Academic journal article Journal of Medical Speech - Language Pathology

Speech Intelligibility in a Speaker with Idiopathic Parkinson's Disease before and after Treatment

Academic journal article Journal of Medical Speech - Language Pathology

Speech Intelligibility in a Speaker with Idiopathic Parkinson's Disease before and after Treatment

Article excerpt

A speaker with hypokinetic dysarthria secondary to idiopathic Parkinson's disease (PD) was studied before and after Lee Silverman Voice Treatment (LSVT [R]) to evaluate treatment-related changes in intelligibility of connected speech. He presented with reduced loudness and a weak, breathy voice quality (in addition to monoloudness, monopitch, short phrases, and increased rate). Following treatment, a louder, less breathy voice quality was perceived. Sentence productions were recorded on each of 3 days before and after LSVT [R]. These were presented to five healthy listeners, under carefully psychoa-coustically controlled conditions, with equalization of intensity of signal presentation of all utterances. Listeners typed what they thought the speaker said, and percent words correctly understood were calculated. Additionally, harmonic amplitude differences and rate of syllable production were also analyzed for each utterance. Results indicated a significant improvement in intelligibility following treatment (p < .01), Rate of articulatory production did not differ significantly from pre-to post-LSVT [R]; however, harmonic amplitudes (re: H1) increased significantly (p < .05) posttreatment as part of an overall upward redistribution of spectral energy. We propose that salience of formants due to increased harmonic energy, resulting from treatment- related phonatory changes, accounts in part for the improved intelligibility exhibited by this speaker following LSVT [R].

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Hypokinetic dysarthria associated with Parkinson's disease (PD) exhibits reduced intelligibility with decreased loudness, monoloudness, monopitch, imprecise articulation, and disordered speaking rate (Duffy, 2005). A widely used speech rehabilitation method for PD is the Lee Silver-man Voice Treatment (LSVT [R]; Ramig, Pawlas, & Countryman, 1995), an intensive voice/respiratory treatment focusing on increased vocal loudness through increasing vocal fold adduction. LSVT [R] has a well-developed evidence base, including randomized controlled trials (Ramig et al., 2001).

Improved intelligibility is reported in PD post-LSVT [R] (Ramig Bonitati, Lemke, & Horii, 1994; Ramig, Countryman, Thompson, & Horii, 1995; Sapir, Ramig, Hoyt, et al., 2002). These studies, however, have used various subjective self-ratings and listener ratings and have not controlled intensity of signal presentation as part of experimental protocol. An alternative approach to intelligibility measurement involves transcription of utterances, deriving percentage of words correctly understood. Presentation of pre-versus posttreatment signals at equivalent intensity is of interest because it provides intelligibility evaluation independent of increased speaker loudness, the primary treatment variable. Improved intelligibility then would suggest bases in alternative signal factors such as reduced speaking rate (Yorkston, Hammen, Beukelman, & Traynor, 1990), enhanced articulatory dynamics (Dromey, 2000), or relative amplitude alterations within the frequency spectrum (Cannito et al., 2006).

This study examined intelligibility of conneeted speech produced by a speaker with PD, before and after LSVT [R]. Given equivalent intensity of signal presentation for pre-and posttereatment utterances, we hypothesized that there would be significant improvement in percent words understood following LSVT [R]. In this study, signals were presented in competing noise both to offset ceiling effects on intelligibility and to approximate more natural listening conditions in which ambient noise is typically present. Acoustic spectral and temporal characteristics of the utterances also were examined to identify portential signal differences that may account for hypothesized intelligibility changes.

METHOD

The speaker, a working college professor, was a 67-year-old male, diagnosed with idiopathic PD who had not undergone prior speech therapy. …

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