Developmental Patterns in Children’s Speech: Patterns of Spectral Change in Vowels

Abstract

The aim of this chapter is to compare the patterns of spectral change in American English vowels spoken by children and adults from the North Texas region. Children’s speech differs from adult speech in several important ways. First, children have smaller larynges and supra-laryngeal vocal tracts than adults, with the result that their formants and fundamental frequencies are higher. Second, the temporal and spectral properties of children’s speech are inherently more variable, a consequence of developmental changes in motor control. Both of these sources of variability raise interesting questions for the representation of vowel inherent spectral change (VISC) and theories of vowel specification. Acoustic analyses of children’s vowels indicate reliable VISC properties as early as age five, the youngest group studied here. Consistent with developmental changes in vocal tract anatomy, the frequencies of vowel formants show an overall systematic decrease with age, and these changes are larger in males than females. The effects of age on formant frequencies vary somewhat from vowel to vowel, but these discrepancies do not appear to interact systematically with VISC. Pattern classification tests indicate that (1) vowels are more accurately recognized when two analysis frames, sampled around 20 and 70 % of the vowel duration, are presented to the classifier, compared to any single frame; (2) adding a third analysis frame does not yield substantially higher recognition scores; and (3) the optimum locations for sampling the formant trajectory are consistent across different age groups of children.