Speech rate effects upon intelligibility and acceptability of dysarthric speech.

Sentences recorded by four speakers with dysarthria and two control speakers were presented to listeners at three different rates: habitual, a 30% slower rate and a 30% higher rate. Rate changes were made by digitally manipulating the habitual sentences. Thirty young normal adult listeners rated the sentences for intelligibility (per cent correct words) and acceptability (via 9-point equal interval scale ranging from "terrible" through "excellent"). Intelligibility for each speaker remained unchanged across rate changes. Acceptability improved as rates increased for the two more intelligible impaired speakers. For the less intelligible impaired speakers, ratings were better and similar for the habitual and fast speaking rate conditions. Results are discussed in terms of the objective nature of intelligibility ratings vs. the subjective ratings of acceptability.