The influence of speaking rate on articulatory hypokinesia in parkinsonian dysarthria.

This study addressed the question of whether or not speaking rate influences articulatory hypokinesia in dysarthria associated with Parkinson's disease. Analyses of parkinsonian speech samples revealed mean speaking rates consistent with normal controls. Thus, speaking rate was not abnormal overall in this group of dysarthric subjects. Kinematic analyses of labial displacement amplitude, peak instantaneous velocity, and movement time were made during repetitive syllable production spoken at two speaking rates: 3-5 syllables/sec and 5-7 syllables/sec. The results suggested that labial movements were normal at the slower of the two speaking rates. Conversely, labial movements became hypokinetic as speaking rate increased to the rate consistent with conversational speech. These findings provide a physiologic basis for the perception of hypokinetic dysarthria in Parkinson's disease and suggest that speaking rate may be an important control variable contributing to articulatory hypokinesia in Parkinson's disease. Moreover, these findings provide quantitative evidence that articulatory hypokinesia plays a dominant role in the perception of parkinsonian dysarthria.