When Additional Training Isn't Enough: Further Evidence That Unpredictable Speech Inhibits Adaptation.

Purpose Robust improvements in intelligibility following familiarization, a listener-targeted perceptual training paradigm, have been revealed for talkers diagnosed with spastic, ataxic, and hypokinetic dysarthria but not for talkers with hyperkinetic dysarthria. While the theoretical explanation for the lack of intelligibility improvement following training with hyperkinetic talkers is that there is insufficient distributional regularity in the speech signals to support perceptual adaptation, it could simply be that the standard training protocol was inadequate to facilitate learning of the unpredictable talker. In a pair of experiments, we addressed this possible alternate explanation by modifying the levels of exposure and feedback provided by the perceptual training protocol to offer listeners a more robust training experience. Method In Experiment 1, we examined the exposure modifications, testing whether perceptual adaptation to an unpredictable talker with hyperkinetic dysarthria could be achieved with greater or more diverse exposure to dysarthric speech during the training phase. In Experiment 2, we examined feedback modifications, testing whether perceptual adaptation to the unpredictable talker could be achieved with the addition of internally generated somatosensory feedback, via vocal imitation, during the training phase. Results Neither task modification led to improved intelligibility of the unpredictable talker with hyperkinetic dysarthria. Furthermore, listeners who completed the vocal imitation task demonstrated significantly reduced intelligibility at posttest. Conclusion Together, the results from Experiments 1 and 2 replicate and extend findings from our previous work, suggesting perceptual adaptation is inhibited for talkers whose speech is largely characterized by unpredictable degradations. Collectively, these results underscore the importance of integrating signal predictability into theoretical models of perceptual learning.