A THEORY OF NEUROLINGUISTIC DEVELOPMENT

This article offers a developmental theory of language and the neural systems that lead to and subserve linguistic capabilities. Early perce ptual experience and discontinuities in linguistic development suggest that language develops in four phases that occur in a fixed, interdep endent sequence. In each phase of language, a unique ontogenetic funct ion is accomplished. These functions have proprietary neural systems t hat vary in their degree of specialization. Of particular interest is an analytical mechanism that is responsible for linguistic grammar. Th is mechanism is time-locked and can only be turned on in the third pha se. Confirming evidence is provided by children who are delayed in the second phase of the language learning process. These children store i nsufficient lexical material to activate their analytic mechanism. Ina ctivation behaves like damage, shifting language functions to homologo us mechanisms in the nondominant hemisphere, thereby increasing functi onal and anatomical symmetry across the hemispheres. This atypical ass embly of neurolinguistic resources produces functional but imperfect c ommand of spoken language and may complicate learning of written langu age. The theory thus offers a different role for genetics and early ex perience, and a different interpretation of neuroanatomic findings, fr om those entertained in most other proposals on developmental language disorders. (C) 1997 Academic Press.