The current study reports that lip rounding inhibits centralization of “unstressed” full vowels (e.g., æ in activity, ɔ: in audition) along the F1 dimension in American English. In the previous ASA meeting, I reported that unstressed æ and ɛ underwent centralization along the F1 dimension, whereas unstressed ɔ: and oʊ did not. The former are lax, unrounded, front, while the latter are tense, rounded, back. It remained unclear whether tenseness, roundedness, or backness was responsible for inhibiting the F1-related centralization of the latter. In the present study, six native speakers of American English produced words containing full vowels (iː, ɪ, eɪ, ɛ, æ, ʌ, ɑː, ɔː, oʊ, uː) in initial syllables with varying stress levels (P: primary, S: secondary, U: unstressed). F1 values at the vowel midpoint were measured, and absolute differences were calculated between P and U (P–U), and between S and U (S–U). Multiple linear mixed models were fit separately to P–U and S–U as dependent variables, with each model including one of the following as a fixed effect: tenseness, lip rounding, or backness. Model comparisons revealed that, for both P–U and S–U, the model with lip rounding as the fixed effect provided the best fit.
Mariko Sugahara (Wed,) studied this question.