Intrinsic laryngeal muscle activity and vocal fold adduction patterns in female vocal registers: chest, chestmix, and headmix

Although there have been numerous investigations of laryngeal muscle activity during phonation in the chest and falsetto/head registers in trained and untrained classical singers and non-singers, no research has been conducted examining laryngeal muscle activity during phonation in the chestmix register, a register used extensively by many female commercial singers, particularly for the production of higher frequencies. The purpose of this study was to test the hypothesis that commercial singers produce chestmix by maintaining or increasing adduction of the vocal processes and by engaging the thyroarytenoid muscle to a greater degree than they would to produce a head register sound. Simultaneous recordings of thyroarytenoid and cricothyroid muscle activity, videonasendosopy, and audio were obtained from seven female commercial singers (5 trained, 2 untrained) during sustained phonation and song phrases produced in chest, chestmix, headmix, and head registers. Thryoarytenoid and cricothyroid muscle activity was normalized to a percent of mean maximum activity and compared across registers and frequencies both within subjects and across subjects. Video stills of vocal processes adduction patterns were rated for degree of vocal processes adduction and also compared across register and frequency within and across subjects. All audio samples were rated for register by two singing teachers and audio samples of sustained phonation were analyzed via Fast Fourier Transform to measure the number and energy of the harmonics present in each sample. Interjudge and intrajudge reliability tests were performed for both the vocal processes adduction rating and audio sample rating tasks. Results from the study confirmed the hypothesis and showed that thyroarytenoid activity and adduction of the vocal processes was greater for chestmix than headmix or head, particularly during production of higher frequencies, but less than for chest productions. Cricothyroid activity was similar for chestmix, headmix and head during production of lower frequencies, but greater for chestmix during production of higher frequencies.