Changes in vowel space and formant frequencies in Parkinson's

disease following intensive voice therapy (LSVT)

By J.L. Spielman, L. O. Ramig, B.H. Story, and C. Fox


            Reduced vowel space has been documented in the speech of individuals with a variety of neurological disorders, including Parkinson’s disease (PD) (Tjaden, 1999), and may be associated with decreased speech intelligibility (Turner et al., 1995). The purpose of the present study was to examine the effects of vocal loudness training (Lee Silverman Voice Treatment, LSVT®) on vowel production in a group of subjects with Parkinson’s disease.  In this study, 13 male subjects with PD were randomly assigned to a treatment or non-treatment group, and 6 male subjects acted as neurologically normal controls. Treatment subjects received one month of intensive voice therapy (LSVT®), while other subjects received no treatment. Data were collected three times prior to treatment and twice immediately following treatment. Formant frequencies were measured for multiple repetitions of vowels /i/, /u/ and /A/ drawn from standard sentences and averaged to create vowel space triangles for each group. It was found that only the LSVT® group significantly increased vowel space following treatment. Further analysis revealed that all subjects and all three vowels contributed to vowel space increases in the treatment group. These results indicate that the LSVT® was effective in increasing vowel space in PD despite the exclusive therapeutic focus on phonation.