A model for neurologic sources of vocal instability
Ingo R. Titze · The Journal of the Acoustical Society of America · 1988
The activation and relaxation characteristis of thyroarytenoid and cricothyroid muscle twitches are used as basic building blocks to simulate a tetanic contraction in the laryngeal muscles. Approximately 100 motor units are used with random phase relationships and randomized firing rates. The fundamental frequency of the voice is calculated from the simulated tensions, and it is shown that jitter and shimmer vary inversely with mean motor unit firing rate and with the number of motor units within a given muscle. Jitter and shimmer vary directly with the coefficient of variation of motor unit size. Some low-frequency variations in F0 (tremor-like variation) are correlated with the mean firing rate of large single motor units. [Work supported by NINCDS Grant No. NS24409–02.]