Clinically Important Change in Speech Intelligibility from Different Perspectives

Abstract

The purpose of the current study was to estimate the minimal clinically important difference (MCID) of sentence intelligibility in neurologically healthy controls and in speakers with dysarthria due to multiple sclerosis (MS) and Parkinson’s disease (PD) as determined by speech-language pathologists (SLPs) and inexperienced listeners. Sixteen neurologically healthy adults, 16 speakers with MS, and 16 speakers with PD were audio-recorded reading aloud the same set of sentences in habitual, clear, fast, loud, and slow speaking conditions. Ten experienced SLPs and 240 crowdsourced listeners heard paired conditions from a speaker and indicated if one condition was more understandable than another. Listeners then used a global ratings of change scale (GROC) to indicate how much more understandable that condition was than the other. Ratings were compared with intelligibility scores derived for a previous study via orthographic transcriptions from inexperienced listeners. Receiver operating characteristic (ROC) curves and average intelligibility change per level of the GROC were evaluated to determine the sensitivity, specificity, and accuracy of potential cutoff scores in intelligibility for determining clinically important change. Average intelligibility differences between the paired samples were also calculated. The MCID of intelligibility was determined to be ~12% for SLPs and for experienced listeners, but a few interesting dissimilarities will be explored. The current work is a critical step toward development of a universal language with which to evaluate changes in intelligibility as a result of speech-language therapy and disease progression.

Frits van Brenk

External consultant in the Motor Speech Disorders Laboratory

My research and teaching interests include motor speech disorders, clinical linguistics, experimental psycholinguistics, speech science, and research methods.