The Effects of Humming on the Prephonatory Vocal Fold Motions Under High-Speed Digital Imaging in Nondysphonic Speakers

Objectives. This study aimed to investigate whether humming affects the adductive motion of the vocal folds and transient glottal closure in the prephonatory adjustment phase of vocal onset using high-speed digital imaging ( HSDI) and a motion analysis software program. Methods. Twenty normal healthy adults without any vocal abnormalities were enrolled. While a transnasal flexible fiberscope connected to a high-speed camera was inserted, each participant was asked to perform three phonatory tasksnatural /e:/phonation, loud /e:/phonation, and humming /m:/phonation-and laryngeal HSDI movies (4000 frame/s) were recorded. On each HSDI movie, the duration of the prephonatory glottal closure was measured. In addition, using motion analysis, the changes in the angle between the bilateral vocal folds during vocal fold adduction and the average angular velocity in the ranges of 100%-80%, 80%-20%, and 20%-0% from all of the angular changes were analyzed. Results. The angular changes showed sigmoid and polynomial-like curves during the natural/humming and loud phonation, respectively, and the 80%-20% and 20%-0% average velocities were the highest during the natural/humming and loud phonation, respectively. The humming phonation decreased all of the average regional velocities, eliminated the transient prephonatory glottal closures observed during the natural and loud phonation, and induced a greater value for the minimal angle than the natural phonation. Conclusions. The present study demonstrates that humming encourages easy vocal initiation by decelerating the vocal fold adductive motion throughout the prephonatory adjustment phase and alleviating transient prephonatory laryngeal closure, leading to gradual and smooth vocal fold positioning.