Effects of voice therapy on relative fundamental frequency during voicing offset and onset in patients with vocal hyperfunction.

PURPOSE The purpose of this study was to determine whether the relative fundamental frequency (RFF) surrounding a voiceless consonant in patients with hyperfunctionally related voice disorders would normalize after a successful course of voice therapy. METHOD Pre- and posttherapy measurements of RFF were compared in 16 subjects undergoing voice therapy for voice disorders associated with vocal hyperfunction. RESULTS A 2-way analysis of variance showed a statistically significant effect of both cycle of vibration near the consonant and therapy phase (pre- vs. post-), with p < .001. A post hoc paired Student's t test showed that posttherapy RFF measurements were significantly higher (more typical; p < .0001) than pretherapy measurements. CONCLUSIONS Prior to therapy, participants exhibited lowered RFF values, similar to those found previously (Stepp, Hillman, & Heaton, 2010). After successful completion of voice therapy, RFF values increased toward patterns seen previously in individuals with healthy typical voice. The goal of voice therapy in these patients was to reduce laryngeal muscle tension; therefore, the increase of RFF toward more typical values may be indicative of decreased baseline laryngeal muscle tension resulting from therapy. Results are discussed further in terms of necessary research to incorporate RFF as a clinical measure of vocal hyperfunction.