Evaluating and comparing behavioural and electrophysiological estimates of neural health in cochlear implant users

Brochier, Tim; Guérit, François; Garcia, Charlotte; Deeks, John M.; Bance, Manohar; Carlyon, Robert P.

doi:10.31234/osf.io/2kp7x

Cited by 8 publications

(19 citation statements)

References 1 publication

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“…Our paradigm seems more promising in measuring the charge integration properties of the SGNs at MCL than at detection threshold. This contrasts with most proposed psychophysical predictors of neural health that generally focus on the across-electrode variation in the effects of parameters such as inter-phase gap, pulse rate, and stimulus polarity, at detection threshold (Bierer and Faulkner 2010;Pfingst et al 2015;Carlyon et al 2018;Goehring et al 2019;Jahn and Arenberg 2019a, b;Brochier et al 2020;Mesnildrey et al 2020). Although there might indeed be more across-electrode variability at threshold (because of stimulating more targeted populations of neurons), it is worth nothing that some of these measures correlate between threshold and MCL (e.g.…”

Section: Further Research Directionsmentioning

confidence: 93%

Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users

Guérit

Marozeau

Epp

et al. 2020

JARO

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The effect of the relative timing between pairs of same-polarity monophasic pulses has been studied extensively in single-neuron animal studies and has revealed fundamental properties of the neurons. For human cochlear implant listeners, the requirement to use charge-balanced stimulation and the typical use of symmetric, biphasic pulses limits such measures, because currents of opposite polarities interact at the level of the neural membrane. Here, we propose a paradigm to study same-polarity summation of currents while keeping the stimulation charge-balanced within a short time window. We used pairs of mirrored pseudo-monophasic pulses (a long-low phase followed by a short-high phase for the first pulse and a short-high phase followed by a long-low phase for the second pulse). We assumed that most of the excitation would stem from the two adjacent short-high phases, which had the same polarity. The inter-pulse interval between the short-high phases was varied from 0 to 345 μs. The inter-pulse interval had a significant effect on the perceived loudness, and this effect was consistent with both passive (membrane-related) and active (ion-channel-related) neuronal mechanisms contributing to facilitation. Furthermore, the effect of interval interacted with the polarity of the pulse pairs. At threshold, there was an effect of polarity, but, surprisingly, no effect of interval nor an interaction between the two factors. We discuss possible peripheral origins of these results.

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Section: Further Research Directionsmentioning

confidence: 93%

Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users

Guérit

Marozeau

Epp

et al. 2020

JARO

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“…The use of different measures and criteria between studies to select electrode channels for deactivation could have led to the mixed results. Furthermore, it is likely that different measures of electrode-nerve distance and presumed neural health along the cochlea interact and influence the spread of excitation in a complex manner so that the optimal selection of electrodes for improving speech-in-noise performance is not obvious (Brochier et al 2020). Generally, all of the site-selection studies each used only a single measure to guide the selection of deactivated channels without taking into account all the aspects of electrode-nerve distance, local neural health and their interactions.…”

Section: Introductionmentioning

confidence: 99%

Using Spectral Blurring to Assess Effects of Channel Interaction on Speech-in-Noise Perception with Cochlear Implants

Goehring

Arenberg

Carlyon

2020

JARO

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Cochlear implant (CI) listeners struggle to understand speech in background noise. Interactions between electrode channels due to current spread increase the masking of speech by noise and lead to difficulties with speech perception. Strategies that reduce channel interaction therefore have the potential to improve speech-in-noise perception by CI listeners, but previous results have been mixed. We investigated the effects of channel interaction on speech-in-noise perception and its association with spectro-temporal acuity in a listening study with 12 experienced CI users. Instead of attempting to reduce channel interaction, we introduced spectral blurring to simulate some of the effects of channel interaction by adjusting the overlap between electrode channels at the input level of the analysis filters or at the output by using several simultaneously stimulated electrodes per channel. We measured speech reception thresholds in noise as a function of the amount of blurring applied to either all 15 electrode channels or to 5 evenly spaced channels. Performance remained roughly constant as the amount of blurring applied to all channels increased up to some knee point, above which it deteriorated. This knee point differed across listeners in a way that correlated with performance on a non-speech spectro-temporal task, and is proposed here as an individual measure of channel interaction. Surprisingly, even extreme amounts of blurring applied to 5 channels did not affect performance. The effects on speech perception in noise were similar for blurring at the input and at the output of the CI. The results are in line with the assumption that experienced CI users can make use of a limited number of effective channels of information and tolerate some deviations from their everyday settings when identifying speech in the presence of a masker. Furthermore, these findings may explain the mixed results by strategies that optimized or deactivated a small number of electrodes evenly distributed along the array by showing that blurring or deactivating one-third of the electrodes did not harm speech-in-noise performance.

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“…However, it should be noted that focussed thresholds are not the only measure believed to be affected by neural health (Pfingst, et al, 2015). A recent study (Brochier, et al, 2020) obtained several such measures, including the effect of IPG on ECAPs and the effects of pulse rate and stimulus polarity of behavioral thresholds. They found that none of these measures correlated with each other, and used a biophysical model (Joshi, et al, 2017) The lack of correlation between the two could therefore be due to inaccuracies in either estimate.…”

Section: Discussionmentioning

confidence: 99%

The Panoramic ECAP Method: estimating patient-specific patterns of current spread and neural health in cochlear implant users

Garcia¹,

Goehring²,

Cosentino³

et al. 2020

Preprint

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The knowledge of patient-specific neural excitation patterns from cochlear implants can provide important information for optimising efficacy and improving speech perception outcomes. The Panoramic ECAP (or ‘PECAP’) method (Cosentino, et al., 2015) uses forward-masked electrically evoked compound action potentials (ECAPs) to estimate neural activation patterns of cochlear implant (CI) stimulation. The algorithm requires ECAPs be measured for loudness-balanced stimuli from all combinations of probe and masker electrodes, and takes advantage of ECAP amplitudes being a result of the overlapping excitatory areas of both probes and maskers. Here we present an improved version of the PECAP algorithm that imposes biologically realistic constraints on the solution and produces separate estimates of current spread and neural health along the length of the electrode array. The algorithm was evaluated for reliability and accuracy in three ways: (1) computer-simulated current-spread and neural-health scenarios, (2) comparisons to psychophysical correlates of neural health and electrode-modiolus distances in human CI users, and (3) detection of simulated neural ‘dead’ regions (using forward masking) in human CI users. The PECAP algorithm reliably estimated the computer simulated scenarios. A moderate but significant negative correlation between focused thresholds and PECAP’s neural health estimates was found, consistent with previous literature. It also correctly identified simulated dead regions in seven CI users. The revised PECAP algorithm provides an estimate of the electrode-to-neuron interface in CIs that could be used to inform and optimize CI stimulation strategies for individual patients in clinical settings.

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Evaluating and comparing behavioural and electrophysiological estimates of neural health in cochlear implant users

Cited by 8 publications

References 1 publication

Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users

Effect of the Relative Timing between Same-Polarity Pulses on Thresholds and Loudness in Cochlear Implant Users

Using Spectral Blurring to Assess Effects of Channel Interaction on Speech-in-Noise Perception with Cochlear Implants

The Panoramic ECAP Method: estimating patient-specific patterns of current spread and neural health in cochlear implant users

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