Abstract
The vowel space area (VSA) has been used as an acoustic metric of dysarthric speech, but with varying degrees of success. In this study, the authors aimed to test an alternative metric to the VSA-the formant centralization ratio (FCR), which is hypothesized to more effectively differentiate dysarthric from healthy speech and register treatment effects. Speech recordings of 38 individuals with idiopathic Parkinson's disease and dysarthria (19 of whom received 1 month of intensive speech therapy [Lee Silverman Voice Treatment; LSVT LOUD]) and 14 healthy control participants were acoustically analyzed. Vowels were extracted from short phrases. The same vowel-formant elements were used to construct the FCR, expressed as (F2u + F2a + F1i + F1u) / (F2i + F1a), the VSA, expressed as ABS([F1i x (F2a - F2u) + F1a x (F2u - F2i) + F1u x (F2i - F2a)] / 2), a logarithmically scaled version of the VSA (LnVSA), and the F2i /F2u ratio. Unlike the VSA and the LnVSA, the FCR and F2i/F2u ratio robustly differentiated dysarthric from healthy speech and were not gender sensitive. All metrics effectively registered treatment effects and were strongly correlated with each other. Albeit preliminary, the present findings indicate that the FCR is a sensitive, valid, and reliable acoustic metric for distinguishing dysarthric from unimpaired speech and for monitoring treatment effects, probably because of reduced sensitivity to interspeaker variability and enhanced sensitivity to vowel centralization.
Highlights
Acoustic analysis has the potential of providing quantitative, objective, and precise means to help depict the presence, severity, and characteristics of motor speech disorders, and to help monitor deterioration or improvement in speech with disease progression, recovery, or treatment effects (e.g., Kent, Weismer, Kent, Vorperian, & Duffy, 1999)
The present study deals primarily with issues and potential alternatives related to acoustic methods of measuring vowel articulation impairment in individuals with dysarthria secondary to idiopathic Parkinson disease (IPD); the information gathered from this study may have implications for other types of dysarthria, such as those associated with amyotrophic lateral sclerosis, multiple sclerosis, traumatic brain injury, and cerebral palsy (CP)
Unlike the vowel space area (VSA) and logarithmically scaled version of the VSA (LnVSA), the Formant centralization ratio (FCR) and F2i/F2u were insensitive to gender effects, and were associated with relatively small coefficient of variation (CV) values
Summary
Acoustic analysis has the potential of providing quantitative, objective, and precise means to help depict the presence, severity, and characteristics of motor speech disorders, and to help monitor deterioration or improvement in speech with disease progression, recovery, or treatment effects (e.g., Kent, Weismer, Kent, Vorperian, & Duffy, 1999). The most relevant acoustic parameters for the perception and production of vowels are the frequencies of the first two formants, F1 and F2 (Hillenbrand, Getty, Clark, & Wheeler, 1995). We test an alternative metric -- Formant centralization ratio (FCR) -- that is hypothesized to more effectively differentiate dysarthric from healthy speech and register treatment effects. Conclusions—Albeit preliminary, the present findings indicate that the FCR is a sensitive, valid and reliable acoustic metric for distinguishing dysarthric from normal speech and for monitoring treatment effects, probably so because of reduced sensitivity to inter-speaker variability and enhanced sensitivity to vowel centralization
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