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Vowel Harmonic Amplitude Differences in a Speaker with Hypokinetic Dysarthria Before and After Treatment
Michael P. Cannito, Debra M. Suiter, Teresa Wolf, Lesya Chorna, Dorian Beverly

A speaker with hypokinetic dysarthria secondary to idiopathic Parkinson’s disease was studied before and after Lee Silverman Voice Treatment (LSVT) to evaluate treatment-related changes in acoustic vowel spectra during connected speech. He presented with reduced loudness, and a weak, breathy voice quality (in addition to monoloudness, monopitch, short phrases and increased rate). Single word intelligibility was 62%. Following treatment a stronger, less breathy voice quality was perceived. Vowel nuclei from CVC syllables produced in a carrier phrase were recorded on three consecutive days before and after LSVT. Overall vowel intensity (dB re: SPL) was calculated relative to known calibration signals. Amplitudes were measured for the first and second harmonics as well as harmonics at the first, second and third formants using the fast fourier transformation (FFT) method from the Kay Computer Speech Laboratory. Following Hanson (1997) harmonic amplitude differences (H1-H2, H1-HF1, H1-HF2, H1-HF3) were calculated. Results demonstrated an expected increase in overall loudness after treatment. Additionally, all harmonic amplitude differences decreased significantly following LSVT. These were associated with an upward redistribution of harmonic energy evident in the acoustic spectra. Acoustic findings were stable across days (pre vs post) and similar changes were observed in selected vowel segments excerpted from sustained /ah/, reading and monologue. Harmonic amplitude changes probably account for perceived improvement in the speaker’s voice quality following treatment. Increased harmonic amplitudes at formant frequencies also may contribute to improved intelligibility reported following LSVT in prior literature. Laryngeal mechanisms underlying observed acoustic changes will be considered.

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