| Description |
Vocal tremor is a neurogenic voice disorder characterized by rhythmic modulation of pitch and loudness during sustained phonation and is acoustically measured as modulation of formants, fundamental frequency (fo), and sound pressure level (SPL). To date, links between oscillating vocal tract structures and acoustic modulation of the first two formants were shown in those with vocal tremor. However, laryngeal and respiratory contributions to acoustic modulation patterns in those with vocal tremor are difficult to separate. The purpose of this study was to compare acoustic patterns associated with volitional laryngeal versus respiratory structure oscillations in trained singers. Laryngeal oscillation was hypothesized to correspond with fo modulation patterns, whereas respiratory system oscillation was hypothesized to correspond with SPL modulation. Ten classically trained female singers with no less than 5 years' experience and no history or current complaints of voicing problems were recruited between 40-65 years of age. All participants underwent simultaneous recording of nasoendoscopic views of the larynx, respiratory kinematic and acoustic signals during three trials of sustained phonation of /i/ using either vibrato or the Accented Method of Voicing (AMV). Normalized measures of signal modulation rate and magnitude were completed on the acoustic (fo and SPL) and kinematic recordings. A mixed effects logistic regression compared within subject measurement differences between voicing conditions. The results showed significantly greater magnitude of respiratory kinematics during AMV (47.5% (+1.2)) than for vibrato (0% (+0) (p < .001) corresponding with significantly greater SPL modulation magnitude (AMV = 40% (+20); vibrato = (10% (+0)), respectively (p = .026). A significant difference was also found between voicing conditions for modulation rate of fo (p = .049) and SPL (p < .001). The rates of modulation during AMV were slower (fo = 2.8 (+ .8) Hz; SPL = 2.1 (+ .7) Hz) than for vibrato (fo = 5.1 (+ .7) Hz; SPL = 5 (+ .6) Hz). However, laryngeal kinematic and acoustic fo and SPL magnitude patterns did not differ between voicing conditions. Outcomes support predicted contributions of the respiratory system to voicing modulation; however, the larynx appears interactive with the respiratory and other speech structures during voicing. |
