ABSTRACT
Many children fail to develop language normally, for a variety of reasons. The most obvious cause, perhaps, is a congenital hearing impairment, where the consequent lack of access to spoken input from the ambient language seriously inhibits the development of linguistic competence. For other children, their inability to acquire their language at the same rate as their peers may be linked to cognitive abilities which are outside normal limits: “language development is an area of specific additional difficulty for many children with Down syndrome” (Chapman, 1995, p. 641; see also Tager-Flusberg, this volume). For other chil dren still, normal conditions for acquisition are interrupted by brain injury, with consequences for their language learning (Eisele & Aram, 1995). And in the behavioural syndrome referred to as autism, as Tager-Flusberg (1988, this volume) points out, atypical language development is one of the core character istics. In this chapter, in contrast, we consider the children for whose non normal language acquisition there is no identifiable physical or psychological basis. These individuals have normal hearing, intelligence within normal limits, an apparently intact neurological substrate, and no behavioural or emotional disorder. They nevertheless have persisting linguistic difficulties. The term used to describe this phenomenon is “specific language impairment” (henceforth SLI). This is a puzzling condition, affecting nearly three times as many boys as girls, in a small percentage of the population. We know that unless one or more of these factors (hearing impairment, cognitive deficit, neurological damage) is present, language acquisition is robust in the face of a wide range of circum stances and environments. The vast majority of children learn the phonology and
grammar of the language of their community, and a significant proportion of its vocabulary, in their pre-school years. What is it that inhibits similar learning in SLI children? As we shall see, there is as yet no satisfactory answer to this question. Before addressing it we review the subject selection criteria for SLI individuals in more detail, and summarise what is known about the effects of SLI on the grammars of learners of English and of other languages.
