Gradations in a pattern of neuromuscular activity associated with stuttering.

EMGs were recorded from muscles of the lip, jaw, and neck during conversational speech of 17 stuttering subjects. Averaged power spectra and coherence between pairs of EMGs were computed. Results indicate that tremorlike oscillations in the range of 5-15 Hz and high amplitudes of EMGs occupy a common continuum of motor patterns that may occur in stuttering. In subjects whose results fell at the strong end of this continuum, stuttered speech was distinguished by widely distributed, high-amplitude oscillations and relatively high coherence at the frequency of oscillation. At the other extreme, neither oscillatory activity nor amplitude was greater for stuttered speech; in fact stuttered and fluent speech were often associated with approximately equal EMG amplitude. These results suggest that there is not a single set of physiological events that uniformly characterize stuttering in all individuals; rather, events such as the occurrence of high-amplitude oscillations occur at different strengths in different individuals.