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Figure 7 Distribution of current flow for the N280 peak elicited by closed-class words in English. Maps in the top row show the prominent response in the left hemisphere of hearing subjects (blue, marked by arrow). Bottom row maps display results from congenitally deaf individuals who lack the response (arrow). Reprinted from Neville, Mills, and Lawson (1992), Cerebral Cortex 2, 244-258, with permission of Oxford University Press.

Figure 7 Distribution of current flow for the N280 peak elicited by closed-class words in English. Maps in the top row show the prominent response in the left hemisphere of hearing subjects (blue, marked by arrow). Bottom row maps display results from congenitally deaf individuals who lack the response (arrow). Reprinted from Neville, Mills, and Lawson (1992), Cerebral Cortex 2, 244-258, with permission of Oxford University Press.

mature organization of the language systems of the brain. When hearing adults read English (their first language), there is robust activation within the left (but not the right) hemisphere and in particular within the inferior frontal (Broca's) region. When deaf people read English (their second language, learned late and imperfectly), there is no activation of these regions observed within the left hemisphere. Is the lack of left hemisphere activation in the deaf linked to the lack of auditory experience with language or to incomplete acquisition of the grammar of the language? ASL is not sound-based but displays each of the characteristics of all formal languages, including complex grammar (that makes extensive use of spatial location and hand motion). Studies of the same deaf subjects when viewing sentences in their native ASL clearly showed activation within the same inferior frontal region of the left hemisphere that is active when native speakers of English process English. These data suggest that there is a strong biological bias for these neural systems to mediate grammatical language regardless of the structure and modality of the language acquired. However, if the language is not acquired within the appropriate time window, this strong bias is not expressed. Biological constraints and language experience inter act epigenetically as has been described for the other systems mentioned earlier.

The fMRI data also indicate a robust role for the right hemisphere in processing ASL. These results suggest that the nature of the language input shapes the organization of the language systems of the brain. Further research is necessary to specify the different times in human development when particular types of input are required for optimal development of the many systems and subsystems important in language processing.

Adult Dyslexia

Adult Dyslexia

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