Investigating the effect of blurring and focusing current in cochlear implant users with the Panoramic ECAP method

Purpose: For some cochlear implants (CIs), it is possible to focus electrical stimulation by partially returning current from the active electrode to adjacent, intra-cochlear electrodes (partial tripolar (pTP) stimulation). Another method achieves the opposite: “blurring” by stimulating multiple electrodes simultaneously. The Panoramic ECAP Method (PECAP) provides a platform to investigate their effects in detail by measuring Electrically-Evoked Compound Action-Potentials (ECAPs) and estimating current spread and neural responsiveness along the length of the CI electrode array. We investigate how sharpening and broadening the electrical current spread is reflected in PECAP estimates. Methods: PECAP measurements were recorded at most comfortable level in 12 ears of Advanced Bionics CI users. Focused thresholds were also determined using steered quadrupolar (sQP) stimulation. For the electrodes with the highest and lowest sQP thresholds, additional PECAP measurements were recorded whilst stimulating in pTP mode and in “blurred” mode with 3 or 5 adjacent electrodes simultaneously stimulated. Current spread and neural responsiveness were then estimated along the electrode array using PECAP. Results: PECAP revealed increased current-spread estimates for blurred stimulation for the targeted electrodes towards the apex of the cochlea. Mixed results for pTP stimulation were found, with increased current spread in two ears, decreased current spread in one ear, and no effect in five. Conclusion: When stimulating multiple electrodes simultaneously, PECAP detected localized increases in current spread toward the apex (but not the base) of the cochlea. pTP stimulation showed mixed effects on PECAP current-spread estimates. These findings are in line with behavioral speech perception studies.