Relationship between channel interaction and spectral-ripple discrimination in cochlear implant users

Abstract

Cochlear implant (CI) users can achieve remarkable speech understanding, but there is great variability in outcomes that is only partially accounted for by age, residual hearing, and duration of deafness. Results might be improved with the use of psychophysical tests to predict which sound processing strategies offer the best potential outcomes. In particular, the spectral-ripple discrimination test offers a time-efficient, nonlinguistic measure that is correlated with perception of both speech and music by CI users. Features that make this "one-point" test time-efficient, and thus potentially clinically useful, are also connected to controversy within the CI field about what the test measures. The current work examined the relationship between thresholds in the one-point spectral-ripple test, in which stimuli are presented acoustically, and interaction indices measured under the controlled conditions afforded by direct stimulation with a research processor. Results of these studies include the following: (1) within individual subjects there were large variations in the interaction index along the electrode array, (2) interaction indices generally decreased with increasing electrode separation, and (3) spectral-ripple discrimination improved with decreasing mean interaction index at electrode separations of one, three, and five electrodes. These results indicate that spectral-ripple discrimination thresholds can provide a useful metric of the spectral resolution of CI users.

Using speech sounds to test functional spectral resolution in listeners with cochlear implants

“…The most popular methods of testing spectral resolution for CI listeners are non-linguistic tasks such as electrode discrimination (Nelson et al, 1995;Zwolan et al, 1997), electrode pitch ranking (Donaldson and Nelson, 2000), and spectral ripple discrimination (Henry et al, 2005;Won et al, 2007;Jones et al, 2013). Many of these tests have shown a relationship between spectral resolution and speech perception, but each test is limited in important ways that are addressed in the current study.…”

Spectral and Temporal Analysis of Simulated Dead Regions in Cochlear Implants

“…They demonstrated that larger electrode separation significantly improved spectralripple discrimination, suggesting that less channel interaction would provide better spectral-ripple discrimination performance for CI users. This hypothesis was further supported by significant correlations with channel-interaction index (Jones et al 2013) and electrically evoked compound action potentials (Won et al 2014).…”

“…We simulated a current decay rate of 1 dB/ mm, which is comparable to the slopes of the forwardmasked psychophysical spatial tuning curves for monopolar stimulation (Nelson et al 2008) and to the highest level of channel interactions reported for users of the HiRes90K ™ implant devices (Jones et al 2013). The synthesis filters in the Bredistributedĉ onditions were the same as in the Bdroppedĉ onditions, thus the difference between the two frequency remapping conditions was in the analysis filters only.…”

“…Three different non-speech psychoacoustic experiments were also performed. Spectral-ripple discrimination was evaluated to assess listeners' sensitivity to spectral envelope cues (Won et al 2007(Won et al , 2014Jones et al 2013). Temporal modulation detection was used to evaluate listeners' sensitivity to temporal envelope cues.…”

Low-frequency fine-structure cues allow for the online use of lexical stress during spoken-word recognition in spectrally degraded speech

“…The current signal processing strategies for CIs are designed to preserve temporal envelope cues (i.e., amplitude changes over time) for speech recognition, while discarding the spectral and temporal fine-structure cues [i.e., the carrier defined by the Hilbert transform (Hilbert, 1912)] that are important for pitch perception (Smith et al, 2002;Zeng et al, 2005). The reduced frequency selectivity in CI listening is also due to other factors, including limited neural survival, current spread, and channel interaction (e.g., Bierer et al, 2011;Fu and Nogaki, 2005;Hughes, 2008;Jones et al, 2013;Pfingst et al, 2011). The spectral details provided by CIs resemble that of 4-8 channels of vocoded speech to normal-hearing listeners (Fishman et al, 1997;Friesen et al, 2001;Stickney et al, 2004).…”