Intentional responses to kinesthetic stimuli in orofacial muscles: implications for the coordination of speech movements.

Reaction times (RTs) from human orofacial muscles were obtained with labial displacement and auditory stimuli to evaluate the potential for contributions by these sensorimotor processes to speech movement coordination. Because speech requires both concurrent and sequential movements, intramovement (labial stimulus, labial response) and intermovement (labial stimulus, lingual response) RT minima were examined. Intramovement and intermovement RT minima were from 46 to 52 msec. Response-related reductions in background muscle activity were observed with latencies as short as 35 msec. These observations indicate a potentially important role for RT processes in the coordination of speech movements. These control processes would appear to be open-loop and predictive.