Babbling elicits simplified caregiver speech: Findings from natural interaction and simulation

What is the function of babbling in language learning? Our recent findings suggest that infants' immature vocalizations may elicit simplified linguistic responses from their caregivers. The contributions of parental speech to infant development are well established; individual differences in the number of words in infants' ambient language environment predict communicative and cognitive development. It is unclear whether the number or the diversity of words in infants' environments is more critical for understanding infant language development. We present a new solution that observes the relation between the total number of words (tokens) and the diversity of words in infants' environments. Comparing speech corpora containing different numbers of tokens is challenging because the number of tokens strongly influences measures of corpus word diversity. However, here we offer a method for minimizing the effects of corpus size by deriving control samples of words and comparing them to test samples. We find that parents' speech in response to infants' babbling is simpler in that it contains fewer word types; our estimates based on sampling also suggest simplification of word diversity with larger numbers of tokens. Thus, infants, via their immature vocalizations, elicit speech from caregivers that is easier to learn.