David J. Ostry
McGill Univ., Montreal, PQ H3A 1B1, Canada
Vincent L. Gracco
Haskins Labs., New Haven, CT 06511
Does the nervous system take account of upcoming phonetic context when planning successive movements of a speech articulator? The kinematics of intra-articulator coarticulation are readily measurable in empirical studies and may appear to be centrally controlled on the basis of kinematic changes which arise in response to upcoming phonetic segments. However, without explicit models of speech articulators, measured kinematic effects correctly attributable to central planning cannot be distinguished from the kinematic patterns which are due to dynamics and are not represented in the underlying control. In the present paper, this question is addressed by comparing the results of empirical and modeling studies of jaw motion. The simulated kinematics of sagittal plane jaw rotation and horizontal jaw translation are compared to empirical studies in which subjects produce CVC sequences at a normal rate and volume. The jaw motion simulations show that even when control signals underlying the initial CV transition are fixed, ``anticipatory'' kinematic patterns vary in amplitude and duration as a function of upcoming context. This suggests that unplanned effects due to articulator dynamics must be accounted for before drawing conclusions about the role of central control in intra-articulator coarticulation. [Work supported by NIH Grant CD-00594.]