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Research shows that jaw deviations follow lexical and phrasal stress patterns reflecting the rhythmic structure of English (Erickson 2002, 2010; Erickson et al., in press; Menezes 2003; Menezes et al., 2003). Syllable strength thus can be determined by the amount of jaw displacement regardless of the target vowel. This study systematically analyzes jaw displacement based on the intrinsic variations in vowel height. EMA recordings were analyzed of one speaker producing a short phrase wherein 11 English vowels were spoken in a controlled phonetic environment. The phrase used was "Type X first" where, X is a closed monosyllabic word containing the target vowel surrounded by stop consonants. Stop consonants allow the jaw to start from the bite plane and return to the bite plane therefore all deviations of the jaw are attributed to the articulation of the vowel. The target word was produced in phrase initial, middle and final positions. Comparisons were made across vowel height, tongue root advancement and phrase position. Preliminary findings reveal that jaw displacement was significantly different at the level of p=.05 for vowels based on all three parameters: Vowel height, vowel tense/lax and phrasal positioning.
Menezes et al. (Tue,) studied this question.