Association of orofacial with laryngeal and respiratory motor output during speech

By M.D. McClean and S.M. Tasko

Speech motor coordination most likely involves synaptic coupling among neural systems that innervate orofacial, laryngeal, and respiratory motor units. The nature and strength of this coupling was studied indirectly by correlating orofacial speeds with fundamental frequency, vocal intensity, and inspiratory volume during speech. Fourteen adult subjects repeated a simple test utterance at varying rates and intensities while recordings were obtained of the acoustic signal and movements of the upper lip, lower lip, tongue, jaw, rib cage, and abdomen. Across subjects and orofacial structures, orofacial speed showed significant correlations with fundamental frequency in 42 of 56 cases (14 subjects x 4 structures), with intensity in 35 of 56 cases, and with inspiratory volume in 14 of 56 cases. These results support the view that there is common neural drive during speech production to orofacial, laryngeal and respiratory muscle systems. Comparisons between the four orofacial structures revealed higher correlations for the jaw relative to lips and tongue in 90 of 126 cases (p < 0.0001). This suggests that among orofacial muscle systems studied, the jaw has the strongest neural connectivity with the laryngeal and respiratory systems.