The importance of temporal-fine structure to perceive time-compressed speech with and without the restoration of the syllabic rhythm.

Intelligibility of time-compressed (TC) speech decreases with increasing speech rate. However, intelligibility can be restored by 'repackaging' the TC speech by inserting silences between the syllables so that the original 'rhythm' is restored. Although restoration of the speech rhythm affects solely the temporal envelope, it is unclear to which extent repackaging also affects the perception of the temporal-fine structure (TFS). Here we investigate to which extent TFS contributes to the perception of TC and repackaged TC speech in quiet. Intelligibility of TC sentences with a speech rate of 15.6 syllables per second (sps) and the repackaged sentences, by adding 100 ms of silence between the syllables of the TC speech (i.e., a speech rate of 6.1 sps), was assessed for three TFS conditions: the original TFS and the TFS conveyed by an 8- and 16-channel noise vocoder. An overall positive effect on intelligibility of both the repackaging process and of the amount of TFS available to the listener was observed. Furthermore, the benefit associated with the repackaging TC speech depended on the amount of TFS available. The results show TFS contributes significantly to the perception of fast speech even when the overall rhythm/envelope of TC speech is restored.