Phrase Structure in a Computational Model of Child Language Acquisition

The problem of the acquisition of morpho-syntactic rules, as addressed by a number of existing computational models, is introduced. A distinction is made between ‘innatist’ models which presuppose the importance of innate linguistic knowledge (specifically, syntactic categories and X-Bar Theory), and ‘empiricist’ models, which reject such assumptions. It is argued that ‘empiricist’ models better account for such features of child language acquisition as gradual development. However, existing ‘empiricist’ models are inadequate insofar as the grammars acquired are finite-state, as opposed to phrase-structure, grammars. The problem of phrase structure acquisition in an ‘empiricist’ model is addressed. The problem is characterized as that of developing a model of acquisition in which the kind of information embodied in X-Bar Theory can be directly derived from the semantic inputs to learning. The solution offered closely identifies phrase structure acquisition with lexical acquisition and segmentation. A computational model in which these processes have been implemented is described. This acquires a finite-state grammar and later a phrase-structure grammar, thereby providing a gradual and continuous model of child language development. The account given of lexical acquisition and segmentation is novel, in that lexical acquisition precedes the acquisition of segmentation.