The importance of a broad bandwidth for understanding "glimpsed" speech

When a target talker speaks in the presence of competing talkers, the listener must not only segregate the voices but also understand the target message based on a limited set of spectrotemporal regions ("glimpses") in which the target voice dominates the acoustic mixture. Here, the hypothesis that a broad audible bandwidth is more critical for these sparse representations of speech than it is for intact speech is tested. Listeners with normal hearing were presented with sentences that were either intact, or progressively "glimpsed" according to a competing two-talker masker presented at various levels. This was achieved by using an ideal binary mask to exclude time-frequency units in the target that would be dominated by the masker in the natural mixture. In each glimpsed condition, speech intelligibility was measured for a range of low-pass conditions (cutoff frequencies from 500 to 8000 Hz). Intelligibility was poorer for sparser speech, and the bandwidth required for optimal intelligibility increased with the sparseness of the speech. The combined effects of glimpsing and bandwidth reduction were well captured by a simple metric based on the proportion of audible target glimpses retained. The findings may be relevant for understanding the impact of high-frequency hearing loss on everyday speech communication.