Tongue- and Jaw-Specific Articulatory Underpinnings of Reduced and Enhanced Acoustic Vowel Contrast in Talkers With Parkinson's Disease

Abstract

Purpose This study sought to identify the articulator-specific mechanisms that underlie reduced and enhanced acoustic vowel contrast in talkers with dysarthria due to Parkinson's disease (PD). Method Seventeen talkers with mild-moderate dysarthria due to PD and 17 controls completed a sentence repetition task using typical, slow, loud, and clear speech. Tongue and jaw articulatory movements were recorded using 3D electromagnetic articulography. Independent tongue displacements, jaw displacements, and acoustic vowel contrast were calculated for the diphthong /aɪ/ embedded in the word kite. Results During typical speech, independent tongue displacement, but not jaw displacement, contributed significantly to the intertalker variance in acoustic vowel contrast. Loudness-related acoustic vowel contrast gains were predominantly jaw driven in controls but driven by the tongue and jaw in talkers with PD. Further, in both groups, clarity-related acoustic vowel contrast gains were predominantly jaw driven. Finally, in both groups, rate-related acoustic vowel contrast gains were predominantly tongue driven; however, the jaw also contributed. These jaw contributions were greater in the PD group than in the control group. Conclusions Findings suggest that a tongue-specific articulatory impairment underlies acoustic vowel contrast deterioration in talkers with PD, at least during the early stages of speech decline. Findings further suggest that slow speech engages the impaired tongue more than loud and clear speech in talkers with PD. However, slow speech was also associated with an abnormally strong jaw response in these talkers, which suggests that a compensatory articulatory behavior may also be elicited.

Figure 1.

Mean jaw displacements (top panels), mean independent tongue displacements (middle panels), and mean acoustic vowel contrast (bottom panels) across speech conditions. Note that jaw displacements (log-transformed) are the calculated jaw displacements (jaw_adj) based on the decoupling algorithm (see text for details). PD = Parkinson's disease; PHON/PROS = subgroup with perceived phonatory and prosodic impairments; ARTIC/PHON/PROS = subgroup with perceived articulatory, phonatory, and prosodic impairments.

Figure 2.

Scatter plot of jaw displacements (jaw_adj) and acoustic vowel contrast (left panel) as well as independent tongue displacement and acoustic vowel contrast (right panel) during typical speech. The gray-shaded circles indicate data of COM23 (filled circles) and PDM21 (open circles). PD = Parkinson's disease; PD PHON/PROS = subgroup of talkers with PD with perceived phonatory and prosodic impairment; PD ARTIC/PHON/PROS = subgroup of talkers with PD with perceived articulatory, phonatory, and prosodic impairment.