Short-latency changes in voice F-0 and neck surface EMG induced by mechanical perturbations of the larynx during sustained vowel phonation

Nineteen healthy young adult males with normal voice and speech attempted t o sustain the vowel /u/ at a constant pitch (target: 180 Hz) and a constant and comfortable loudness level while receiving a sudden mechanical perturb ation to the larynx (thyroid prominence) via a servo-controlled probe. The probe moved toward or away from the larynx in a ramp-and-hold fashion (3.3- mm displacement, 0.7 N force, 20-ms rise time, 250-ms duration) as the subj ects attempted to maintain a constant probe-larynx pressure. Eighty stimuli were applied in each direction, one stimulus per phonation. Pairs of surfa ce electromyography (EMG) electrodes were attached to the skin of the anter ior neck over laryngeal, infra-laryngeal, and supralaryngeal areas. The rec tified EMG signals, the voltage analog of the voice fundamental Frequency ( VAF(0)), and the voltage analog of the probe displacement were digitized an d signal-averaged relative to the onset of the stimulus. Sudden perturbatio n of the larynx induced an instantaneous decrease or increase in VAF(0), de pending on the direction of the probe's movement, and a short-latency incre ase in the EMG (30-35 ms) and VAF(0) (55-65 ms). We argue that the instanta neous VAF(0) change was related to a mechanical effect, and the short-laten cy VAF(0) and EMG changes to reflexogenic effects-the latter most likely as sociated with both intrinsic and extrinsic laryngeal sensorimotor mechanism s. Further physiological studies are needed to elucidate the sources of the VAF(0) and EMG responses. Once elucidated, the present method may provide a powerful noninvasive tool for studying laryngeal neurophysiology. The the oretical and clinical implications of the present findings ore addressed.