The resolution of spectral peaks by cochlear implant and normal-hearing listeners

Abstract

The ability to resolve spectral peaks is important in the discrimination of speech. This study investigated the differences in spectral resolution abilities between cochlear implant (CI) and normal-hearing (NH) listeners, and among CI listeners having different speech perception abilities. CI listeners using the Cochlear Ltd. CI-24M implant and SPrint processor, and NH listeners participated. The stimuli were rippled-spectrum noise signals, with ripple densities of approximately 1, 1.5, 2, 3, 4, 6, 8, 16, 32, 64, 126, and 252 peaks between 0 and 8 kHz. The stimuli were presented to the CI subjects (CIS) using a 12-channel CIS speech processing strategy via the direct processor input, and to NH subjects via headphones through a 12-channel CI simulation. The highest resolvable ripple density was determined for each listener as the ripple density at which an interchange of peak and trough positions in the rippled spectrum was discriminated at the 70.7% correct level. This efficient method of measuring ripple density resolution indicates that CI listeners have poorer spectral resolution abilities than NH listeners when listening with 12 channels. The relationship between ripple density resolution and vowel recognition in CI listeners will be discussed. [Work supported by NIDCD.]