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Intelligibility in Parkinson Disease: Effects of Speech Task
K. Tjaden and G. Greenman

Abstract: Most published intelligibility tests for dysarthria provide an index of speech severity at the single-word or sentence level. The extent to which these types of speech tasks reflect intelligibility for conversational speech has not been studied much. The issue may be especially important in the case of Parkinson disease (PD) as intelligibility may be preserved in single-word or sentence-level laboratory tasks, but may be degraded in conversation. For the present study, intelligibility estimates for speech samples produced by 12 speakers with dysarthria secondary to PD were compared for three types of speech materials, including single words, phrases from a reading passage, and phrases from a conversational monologue. Both direct magnitude estimation (DME) and orthographic transcription were used to index intelligibility for the reading passage, thereby allowing for comparison of two types of intelligibility measures for one speech task. There was a significant correlation between percent correct scores for the single-word task and for orthographic transcription scores for the reading passage, but the correlation between the two intelligibility measures for the reading task was not statistically significant. There was no relationship between single word intelligibility and conversational intelligibility. Scaled estimates of intelligibility for the reading task also were not strongly predictive of scaled estimates of intelligibility for conversation, but the correlation between percent correct scores for orthographic transcription of the reading passage and scaled estimates of intelligibility for conversation was statistically significant. Findings suggest the importance of developing tools for measuring conversational intelligibility in dysarthria.

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