MECHANISMS OF SPEECH MOTOR CONTROL

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The overall objective of the proposed research continues to be to identify basic control processes and fundamental organizing principles for speech production. The present proposal reflects an expansion of the previous project by including a group of collaborators that together will bring diverse and complementary skills and theoretical approaches to bear on some fundamental problems associated with speech motor control. The research is motivated by two basic assumptions. First, speech production is a specialized behavior that functions according to general principles of motor behavior. Thus, investigations of speech movement control and coordination provide important insight into fundamental nervous system principles and their task-dependent adaptations. Second, in order to assess the underlying central organization of the speech motor system, it is necessary to combine empirical studies with detailed modeling. The approach we are taking combines modeling studies with empirical studies which test assumptions about central control. Only in this way is it possible to separate the physiological control signals from the remainder of the biophysical system. The specific aims of the proposed research are: l) To identify the degrees of freedom for jaw, lips and tongue, to characterize how motions in different degrees of freedom are coordinated within each of these articulators , and to identify the electromyographic patterns associated with these basic motions. Empirical data are compared with computer simulations based on the equilibrium point (EP) hypothesis, which makes explicit predictions of both motion kinematics and electromyographic patterns. 2) To determine patterns of inter-articulator coordination based on functional principal component analyses (Ramsay & Dalzell, 1991). The analysis focuses on the patterns of kinematic co-variation among motions of the jaw, lips and tongue in each of their degrees of freedom .3) To examine the sensitivity of intra-articulator motions of the jaw, lips, and tongue to phonetic context. Empirical target shift studies and studies that examine the positions of articulators, and the magnitude and direction of motions are compared with modeling studies to determine the relative contributions of central commands, workspace geometry and articulator dynamics to intra-articulator coarticulation of each of the lips, jaw and tongue. 4) To continue development of a physiological model of jaw movement by including more physiologically-relevant components to the model and incorporating data from the EMG, kinematic, and biomechanical investigations. Finally the data collected in from all components of this research will be used to expand the current physiological model of jaw motion to include the lips and tongue and ultimately their dynamic interaction.