Humming Facilitates a Gradual Increase in Vocal Intensity by Alleviating the Enhancement of Vocal Fold Contact and Supraglottic Constriction

SUMMARY Objectives This study aimed to assess whether or not humming can help increase vocal intensity gradually with only a slight increase in the glottal contact and supraglottic compression. Methods Seventeen healthy nondysphonic speakers were asked to perform two phonatory tasks in order: gradually increasing vocal loudness (crescendo) during sustained phonation of a vowel or production of a hum (vowel- or humming-crescendo task: VCT or HCT, respectively), while the sound pressure levels (SPL), electroglottographic (EGG) signals and high-speed laryngeal movies were simultaneously recorded. The glottal contact parameter of the EGG signals and the glottal opening and laryngeal outlet parameters as well as the duration of prephonatory transient glottal closure on the laryngeal movies were calculated. Results With a gradual SPL increase during both tasks, most participants showed a progressive decrease in the LO, but no discernible change in the EGG glottal contact. In comparisons between tasks, an HCT produced a significantly lower SPL, greater laryngeal outlet parameter value and shorter prephonatory transient glottal closure duration than a VCT. A significant difference between tasks was found in the proportion of failed task performance due to an abrupt SPL increase (41% and 6% in VCT and HCT, respectively; P  = 0.011), and the failed VCTs showed a significantly higher EGG contact parameter value than the successful VCTs. Conclusion These results demonstrate that during an gradual increase in vocal intensity, humming alleviates the enhancement in both the glottal contact and supraglottic compression, leading to the prevention of an abrupt increase in vocal intensity instead of adequate vocal output.