Linguistics An Introduction

In the introduction (pp. 11ff.), we offered some preliminary remarks on the types of language disorders which are of most interest to the linguist. These are aphasia and Specific Language Impairment (SLI) and it is important that we re-emphasise a very important difference between these. Aphasia is a disorder of language and speech that is caused by a brain lesion which may be due to an accident or a stroke, after language has been acquired in the normal way; before the brain lesion occurred, aphasics had normally functioning language systems. By contrast, SLI is a term covering disorders in the normal acquisition of language without there being any clear primary deficit. Despite their linguistic problems, SLI children and adults have normal non-verbal IQs, no hearing deficits and no obvious emotional or behavioural disturbances; unlike aphasics, SLI subjects have never acquired language in the normal way.

Aphasia provides us with a potentially valuable source of information as to how linguistic representations are implemented in the brain. It is reasonable to suppose that we might learn how a machine (or any other physical device, such as the human brain) works by investigating how it goes wrong. In aphasic patients, there is typically some residual language left after brain damage, indicating that the knowledge of language can be selectively impaired by brain lesions, and it is by carefully studying the range and nature of such selective impairments that we hope to learn something about the interconnections of the brain mechanisms underlying language.