Effects of linear and nonlinear speech rate changes on speech intelligibility in stationary and fluctuating maskers

Algorithmic modifications to the durational structure of speech designed to avoid intervals of intense masking lead to increases in intelligibility, but the basis for such gains is not clear. The current study addressed the possibility that the reduced information load produced by speech rate slowing might explain some or all of the benefits of durational modifications. The study also investigated the influence of masker stationarity on the effectiveness of durational changes. Listeners identified keywords in sentences that had undergone linear and nonlinear speech rate changes resulting in overall temporal lengthening in the presence of stationary and fluctuating maskers. Relative to unmodified speech, a slower speech rate produced no intelligibility gains for the stationary masker, suggesting that a reduction in information rate does not underlie intelligibility benefits of durationally modified speech. However, both linear and nonlinear modifications led to substantial intelligibility increases in fluctuating noise. One possibility is that overall increases in speech duration provide no new phonetic information in stationary masking conditions, but that temporal fluctuations in the background increase the likelihood of glimpsing additional salient speech cues. Alternatively, listeners may have benefitted from an increase in the difference in speech rates between the target and background.