Comparing Lexical Cues in Listener Processing of Dysarthria and Speech in Noise

Purpose: The frequency of a word and its number of phonologically similar neighbors can dramatically affect how likely it is to be accurately identified in adverse listening conditions. This study compares how these two cues affect listeners' processing of speech in noise and dysarthric speech. Method: Seven speakers with moderate hypokinetic dysarthria and eight healthy control speakers were recorded producing the same set of phrases. Statements from control speakers were mixed with noise at a level selected to match the intelligibility range of the speakers with dysarthria. A binomial mixed-effects model quantified the effects of word frequency and phonological density on word identification. Results: The model revealed significant effects of word frequency (b = 0.37, SE = 0.12, p = .002) and phonological neighborhood density (b = 0.40, SE = 0.12, p = .001). There was no effect of speaking condition (i.e., dysarthric speech vs. speech in noise). However, a significant interaction was observed between speaking condition and word frequency (b = 0.26, SE = 0.04, p < .001). Conclusions: The model's interactions indicated that listeners were more strongly influenced by the effects of word frequency when decoding moderate hypokinetic dysarthria as compared to speech in noise. Differences in listener reliance on lexical cues may have important implications for the selection of communication-based treatment strategies for speakers with dysarthria.