Language, modality and the brain.
Studies of the signed languages of deaf people have shown that fully expressive languages can arise, outside of the mainstream of spoken languages, that exhibit the complexities of linguistic organization found in all spoken languages. Thus, the human capacity for language is not linked to some privileged cognitive-auditory connection. However, the formal properties of languages (spoken or signed) appear to be highly conditioned by the modalities involved in their perception and production. Multi-layering of linguistic elements and the use of space in the service of syntax appear to be modality-determined aspects of signed languages. Analyses of patterns of breakdown of signed languages provide new perspectives on the nature of cerebral organization for language. The studies reviewed in this article show that the left cerebral hemisphere in man is specialized for signed as well as spoken languages, and thus may have an innate predisposition for language, independent of language modality.