Regularity Matters: Unpredictable Speech Degradation Inhibits Adaptation to Dysarthric Speech

Abstract

Purpose Listener-targeted perceptual training paradigms, which leverage the mechanism of perceptual learning, show strong promise for improving intelligibility in dysarthria, offsetting the communicative burden from the speaker onto the listener. Theoretical models of perceptual learning underscore the importance of acoustic regularity (i.e., signal predictability) for listener adaptation to degraded speech. The purpose of the current investigation was to evaluate intelligibility outcomes following perceptual training with hyperkinetic dysarthria, a subtype characterized by reduced signal predictability. Method Forty listeners completed the standard 3-phase perceptual training protocol (pretest, training, and posttest) with 1 of 2 talkers with hyperkinetic dysarthria. Perceptual data were compared to a historical data set for 1 other talker with hyperkinetic dysarthria to examine the effect of perceptual training on intelligibility. Results When controlling for pretest intelligibility, regression results suggest listeners of the 2 novel talkers with hyperkinetic dysarthria performed comparably to the listeners of the original talker on the posttest following training. Furthermore, differences between pretest and posttest intelligibility failed to reach clinical significance for all 3 talkers and statistical significance for 2 of the 3. Conclusion The current findings are consistent with theoretical models of perceptual learning and suggest that listener adaptation to degraded speech may be negligible for talkers with dysarthria whose speech is marked by reduced signal predictability.

Figures

Figure 1.

Key conclusions from published studies, illustrating significant intelligibility improvements from pretest to posttest for ataxic (Borrie et al., 2017a, 2017b; Lansford et al., 2018), spastic (Borrie & Schäfer, 2015), and hypokinetic dysarthria (Borrie et al., 2018), but not for hyperkinetic dysarthria (Borrie et al., 2018).

Figure 2.

The distributions of intelligibility improvement for each listener within each talker. The area under each curve represents the density of responses at each value of improvement (e.g., most listeners for HDM10 had improvement between 2 and 4).

Figure 3.

The average intelligibility scores, indexed by percent words correct, for both pretest and posttest for each talker. The error bars represent SE = ±1.