Sensorimotor Mechanisms in Speech Motor Control*

A conceptual model of speech motor control is developed in which the elemental units for speech are sound-producing coordinated movements of the vocal tract. The perspective taken is that the degrees of control freedom are at a system level; in the operation of the processes that implement the speech motor action. Speech motor control is conceptualized as a multistage parallel process in which vocal tract specifications are activated by central motor commands which interact with a central rhythmic output to produce serial coordinated movements required for sound generation. Vocal tract specifications include the selection of characteristic neuromotor patterns, which map isomorphically onto the phonemes of the language. Coordination of the contributing movements and on-line spatial adjustments within and among vocal tract structures are inherent in the neuromotor patterning and activation processes, respectively. The elemental units are retrievable patterns stored in the central nervous system and instantiated by the directed action of the posterior parietal cortex. Two major brain systems (basal ganglia-supplementary motor area and the cerebellar-premotor area), are proposed to play major roles in implementing neuromotor specifications by modulating the characteristic patterns and the sequencing their actions into larger meaningful units of production. It is the action and interaction of these sensorimotor mechanisms that result in the speech motor patterns characteristic of human verbal communication.