Testing the role of temporal coherence on speech intelligibility with noise and single-talker maskers.

Temporal coherence, where sounds with aligned timing patterns are perceived as a single source, is considered an essential cue in auditory scene analysis. However, its effects have been studied primarily with simple repeating tones, rather than speech. This study investigated the role of temporal coherence in speech by introducing across-frequency asynchronies. The effect of asynchrony on the intelligibility of target sentences was tested in the presence of background speech-shaped noise or a single-talker interferer. Our hypothesis was that disrupting temporal coherence should not only reduce intelligibility but also impair listeners' ability to segregate the target speech from an interfering talker, leading to greater degradation for speech-in-speech than speech-in-noise tasks. Stimuli were filtered into eight frequency bands, which were then desynchronized with delays of 0-120 ms. As expected, intelligibility declined as asynchrony increased. However, the decline was similar for both noise and single-talker maskers. Primarily target, rather than masker, asynchrony affected performance for both natural (forward) and reversed-speech maskers, and for target sentences with low and high semantic context. The results suggest that temporal coherence may not be as critical a cue for speech segregation as it is for the non-speech stimuli traditionally used in studies of auditory scene analysis.