An Examination of the Degrees of Freedom of Human Jaw Motion in Speech and Mastication The kinematics of human jaw movements were assessed in terms of the three orientation angles and three positions that characterize the motion of the jaw as a rigid body. The analysis focused on the identification of the jaw’s independent movement dimensions, and was based on an examination of jaw motion ... Research Article
Research Article  |   December 01, 1997
An Examination of the Degrees of Freedom of Human Jaw Motion in Speech and Mastication
 
Author Affiliations & Notes
  • David J. Ostry
    Department of Psychology, McGill University, 1205 Dr. Penfield Avenue, Montreal QC Canada H3A 1B1
  • Eric Vatikiotis-Bateson
    ATR Human Information Processing Research Laboratories Kyoto, Japan
  • Paul L. Gribble
    Department of Psychology, McGill University, 1205 Dr. Penfield Avenue, Montreal QC Canada H3A 1B1
Article Information
Swallowing, Dysphagia & Feeding Disorders / Speech / Research Articles
Research Article   |   December 01, 1997
An Examination of the Degrees of Freedom of Human Jaw Motion in Speech and Mastication
Journal of Speech, Language, and Hearing Research, December 1997, Vol. 40, 1341-1351. doi:10.1044/jslhr.4006.1341
History: Received December 2, 1996 , Accepted June 2, 1997
 
Journal of Speech, Language, and Hearing Research, December 1997, Vol. 40, 1341-1351. doi:10.1044/jslhr.4006.1341
History: Received December 2, 1996; Accepted June 2, 1997

The kinematics of human jaw movements were assessed in terms of the three orientation angles and three positions that characterize the motion of the jaw as a rigid body. The analysis focused on the identification of the jaw’s independent movement dimensions, and was based on an examination of jaw motion paths that were plotted in various combinations of linear and angular coordinate frames. Overall, both behaviors were characterized by independent motion in four degrees of freedom. In general, when jaw movements were plotted to show orientation in the sagittal plane as a function of horizontal position, relatively straight paths were observed. In speech, the slopes and intercepts of these paths varied depending on the phonetic material. The vertical position of the jaw was observed to shift up or down so as to displace the overall form of the sagittal plane motion path of the jaw. Yaw movements were small but independent of pitch, and vertical and horizontal position. In mastication, the slope and intercept of the relationship between pitch and horizontal position were affected by the type of food and its size. However, the range of variation was less than that observed in speech. When vertical jaw position was plotted as a function of horizontal position, the basic form of the path of the jaw was maintained but could be shifted vertically. In general, larger bolus diameters were associated with lower jaw positions throughout the movement. The timing of pitch and yaw motion differed. The most common pattern involved changes in pitch angle during jaw opening followed by a phase predominated by lateral motion (yaw). Thus, in both behaviors there was evidence of independent motion in pitch, yaw, horizontal position, and vertical position. This is consistent with the idea that motions in these degrees of freedom are independently controlled.

Acknowledgments
This research was supported by NIH grant DC-00594 from the National Institute on Deafness and Other Communication Disorders, USA; ATR Human Information Processing Research Laboratories, Japan; NSERC-Canada; FCAR-Québec. The authors also thank Yoh’ichi Tohkura for his support in this research.
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