Alternating motion rate as an index of speech motor disorder in traumatic brain injury.

The task of syllable alternating motion rate (AMR) (also called diadochokinesis) is suitable for examining speech disorders of varying degrees of severity and in individuals with varying levels of linguistic and cognitive ability. However, very limited information on this task has been published for subjects with traumatic brain injury (TBI). This study is a quantitative and qualitative acoustic analysis of AMR in seven subjects with TBI. The primary goal was to use acoustic analyses to assess speech motor control disturbances for the group as a whole and for individual patients. Quantitative analyses included measures of syllable rate, syllable and intersyllable gap durations, energy maxima, and voice onset time (VOT). Qualitative analyses included classification of features evident in spectrograms and waveforms to provide a more detailed description. The TBI group had (1) a slowed syllable rate due mostly to lengthened syllables and, to a lesser degree, lengthened intersyllable gaps, (2) highly correlated syllable rates between AMR and conversation, (3) temporal and energy maxima irregularities within repetition sequences, (4) normal median VOT values but with large variation, and (5) a number of speech production abnormalities revealed by qualitative analysis, including explosive speech quality, breathy voice quality, phonatory instability, multiple or missing stop bursts, continuous voicing, and spirantization. The relationships between these findings and TBI speakers' neurological status and dysarthria types are also discussed. It was concluded that acoustic analyses of the AMR task provides specific information on motor speech limitations in individuals with TBI.