Objective: To evaluate voice harmonic amplitudes from acoustic spectra of speech produced by subjects with Parkinson’s disease (PD) before and after voice treatment, in order to quantify voice change associated with behavioral voice treatment.

Background: Differences in harmonic amplitudes found at H1, H2, and at harmonics located at the third formant frequency (HF3) have been shown to be significant acoustic indicators of voice quality in normal and disordered speakers.

Methods: This retrospective study employed two existing data sets (Halpern et al, 2012; Cannito et al, 2012) to examine harmonic amplitude differences (HADs) in acoustic spectra of vowels produced by speakers with PD before and after voice treatment targeting increased vocal loudness, specifically LSVT LOUD^TM. Halpern et al’s data set included 16 speakers with Parkinson’s disease before and after LSVT®, as supplemented with the LSVT® Companion^TM system. An immediate treatment onset group was compared with a delayed treatment onset control group. Cannito et al’s data set examined 8 speakers with PD before and after LSVT LOUD and demonstrated significant pre-to-post treatment changes in H1-H2 and H1-F3.

Results: Overall dB levels increased from pre-to-post treatment for both groups of patients. HADs (H1-H2, H1-F3) did not differ between treatment groups in the pre-treatment condition. HADs decreased significantly from pre-to-post treatment, and remained so at follow up, for both treatment groups. There was no significant interaction of treatment condition with specific vowels for either harmonic amplitude difference measure. Post-treatment changes in H1-F3 were associated with a general upward redistribution of vowel spectral energy (decreased spectral tilt) that is indicative of increased glottal closure and improved periodicity of vocal fold vibration. Cannito et al’s data set included sentence intelligibility data from a rigorously controlled listening study. Change in sentence intelligibility was found to be significantly correlated with change in harmonic amplitude difference for H1-F3, r = -.845 (r² = .714).

Conclusions: Results indicate that as spectral tilt decreased, sentence intelligibility increased. Such changes have significant implications for both improved voice quality and speech intelligibility following voice treatment.

Portions of this research were presented at the 2014 Conference on Motor Speech and the 2012 ASHA Convention.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/voice-harmonic-amplitude-differences-before-and-after-lsvt-loudtm-in-parkinsons-disease/