Spectral and Temporal Analysis of Simulated Dead Regions in Cochlear Implants

Abstract

A cochlear implant (CI) electrode in a Bcochlear dead region^will excite neighboring neural populations. In previous research that simulated such dead regions, stimulus information in the simulated dead region was either added to the immediately adjacent frequency regions or dropped entirely. There was little difference in speech perception ability between the two conditions. This may imply that there may be little benefit of ensuring that stimulus information on an electrode in a suspected cochlear dead region is transmitted. Alternatively, performance may be enhanced by a broader frequency redistribution, rather than adding stimuli from the dead region to the edges. In the current experiments, cochlear dead regions were introduced by excluding selected CI electrodes or vocoder noise-bands. Participants were assessed for speech understanding as well as spectral and temporal sensitivities as a function of the size of simulated dead regions. In one set of tests, the normal input frequency range of the sound processor was distributed among the active electrodes in bands with approximately logarithmic spacing (Bredistributedm aps); in the remaining tests, information in simulated dead regions was dropped (Bdropped^maps). Word recognition and Schroeder-phase discrimination performance, which require both spectral and temporal sensitivities, decreased as the size of simulated dead regions increased, but the redistributed and dropped remappings showed similar performance in these two tasks. Psychoacoustic experiments showed that the near match in word scores may reflect a tradeoff between spectral and temporal sensitivity: spectral-ripple discrimination was substantially degraded in the redistributed condition relative to the dropped condition while performance in a temporal modulation detection task degraded in the dropped condition but remained constant in the redistributed condition.

Effects of age and hearing mechanism on spectral resolution in normal hearing and cochlear-implanted listeners

“…To date, the relative importance of frequency resolution and across-channel intensity resolution for SRD in CI listeners has not been determined. While evidence that CI listeners with better frequency resolution show better SRD scores has been reported (Won et al, 2011;Jones et al, 2013;Won et al, 2015), it is not clear whether across-channel intensity resolution is an important underlying factor. Before SRD can be adapted as a measure of device efficacy for young CI listeners, it is important to understand the relative importance, and the rates of development, of these underlying factors.…”

The Characteristics of Adults with Severe Hearing Loss

“…When dead regions are present, any consonant information obtained via off-frequency listening is less likely to be interpretable (e.g., Won et al, 2015). The proportion of our test participants with positive TEN tests was lower than in other studies with similar audiograms (Ahadi et al, 2015; Moore et al, 2003; Preminger et al, 2005).…”

Spectral Ripple Discrimination in Normal-Hearing Infants

“…In SRD, noises with modulated, or “rippled,” power spectra are presented and listeners are asked to respond when the ripple is shifted in phase so that the peaks and troughs in the power spectrum of a target stimulus are inverted relative to a reference stimulus (Lopez Valdes et al 2014, Jeon et al 2015, Won et al 2015). The task can be made progressively more difficult either by increasing the ripple density (density approach) or by reducing the peak to trough depth intensity (depth approach) until the listener is unable to discriminate the target and reference stimuli.…”