Rating the intelligibility of dysarthic speech amongst people with Parkinson’s Disease: a comparison of trained and untrained listeners

Intelligibility of speech is a key outcome in speech and language therapy (SLT) and research. SLT students frequently participate as raters of intelligibility but we lack information about whether they rate intelligibility in the same way as the general public. This paper aims to determine if there is a difference in the intelligibility ratings made by SLT students (trained in speech related topics) compared to individuals from the general public (untrained). The SLT students were in year 2 of a BSc programme or the first 6 months of a MSc programme. We recorded 10 speakers with Parkinson’s disease (PD) related speech reading aloud the words and sentences from the Assessment of Intelligibility of Dysarthric Speech. These speech recordings were rated for intelligibility by ‘trained’ raters and ‘untrained’ raters. The effort required to understand the speech was also reported. There were no significant differences in the measures of intelligibility from the trained and untrained raters for words or sentences after adjusting for speaker by including them as a covariate in the model. There was a slight increase in effort reported by the untrained raters for the sentences. This difference in reported effort was not evident with the words. SLT students can be recruited alongside individuals from the general public as naïve raters for evaluating intelligibility in people with speech disorders.