Time-varying spectral change in the vowels of children and adults

Recent studies have shown that time-varying changes in formant pattern cont ribute to the phonetic specification of vowels. This variation could be esp ecially important in children's vowels, because children have higher fundam ental frequencies (f(0)'s) than adults, and formant-frequency estimation is generally less reliable when f(0) is high. To investigate the contribution of time-varying changes in formant pattern to the identification of childr en's vowels, three experiments were carried out with natural and synthesize d versions of 12 American English vowels spoken by children (ages 7, 5, and 3 years) as well as adult males and females. Experiment 1 showed that (i) vowels generated with a cascade formant synthesizer (with hand-tracked form ants) were less accurately identified than natural versions; and (ii) vowel s synthesized with steady-state formant frequencies were harder to identify than those which preserved the natural variation in formant pattern over t ime. The decline in intelligibility was similar across talker groups, and t here was no evidence that formant movement plays a greater role in children 's vowels compared to adults. Experiment 2 replicated these findings using a semi-automatic formant-tracking algorithm. Experiment 3 showed that the e ffects of formant movement were the same for vowels synthesized with noise excitation (as in whispered speech) and pulsed excitation (as in voiced spe ech), although, on average, the whispered vowels were less accurately ident ified than their voiced counterparts. Taken together, the results indicate that the cues provided by changes in the formant frequencies over time cont ribute materially to the intelligibility of vowels produced by children and adults, but these time-varying formant frequency cues do not interact with properties of the voicing source. (C) 2000 Acoustical Society of America. [S0001-4966(oo)01410-7].