Perceptual Outcome Measures for Supplementing Transcription Intelligibility in Speakers with Parkinson’s Disease and Mild Dysarthria

Introduction: Intelligibility is the gold-standard metric of speech function in dysarthria; however, intelligibility alone may not capture subtle speech impairments. This study evaluated the extent to which related, but distinct, perceptual metrics of listener effort, speech severity, and speech naturalness were sensitive to mild speech impairment in speakers with Parkinson’s disease (PD), providing supplemental information to transcription intelligibility. Methods: Speech samples were collected from 30 speakers with PD and 14 healthy controls. Listeners judged intelligibility using orthographic transcription and provided visual analog scale (VAS) judgments of listener effort, speech severity, and speech naturalness. A correlation analysis assessed the convergent validity between metrics. Linear mixed-effects analysis assessed differences between perceptual metrics. Results: VAS ratings of listener effort were most strongly correlated with intelligibility, while speech naturalness had the weakest relationship to other perceptual measures and the poorest listener reliability. Transcription intelligibility scores were equivalently high for PD and control groups. VAS ratings of listener effort, speech severity, and speech naturalness were significantly lower than intelligibility scores across both groups. Conclusion: For speakers with mild PD, transcription intelligibility did not capture subtle speech deficits detected by VAS metrics. Supplemental perceptual metrics provided a fuller picture of the speech impairment in these individuals.