Internally Versus Externally Cued Speech in Parkinson's Disease and Cerebellar Disease

Purpose: The purpose of this study was to examine the effects of an internally versus externally cued speech task on perceived understandability and naturalness in speakers with Parkinson's disease (PD) and cerebellar disease (CD). Method: Sentences extracted from a covertly recorded conversation (internally cued) were compared to the same sentences read aloud (externally cued) by speakers with PD and a clinical comparison group of speakers with CD. Experienced listeners rated the speech samples using a visual analog scale for the perceptual dimensions of understandability and naturalness. Results: Results suggest that experienced listeners rated the speech of participants with PD as significantly more natural and more understandable during the reading condition. Participants with CD were also rated as significantly more understandable during the reading condition, but ratings of naturalness did not differ between conversation and reading. Conclusions: Speech tasks can have a pronounced impact on perceived speech patterns. For individuals with PD, both understandability and naturalness can improve during reading tasks versus conversational tasks. The speech benefits from reading may be attributed to several mechanisms, including possible improvement from an externally cued speech task. These findings have implications for speech task selection in evaluating individuals with dysarthria.