Lexical diversity and language development

AbstractPrevious research has demonstrated a relationship between quantity of language input and children’s rate of language development: Children who hear more words learn faster. This work takes on two mutually-constraining questions: (1) How should we define quality, and (2) what is the relationship between input quality and language development? We analyzed a longitudinal corpus of interactions between 50 children and their parents using four measures of lexical diversity: Type Token Ratio (TTR), Moving Average TTR, and two more recent measures—vocd-D and MTLD. We found that only MTLD gave a prima-facie correct characterization of children’s development, and parents’ MTLD was correlated with children’s over development. Results of simulations showed that MTLD was distinct from the other measures in it’s sensitivity to both lexical diversity and word order, suggesting that “quality” should be defined not just by diversity of words, but also by the variability of sentence structures in which they occur.

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