Effect of electrode impedance on spread of excitation and pitch perception using electrically coupled "Dual-Electrode" stimulation

Objectives: In newer-generation Cochlear Ltd. cochlear implants, two adjacent electrodes can be electrically coupled to produce a single contact or "dual electrode" (DE). The goal of the present study was to evaluate whether relatively large impedance differences (>3.0 kOhms) between coupled electrodes affect the excitation pattern and pitch percepts produced by the DE. Design: Fifteen electrode pairs in six recipients were tested. Neural spread-of-excitation patterns and pitch perception were measured for adjacent physical electrodes (PEs) and the resulting DE to determine if the lower-impedance PE in the pair dominates the DE response pattern. The results were compared with a "normative sample" (impedance differences <3.0 kOhms) from two earlier studies. Results: In general, spread-of-excitation patterns for DEs more closely approximated those of the lower-impedance PE in each pair. The DE was more easily distinguished in pitch from the higher-impedance PE than the lower-impedance PE. The electrically evoked compound action potential and perceptual results generally differed from those of the normative group. Conclusions: Impedance differences between adjacent PEs should be considered if DE stimulation is implemented in future research studies or clinical coding strategies.