Harmonic Amplitude Differences Before and After Voice Treatment for Parkinson's Disease and Their Relationship to...

This study examined harmonic amplitude differences (HADs) in acoustic spectra of vowels /ɛ, æ, ʌ/ produced by persons with Parkinson's disease (PD) before and after Lee Silverman Voice Treatment (LSVT LOUD®). Recordings of speech from two previously published studies were employed for this purpose. Study 1 was a randomized control trial that demonstrated increased vocal intensity following treatment that was maintained at follow-up. Study 2 was a listening experiment that demonstrated increased sentence intelligibility in PD following LSVT LOUD®. In the present study, HADs were analyzed from target vowels excerpted from these archival recordings obtained before and after voice treatment.

For study 1 data, recordings of the Rainbow Passage produced by 16 persons with PD were analyzed to obtain HADs for H1-H2 and H1-A3 from selected vowels. Pearson correlations of change in HADs with change in overall intensity (dB rms) were also examined. For study 2 data, HADs for H1-H2, H1-A1, H1-A2, and H1-A3 were obtained from vowels excerpted from recordings of specific test sentences before and after LSVT LOUD®. Correlations of change in HADs from pre-to-post LSVT LOUD® with change in sentence intelligibility scores of normal-hearing listeners were examined.

dB levels increased from pre-to-post treatment for both PD participant groups. For Study 1 recordings, H1-H2 and H1-A3 decreased significantly from pre-to-post treatment and remained so at follow-up. Change in overall vocal intensity (dB rms) was moderately negatively correlated with change in H1-H2 and H1-A3. For Study 2, all HADs measurements decreased significantly from pre-to-post treatment. Changes in H1-A2 and H1-A3 were highly negatively correlated with increases in sentence intelligibility.

Post-treatment changes in HADs were associated with a general upward redistribution of vowel spectral energy (decreased spectral tilt) that is associated with increased glottal closure and improved periodicity of vocal fold vibration. Such changes are indicative of improved voice quality and speech intelligibility in PD following LSVT LOUD®.