Evaluation of Visual Feedback for fo and SPL in Subglottal Pressure Measurements—A Methodological Study

Subglottal pressure is a clinically relevant parameter for assessment of voice disorders and correlates to fo and sound pressure level (SPL). The aim of the current study was to evaluate the use of a visual target for feedback of fo and SPL in subglottal pressure measurements in habitual voice and at phonation threshold level with a syllable string and a phrase for the purpose of improving the reliability of subglottal pressure measurements. Data from 12 vocally healthy women (29-61 years) was analyzed. Subglottal pressure was measured and compared in three conditions A: in habitual voice versus at phonation threshold, B: production of a syllable string versus a phrase, C: with visual feedback of fo and SPL versus no visual feedback. Two raters analyzed the pressure data for calculations of intra- and interrater reliability and found in general high agreement (Intra-rater agreement between 96% and 98% for habitual voice and 91% and 88% for phonation threshold. Inter-rater agreement was 95% for habitual voice and 80% for phonation threshold.). The procedure generated a large amount of valid pressure data for the habitual voice recordings but not for those at phonation threshold. No major differences were found between the syllable string and the phrase. The main advantage of visual feedback was to control for SPL in recordings of habitual voice, but less advantage was observed at the phonation threshold. Surprisingly, 10 of 12 participants phonated slightly closer to the target fo without visual feedback. The procedure appears to improve control of SPL at habitual voice. The control of fo was improved for participants with large fo deviations but slightly deteriorated for participants with small deviations. Thus, the procedure using visual feedback has the potential to improve the reliability of subglottal pressure measurements.