Acoustic Measure of Vocal Strain Based on Glottal Airflow Periodicity

In the clinical practice of dysphonia, the effects of treatment are traditionally monitored by a sequence of auditory-perceptual assessments aimed at measuring vocal quality for the patient. Alternatively, acoustic measurement of vocal quality promises to automate perceptual assessments while keeping the assessments accurate and non-invasive. However, acoustic measures of vocal quality need to be further developed in both functional and technical terms. On the one hand, many of them are susceptible to non-dysphonic perturbations from articulatory movements in continuous speech, while on the other, their accuracy in approximating the generally nonlinear mapping from observation to vocal quality is limited by their use of a linear model. This paper presents an acoustic measure of vocal strain, a specific vocal quality that typically co-occurs with the development of vocal-fold nodules in vocal hyper-function. Vocal strain merits acoustic measurement more than other vocal qualities because its perceptual assessment typically exhibits a lower intra- and inter-rater reliability than the assessment of other vocal qualities. Based on an assumed correlation between vocal strain and the degree of periodicity in vocal-fold vibrations, this paper presents an acoustic measure in which a nonlinear regression model is used to predict the strain from some periodicity features extracted from a glottal airflow estimate. When tested on a set of listener-rated utterances composed mostly of continuous speech, the proposed glottal measure outperformed a direct-analysis measure in producing strain assessments which are consistent with perceptual ratings.