ATR Auditory and Visual Perception Res. Labs., 2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-02, Japan
David J. Ostry
McGill Univ., Montreal, Canada
Typically, during speech, the jaw rotates downward and translates forward during opening movements and follows the opposite path during closing; however, rotations and translations out of the midsagittal plane may also occur. In this study, Optotrak was used to examine jaw motion in six degrees of freedom---three orientations and three positions---relative to the occlusal (bite) plane and the condyle. Native speakers of English (2) and Japanese (2) produced CVCV(schwa) utterances in normal and fast rate as well as in loud speech conditions. As has been reported previously, the principle components of jaw motion were horizontal translation and rotation in the midsagittal plane. However, rotations out of the midsagittal plane are also observed. Yaw about the longitudinal body axis was typically about 3 deg and roll usually less than 2 deg. Magnitude of yaw and roll angles differed little across conditions. The remaining translational components---vertical and lateral---were small in magnitude and uncorrelated with either sagittal plane rotation or horizontal translation.