Effects of speech stimuli and dysarthria severity on intelligibility scores and listener confidence ratings for speakers with cerebral palsy.

This study examined differences among transcription intelligibility scores and listener confidence ratings for three different types of speech stimuli--single words, unrelated sentences, and sentences forming a narrative--all produced by speakers with dysarthria. Twelve speakers with dysarthria of varying severity secondary to cerebral palsy and 144 listeners participated in this study. Results showed that both intelligibility scores and confidence ratings were differentially affected by both stimuli and severity. For speakers with mild, moderate, and severe dysarthria, intelligibility scores were higher for narratives than for either of the other two types of speech stimuli. For speakers with mild dysarthria, sentences were substantially more intelligible than single words. However, for speakers with moderate, severe, and profound dysarthria, the difference in intelligibility scores for sentences and single words was small or nonsignificant. Confidence ratings did not follow the same pattern as intelligibility data, suggesting a mismatch between listeners' perception of their performance and their actual performance on intelligibility tasks.