Adaptation to motion dependent loads in speech production

By D.J. Ostry, S. Tremblay, and D.M. Shiller

 

                Studies of adaptation to motion dependent force fields have provided a useful way to determine the kind of information that is used by the nervous system for the control of movement. Successful adaptation is a demonstration that dynamics and loads are accounted for in motion planning. Typically, upper limb movement to visual targets has served as a model for force field learning and generalization. It has been suggested that orofacial movement in speech production is similarly based on information concerning the geometry and the dynamics of the vocal tract structures, few tests of this idea have been reported. In the current study, we measured acoustic and kinematic adaptation of jaw movement to motion dependent loads using a computer-controlled robotic device that is coupled to the jaw. We show that following multiple repetitions of a single speech utterance, subjects performance approaches patterns observed in the absence of load. As in limb movement, after-effects were observed following the unexpected removal of load indicating that subject adjusted the time-varying control signals to jaw muscles in order to compensate. The results are consistent with the idea that the nervous system takes account of dynamics in orofacial motor planning.