Temporal variation in African American English: The Distinctive Use of Vowel Duration

Abstract

Introduction: African American English (AAE) is a unique dialect of American English that differs systematically from the variety spoken by the White population. Acoustic-phonetic explorations of segmental structure of AAE including vowel and consonant productions are still rare and the current state and developmental direction of AAE in the United States relative to dialects of White American English (WAE) are largely undetermined. Particularly little is known about timing patterns in AAE such as segmental durations, speech rate and rhythm. Objective: The purpose of this study was to better understand temporal variation in AAE by analyzing vowel duration. Methods: The experiment was conducted in a historically well-established southern speech community of African Americans in Pitt County in North Carolina. Sixteen male speakers, eight AAE and eight WAE, read a randomized set of words containing 11 vowels followed by either a voiced stop /d/ or a voiceless stop /t/ for a total 896 tokens. Two measures were used, the absolute duration and the proportional duration (ratio). Results: Compared with WAE speakers, AAE speakers significantly prolonged vowels preceding voiced consonants but the shorter durations of vowels before voiceless consonants did not differ significantly from those of WAE speakers. The proportional measure further established that the temporal contrast between vowels preceding voiced versus voiceless consonants was significantly enhanced in AAE relative to WAE. Furthermore, the tense-lax vowel distinction was reduced in AAE relative to WAE in both voicing contexts. Conclusions: These findings indicate that both the extensive vowel lengthening before voiced stops and the smaller temporal contrast between tense and lax vowels are distinctive features of AAE, signaling a differential use of vowel duration in AAE. The vowel lengthening before voiced stops may serve as the most salient cue with respect to the voicing status of the word final consonant. It may enhance the temporal contrast between vowels, and this contrast may serve as the primary marker of the consonant voicing distinction even if the consonant itself is devoiced or deleted altogether.