The jaw is one of the most important articulators in speech production. Despite this, we know next to nothing about how Japanese speakers use their jaws to produce vowels. Against this background, in order to explore the articulatory nature of Japanese vocalic jaw movements, this paper presents a detailed, quantitative EMA study of the five vowels in Japanese, focusing on the following four specific questions: (1) How many mms does the jaw open for each type of vowel in Japanese?; (2) Does the presence of an onset consonant affect the degrees of jaw opening?; (3) Does the speed of the jaw movement vary depending on how much the jaw opens?; (4) What is the reliable acoustic correlate of the jaw opening? In answer to these questions, the current experiment demonstrates that (1) In Japanese, the degree of the jaw opening is in the order of [a] > [e] > [o] > [i] > [u]; (2) The presence of onset consonant [p] generally decreases the jaw opening; (3) The degrees of the jaw opening and its speed positively correlate; and (4) F1 and duration are reliable acoustic correlates of the jaw opening. Implications of these results for phonetic theories are discussed throughout the paper.
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