Disorders of verbal expression in parkinsonism.

The present study shows that rigor is one of the main causative factors in the parkinsonian speech disorder, whereas tremor ordinarily can only play a minor role. The Fast Fourier Analysis of the frequency spectra demonstrated in parkinsonian speech frequency regions that are energy-deficient and also that the entire frequency spectrum is restricted to a range of 100 to 400 Hz, including the deficient regions, as against the 100- to 700-Hz range in the controls. These analytical findings seem to underline the important role played by the laryngeal and breathing dysfunctions in the parkinsonian voice and speech production.