ABSTRACT
The study of sign languages offers an unusual opportunity for insight into the nature of language processing, because they utilize a sensory modality different from that of spoken languages. The value of such study becomes immediately apparent in the area of the functional organization of the human brain. The literature on cerebral asymmetry of people with normal hearing clearly indicates that the two hemispheres do not subserve the same behavioral functions; instead, the left hemisphere (for right-handers) is specialized for language processes and the right hemisphere primarily for visual-spatial processes. Sign languages display both complex language structures and complex spatial relations; in fact, Poizner and Lane (1978) have found that both the particular way in which American Sign Language (ASL) uses spatial location linguistically and the psychophysical properties of those locations constrained their perception. Because of these dual constraints on its perception, for each of which one hemisphere shows predominant functioning, sign language offers a valuable opportunity for refining our concept of cerebral asymmetry. In addition to illuminating the relative importance of linguistic and visual-spatial properties in determining cerebral asymmetries, research on the lateralization of sign language bears on developmental issues in the organization of the brain and on competing theories of cerebral asymmetry. In order to focus these issues, we first review the literature on cerebral asymmetry in the normally hearing, then the clinical literature on lateralization of sign, and finally examine experimental evidence from studies of cerebral asymmetry in the deaf.
