Diadochokinetic syllable rate and regularity in normal and in spastic and ataxic dysarthric subjects

Rate and regularity of diadochokinetic syllable repetitions of /p/, /t/, and /k/ in 30 normal subjects, 30 subjects with spastic dysarthria, and 30 subjects with ataxic dysarthria were measured by computer. Normal subjects had rates (syllables per second) of 6.4, 6.1, and 5.7; spastic dysarthric subjects, 4.6, 4.2, and 3.5; and ataxic dysarthric subjects, 3.8, 3.9, and 3.4 for /p/, /t/, and /k/, respectively. Spastic and ataxic subjects were significantly slower and more variable than normal subjects and ataxic subjects were significantly more variable than spastic subjects. The significantly slower than normal rate of repetition in the ataxic subjects and the significantly more variable than normal rhythm of repetition in the spastic subjects were unexpected findings and are in contrast with results from perceptually based investigations of dysarthria. The study demonstrates that slowness of syllable repetition is not restricted to spastic dysarthria and that dysrhythmia of syllable repetition is not restricted to ataxic dysarthria, thus suggesting the need for additional quantitative measurements of acoustic features on which certain notions about the dysarthrias are currently based.