The Effect of Word Frequency and Word Probability on Speech Production in Dysarthria

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Word frequency and word probability tend to have an effect on word durations in speech. In healthy speakers, the more frequent and probable a word is in its context, the shorter the word tends to be. This study investigates whether these effects are the same for speakers with dysarthria of different severities. As expected, the results indicate that words with a higher frequency and probability tend to be shorter in duration. However, there was a significant interaction effect of word frequency and dysarthria severity. This effect indicates that the more severe the dysarthria, the less of an effect word frequency has on speakers’ word durations. There was also a trend towards an interaction of forward word probability (FP) and severity on word duration. This showed there was a tendency for FP to have less effect on word duration in speakers with severe dysarthria. However, this interaction was not statistically significant. These results suggest that as the severity of dysarthria increases, the duration of words is less affected by word frequency. These findings may be due to reduced control of the duration of motor speech movements.
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