Relationship between speech and nonspeech (DDK) measures in hypokinetic dysarthria

by Tara L. Whitehill and Esther S-L. Tsang

Nonspeech tasks are used routinely in the evaluation of dysarthric speech. However, the relationship between nonspeech and speech measures remains controversial. The aim of this study was to investigate the relationship between three nonspeech (DDK) measures and two connected speech measures in a group of speakers with hypokinetic dysarthria.

Eleven speakers with Parkinson’s disease, aged between 43 and 78 years, were included. DDK rate was calculated using both visual and auditory information. DDK accuracy (percentage of correct targets) was evaluated perceptually by two judges. DDK occlusion, an acoustic measure of percentage of complete closures, was based on the procedures of Ackermann & Ziegler (1991) and Weismer (1984). Reading rate was calculated as the number of syllables divided by duration. Sentence intelligibility was calculated based on CAIDS (Yorkston, Beukelman & Traynor, 1984) procedures, using six naïve listeners.

There was a moderate correlation between DDK accuracy and sentence intelligibility (r_s = 0.65, p < 0.05), and a moderate correlation between DDK accuracy and DDK occlusion (r_s = 0.74, p < 0.01). All other correlations were nonsignificant.

In conclusion, nonspeech tasks (DDK rate and DDK occlusion) were poor predictors of speech performance, for the connected speech tasks selected. Possible explanations for these findings are presented.