J Neurophysiol (November 1, 2002). 10.1152/jn.00286.2002
Submitted on 17 April 2002
Accepted on 15 July 2002

Relationship Between Jaw Stiffness and Kinematic Variability in Speech

 ¹McGill University, Montreal, Quebec H3A 1B1, Canada;  ²Max Planck Institute, 80799 Munich, Germany;  ³Institut de la Communication Parlée, 38031 Grenoble, France; and  ⁴Haskins Laboratories, New Haven, Connecticut, 06511

Shiller, Douglas M., Rafael Laboissière, and David J. Ostry. Relationship Between Jaw Stiffness and Kinematic Variability in Speech. J. Neurophysiol. 88: 2329-2340, 2002. Humans produce speech by controlling a complex biomechanical apparatus to achieve desired speech sounds. We show here that kinematic variability in speech may be influenced by patterns of jaw stiffness. A robotic device was used to deliver mechanical perturbations to the jaw to quantify its stiffness in the mid-sagittal plane. Measured jaw stiffness was anisotropic. Stiffness was greatest along a protrusion-retraction axis and least in the direction of jaw raising and lowering. Consistent with the idea that speech movements reflect directional asymmetries in jaw stiffness, kinematic variability during speech production was found to be high in directions in which stiffness is low and vice versa. In addition, for higher jaw elevations, stiffness was greater and kinematic variability was less. The observed patterns of kinematic variability were not specific to speechsimilar patterns appeared in speech and nonspeech movements. The empirical patterns of stiffness were replicated by using a physiologically based model of the jaw. The simulation studies support the idea that the pattern of jaw stiffness is affected by musculo-skeletal geometry and muscle-force-generating abilities with jaw geometry being the primary determinant of the orientation of the stiffness ellipse.