Task-specific organization of activity in human jaw muscles.

Coordination of jaw muscle activity for speech production sometimes has been modeled using nonspeech behaviors. This orientation has been especially true in representations of mandibular movement in which the synergy of jaw muscles for speech production has been suggested to be derived from the central pattern generator (CPG) for chewing. The present investigation compared the coordination of EMG activity in mandibular muscles over a range of speech and nonspeech tasks. Results of a cross-correlational analysis between EMG signals demonstrated that the muscle synergies of the mandibular system depend on task demands. Contrary to some of the models discussed, continuous speech production yielded activation patterns that were clearly not related to coordinative patterns generated by the chewing CPG.