Does Early Phonetic Differentiation Predict Later Phonetic Development? Evidence From a Longitudinal Study of /ɹ/...

Purpose We evaluated whether children whose inaccurate /ɹ/ productions showed evidence phonetic differentiation with /w/ at 3.5-4.5 years of age improved in /ɹ/ production over the next year more than children whose inaccurate productions did not show evidence of such differentiation. We also examined whether speech perception, inhibitory control, and vocabulary size predicted growth in /ɹ/. Method A set of typically developing, monolingual English-speaking preschool children (n = 136) produced tokens of /ɹ/- and /w/-initial words at two time points (TPs), at which they were 39-52 and 51-65 months old. Children's productions of /ɹ/ and /w/ were narrowly phonetically transcribed. Children's productions at the earlier time point were rated by naïve listeners using a visual analog scale measure of phoneme goodness; these ratings were used to assess the degree of phonetic differentiation between /ɹ/ and /w/. Results Accuracy for both phonemes varied considerably at both TPs. The growth in accuracy of /ɹ/ between the two TPs was not predicted by any individual-differences measures, nor by the degree of differentiation between /ɹ/ and /w/at the earlier time point. Conclusion Low vocabulary size, low inhibitory control, poor speech perception, and the absence of early phonetic differentiation are not necessarily limiting factors in predicting /ɹ/ growth in individual children in the age range we studied.