Neurological differences.
Aphasia studies show clearly that both spoken and signed languages are controlled in the left hemisphere. Some recent brain research on normal subjects using modern techniques such as positron emission tomography and functional magnetic resonance imaging are suggestive of possible differences in brain organization related to sign language . In particular, recent results find right hemisphere involvement in sign language processing by deaf and hearing native signers . One research group used regional cerebral blood flow and positron emission tomography to examine sign and spoken language representation in hearing native signers (hearing people born to deaf parents who learned sign language as a first language). The two techniques showed bilateral activation (activation in both cerebral hemispheres) for both modalities. Another research group, using event related potentials, similarly found bilateral activation for both modalities, for both deaf and hearing native signers. Using func...