Two experiments investigated whether and how clear speech production enhances intelligibility of English fricatives for normal-hearing listeners and listeners with simulated hearing impairment. Babble thresholds were measured for minimal pair distinctions. Clear speech benefited both groups overall; however, for impaired listeners, the clear speech effect held only for sibilant pairs. Correlation analyses comparing acoustic and perceptual data indicated that a shift of energy concentration toward higher frequency regions and greater source strength contributed to the clear speech effect for normal-hearing listeners, while listeners with simulated loss seemed to benefit mostly from cues involving lower frequency regions.
Bibliographic reference. Maniwa, Kazumi / Jongman, Allard / Wade, Travis (2007): "Acoustic correlates of intelligibility enhancements in clearly produced fricatives", In INTERSPEECH-2007, 406-409.