COARTICULATION OF JAW MOVEMENTS IN SPEECH PRODUCTION - IS CONTEXT SENSITIVITY IN SPEECH KINEMATICS CENTRALLY PLANNED

Coarticulation in speech production is a phenomenon in which the artic ulator movements for a given speech sound vary systematically with the surrounding sounds and their associated movements. Although these var iations may seem to be planned centrally, without explicit models of t he speech articulators, the kinematic patterns that are attributable t o central control cannot be distinguished from those that arise becaus e of dynamics and are not represented in the underlying control signal s. We address the origins of coarticulation by comparing the results o f empirical and modeling studies of jaw motion in speech, The simulate d kinematics of sagittal-plane jaw rotation and horizontal jaw transla tion are compared with the results of empirical studies in which subje cts produce speech-like sequences at a normal rate and volume, The sim ulations examine both ''anticipatory'' and ''carryover'' coarticulator y effects. In both cases, the results show that even when no account i s 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 e mpirically in coarticulation. Because al least some coarticulatory eff ects may arise from muscle mechanics and jaw dynamics and not from cen tral control, these factors must be considered before drawing inferenc es about control in coarticulation.