Abstract
Variability in speech perception scores among cochlear implant listeners may largely reflect the variable efficacy of implant electrodes to convey stimulus information to the auditory nerve. In the present study, three metrics were applied to assess the quality of the electrode-neuron interface of individual cochlear implant channels: the electrically evoked compound action potential (ECAP), the estimation of electrode position using computerized tomography (CT), and behavioral thresholds using focused stimulation. The primary motivation of this approach is to evaluate the ECAP as a site-specific measure of the electrode-neuron interface in the context of two peripheral factors that likely contribute to degraded perception: large electrode-to-modiolus distance and reduced neural density. Ten unilaterally implanted adults with Advanced Bionics HiRes90k devices participated. ECAPs were elicited with monopolar stimulation within a forward-masking paradigm to construct channel interaction functions (CIF), behavioral thresholds were obtained with quadrupolar (sQP) stimulation, and data from imaging provided estimates of electrode-to-modiolus distance and scalar location (scala tympani (ST), intermediate, or scala vestibuli (SV)) for each electrode. The width of the ECAP CIF was positively correlated with electrode-to-modiolus distance; both of these measures were also influenced by scalar position. The ECAP peak amplitude was negatively correlated with behavioral thresholds. Moreover, subjects with low behavioral thresholds and large ECAP amplitudes, averaged across electrodes, tended to have higher speech perception scores. These results suggest a potential clinical role for the ECAP in the objective assessment of individual cochlear implant channels, with the potential to improve speech perception outcomes.
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Acknowledgments
The authors would like to acknowledge Emily Ellis for assistance with data collection, Timothy Holden for analyzing the CT scans, and our subjects for their constant dedication. We also want to thank two anonymous reviewers for their insightful comments, Steven Bierer for his helpful editorial comments when drafting the manuscript, and Lynne A. Werner and the Communication Studies Participant Pool (P30 DC04661) for their support. Finally, we would also like to acknowledge our funding sources, RO1 DC012142 (JAB) and T32 DC 000033 (University of Washington Speech and Hearing Sciences: LAD, Boys Town National Research Hospital: RAS).
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DeVries, L., Scheperle, R. & Bierer, J.A. Assessing the Electrode-Neuron Interface with the Electrically Evoked Compound Action Potential, Electrode Position, and Behavioral Thresholds. JARO 17, 237–252 (2016). https://doi.org/10.1007/s10162-016-0557-9
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DOI: https://doi.org/10.1007/s10162-016-0557-9