The emergence of phonetic segments: evidence from the spectral structure of fricative-vowel syllables spoken by children and adults.

A variety of evidence, including the speech errors of normal and aphasic speakers, and the metalinguistic skills of literate individuals, demonstrates that speech has an underlying phonemic organization. However, we know little about how this organization develops in the child. The purpose of the present study was to test the hypothesis that phoneme-sized phonetic segments emerge as functional units of perceptuomotor control from the child's gradual reorganization of the gestures forming its early words or syllables. We investigated the acoustic structure of syllables produced by young children and adults. Fricative-vowel syllables spoken by 40 subjects (eight adults and eight children at each of the ages 3, 4, 5, and 7 years) were analyzed acoustically to determine how well different syllables-initial fricatives were contrasted and how strongly they were affected by vocalic context. Results indicated two independent developmental trends: The extent to which speakers differentiated between /integral of/ and /s/ increased with age, while the extent to which they coarticulated each fricative with its following vowel decreased. The results support the hypothesis that children initially organize their speech gestures over a domain at least the size of the syllable and only gradually differentiate the syllable into patterns of gestures more closely aligned with its perceived segmental components.