Vowel duration in stressed and unstressed syllables in spontaneous English

Many phonetic “truths” are based on descriptions of controlled speech material, and verifying their validity in spontaneous productions is essential. The present study investigates vowel duration as an acoustic correlate of stress in spontaneous English, in communicatively motivated contexts. By analyzing British and American political debates, this study aims to verify previously reported tendencies – specifically, that stressed vowels are significantly longer than unstressed ones. Our analysis of 16 speakers, based on linear mixed effects models, confirms the significant effect of stress on vowel duration and also considers additional factors influencing segmental duration like vowel length, phrase-final position, vowel height, or the nature of the following segment. In addition to stress, multiple regression analysis identifies vowel length, phrase-final position and vowel height as the most influential vowel duration predictors. Despite the variability of spontaneous speech, vowel duration proves to be a reliable correlate of stress, supporting the findings from controlled-speech research.