Monophthongization of diphthongs in Southern American English: A perception study

The monophthongization of /ai/ is more prevalent than /au/ in Southern American English due to historical, phonetic, and sociolinguistic factors. Phonetically, the tongue movement for /ai/ (low to high front) may be more prone to reduction than for /au/ (low to high back). Sociolinguistically, these changes often signal regional identity. This study investigates the monophthongization of /ai/ to /a/ and /au/ to /a/ in Southern English through two 11-step continua ([a-ai] and [a-au]) presented to listeners for identification. Preliminary data from 4 Southerners and 12 non-Southerners partially support the hypothesis that Southerners perceive /a/ more in the /a-ai/ continuum. Boundary positions for both continua were similar across groups, but Southern speakers showed narrower boundary widths for /a-au/ (M = 0.854) compared to /a-ai/ (M = 1.188), indicating clearer perceptual distinctions for /a-au/. Non-Southerners exhibited consistent boundary widths for /a-ai/ (M = 1.318) and /a-au/ (M = 1.335), suggesting stable perceptual systems unaffected by dialectal variation. These findings reveal that the monophthongization of /ai/ in Southern English reduces perceptual precision, reflecting its greater susceptibility to dialectal variation. In contrast, non-Southerners maintain uniform perceptual precision across continua, highlighting regional dialects' impact on phonetic perception.