The influence of speaker and listener variables on intelligibility of dysarthric speech

Abstract

This study compared changes in speech clarity as a function of speaking context. It is well documented that words produced in sentence contexts yield higher intelligibility than words in isolation for speakers with mild to moderate dysarthria. To tease apart the effect of speaker and listener variables, the current study aimed to quantify differences in word intelligibility by speaking task. Eighteen speakers with dysarthria produced a set of 25 words in isolation and within the context of a sentence. Eighteen listeners heard a randomized sample of the isolated productions, single words extracted from the sentences, and the full unaltered sentences. Listeners transcribed what they heard and rated their confidence. Words produced in isolation were just as intelligible as words produced in sentence context, both of which were more intelligible than extracted words. In other words, speakers reduced articulatory clarity in sentence production compared to isolated productions; listeners were able to cope with this reduction in clarity when they had access to contextual information but not when these cues were removed in the extracted condition. These findings are consistent with Lindblom's hypo-hyperarticulation theory in that adults with dysarthria appear to be modulating articulatory precision based on listener/task variables. This work has implications for clinical practice in that isolated word and sentence production tasks yielded equivalent intelligibility findings.

Learning outcomes: Readers will recognize that speech intelligibility is influenced by speaker and listener variables and thus the choice of speaking and listening task may yield different results. Commonly held clinical belief is that sentence production tasks yield inflated intelligibility scores but we did not find that in this sample. Findings also indicate that speakers with dysarthria may modulate articulatory clarity in response to listener needs which should be considered in treatment planning.

Keywords: Dysarthria; Intelligibility; Listener perception; Speaking task.