HIGH-SPEED DIGITAL IMAGE-ANALYSIS OF VOCAL CORD VIBRATION IN DIPLOPHONIA

Simultaneous recording of vocal fold vibrations and speech signals were performed with three patients having diplophonia using a high-speed digital image recording system developed by the present authors. All three cases studied (1 case of unilateral paralysis of the recurrent nerve; 2 cases of unilateral paralysis of external branch of the superior laryngeal nerve) showed a difference in the vibratory frequency between the left and right vocal folds. The phase difference between the vocal cords varies with time. When it reaches a certain threshold, the phase difference is reset and the vocal cord movements resumes synchrony. When the movements of the vocal cords are in phase, glottal closure is complete and the excitation pattern in the speech waveform is strong, whereas when the movements are out of phase, glottal closure is incomplete and the excitation pattern is weak, resulting in a quasi-periodic vibration in speech waveform.