Investigating the effects of noise-estimation errors in simulated cochlear implant speech intelligibility

A recent study suggested that the most important factor for obtaining high speech intelligibility in noise with cochlear implant recipients is to preserve the low-frequency amplitude modulations of speech across time and frequency by, for example, minimizing the amount of noise in speech gaps. In contrast, other studies have argued that the transients provide the most information. Thus, the present study investigates the relative impact of these two factors in the framework of noise reduction by systematically correcting noise-estimation errors within speech segments, speech gaps, and the transitions between them. Speech intelligibility in noise was measured using a cochlear implant simulation tested on normal-hearing listeners. The results suggest that minimizing noise in the speech gaps can substantially improve intelligibility, especially in modulated noise. However, significantly larger improvements were obtained when both the noise in the gaps was minimized and the speech transients were preserved. These results imply that the correct identification of the boundaries between speech segments and speech gaps is the most important factor in maintaining high intelligibility in cochlear implants. Knowing the boundaries will make it possible for algorithms to both minimize the noise in the gaps and enhance the low frequency amplitude modulations.