Release from masking in cochlear-implant listeners and its relationship to spectro-temporal resolution

Abstract

Release from masking is commonly observed in normal-hearing listeners when fluctuating interferers mask speech perception less than steady interferers at the same signal-to-noise ratio. In contrast, studies of cochlear-implant listeners have historically failed to find masking release with fluctuating maskers. Here, we provide new insights into the relationship between spectro-temporal resolution and release from masking in cochlear-implant and simulated cochlear-implant listeners. Varying degrees of current spread were simulated in normal-hearing listeners using a tone vocoder. Speech reception thresholds were measured with four different interferers: a tone complex, speech-shaped noise, four-talker babble, and a single competing talker. A dynamic spectral ripple detection test was conducted to measure psychophysical spectro-temporal resolution. Results show that overall speech perception was correlated with spectro-temporal ripple detection thresholds. However, some maskers were more sensitive to spectro-temporal resolution than others. Subjects in both groups demonstrated release from masking between the speech-shaped noise and the single competing talker conditions, and the degree of release varied with spectro-temporal ripple sensitivity. These findings shed new light on previous cochlear-implant results, suggesting that individual cochlear-implant listeners with high spectro-temporal resolution may benefit from the temporal fluctuations in certain noise types.