Effects of phonetic context on relative fundamental frequency.

PURPOSE The effect of phonetic context on relative fundamental frequency (RFF) was examined, in order to develop stimuli sets with minimal within-speaker variability that can be implemented in future clinical protocols. METHOD Sixteen speakers with healthy voices produced RFF stimuli. Uniform utterances consisted of 3 repetitions of the same voiced sonorant-voiceless consonant-voiced sonorant speech sequence; moderately variable sentences contained speech sequences with a single voiceless phoneme (/f/, /s/, /ʃ/, /p/, /t/, or /k/); highly variable sentences were loaded with speech sequences using multiple phonemes. Effects of stimulus type (uniform, moderately variable, and highly variable) and phoneme identity (/f/, /s/, /ʃ/, /p/, /t/, and /k/) on RFF means and standard deviations were determined. RESULTS Stimulus type and the interaction of vocal cycle and stimulus type were significant for RFF means and standard deviations but with small effect sizes. Phoneme identity and the interaction of vocal cycle and phoneme identity on RFF means and standard deviations were also significant with small to medium effect sizes. CONCLUSIONS For speakers with healthy voices, uniform utterances with /f/ and /ʃ/ have the lowest standard deviations and thus are recommended for RFF-based assessments. Future work is necessary to extend these findings to disordered voices.