Perception and production of emotional prosodies in people with Parkinson's disease and associated hypokinetic dysarthria

Parkinson’s disease (PD) impedes the perceptual accuracy of vocal emotions, and disrupts the emotional prosodies of affected individuals. However, less has been known of the possible association between these two processes, and if presence of motor speech disorder, hypokinetic dysarthria, would impact on the association. The present study investigated the possible disturbances in the production and the perception of emotional prosodies, and their possible relationship, of individuals with PD and associated hypokinetic dysarthria. Eighteen Cantonese-speaking participants with PD and associated mild-moderate hypokinetic dysarthria, 19 participants with PD but without dysarthria and 40 healthy controls who were matched for age, gender, and educational level were asked to participate in two experiments. In the first experiment, all participants produced semantically neutral sentences using six different emotions (angry, happy, sad, disgusted, surprised and neutral). The speech samples were analyzed for intensity, range of intensity, fundamental frequency, range of fundamental frequency and speech rates. In the second experiment, the participants were asked to listen to the speech samples produced by themselves and others. The participants were then asked to identify the emotions conveyed in the speech samples. Acoustic analysis of emotional prosodies revealed significant group differences. Participants with PD and with hypokinetic dysarthria exhibited significantly reduced range of intensity, higher fundamental frequency, restricted range of fundamental frequency, and significantly faster speech rate when compared to the controls. Participants with PD but without hypokinetic dysarthria showed significantly reduced range of intensity, lower fundamental frequency, reduced range of fundamental frequency, and significantly faster speech rate than the healthy controls. However, all participants with PD, regardless of their hypokinetic dysarthria status, demonstrated unexpectedly higher mean speech intensity than the healthy controls. Results also showed that PD impaired the perceptual accuracy of vocal emotions affected individuals. PD individuals also showed reduced perceptual accuracy for vocal emotions produced by the listeners themselves, but to a lesser extent than their perceptual accuracy when they listened to vocal emotions produced by other people. This finding suggested that at least part of the participants’ emotion processing ability is intact in the early stage of PD disease progression. When comparing the two groups of participants with PD, the presence of hypokinetic dysarthria significantly affected the production of emotional prosodies but not significantly the accuracy of perception of vocal emotions. The results confirmed the presence of impairments in production and perception of vocal emotions in people with PD and associated hypokinetic dysarthria. The correlation between the acoustic parameters of emotional prosodies and the perceptual accuracy of vocal emotions produced by listeners themselves varied from nil to moderate significant. A likely dissociation of production and perception of vocal emotions in PD has been found which is not in line with previous studies that supported a relationship between speech perception and speech production deficits in PD. These findings are of crucial clinical value as they suggest more specific strategies to assess and treat hypokinetic dysarthria associated with PD.