THE ROLE OF INPUT IN LANGUAGE ACQUISITION: HOW CHILD-DIRECTED SPEECH VS. ADULT-DIRECTED SPEECH SHAPES EARLY VOCABULARY DEVELOPMENT IN CHILDREN

Abstract

Child early vocabulary development is largely dependent on the language input children are exposed to, but the relative roles played by child-directed speech (CDS) and adult-directed speech (ADS) are also a point of controversy. This longitudinal study with a duration of 12 months investigated whether the proportion of CDS to overheard ADS, and qualitative attributes of caregiver input was found to predict vocabulary development, both receptive and expressive, in 12-30-month-old children. The families were asked to record 2 home sessions of 60 minutes monthly in specific contexts (free play, mealtime, shared book reading) which were standardized. Tapes were transcribed and coded according to the addressee (CDS vs ADS), amount (tokens/min, utterance counts), quality (lexical diversity, mean length of utterance, repetition, labeling) and interactional (contingency, conversational turns, joint attention marks).

The mixed-effects growth models depicted strong vocabulary growth over time. An increased percentage of CDS was related to more expressive vocabulary increases whereas contingent caregiver responding further intensified expressive increases. In the case of receptive vocabulary, the biggest predictor of growth was lexical diversity, and the CDS effects were relatively insignificant. The results are in favor of an interactionist explanation where vocabulary learning is facilitated by direct address and social contingence of input, and by learning more variety of word types. Findings indicate that there are practical caregiver and early-education intervention goals: more child-directed talk, more contingent responsiveness and more lexical diversity in daily events.