Human Auditory-laryngeal Reflex

Abstract

The mammalian larynx reacts promptly to external stimuli for protective and phonatory purposes. In particular, human speech has been thought to have an elaborate laryngeal control mechanism through the auditory system, although this has not yet been proved by empirical data. In the present study, the mechanism of laryngeal control through the auditory system was studied in terms of change in activity of the intrinsic laryngeal muscles.
Healthy adults maintained phonation at a constant voice pitch while receiving repeated click-sound stimuli in both ears. The voice signal was transduced with a throat microphone and bandpass filtered to isolate the fundamental frequency (FO). Average values for about 40 recordings of this FO voltage at various click-sound stimuli were determind. The muscle activity of the larynx was recorded with bipolar wire electrodes inserted into the crico-thyroid muscles and/or the lateral crico-arytenoid muscles. The induced EMG (electromyographic)potentials were rectified, the average of about 80 values was calculated and the activity change in the intrinsic laryngeal muscles caused by the auditory stimulus was determined.
1) A short-latency change in FO (about 50 msec) was noted in response to auditory stimulation.
2) In most subjects who received sound stimulation of more than 90 dB during high pitch phonation, muscle activity increased with a steady latency, as shown by the electromyogram.
3) The average time from the stimulus to the maximum amplitude of muscle activity was about 26 msec for the crico-thyroid muscle on both sides, about 45 msec for the right lateral crico-arytenoid muscle and about 47 msec for the left lateral cricoarytenoid muscle.