Acoustic Reflections of Vocal Adjustments Elicited With a Standard Reading Passage: Effect of Voice Disorders

This study examined acoustic variations reflecting voice source and vocal tract filter adjustments while reading aloud the "Three Bears Passage" designed for eliciting significant variations in vocal production.

Acoustic analysis was conducted on audio recordings of the passage for 30 adults with voice disorders and 30 age- and sex-matched normal controls. The first four formant frequencies (F1-F4), vocal tract length (VTL) estimated from F3 and F4, and formant dispersion (FD; averaged difference between successive formants) of the vowel /a/ in a keyword of the passage's most dramatic sentence, mean fundamental frequency (f_o) of the sentence and pitch range of the passage were measured with Praat. Measurements were compared across participant groups and across mimicries of bear characters versus a narrator voice.

Significantly lower mean f_o, F1, and F2 were observed for the mimicked Papa Bear compared to Mama and Baby Bears, with more limited mean f_o variations across characters for the disorders group, and formant variations across characters unaffected by voice disorders. No significant differences in VTL and FD were found across characters. Significantly higher F4, larger FD, lower mean f_o, and more restricted pitch range were found for the disorders group relative to normal controls.

Our findings suggested that emotionally expressive speech while reading the passage was accomplished through both source (f_o) and filter (F4, FD) adjustments, with distinct strategies for mimicking the bear characters. Participants with voice disorders showed limitations in pitch modulations, with relatively preserved flexibility for vocal tract modifications. Their significantly larger FD and higher F4 could reflect compensatory vocal tract adjustments including epilarynx tube narrowing and elevated laryngeal positioning. Future studies should incorporate auditory-perceptual, articulatory and imaging measures to better examine the source and filter adjustments and to further validate the passage as a clinical tool for voice assessment and therapy.