Cochlear implant speech recognition with speech maskers

TLDR

Speech recognition was tested in normal‑hearing and cochlear‑implant listeners using target sentences presented with either steady‑state noise or competing talkers at various target‑to‑masker ratios, with normal‑hearing stimuli vocoded to simulate cochlear‑implant processing. Normal‑hearing listeners maintained high intelligibility down to 0 dB TMR and benefited from release from masking with single‑talker maskers, whereas cochlear‑implant listeners and the vocoded simulation showed no masking release and no improvement with a different talker masker, indicating that informational masking and modulation interference—likely due to reduced spectral resolution—limit cochlear‑implant speech recognition in fluctuating maskers.

Abstract

Speech recognition performance was measured in normal-hearing and cochlear-implant listeners with maskers consisting of either steady-state speech-spectrum-shaped noise or a competing sentence. Target sentences from a male talker were presented in the presence of one of three competing talkers (same male, different male, or female) or speech-spectrum-shaped noise generated from this talker at several target-to-masker ratios. For the normal-hearing listeners, target-masker combinations were processed through a noise-excited vocoder designed to simulate a cochlear implant. With unprocessed stimuli, a normal-hearing control group maintained high levels of intelligibility down to target-to-masker ratios as low as 0 dB and showed a release from masking, producing better performance with single-talker maskers than with steady-state noise. In contrast, no masking release was observed in either implant or normal-hearing subjects listening through an implant simulation. The performance of the simulation and implant groups did not improve when the single-talker masker was a different talker compared to the same talker as the target speech, as was found in the normal-hearing control. These results are interpreted as evidence for a significant role of informational masking and modulation interference in cochlear implant speech recognition with fluctuating maskers. This informational masking may originate from increased target-masker similarity when spectral resolution is reduced.