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Vowel harmonic amplitude differences in a speaker with hypokinetic dysarthria before and after treatment.

Article Excerpt
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), and reduced intelligibility. 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. 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 Elemetrics Computerized Speech Lab. Following Hanson (1997), harmonic amplitude differences (H1*-H2*, H1*-F1, H1*-F2, H1*-F3*) were calculated. 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 relatively stable across days (pre vs. post). Harmonic amplitude changes probably account for perceived improvement in the speaker's voice quality following treatment and may contribute to improved intelligibility reported in prior studies. The present findings are a good fit for physiologic data that have previously been reported in association with LSVT.

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Hypokinetic dysarthria associated with Parkinson's disease results in reduced intelligibility with decreased loudness, monopitch, monoloudness, imprecise articulation, and disordered speaking rate. Dromey (2003) has demonstrated acoustically that long-term average vowel spectra are also markedly abnormal, with decreased harmonic energy in the higher frequency range. Vowel spectra were shown to be a powerful marker for weak, breathy voice production in untreated hypokinetic dysarthria. Lee Silverman Voice Treatment (LSVT) is an intensive rehabilitation program that focuses on increased vocal loudness and vocal fold adduction through high phonatory effort (Ramig, Pawlas, & Countryman, 1995). Participants are instructed to "think loud" during sustained vowel production and to "use the same loud good quality voice ... during reading and speaking" (p. 1240; Ramig, Countryman, Thompson, & Horii, 1995). Changes in vocal loudness have also been associated with changes in vocal quality. Dromey, Ramig, and Johnson (1995), for...

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