HOW CHILDREN LEARN TO ORGANIZE THEIR SPEECH GESTURES - FURTHER EVIDENCE FROM FRICATIVE-VOWEL SYLLABLES

Previous studies with fricative-vowel (FV) syllables have shown that t he difference in overall spectrum between fricatives is less in childr en's speech than in that of adults, but that fricative noises show gre ater differences in the region of the second formant (F-2) as a functi on of the upcoming vowel than those of adults at corresponding points in the fricative. These results have been interpreted as evidence that children produce fricatives that are not as spatially differentiated as those of adults and that children initiate vowel gestures earlier d uring syllable production than adults do (Nittrouer, Studdert-Kennedy, & McGowan, 1989). The goals of the present study were (a) to replicat e the previous age-related difference for F-2 with FV syllables; (b) t o test the alternative interpretation that age-related differences in fricative F-2 reflect age-related differences in vocal-tract geometry; (c) to determine whether age-related differences in F-2 (and so, by i nference, in articulatory organization) might extend beyond the syllab le boundaries, perhaps into the schwa of a preceding unstressed syllab le; and (d) to determine if gestures other than fricative gestures sho w less spatial differentiation in children's than in adults' speech. T o these ends, F-2 frequencies were measured in schwa-fricative-vowel u tterances (consisting of the fricatives /s/ and /integral/ and of the vowels /i/ and /a/) from 40 speakers (10 each of the ages of 3, 5, 7 y ears, and adults) at three locations (for the entire schwa, for 10 ms of fricative noise centered at 30 ms before voicing onset, and for 10 pitch periods from vocalic center). Results of several analyses suppor ted four conclusions: (a) the earlier finding was replicated; (b) age- related differences in vocal-tract geometry could not explain the age- related difference in vowel effects on fricative noise; (c) children m aster intersyllabic gestural organization prior to intrasyllabic gestu ral organization; and (d) unlike fricative gestures, children's vowel gestures are more spatially distinct than those of adults.