Testing the relationship between focused thresholds and spatial tuning curves as estimates of electrode–neural interface integrity in cochlear implants

This study explored the electrode–neural interface (ENI) quality in cochlear-implant (CI) users by analyzing the relationship between absolute thresholds, spatial selectivity, and stimulation mode. Two hypotheses were tested: (1) high-quality ENI is associated with low absolute thresholds and narrow psychophysical spatial tuning curves (STCs), and (2) focused stimulation modes, such as steered quadrupolar (sQP), produce narrower STCs than the standard monopolar (MP) stimulation mode. Twenty-one CI users (30 ears) were included. Absolute thresholds were measured across each electrode array using focused stimulation, and STCs in both MP and sQP were measured for the two electrodes on each array with the highest and lowest focused thresholds. Consistent with hypothesis 2, STCs were broader with MP than sQP stimulation. However, neither STC bandwidths/slopes nor overall dynamic ranges were significantly different between the high- and low-threshold electrodes. Speech perception scores using PRESTO-N sentences were significantly correlated with MP threshold variability across the array, but not with sQP variability or STC measures. In summary, while focused stimulation produced narrower STCs than MP stimulation, lower focused thresholds did not predict narrower STCs, inconsistent with a strong relationship between ENI, focused thresholds, and STCs. [Work supported by NIH grant R01DC012262.]