Effects of context on intelligibility and comprehensibility of severely dysarthric speech

This study sought to characterize the relative efficacy of augmentative and alternative communication (AAC) strategies that facilitate top-down knowledge (topic cues), bottom-up knowledge (alpha cues), both top-down and bottom-up knowledge (mixed cues), and a control condition in which no extrinsic knowledge was provided to listeners. The two dependent variables examined were intelligibility and comprehensibility. Specific purposes of this study were to: determine which type of extrinsic information is most effective in enhancing speech intelligibility and speech comprehensibility within sentential and narrative contexts, and determine the nature of the relationship between intelligibility and comprehensibility within sentential and narrative contexts for each of the four conditions. Seventy-four normal listeners heard the speech of four women with severe dysarthria secondary to cerebral palsy under four conditions—no cues, topic cues, alpha cues, and mixed cues. Within sentence intelligibility and narrative intelligibility, results showed that mixed cues yielded significantly higher scores than any other cue condition, and no cues yielded significantly lower scores than any other cue condition. Provision of alpha cues resulted in significantly higher intelligibility than topic cues. Within sentence and narrative comprehensibility, the same pattern of results was present as those observed for sentence and narrative intelligibility with one exception. Within sentence comprehensibility, topic and alpha cue conditions did not differ. The relationship between intelligibility and comprehensibility varied among cue conditions and stimulus contexts. However, in general this relationship was weak yet positive in direction. The only significant relationship within sentences was for topic cues. Within narratives, significant relationships between intelligibility and comprehensibility occurred for topic, alpha and mixed cue conditions. Descriptive results showed that intelligibility scores were generally higher than comprehensibility scores. In addition, scores for narratives were generally higher than scores for unrelated sentences. Overall results suggest that bottom-up information (alpha cues) enhances intelligibility and comprehensibility more than top-down information (topic cues). When both types of cues are provided to listeners simultaneously (mixed cues), intelligibility and comprehensibility scores are maximized relative to either in isolation