Speech Motor Stability in IPD: Effects of Rate and Loudness Manipulations


Increasing phonatory effort, an integral component of the Lee Silverman Voice Treatment, LSVT, has been identified as an effective management strategy for adults with hypokinetic dysarthria associated with Parkinsonism. The present study compares the effects of increased loudness on lower lip movements to those of changes in speaking rate, another approach to the treatmentm of hypokinetic dysarthria. Movements of the lower lip/jaw during speech were recorded from 8 adults with IPD, 8 healthy aged adults, and 8 young adults. The spatiotemporal index (STI), a measure of spatial and temporal variability, revealed that for all speaker groups slow rate was associated with the most variability. Compared to the other conditions, STI values from the loud condition were closest to those from habitual speech. Also, the normalized movement pattern for the loud condition resembled that of habitual speech. It is hypothesized that speaking loudly is associated with a spatial and temporal organization that closely resembles that used in habitual speech, which may contribute to the success of the LSVT.

Idiopathic Parkinson’s disease (IPD) affects as many as 10% of Americans over the age of 60 (Schoenberg, 1987). In addition to the cardinal symptoms of rigidity, tremor, and hypokinesia, an estimated 75%– 100% of adults diagnosed with IPD develop speech and voice problems (Canter, 1965; Logemann, Fisher, Boshes, & Blonsky, 1978; Oxtoby, 1982; Streifler & Hofman, 1984). Such speech impairments are typical of hypokinetic dysarthria, a motor speech disorder characterized by short rushes of speech, imprecise consonants, hoarse and breathy voice, reduced prosody, and reduced loudness (Aronson, 1990; Boshes, 1966; Critchley, 1981). Although pharmacological and surgical treatments may alleviate motor disturbances of the limbs and, to some extent, the speech and voice impairments in some patients with IPD (see Schulz & Grant, 2000 for review), behavioral speech therapy remains the most effective treatment for the speech and voice symptoms of optimally medicated patients (Schulz & Grant, 2000)…