MECHANISMS OF SPEECH MOTOR CONTROL

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The overall objective of the proposed research is to identify basic control processes and fundamental organizing principles underlying the control and coordination of speech movements. Within this broader objective are four specific aims: 1) to detail the time- varying motor control properties, 2) to evaluate the extent and degree of sensorimotor contributions to the control, 3) to describe the interaction of the mechanical properties of certain articulators with the ongoing control process, and 4) to characterize the coordination and sequential timing relations during various speech movements. An important component of the proposed research involves the analysis of multiple muscle actions and resulting movements following unanticipated perturbations applied to the lips and jaw prior to and during various speech movement gestures. By systematically varying the timing and waveform characteristics of the perturbations it will be possible to identify afferent-sensitive phases of movement and evaluate the time-varying nature of the underlying control schemes. As such, perturbation of motor output is viewed as a probe into the dynamic nature of the control system as well as a means to evaluate the contributions of somatic sensory afferents to the control of motor output. A second component of the proposed research involves descriptive analysis of multiple muscle and movement variations associated with the production of various sounds and sound combinations requiring differing degrees of lip and jaw actions. To complement the integrative nature of the proposed experiments are preliminary investigations of the mechanical properties of the lips and jaw as they may contribute to or constrain speech movement production. The significance of any hypothetical operation, be it movement scaling or coarticulation, should not be interpreted without consideration of the properties of the physical plant through which behavior is manifest. Overall, the data obtained from the proposed studies should provide important information on the speech motor process from a multidimensional perspective reflecting central-peripheral interactions, time-varying control principles, and serial aNd parallel adjustments of multiple articulators as they reflect on the neurophysiological substrate of speech motor behavior.