Speech Understanding With Various Maskers in Cochlear-Implant and Simulated Cochlear-Implant Hearing: Effects of Spectral Resolution and Implications for Masking Release

The purpose of this study was to investigate the relationship between psychophysical spectral resolution and sentence reception in various types of interfering backgrounds for listeners with cochlear implants and normal-hearing subjects listening to vocoded speech. Spectral resolution was measured with a spectral modulation detection (SMD) task. For speech testing, maskers included stationary speech-shaped noise (SSN), four-talker babble, multitone noise, and a competing talker. To explore the possible trade-offs between spectral resolution and susceptibility to different types of maskers, the degree of simulated current spread was varied within the vocoder group, achieving a range of performance for SMD and speech tasks. Greater simulated current spread was detrimental to both spectral resolution and speech recognition, suggesting that interventions that decrease current spread may improve performance for both tasks. Better SMD sensitivity was significantly correlated with improved sentence reception. In addition, differences in sentence reception across the four maskers were significantly associated with SMD across the combined group of cochlear-implant and vocoder subjects. Masking release (MR) was quantified as the signal-to-noise ratio difference in speech reception threshold between the SSN and competing talker. Several individual cochlear-implant subjects demonstrated substantial MR, in contrast to previous studies, and the degree of MR increased with better SMD thresholds across subjects. The results of this study suggest that alternative masker types, particularly competing talkers, are more sensitive than stationary SSN to differences in spectral resolution in the cochlear-implant population.