Assessment of tongue weakness and fatigue.

Assessment of nonspeech tongue function is common in speech-language pathology. This paper reviews techniques used to determine tongue strength and endurance, and describes a constant-effort task. These techniques are intended to reveal and quantify the presence of weakness or fatigue of the tongue. The consequences of performing these tasks with and without a bite block, used to fix jaw position, are considered. Whether nonspeech tongue impairment is associated with speech dysfunction in Parkinson's disease is another topic of interest. Past studies indicated reduced tongue strength and endurance in Parkinson's disease, but these measures did not correlate with speech measures. It was hypothesized that weakness and fatigue need to be impaired to a "critical" level before speech is perceptibly affected. To examine whether experimentally induced tongue fatigue affects speech, normal speakers performed prolonged strenuous tongue exercise. Speech deteriorated following these exercises. A new investigation examines whether 1 hour of speech-like tongue exercise (rapid syllable repetitions) affects dysarthric speech. Preliminary data from 6 participants with Parkinson's disease, 1 person with bulbar ALS, and 6 neurologically normal control subjects indicate that sentences sound more precise but less natural after the exercises. Surprisingly, results did not differ significantly between the groups. Continued collection of data and refinement of tasks will contribute to our understanding of the potential relationships between weakness, fatigue, and speech.