Adaptation
to motion dependent loads in speech production
By D.J. Ostry,
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.