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

Simultaneous recording of vocal fold vibrations and speech signals wer e performed with three patients having diplophonia using a high-speed digital image recording system developed by the present authors. All t hree cases studied (1 case of unilateral paralysis of the recurrent ne rve; 2 cases of unilateral paralysis of external branch of the superio r laryngeal nerve) showed a difference in the vibratory frequency betw een the left and right vocal folds. The phase difference between the v ocal cords varies with time. When it reaches a certain threshold, the phase difference is reset and the vocal cord movements resumes synchro ny. When the movements of the vocal cords are in phase, glottal closur e is complete and the excitation pattern in the speech waveform is str ong, whereas when the movements are out of phase, glottal closure is i ncomplete and the excitation pattern is weak, resulting in a quasi-per iodic vibration in speech waveform.