Perceptual adaptation to regional vowel variation

Abstract

Listeners cope with between-talker phonetic variation by adapting their phonemic category boundaries based on evidence from individuals’ speech. The current project examined perceptual adaptation to dialect-based variation in the vowels /ɛ/ and /ʌ/, which have lower second formant (F2) frequencies in the Northern dialect of American English relative to the Midland dialect. In a forced-choice lexical identification task, participants identified auditory word tokens which contained vowels along an /ɛ/-/ʌ/ continuum. Words were presented in carrier sentences spoken by either a Northern or Midland talker, and phonemic category boundaries were estimated based on perception of the vowel continuum. Phonemic category boundaries occurred at lower F2s when stimulus words were presented in Northern sentences rather than Midland sentences, indicating perceptual adaptation consistent with the acoustic difference between the dialects. However, this effect was influenced by the phonetic content of the carrier sentence. Adaptation was only consistently found for carrier sentences that included natural tokens of /ɛ/ or /ʌ/, even though all carrier sentences included dialect-specific phonetic features. This suggests that participants were not sensitive to patterns of co-variation among vowels within the two dialects. Rather, they adapted their /ɛ/-/ʌ/ boundary for individual talkers only when provided with direct evidence for that boundary.