Investigating the underlying causes of SLI: A non-sign repetition test in British Sign Language

There is controversy over the specificity of Specific Language Impairment (SLI), and whether it is caused by a deficit general to cognition or in mechanisms specific to language itself. We argue that evidence to resolve these conflicting positions could come from the study of children who are acquiring sign language and have SLI. Whereas speech is characterized by rapid temporal changes, the phonology of sign languages relies on the integration of visual information that is often produced simultaneously. These differences in the way linguistic information is processed can allow us to investigate whether SLI is caused by a sensory processing deficit, by a deficit specific to language, or by a deficit in phonological short term memory. One marker for SLI in spoken languages is difficulty repeating non-words, particularly those with complex phonological structures. We report on the development of a non-sign repetition task for BSL users, piloted on deaf children, which is sensitive to age. Non-sign items were graded in terms of phonological complexity, and reveal systematic error patterns as a function of that complexity. We conclude by discussing how this test can be used to probe the underlying nature of language impairments.