Asymmetric and symmetric vocal fold oscillation in the excised squirrel monkey larynx

The larynges of nine squirrel monkeys were harvested, dissected, mounted on a tapered pseudotracheal tube, and phonated using heated and humidified air. The patterns of oscillation of the vocal folds were videotaped with stroboscopic illumination, and simultaneous measurements of airflow, subglottal pressure, and audio signal were obtained. The pressure wave and audio signal were subjected to spectral and phase portrait analysis methods. It was found that the left vocal fold tended to oscillate at lower subglottal pressure compared to the right vocal fold. This resulted in unilateral oscillation. Bilateral oscillation was seen at higher subglottal pressures. Patterns of symmetric and asymmetric bilateral oscillations were observed.