Disentangling early language development: modeling lexical and grammatical acquisition using an extension of case-study methodology.

The early lexical and grammatical development of 1 male child is examined with growth curves and dynamic-systems modeling procedures. Lexical-development described a pattern of logistic growth (R2 = .98). Lexical and plural development shared the following characteristics: Plural growth began only after a threshold was reached in vocabulary size; lexical growth slowed as plural growth increased. As plural use reached full mastery, lexical growth began again to increase. It was hypothesized that a precursor model (P. van Geert, 1991) would fit these data. Subsequent testing indicated that the precursor model, modified to incorporate brief yet intensive plural growth, provided a suitable fit. The value of the modified precursor model for the explication of processes implicated in language development is discussed.