Vocal cord vibration and speech waveform in diplophonia.

Abstract

Simultaneous recording of vocal cord vibration and speech signal was conducted on the three diplophonic cases using a high-speed digital imaging technique recently developed at our institute. All three cases [unilateral paralysis of recurrent nerve(1) and external branch of superior laryngeal nerve(2)] show a difference in the vibratory frequency between the left and right vocal folds. During successive cycles, the phase difference progressively becomes larger. At a certain point, when it exceeds a threshold, the phase difference is reset and the vocal cord movements resume synchrony. This pattern is in good agreement with that described by Moore. When the movements of the vocal cords are in phase, the glottal closure is complete and the excitation pattern in speech waveform is large, whereas when the movements are out of phase, the glottal closure is incomplete and the excitation pattern is weak. This quasiperiodic variation in speech waveform appears to be related to the diplophonic voice quality in the present cases.