The Effects of Modified Speech Styles on Intelligibility for Non-Native Listeners

Speech output, including modified and synthetic speech, is used increasingly in natural settings where message reception might be affected by noise. Recent evaluations have demonstrated the effect of different speech styles on intelligibility for native listeners, but their impact on listening in a second language is less well-understood. The current study measured the intelligibility of four speech styles in the presence of stationary and fluctuating maskers for a non-native listener cohort, and compared the results with those of native listeners on the same task. Both groups showed a similar pattern of effects, but the scale of intelligibility gains and losses with respect to plain speech was significantly compressed for the non-native group relative to native listeners. In addition, non-native listeners identified speech from the four styles in the absence of noise, revealing that styles shown to be beneficial in noise lost their benefits or were harmful in quiet conditions. This result suggests that while enhanced styles lead to gains by reducing the effect of masking noise, the same styles distort the acoustic-phonetic integrity of the speech signal. More work is needed to develop speech modification approaches that simultaneously preserve speech information and promote unmasking.