DEVELOPMENT OF CEREBRAL SPECIALIZATIONS

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DESCRIPTION: (Adapted From The Investigator's Abstract): The broad goals are to characterize experience-dependent changes in the developing human brain and to test the hypothesis that they are determined by multiple, specific critical periods. The investigators will characterize the effects of auditory deprivation on the functional organization of the visual system, and the effects of acquisition of a visual-manual language (American Sign Language, ASL) and the effects of delayed exposure to language on the functional organization of different language systems of the brain. The investigators will test different conceptions of the identity and organization of subsystems within vision and language in studies of normal hearing adults. They will determine the nature of the effects and the time periods when altered experience affects the normal development of these systems in studies of congenitally and later deafened individuals, and in native and late leamers of ASL and English. The investigators will record event-related brain potentials (ERPS) and changes in blood oxygenation levels employing functional magnetic resonance imaging (FMRI) to characterize the timing and the location of neural activation as these groups of subjects perform tasks designed to activate specific aspects of sensory and language functions. They will assess the hypothesis, raised by our previous behavioral, ERP and FMRI studies, that there is considerable functional specificity in the alterations in the visual system and the language systems that can occur following auditory deprivation and that: 1. congenitally deaf subjects are more accurate and display faster and more extensive neural activation than normal hearing Ss when detecting, localizing and attending to visual events in the far periphery of the visual fields; 2. the neural systems that mediate this processing are more extensive in deaf Ss and include areas that process auditory information in normal hearing Ss; 3. there are several distinct subsystems within language and these differ in the degree to which they are dependent on and modified by language experience; 4. there is overlap in the neural systems within the left hemisphere that process ASL and English, but there is also extensive activation of the temporal and parietal regions of the right hemisphere for processing ASL only. Since these studies will determine the multiple, different time periods in human development when specific inputs from the environment have the greatest impact, the results will carry implications for the time periods when specific educational programs would optimize development in hearing and deaf children.