Processing a dynamic visual-spatial language: psycholinguistic studies of American Sign Language.

American Sign Language (ASL) has evolved within a completely different biological medium, using the hands and face rather than the vocal tract and perceived by eye rather than by ear. The research reviewed in this article addresses the consequences of this different modality for language processing, linguistic structure, and spatial cognition. Language modality appears to affect aspects of lexical recognition and the nature of the grammatical form used for reference. Select aspects of nonlinguistic spatial cognition (visual imagery and face discrimination) appear to be enhanced in deaf and hearing ASL signers. It is hypothesized that this enhancement is due to experience with a visual-spatial language and is tied to specific linguistic processing requirements (interpretation of grammatical facial expression, perspective transformations, and the use of topographic classifiers). In addition, adult deaf signers differ in the age at which they were first exposed to ASL during childhood. The effect of late acquisition of language on linguistic processing is investigated in several studies. The results show selective effects of late exposure to ASL on language processing, independent of grammatical knowledge.