Abstract and Keywords
For more than a century we have known that the left hemisphere of the human brain is critical for producing and comprehending spoken languages. Evidence from brain-injured deaf signers and from neuroimaging studies indicates that the left cerebral hemisphere is also critical to processing signed languages. This chapter presents evidence that the left hemisphere specialization for language can be dissociated from symbolic gesture, motor control, and spatial cognitive abilities. Damage to distinct left perisylvian areas causes specific types of language impairment for both signers and speakers, and damage outside of these areas does not give rise to aphasic deficits. Specifically, neuroimaging and lesion data indicate that Broca’s area and Wernicke’s area play critical roles in sign language production and comprehension. Data from right hemisphere–damaged signers and speakers indicates that the right hemisphere is involved in discourse processing. In addition, the right hemisphere appears to be uniquely involved in the production and comprehension of spatial descriptions in sign language. Overall, both neural plasticity and invariance are observed for the neural organization of sign language. Neural plasticity is observed for auditory-related cortex (Wernicke’s area), which has received little or no auditory input, but nonetheless is engaged in processing the visual input of sign language. Neural invariance within left perisylvian structures points to a biological or developmental bias for these neural structures to mediate language at a more abstract level, divorced from the sensory and motoric systems that perceive and transmit language.
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