Human laryngeal responses to auditory stimulation

In spite of various claims for the presence and functional significance of brainstem reflexes in phonatory control, very little is known about these reflexes in humans. The present study was aimed at studying auditory-laryngeal reflexes in human subjects during sustained phonation. Fourteen subjects sustained phonation at constant voice pitch and voice intensity while receiving auditory stimulation with clicks of different intensity levels. Electromyographic (EMG) recordings from the cricothyroid muscle were obtained in two of the subjects. The voice signal was transduced with a throat microphone and bandpass filtered to isolate the fundamental frequency (F0). The filtered signal was fed to a frequency meter, which yielded a voltage proportional to F0. This F0 voltage and the rectified EMG were signal averaged relative to the click. Short-latency changes in F0 (50 ms) and in cricothyroid EMG (11 ms) were observed in response to auditory stimulation. The magnitude of the EMG and F0 responses were well correlated with each other and with the intensity of the stimulus. The EMG response did not habituate with repeated stimulation. The neuromuscular origins of the auditory-laryngeal reflexes and their significance to phonatory control are discussed.