Gender Perception After Raising Vowel Fundamental and Formant Frequencies: Considerations for Oral Resonance Research.

Objectives: Voice feminization therapy for male-to-female transgender women typically targets increasing fundamental frequency (F). Increasing vowel formant frequencies (FFs) has also been proposed. To better understand formant conditions that shift listeners' perception of gender from male to "not-male," individual and combined vowel FFs were incrementally raised, whereas F was held constant at a gender-ambiguous level.

Methods: The study used a prospective, experimental group design. Using a customized MATLAB program, vowels (/i/, /æ/, /ɑ/, and /u/) spoken by an adult were manipulated by isolating and increasing FF until they matched those of a woman. Listeners heard randomized samples and perceptually categorized each as male, female, or gender neutral. The latter two choices were combined and labeled not-male.

Results: Chi-square analyses revealed that listeners rated samples as not-male for /ɑ/ and /æ/ with all three formants shifted or individual formants shifted at >60%. Individual analysis of vowels, formants, and shifted FF using Kruskal-Wallis revealed a statistical significance for vowels only.

Conclusions: Results suggest that voice was convincingly perceived as not-male, for vowels characterized by a high F frequency, and that raising FFs for all four vowels increased (in varying amounts) the perception of voice femininity beyond that of raising F alone.