Direction of Cepstral Peak Prominence Change Moderates Divergent Kinematic Responses to Voice Stimulability Testing

Stimulability testing is frequently used in managing phonotraumatic vocal fold lesions (PVFLs) to identify strategies that may improve phonatory ease and quality, but little is known about what immediate physiological changes occur during stimulability testing. High-speed videoendoscopy (HSV) enables direct visualization of vocal fold kinematics, and cepstral peak prominence (CPP) is an objective acoustic correlate of voice quality and spectral periodicity. Though increases in CPP are traditionally interpreted as improvement, CPP may instead reflect movement toward the individual's optimal physiological target. For some, therapeutic focus involves reducing pressed phonation and increasing airflow, which may decrease CPP despite perceptual improvement. For others, efficient resonance and balanced phonation could increase CPP. This study examined whether (1) average HSV parameters change after stimulability testing and (2) CPP direction reflects distinct kinematic patterns.

Twenty-seven women with PVFLs were assessed before and after a standardized stimulability protocol using resonant voice facilitators. HSV was conducted on /i:/ in the modal register using a transoral rigid scope. Exams were collected at 4000 frames per second. HSV parameters included closing quotient (ClQ), normalized maximum area declination rate (MADRn), speed index (SI), stiffness index (STI), phase asymmetry index (PAI), time periodicity, and waveform symmetry index. CPP was extracted from simultaneous acoustic recordings. Paired t tests examined pre- to post-changes in HSV variables and CPP. Exploratory analyses tested whether the CPP direction of change (increase vs. decrease) moderated physiologic response (time × group).

As a single cohort, no significant pre/post-changes were observed in HSV parameters or CPP. Time × CPP change direction interactions were significant for ClQ, SI, and STI and approached significance for MADRn. Reduced CPP was associated with slower, less forceful closure.

Reduction of CPP after stimulability testing showed kinematic changes consistent with reduced hyperfunction, evidenced by reduced closure abruptness and a shift toward less pressed phonation behavior. Increased CPP showed vibratory patterns associated with faster vocal fold closure, consistent with enhanced resonance. While both groups reported improvement, they achieved this through different physiological pathways. Lack of overall group change may conceal meaningful subgroups defined by therapeutic target. Findings provide preliminary support for CPP as an accessible indicator of individualized physiological shifts following stimulability testing.