Published online by Cambridge University Press: 28 November 2008
Since the publication of Nelson's (1973) monograph, several studies have reported significant correlations between variation in children's early vocabulary composition and differences in the functional characteristics of mothers' child-directed speech. However, it is still not clear how these relations are actually mediated. The present study attempts to investigate thís issue by differentiating and testing two alternative explanations of the relations found in previous research on data from a study of eight mother–infant dyads between 0;11 and 1;8. Despite replicating previous findings of a relation between maternal descriptiveness and the proportion of nouns and maternal directiveness and the proportion of verbs in children's early vocabularies, the results reveal no relation between differences in mothers' interactional behavior and differences in the functional characteristics of their children's spontaneous speech. On the other hand, specific relations were found between children's referential vocabularies and maternal descriptives that included nouns and between children's verb vocabularies and maternal directives that included verbs. These findings not only raise doubts about the validity of a functional similarity account of relations between maternal speech characteristics and variation in early vocabulary composition, but also suggest that they may be better understood in terms of the interaction between processing mechanisms that are common to all children and differences in the structure of the input to which different children are actually exposed.