are most altered by environmental input, and the time periods when they are most modifiable, these studies will contribute information of practical significance for the development, refinement and evaluation of educational and habilitative programs.
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