Examining the Effect of Volitionally Altering Fundamental Frequency on Measures Associated With Vocal Hyperfunction

Speech-language pathologists who work with transgender and nonbinary individuals are often concerned about introducing vocal hyperfunction (VH) while supporting the use of a more gender-congruent voice. The current study examined the effects of volitionally altering fundamental frequency (f_o) on measures associated with VH. Forty (20 female, 20 male) speakers with no vocal complaints and who did not identify as transgender were recruited. Speakers were recorded in two conditions: habitual f_o and altered f_o. In the altered f_o condition, speakers volitionally altered their f_o by two semitones in the stereotypical direction desired by transgender and nonbinary speakers with the same vocal anatomy: females lowered their f_o and males raised their f_o. A total of 13 acoustic, aerodynamic, videostroboscopic, and perceptual (self- and other) measures were assessed. Of the 13 measures, 7 were statistically affected by the two-way interaction between sex and f_o condition. Only three measures had medium or larger effect sizes. Compared to using a habitual f_o, females used longer vocal tract lengths, and higher smoothed cepstral peak prominences (CPPS) and low to high (L/H) ratios when lowering f_o and males used shorter vocal tract lengths and lower L/H ratios when raising f_o. In general, vocalizations produced with a volitionally altered f_o were more consistent with those in speakers with VH than vocalizations produced with a habitual f_o. In response to altering f_o, females had more measures that differed than males. This is counter to expectations given that males raised their f_o and using a higher f_o is associated with increased laryngeal tension. That being said, many of the changes reflected the physiological adjustments required to achieve an externally specified f_o target.