Ethnolectal and generational differences in vowel trajectories: Evidence from African American English and the Southern Vowel System

Despite their potential for elucidating fine-grained differences across ethnolects and regional dialects, vowel trajectories are neglected in sociolinguistics as group comparisons tend to rely upon F1/F2 steady-state measures. In this paper we demonstrate that comparisons of dynamic aspects of vowel production are crucial for comparing groups that may superficially align in steady-state production values. Specifically, we compare the front lax vowels BIT, BET, and BAT from the Southern Vowel Shift to those of the African American Vowel System in Piedmont, North Carolina. Data from eight older-generation European American participants from Raleigh, North Carolina, and twenty younger-generation African American participants from Piedmont, NC, come from sociolinguistic interviews. Using force-aligned TextGrids, F1 and F2 were semi-automatically measured at 21 equally-spaced time-points within each vowel. Functional data analysis was used to model vowel curvature for each group allowing for holistic descriptions of trajectory shape. Cubic coefficients, a measure of curvilinear contour shape, and their interaction with vowel duration were then compared through visual and statistical analysis. Our results reveal that SVS vowels for European Americans follow diphthongal trajectories, while African American vowels are more monophthongal. Interactions between duration and trajectory shape also differ across groups. As such, formant trajectories and other dynamic information form a central component of linguistic diversity in the region. Functional data analysis illustrates that differences in vowel formant trajectories are a key marker of regional sound systems and ethnolectal vowel variation in Southern English in the Piedmont region of North Carolina.