Listener Perception of Monopitch, Naturalness, and Intelligibility for Speakers With Parkinson's Disease

Abstract

Purpose: Given the potential significance of speech naturalness to functional and social rehabilitation outcomes, the objective of this study was to examine the effect of listener perceptions of monopitch on speech naturalness and intelligibility in individuals with Parkinson's disease (PD).

Method: Two short utterances were extracted from monologue samples of 16 speakers with PD and 5 age-matched adults without PD. Sixteen listeners evaluated these stimuli for monopitch, speech naturalness and intelligibility using the visual sort and rate method.

Results: Naïve listeners can reliably judge monopitch, speech naturalness, and intelligibility with minimal familiarization. While monopitch and speech intelligibility were only moderately correlated, monopitch and speech naturalness were highly correlated.

Conclusions: A great deal of attention is currently being paid to improvement of vocal loudness and thus speech intelligibility in PD. Our findings suggest that prosodic characteristics such as monopitch should be explored as adjuncts to this treatment of dysarthria in PD. Development of such prosodic treatments may enhance speech naturalness and thus improve quality of life.

Figure 1.

An illustration of the graphical user interface used for the collection of perceptual judgments. Each of the diamond markers represents a sound clip.

Figure 2.

Perceptual judgments across 21 speakers. Subplots represent (a) Perceived monopitch, (b) perceived speech naturalness, and (c) perceived speech intelligibility. Each of the speakers are shown on the abscissa and ordered from low to high perceived pitch variability. The same order of speakers is maintained for subplots (b) and (c). Box plots based on results from the 12 listeners show the median, 25th, and 75th percentile, SD, and outliers.

Figure 3.

Mean perceived (a) speech naturalness and (b) speech intelligibility plotted as a function of perceived monopitch. Values closer to 0 reflect greater monopitch (low pitch variability), and values closer to 100 reflect less monopitch (high pitch variability). Symbols or markers represent judgments averaged across 12 listeners.

Figure 4.

Mean perceived speech naturalness (left) and speech intelligibility (right) plotted as a function of perceived monopitch. Values closer to 0 reflect greater monopitch (low pitch variability), and values closer to 100 reflect less monopitch (high pitch variability). Top row represents judgments for utterance 1, and bottom row represents judgments for utterance 2. Symbols or markers represent judgments averaged across 12 listeners.

Figure 5.

Mean perceived speech naturalness (left column) and speech intelligibility (right column) plotted as a function of perceived monopitch for PD speakers. Each row represents the overall degree of dysarthria severity (top = mild; center = moderate; bottom = severe). On the x-axis, values closer to 0 reflect greater monopitch (low pitch variability), and values closer to 100 reflect less monopitch (high pitch variability).