Durational and spectral differences in American English vowels: dialect variation within and across regions

Spectral differences among varieties of American English have been widely studied, typically recognizing three major regionally diagnostic vowel shift patterns [Labov, Ash, and Boberg (2006). The Atlas of North American English: Phonetics, Phonology and Sound Change (De Gruyter, Berlin)]. Durational variability across dialects, on the other hand, has received relatively little attention. This paper investigates to what extent regional differences in vowel duration are linked with spectral changes taking place in the Northern, Western, and Southern regions of the U.S. Using F1/F2 and duration measures, the durational correlates of the low back vowel merger, characteristic of Western dialects, and the acoustic reversals of the front tense/lax vowels, characteristic of Southern dialects, are investigated. Results point to a positive correlation between spectral overlap and vowel duration for Northern and Western speakers, suggesting that both F1/F2 measures and durational measures are used for disambiguation of vowel quality. The findings also indicate that, regardless of region, a durational distinction maintains the contrast between the low back vowel classes, particularly in cases of spectral merger. Surprisingly, Southerners show a negative correlation for the vowel shifts most defining of contemporary Southern speech, suggesting that neither spectral position nor durational measures are the most relevant cues for vowel quality in the South.