The Effect of Intentional Voice Quality Alteration on Mental Effort as Measured via Pupillometry and Self-Report Scales.

Purpose: Mental effort is theoretically and qualitatively known to increase when individuals intentionally alter their voice quality, as they learn to do in voice therapy or voice training. The purpose of this study was to examine the effect of voice quality alteration on mental effort using both (objective) cognitive pupillometry methods and (subjective) self-report scales, as well as to examine the association between these two measurement approaches. Method: In a within-participant repeated-measures design, the intentional production of three voice qualities--fry, breathy, and twang--was compared to habitual voice production for its effect on pupil dilation and on the Borg Category Ratio-10 Mental Effort Scale and the National Aeronautics and Space Administration Task Load Index Mental Effort subscale. Results: For all three intentionally altered voices--fry, breathy, and twang--pupil dilation and perceived self-report yielded significant positive effects with very large effect sizes. The association between pupil dilation in millimeter and selfreport scale values was significant, moderate, and positive. Exploratory investigation also suggested that twang and breathy voices were more demanding than fry, and that a baseline subtraction was more meaningful and powerful approach to baseline correction than baseline division. Conclusions: As hypothesized, intentional voice quality change yields both significant increases in pupil dilation and perceived mental effort. These measures were moderately associated. Findings are fundamental to clinical and artistic endeavors requiring intentional voice quality change. [ABSTRACT FROM AUTHOR]