Characteristics of speaking rate in the dysarthria associated with amyotrophic lateral sclerosis

The ability to alter speaking rate was studied in a group of 9 subjects with amyotrophic lateral sclerosis (ALS) and 9 age- and gender-matched, neurologically intact controls. Subjects were instructed to speak at three different rates (i.e., habitual, twice as fast as habitual, and one-half as fast as habitual). Speaking rate, articulation rate, and pause duration and frequency were calculated. The proportional increase in speaking rate was similar between the groups; however, the dysarthric speakers slowed rate to a smaller extent. Articulation rate and pause duration and frequency covaried with speaking rate in a similar manner for both groups. There was evidence that dysarthric speakers showed a greater dependence on pause duration and frequency, as compared to articulation rate, especially when increasing rate. In addition, although it was found that the slope of the function relating phrase duration to phrase length in syllables was statistically significant for both normal and dysarthric speakers, the slope of the function was significantly more shallow for the dysarthric speakers. Perceptual judgments of speaking rate indicated that dysarthric speakers spoke faster for a given physical speaking rate. Finally, results suggested that the function relating physical to perceived speaking rate grew more rapidly for dysarthric as compared to normal speakers. Discussion focuses on the importance of these findings to rate manipulation therapies and models of speaking rate in dysarthric speech.