[Significance of "on-off phonation test" to detect oral diadochokinesia in dysarthric patients].

Oral diadochokinetic abilities in 6 patients with ataxic dysarthria (ATAXICs), 6 with spastic dysarthria (SPASTICs), 3 with parkinsonism (PARKINs), and 6 normal subjects (NORMALs) were investigated using repetition of monosyllable /pa/ and "on-off phonation test" in which they had been requested to repeat interrupted vowel /a/ as fast as possible. Oscillographic as well as photographic records of the speech acoustic signal were obtained to analyse interval for a syllable, which consisted of voiced and unvoiced intervals, and peak-value of voiced interval. The results were as follows: 1) ATAXICs and SPASTICs showed prolonged interval for a syllable, yet that of PARKINs was within normal range, when tested either in /a/ or in /pa/. 2) Standard deviation and coefficient of variation for intervals of syllable and those of peak-values in voiced interval could not distinguish their characteristics among ATAXICs, SPASTICs, and PARKINs. 3) In "on-off phonation test", ATAXICs showed prolonged unvoiced intervals, while SPASTICs did prolonged voiced intervals. Results suggested that hypotonic laryngeal muscles in ATAXICs might result in prolongation of unvoiced interval, but that prolonged voiced interval related to biased hypertonus of laryngeal adductor. It is concluded that "on-off phonation test" could, with reasonable sensitivity, reflect the phonatory dynamics of laryngeal muscles in dysarthric patients.