Language and cognitive development in a grammatical sli boy: Modularity and innateness

Abstract

This paper aims to provide insight into the contentious issue of the hypothesised innate basis to domain specific, modular aspects of language [Fodor, F.J., The Modularity of Mind. MIT Press, Cambridge, MA, 1983; Chomsky, N., Lectures on government and binding. Foris, Dordrecht, 1981]. In order to do this a distinction is made between modular language abilities, non-modular language abilities (i.e. language abilities outside the language module in question) and non-linguistic cognitive tasks. Based on this distinction, a series of investigations were carried out into the abilities of a 10 year old boy (AZ) with Grammatical specific language impairment. The investigations of modular language abilities focused on inflectional morphology (agreement, and regular and irregular past tense marking) and syntax (knowledge and use of phrase structure, thematic role assignment and Binding Principles). The investigations of non-modular language abilities included tests of pragmatic inference and verbal analogical reasoning. Non-linguistic assessments included standardised tests and a test of visual transitive inference. A clear dissociation was revealed between AZ's severely impaired modular language abilities and good non-modular and non-linguistic abilities. AZ's performance on the tests was compared with 36 younger language control children (aged 5:4–8:9) and 12 age matched control children. Z-scores computed for AZ's performance in comparison with the normal children, based on standardised language measures (vocabulary, morphology) and his chronological age, revealed a significant impairment in morpho-syntactic abilities and normal or above average abilities on the non-modular language tasks and non-linguistic cognitive tasks. I propose that the discreteness of AZ's language impairment indicates that an underlying modular language impairment is the most parsimonious explanation for his deficit. A deficit with syntactic structural representations characterised by the Representational Deficit for Dependent Relationships [van der Lely, H.K.J. and Stollwerck, L., Binding theory and specifically language impaired children. Cognition, 1997.]can account for his morphological and syntactic impairments. The data provide empirical evidence to support the innate bases to domain specific and modular aspects of language.