The effects of flattening fundamental frequency contours on sentence intelligibility in speakers with dysarthria

This study explored the relationship between F0 variability and intelligibility in persons with motor speech disorders. The literature suggests that monopitch may have detrimental effects on the intelligibility of individuals with dysarthria (and other speech disorders), but few studies have examined the independent effect of a flat F0 contour on intelligibility in speakers with articulatory difficulties. An LPC resynthesis technique was used to reduce the speakers' sentence F0 range by 25%, 50% and 100% (flattened F0). Two dysarthric speaker groups were evaluated, one with prosodic inadequacy and imprecise articulation (hypokinetic) and one with imprecise articulation only (UUMN). Speech intelligibility was assessed using a word transcription task and an interval-scaling task. Results argue strongly for the perceptual importance of sentence-level F0 variations on speech intelligibility even when the F0 range is severely restricted. Results also suggest that the contribution of F0 to intelligibility may vary with type of dysarthria.