Language impairments in sign language: breakthroughs and puzzles

Abstract

Background: Specific Language Impairment (SLI) has previously solely been documented for children acquiring spoken languages despite informal reports of deaf children with possible sign language disorder. Aims: This research evaluates current theories of SLI in light of cases of sign language impairment. Current explanations for SLI include deficits in processing the acoustic signal, phonological short-term memory and grammatical computation. Methods: We report the case of a deaf child deaf exposed to British Sign Language (BSL) from birth with no cognitive or social impairments, with significant developmental deficits in the comprehension and production of BSL grammar but not phonology or vocabulary, based on formal assessment and linguistic analyses of his everyday sign communication in comparison with age matched unimpaired signers. Results: We show that linguistic processing difficulties with BSL verb morphology underlie the child’s poor performance compared with same-age native signers. Conclusions: SLI in children exposed to a soundless language is not explainable by deficits in the auditory processing of the speech signal. The appearance of linguistic impairments in sign and spoken languages in comparable domains provides evidence that some types of SLI involve higher-level problems with the abstract epresentation of rules and grammar.