Vowel locus equations as a measure of vowel coarticulatory aggressiveness

Abstract

Studies in locus equations, a quantification of the degree to which F2 at vowel onset (or consonant place) can be predicted by F2 at vowel midpoint (or vowel place), have shown that the slope of locus equations is a reverse measure of coarticulatory resistance of consonants, in consonant-vowel (CV) sequences with C fixed and V varying. This study presents the first application of locus equations to the measure of coarticulatory properties of vowels. The locus equations analysis for vowels, on our articulatory data (collected with electromagnetic articulograph, EMA) of CV syllables from 7 Taiwan Mandarin speakers, with V fixed and C varying, shows that vowel /i/ has the greatest slope among vowels at tongue body, whereas vowel /a/ and /u/ mostly do not distinguish from each other, and at the tongue tip, the slope does not vary across the three vowels /i/, /a/ and /u/. Based on the CV model theory of gestural coordination (C-V in-phase relation) and the formula of linear regression, we claim that the slope of vowel locus equations is positively related to coarticulatory aggressiveness of vowel, which is further supported by a comparison with a well-established measure of vowel coarticulatory aggressive, based on contextual variability, on the same data.