Vocal Tract Configurations of Professional Operatic Singers During Sustained Phonation

In voice production, interactions occur between the oscillating vocal folds, the respiratory system, and the vocal tract. However, it is not yet sufficiently understood how the respiratory system could affect the vocal tract configuration. It is hypothesized that a reduction in tracheal pull, caused by decreasing lung volume, along with shifts in dominant exhalation forces (from inspiratory to expiratory muscles), leads to a larynx elevation with shortening of the vocal tract tube, and consecutively, articulatory adjustments to preserve consistent sound quality.

Seventeen professional operatic singers performed a maximum phonation time task on comfortable pitch while being recorded with dynamic 2D-magnetic resonance imaging (MRI) (25 fps, pixel resolution of 1.6 x 1.6 mm²) including simultaneous audio recording. From the MRI footage, articulatory movements were calculated for vertical larynx position, pharynx width at the narrowest point, lip opening, jaw opening, and jaw protrusion. Spectral data were extracted from the audio signals after noise reduction.

The larynx moved in cranial direction in 5 of 9 female and 3 of 8 male participants during the phonatory exhalation. Such movement was directly counteracted by other articulators in four cases. In 12 of the subjects, articulatory and/or spectral events in the form of adaptions or twitches occurred around and after 50% of the phonation time. Most subjects exhibited changes in articulator positioning as well as adjustments to the subsequently sustained fundamental frequency during the first and last 10% of the sustained phonation.

The articulatory movements during the task were non-systematic. Sudden events/adaptations in the second half of the phonatory exhalation could potentially mark a passage of the REL. The cranial movement of the larynx could be attributed to the decreasing tracheal pull; however, this was not evident in all subjects, suggesting a high degree of individuality in the regulation of respiratory movement in relation to vertical larynx position. Overall, the data indicate that it is important to consider continuous and sudden articulatory movements during sustained measurements.