Objectives: Pitch change during voice production is under the control of auditive and kinesthetic feedback phenomenona. The aim of the study was to determine the role of larynx kinesthetic feedback in speech production control.
Materials and methods: To validate our laryngeal model, five porcine larynges were excised and placed on a test bench consisting of a blower and a laser photoglottometer for measurement of vocal cord vibration. We applied vibratory stimuli to the cricothyroid muscles to determine whether vibrators supplied by a generator alter the biomechanics of the larynx. Fundamental frequency (F0) was recorded under three conditions--larynx on vibration--larynx on vibration with vibrators activation--larynx on rest and vibrators activation. Once validated, 7 male and 7 female, mean age 29 years, were enrolled. Vibrators were positioned on cricothyroid muscles, cricoid and thyroid cartilages. Masking noise was used. Fundamental frequency, intensity and speech time production was measured during speech production under three conditions--normal speech, vibrators activation, and masking activation.
Results: The preliminary study demonstrated that larynx on vibration with vibrators activation doesn't alter the vocal fold F0. For the human trial, between normal speech and vibrators activation conditions, we found a significant difference (p= 0.045 for male, p= 0.010 for female) in intonation, and no significant difference for intensity and speech time. Between normal speech and masking activation conditions, no significant differences were measured for any condition.
Conclusion: Use of the vibrators is a reliable method to allow the evaluation of larynx kinesthetic feedback in speech production control.