Comparing Word Diversity Versus Amount of Speech in Parents’ Responses to Infants’ Prelinguistic Vocalizations

Our prior research posits that the prelinguistic vocalizations of infants may elicit caregiver speech which is simplified in its linguistic structure. Caregivers’ speech clearly contributes to infants’ development; infants’ communicative and cognitive development are predicted by their ambient language environment. There are at least two sources of variation in infants’ language environment: 1) the number and 2) the diversity of words infants hear. We compare the change in the total number of words (tokens) to the diversity of words against one another. Distributions of words of differing sizes are difficult to compare to one another because the size of the distribution largely determines the word diversity of the distribution. A novel approach to minimizing the challenges of comparing distributions of words is applied to data which were previously reported. We also conducted a new simulation study to estimate the probability that these results are expected by chance. We found that the linguistic structure of caregivers’ responses to infants’ prelinguistic vocalizations has fewer word types as compared to infant-directed but noncontingent speech. Our new method shows that contingent word distributions remain simplified as the number of total words sampled increases. By vocalizing, infants elicit caregiver speech, which is simpler in structure and may be easier to learn.