ASA 127th Meeting M.I.T. 1994 June 6-10

3pSP10. A model of jaw movement control based on the equilibrium point hypothesis.

R. Laboissierre

Inst. de la Commun. Parlee, INPG, 46 Ave. Felix Viallet, 38031 Grenoble Cedex 1, France

D. J. Ostry

McGill Univ., Montreal, Canada

A. G. Feldman

Univ. of Montreal, Montreal, Canada

A seven muscle model of human jaw and hyoid motion based on the equilibrium point hypothesis of motor control ((lambda) model) is presented. The form of central neural control signals underlying speech and whether jaw muscle geometry needs to be accounted for in speech planning is explored. According to the model, central neural commands specify the equilibrium position of the jaw by controlling the muscle lengths ((lambda)'s) at which motoneuron recruitment begins. Motor functions are specified by various combinations of (lambda)'s. One combination of (lambda)'s is associated with the level of coactivation of muscles. Others are associated with motions in specific degrees of freedom such as jaw rotation and translation. The vertical and horizontal positions of the hyoid may also be controlled. These control signals may act alone or be superimposed to produce combinations of rotation, translation, and muscle cocontraction. It is demonstrated that in each phase of movement, constant velocity shifts in threshold lengths of all muscles can account for patterns of jaw motion in speech. It is also assessed whether the same commands for rotation and translation would produce essentially the same movements from any starting jaw position. [Work supported by ATR Human Information Processing Research Laboratories, Japan; NSERC, Canada; Quebec-France.]