Michael D. McClean
John L. Clay
Audiol. and Speech Ctr., Walter Reed Army Med. Ctr., Washington, DC 20307-5001
In order to clarify the nature of EMG-kinematic relationships involved in speech production, a rudimentary computer model of the lower lip as a neuromechanical system was developed. The model consists of three muscles having forcing functions that act on a common point. Each muscle is treated as a set of single motor units with associated motoneuron spike activity and muscle-unit twitch forces. The temporal patterns of motoneuron spike trains, which serve as the system input, are based on single motor unit EMG recordings obtained during syllable repetition [M. McClean and J. Clay, Society for Neuroscience Abstracts 19, 229.15 (1993)]. System output is evaluated in terms of lower-lip movement through the midsagittal plane. Simulations produce realistic movement patterns when they are constrained by reasonable assumptions about motor unit intrinsic properties, muscle force angles, and relative timing of motoneuron spike trains. Initial applications of the model have focused on the mechanisms of speech rate control. Different rates of syllable production are established by the overall temporal patterns of motoneuron spike trains, and the effects of varying system parameters are evaluated at each rate.