Effect of Dysarthria Type, Speaking Condition, and Listener Age on Speech Intelligibility.

PURPOSE: The aim of this study was to examine the effect of loud and slow speech cues on younger and older listeners' comprehension of dysarthric speech, specifically, (a) whether one strategy, as opposed to the other, promoted greater intelligibility gains for different speaker groups; (b) whether older and younger listeners' understandings were differentially affected by these strategies; and (c) which acoustic changes best predicted intelligibility gain in individual speakers. METHOD: Twenty younger and 40 older listeners completed a perceptual task. Six individuals with dysarthria produced phrases across habitual, loud, and slow conditions. The primary dependent variable was proportion of words correct; follow-up acoustic analyses linked perceptual outcomes to changes in acoustic speech features. RESULTS: Regardless of dysarthria type, the loud condition produced significant intelligibility gains. Overall, older listeners' comprehension was reduced relative to younger listeners. Follow-up analysis revealed considerable interspeaker differences in intelligibility outcomes across conditions. Although the most successful speaking mode varied, intelligibility gains were strongly associated with the degree of change participants made to their vowel formants. CONCLUSIONS: Perceptual outcomes vary across speaking modes, even when speakers with dysarthria are grouped according to similar perceptual profiles. Further investigation of interspeaker differences is needed to inform individually tailored intervention approaches.