Sungbok Lee
Central Inst. for the Deaf, 818 S. Euclid, St. Louis, MO 63110
Sensitivity of formants to perturbations of the location and degree of tongue constriction was studied. These two tongue parameters were extracted from vowel-like midsagittal tongue shapes (N=321) generated using a tongue model [Harshman et al., J. Acoust. Soc. Am. 62, 693--707 (1977)]. The tongue shape data were arranged such that the tongue parameters vary montonically. Lip opening was varied from 0.3 to 6.0 cm[sup 2] in 0.3-cm[sup 2] steps and the first three formants of each vocal tract were computed. Formant sensitivity was evaluated as dF/dA (Hz/mm), where dA is perturbation in a tongue parameter and dF is the corresponding formant change, and was plotted as a function of the location of tongue constriction. The results can be interpreted in terms of the formant variability, or stability, of a given vocal tract configuration. One finding is that at the tongue position associated with the vowel /u/ the formants are very stable under perturbation of the location of constriction. However, the same position is found to be the most unstable position for both F2 and F3 under perturbation of the degree of constriction. This may explain the largest F2 and F3 variations of /u/ in a set of normalized production data of vowels [Syrdal and Gopal, J. Acoust. Soc. Am. 79, 1086--1100 (1986)]. [Work supported by NIDCD, DC 00296.]