Formant Transitions in Ataxic Speech: The Shape and Speed of Formant Trajectories in Individuals with Multiple Sclerosis and Control Speakers

摘要

Trying to identify the acoustic bases of reduced intelligibility, investigators have paid special attention to the behavior of the second formant (F2) examining its extent, duration, and rate of change. In theoretical and clinical work, it would be useful to be able to measure speaking rate defined in terms of both movement speed and number of units per second, and to be able to measure the F2 slope independent of an individual's general rate of speech. The present study evaluates a method for numerically specifying the shape and speed of formant trajectories. The procedure consists of fitting damped exponentials to transitions traced from spectrograms, and determining their time constants. The formant transitions of 10 speakers with ataxic dysarthria due to multiple sclerosis (MS) and 10 control speakers, pronouncing the syllables /da:/, /do:/, and /du:/ in a carrier phrase were analyzed. Results showed that the time constants were significantly different in the two groups. Speakers with MS were slower, and given that this measure is independent of speaking rate, we can conclude that the actual articulatory movements were slower. Future research efforts will focus on exploring the formant trajectories in more speakers with varying severities of dysarthria as well as determining the effects of phonetic context, stress, and word length.