Analysis and modeling of 3D jaw motion in speech and mastication

Examines the jaw's contribution to functionally distinct orofacial activities such as mastication and speech. We focus on the degrees-of-freedom (DOF) of jaw motion, the coordination of the jaw with other orofacial articulators, and modeling studies of jaw motion control. Jaw DOF were obtained from the six component rotations and translations which fully describe rigid body jaw motion. Mastication and speech were characterized by independent motion in four DOF. However the relative prominence of the constituent movements differed in the two behaviors: for speech, pitch rotation, vertical and horizontal translation were most prominent; for mastication, pitch, yaw, and sagittal plane translation were dominant. Jaw motion is coordinated with motion of the tongue. Even though the jaw is usually thought of as an indirect or remote speech articulator, it mirrors the behavior of proximal vocal tract constrictions made by the tongue. The authors' empirical studies have contributed to the development of vocal tract models. In a control model of the tongue, jaw, hyoid bone and larynx, motor command inputs to modeled muscles are transformed into functionally appropriate movements. In other modeling, the mapping between muscles for jaw opening and closing and subsequent jaw motion has been successfully estimated using linear and nonlinear techniques. We have also demonstrated that the jaw is a major component of the correlation between the time-varying behavior of the vocal tract and facial motion. Its contribution to speech-related facial motion is so strong that motions of the tongue tip, for example, can be reliably estimated from the 3D motion of the facial surface.