Motor impairment in Wilson's disease, II: Slowness of speech.

The maximal syllable production rate (MSPR) and the ability to reproduce a given target frequency in the 1 to 8 Hz range by repeating the short syllable "ta" was tested in 20 patients with Wilson's disease (WD) and 20 normal subjects. MSPR was significantly reduced in the WD-patients. In the 1 to 5 Hz range normal subjects as well as WD-patients tended to produce slightly higher frequencies than the target frequencies. This hastening was maximal in normals between 4 to 5 Hz whereas in the WD-patients hastening mainly occurred between 3 to 4 Hz. The test results showed a considerable variation across the patients. This variation can be interpreted on the basis of the theory of coupled oscillators. Comparison of speech and finger movements revealed a highly significant correlation between MSPR and the highest possible frequency of voluntary alternating index finger movements. As an application of the presented test treatment effects on speech movements were demonstrated.