Journal of Neuroscience, Vol 16, 1570-1579, Copyright © 1996 by Society for Neuroscience
Coarticulation of jaw movements in speech production: is context sensitivity in speech kinematics centrally planned?
DJ Ostry, PL Gribble and VL Gracco
McGill University, Montreal, Quebec, Canada.
Coarticulation in speech production is a phenomenon in which the
articulator movements for a given speech sound vary systematically with the
surrounding sounds and their associated movements. Although these
variations may seem to be planned centrally, without explicit models of the
speech articulators, the kinematic patterns that are attributable to
central control cannot be distinguished from those that arise because of
dynamics and are not represented in the underlying control signals. We
address the origins of coarticulation by comparing the results of empirical
and modeling studies of jaw motion in speech. The simulated kinematics of
sagittal-plane jaw rotation and horizontal jaw translation are compared
with the results of empirical studies in which subjects produce speech-like
sequences at a normal rate and volume. The simulations examine both
"anticipatory" and "carryover" coarticulatory effects. In both cases, the
results show that even when no account is taken of context at the level of
central control, kinematic patterns vary in amplitude and duration as a
function of the magnitude of the preceding or following movement, in the
same manner as that observed empirically in coarticulation. Because at
least some coarticulatory effects may arise from muscle mechanics and jaw
dynamics and not from central control, these factors must be considered
before drawing inferences about control in coarticulation.