Vowel trajectories of African Americans in Georgia, USA

Within the United States, dialectal variation is often characterized by vowel shifts: systematic differences in vowels' relative qualities and vowel-inherent dynamics. The African American Vowel Shift (AAVS), in particular, includes raising and fronting of front lax /ɪ ɛ æ/, among other features. The more recent pan-regional Low Back Merger Shift (LBMS), by contrast, includes lowering and backing of the same vowels. We evaluate these two shifts in an audio corpus of over 40 Black speakers from the Southern state of Georgia. Speakers, born between the 1930s and 2000, represent five demographic generations. Normalized formant values (F1,F2) from five temporal points per token are input to Generalized Additive Mixed Models (GAMMs). We test for significant changes in vowels' trajectories across time by fitting Year of Birth as a continuous smooth term. Additionally, we use linear mixed-effects modeling to test for raising versus lowering on the (F2–F1) front-vowel diagonal, across generations. Evidence from GAMMs and linear modeling indicates raised positions of /ɪ ɛ æ/ among older generations (1950s–1980s), followed by significant retraction from 1990–2000. These acoustic results are consistent with strengthening of the AAVS in the third quarter of the 20th Century, followed by a rapid transition to the pan-regional LBMS.