Postlingually Deafened Adult Cochlear Implant Users With Prolonged Recovery From Neural Adaptation at the Level of the Auditory Nerve Tend to Have Poorer Speech Perception Performance

Abstract

This study investigated the effects of two temporal response properties of the auditory nerve (i.e., neural adaptation and recovery from neural adaptation) on speech perception performance in postlingually deafened adult cochlear implant (CI) users.Design: Study participants included 18 postlingually deafened adults who were Cochlear Nucleus device users with a full electrode array insertion in the test ear(s). Neural adaptation and adaptation recovery of the auditory nerve (AN) were evaluated using electrophysiological measures of the electrically evoked compound action potential (eCAP). The amount of neural adaptation was quantified by the adaptation index within three time windows: 0 to 8.89 (window 1), 44.44 to 50.00 (window 2), and 94.44 to 100.00 ms (window 3). The speed of neural adaptation was estimated using a two-parameter power law function. To evaluate adaptation recovery of the AN, eCAPs to the last pulse of the 100-ms pulse train were recorded at masker-probe-intervals ranging from 1.054 to 256 ms in logarithmic steps. The amount of adaptation recovery was quantified by the adaptation recovery ratio. The time-constant of adaptation recovery was estimated using an exponential function with up to three components. Speech perception performance was evaluated by measuring consonant-nucleus-consonant (CNC) word scores presented in quiet and in speech-shaped noise at a signal-to-noise ratio (SNR) of +10 dB. One-tailed Pearson Product Moment correlation tests were used (1) to assess the associations among parameters of neural adaptation and adaptation recovery and (2) to evaluate the strength of association between these parameters and CNC word scores measured in quiet and in noise. The contributions of different parameters quantifying neural adaptation and adaptation recovery on speech perception scores were evaluated using multivariable linear regression analyses. Results:The Pearson Product Moment correlation coefficient demonstrated a moderate, negative correlation between the speed of adaptation recovery and CNC word scores measured in quiet and in noise. The speed of adaptation recovery accounted for 14.1% of variability in CNC word scores measured in quiet and 16.7% of variability in CNC word scores measured in noise. The correlation strengths between CNC word scores and the adaptation index, the adaptation recovery ratio and the speed of neural adaptation ranged from negligible to weak. Conclusions:The speed of adaptation recovery plays a more important role than other features of neural adaptation and adaptation recovery of the AN in speech perception in postlingually deafened adult CI users. Patients with prolonged adaptation recovery tend to show poorer speech perception performance.

The relationship between electrophysiological measures of the electrically evoked compound action potential and cochlear implant speech perception outcomes

“…Specifically, results of previously published studies suggest that the presence of AN response to electrical stimulation (i.e., the presence of the electrically evoked compound action potential, eCAP), faster recovery from refractoriness, and faster growth of eCAP amplitudes with increasing stimulation level are associated with better speech perception in CI users (for a review, see van Eijl et al, 2017). More recently, it has been shown that better speech perception outcomes are associated with higher effectiveness of the CI electrodes in stimulating the targeted AN fibers (i.e., electrode-to-neuron interface, ENI, Bierer, 2010; Skidmore et al, 2021; Arjmandi et al, 2022), and faster recovery from neural adaptation (NA) induced by prior stimulation (He et al, 2022c). Based on these promising results, we took a bottom-up approach in this study to determine/identify peripheral factors that are important for speech perception outcomes in CI users.…”

“…Therefore, eCAPs measured in response to single-pulse and paired-pulse stimulation can be considered as a functional readout for the quality of the ENI (Skidmore et al, 2022a). The temporal response properties of the AN evaluated in this study included NA and recovery from NA (i.e., adaptation recovery, AR) induced by trains of biphasic pulses with constant amplitudes (e.g., Wilson et al, 1997; Hay-McCutcheon et al, 2005; Hughes et al, 2012; Zhang et al, 2013; Ramekers et al, 2015; He et al, 2016; Mussoi & Brown, 2019; He et al, 2022a, b, c, d) and the sensitivity to sinusoidal amplitude modulation (AM) cues implemented in the pulse-train stimulation (Nourski et al, 2007; Tejani et al, 2017; Riggs et al, 2021). NA and AR of the AN were selected as measures of interest because of their essential roles in accurately encoding speech sounds (Delgutte, 1980; Johnson, 1980; Delgutte & Kiang, 1984).…”

“…Their results showed a significant, positive correlation between the ENI index and CNC word and AziBio sentence scores. He et al (2022c) investigated the effects of NA and AR of the AN on CNC word scores measured in quiet and in noise at a signal-to-noise ratio (SNR) of +10 dB in post-lingually deafened adult CI users. Their results showed a nonsignificant relationship between NA of the AN and CNC word scores measured in both conditions.…”

“…In addition, the speed of AR was quantified using different methods in these two studies. These methodological differences might account for the inconsistent results reported in Mussoi & Brown (2019) and He et al (2022c). Finally, He et al (2022d) evaluated the association between AN sensitivity to AM cues and CNC word scores measured in quiet and in noise at a SNR of +10 dB.…”

“…The noise conditions with SNRs of +10 and +5 dB are most commonly used in clinical practice for CIs (Carlson et al, 2018). Previous studies either tested speech perception performance only in quiet (Zhang et al, 2013; Skidmore et al, 2021), using another speech test (Mussoi & Brown, 2019), or did not include the noise condition with a SNR of +5 dB (He et al, 2022a, c, d). These caveats limit the clinical application of these previously reported results.…”