Motor control for a physiological articulatory model involving muscle antagonism

By J. Dang and K. Honda

A 3D physiological articulatory model with a target-based control strategy has been developed by the authors. This study introduces muscle antagonism in the control strategy to insure both stability and controllability of the tongue and jaw. Articulatory targets in the model are defined by goal positions for three control points (CPs) of jaw, tongue tip, and tongue dorsum, where the CP (usually one of the three) crucial for producing a phoneme is defined directly by a goal position and the others are predicted mainly according to the corresponding CP in the following targets. To realize the coarticulation, distribution of articulatory movements of the CPs was investigated based on X-ray microbeam data, and used as a constraint for the predicted goal positions. To guarantee the movement of the crucial CP, activation of the antagonist muscles is reduced by accounting for the negative components of the movement parallel to the muscle contraction force vector. This procedure is realized by introducing weight coefficients for the antagonist muscles in calculation of the total muscle activation signals. After accounting for the muscle antagonism, model behaviors are improved in static configurations and dynamic characteristics.