Lip and Jaw Motor Control during Speech: Motor Reorganization Responses to External Interference

Step function resistive loads were applied selectively to jaw movements during ongoing speech production. These loads were intentionally initiated during the jaw closing movement associated with the production of bilabial stops, resulting in a situation where bilabial closure would be disrupted if ongoing control were open‐loop. Three subjects were observed during control and experimental conditions. In almost all utterance where a load was introduced, closure of the lips was achieved and the bilabial stop was adequately produced. To assess the nature of this closed‐loop control, displacement of the upper lip, lower lip, and jaw (in the inferior‐superior dimension) were recorded along with EMG from the medial pterygoid, anterior tem‐poralis, masseter, and orbicularis otis superior muscles. Based on the observation of these variables, it appears that the muscles of the lips as well as those of the jaw were involved in feedback‐controlled motor reorganization.