Uniformity of inherent vowel duration across speakers of American English

Abstract

Vowel duration is determined by a number of factors in American English (e.g., Klatt, 1976), including the tense vs. lax distinction (e.g., /i/-/ɪ/, /u/-/ʊ/) and the relation between duration and vowel height (e.g., Lehiste, 1970). A large body of research has identified segment-internal factors in data averaged over many speakers (e.g., Crystal and House, 1988; Hillenbrand et al., 1995), but few studies have investigated the inherent vowel duration patterns of individuals (cf. House, 1961). Stressed vowel productions (>2 million tokens) were identified by forced alignment in connected speech recordings of 390 speakers (209 female) from the Mixer 6 corpus (Chodroff et al., 2016). For each speaker, mean durations of ten stressed vowels (/i ɪ e ɛ æ a ʌ o ʊ u/) were calculated after outlier exclusion. The resulting duration patterns were strongly correlated across pairs of speakers (Pearson r: mean = 0.936, 95% CI [0.935, 0.936], range [0.559, 0.999]), and PCA identified a single component, plausibly indexing global speaking rate, that accounted for more than 82% of the variance. These results establish that inherent vowel duration is highly uniform across speakers, a type of structured phonetic variation that has implications for models of perceptual adaptation.