Abstract
A few clinical reports and empirical studies have suggested a possible deficit in the perception of speech in individuals with Parkinson's disease. In this paper, these studies are reviewed in an attempt to support clinical anecdotal observations by relevant empirical research findings. The combined evidence suggests a possible deficit in patients' perception of their own speech loudness. Other research studies on the perception of speech in this population were reviewed, in a broader scope of the perception of emotional prosody. These studies confirm that Parkinson's disease specifically impairs patients' perception of verbal emotions. However, explanations of the nature and causes of this perceptual deficit are still limited. Future research directions are suggested.
Highlights
Parkinson’s disease is generally believed to be caused by a loss of dopaminergic cells in the substantia nigra pars compacta of the basal ganglia [1] Reduction of dopamine limits the ability of the basal ganglia to coordinate inhibitory and excitatory neural motor signals in cortical-subcortical circuits
The improvement in loudness regulation by raising attentional effort observed in this study suggests the involvement of executive function [31]
There was no significant difference in a depression index between the two groups, indicating that depression could not account for the impairment of perception of vocal emotions found in the participants with Parkinson’s disease
Summary
Parkinson’s disease is generally believed to be caused by a loss of dopaminergic cells in the substantia nigra pars compacta of the basal ganglia [1] Reduction of dopamine limits the ability of the basal ganglia to coordinate inhibitory and excitatory neural motor signals in cortical-subcortical circuits. Another common observation is the ability of individuals with Parkinson’s disease to improve their loudness (and other aspects of speech production) when prompted to do so, in a clinical or laboratory setting, but with a return to reduced loudness and poorer speech production upon leaving the clinical setting This phenomenon has posed some challenges for research studies, as discussed later in this paper. A parallel development has been a recent research interest in a possible deficit of the perception of emotion by individuals with Parkinson’s disease. As the transmission of emotion through speech is conveyed using dimensions such as loudness, pitch, and duration, we summarize recent findings from this line of research in this paper
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