Human jaw movement in mastication and speech.

The study of jaw movement in humans is a primary source of information about the relationship between voluntary movement and more primitive motor functions. This study focused on the geometric form of the velocity function, as measured by linear voltage displacement transducer. Movement amplitudes, maximum velocities and durations were greater in mastication than in speech. Nevertheless, there were detailed similarities in the shape of the normalized velocity functions. In jaw-closing movements, the normalized functions were similar in form over differences in rate, movement amplitude (speech movements) and the compliance of the bolus (mastication). In opening movements, the functions for mastication and speech were again similar over differences in amplitude and compliance. However, they differed in shape for fast and slow movements. Normalized acceleration and deceleration durations were approximately equal in rapid movements, whereas, for slower movements, deceleration took substantially longer than acceleration.