A Model for Neurologic Sources of Aperiodicity in Vocal Fold Vibration The time course of a force twitch in the thyroarytenoid muscle is modeled, and trains of twitches are summed to simulate force tetani. By incorporating means and standard deviations of motoneuron firing rates, and by applying random phase relationships between simulated motor units, a quantitative model of the ripple of ... Research Article
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Research Article  |   June 01, 1991
A Model for Neurologic Sources of Aperiodicity in Vocal Fold Vibration
 
Author Affiliations & Notes
  • Ingo R. Titze
    Department of Speech Pathology and Audiology The University of Iowa; and The Recording and Research Center Denver Center for the Performing Arts, CO
  • Requests for reprints should be sent to Ingo R. Titze, PhD, Voice Acoustics and Biomechanics Laboratory, Department of Speech Pathology and Audiology, The University of Iowa, Iowa City, IA 52242.
Article Information
Speech / Research Articles
Research Article   |   June 01, 1991
A Model for Neurologic Sources of Aperiodicity in Vocal Fold Vibration
Journal of Speech, Language, and Hearing Research, June 1991, Vol. 34, 460-472. doi:10.1044/jshr.3403.460
History: Received January 26, 1990 , Accepted July 13, 1990
 
Journal of Speech, Language, and Hearing Research, June 1991, Vol. 34, 460-472. doi:10.1044/jshr.3403.460
History: Received January 26, 1990; Accepted July 13, 1990

The time course of a force twitch in the thyroarytenoid muscle is modeled, and trains of twitches are summed to simulate force tetani. By incorporating means and standard deviations of motoneuron firing rates, and by applying random phase relationships between simulated motor units, a quantitative model of the ripple of vocal fold tension is obtained. From this ripple, perturbations in fundamental frequency are calculated as a function of the number of motor units in the muscle, the mean and standard deviation of the firing rate of dominant motoneurons, and the variability in the size (twitch amplitude) of the motor units. Predicted perturbations range between 0.2% and 1.2%, depending on the choice of parameters. Perturbation decreases with the number of motor units and with increased mean firing rate, but increases with the variability in motor unit size and with variability in the firing rate. Techniques are discussed by which neurologic jitter might be isolated from other sources of irregularity in vocal fold vibration.

Acknowledgments
The author is indebted to the National Institutes of Health for support of this work under Grant No. NS 24409-02. Discussions with Dr. Erich Luschei and the use of some of his laboratory facilities were highly valued. Special appreciation goes to Linnie Southard for manuscript preparation and to David Druker for graphic support.
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