Is there an order of loss of sounds in speakers with Parkinson’s disease?

Read, Jennifer, Miller, Nick and Kitsou, Nikoletta (2018) Is there an order of loss of sounds in speakers with Parkinson’s disease? Clinical Linguistics & Phonetics, 32 (11). pp. 997-1011. ISSN 0269-9206

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Abstract

Influential reports on speech changes in people with Parkinson’s disease (PD; Logemann et al., 1978, 1981) reported a posterior to anterior pattern of loss of speech sound accuracy. These claims have never been examined. In a partial replication of Logemann et al.’s work, we examined whether posterior lingual sounds are most affected in people with Parkinson’s disease, followed by anterior lingual sounds and then labial sounds. Ninety-nine people with PD (age: mean 70.7, SD 8.46; time since diagnosis: mean 6.97, SD 6.2) with mild to severe overall motor symptoms (Hoehn and Yahr stages 1–5, median 2.5) completed a diagnostic intelligibility test. This was scored by 60 listeners unfamiliar with PD and dysarthric speech. We calculated the proportion of posterior versus anterior lingual versus labial sounds misrecognized by the listeners. We compared profiles of misperceived sounds within and across Hoehn and Yahr stages of severity and in relation to Unified Parkinson’s Disease Rating Scale (UPDRS) and speech intelligibility scores. Speech accuracy declined significantly in relation to overall motor impairment for labial and anterior lingual sounds but not for velar sounds. Speech sound accuracy was strongly associated with intelligibility outcomes (p = < 0.01). Contrary to previous assertions, there was no evidence supporting the existence of a posterior to anterior order of ‘loss’ of oral speech sounds in people with PD, nor an interaction of anterior-posterior speech profile changes with Hoehn and Yahr stage. Findings support the notion that a common underlying impairment of movement downscaling affects all sounds similarly and simultaneously in PD from the start.