Effects of electrode design and configuration on channel interactions

A potential shortcoming of existing multichannel cochlear implants is electrical-field summation during simultaneous electrode stimulation. Electrical-field interactions can disrupt the stimulus waveform prior to neural activation. To test whether speech intelligibility can be degraded by electrical-field interaction, speech recognition performance and interaction were examined for three Clarion electrode arrays: the pre-curved, enhanced bipolar electrode array, the enhanced bipolar electrode with an electrode positioner, and the Hi-Focus electrode with a positioner. Channel interaction was measured by comparing stimulus detection thresholds for a probe signal in the presence of a sub-threshold perturbation signal as a function of the separation between the two simultaneously stimulated electrodes. Correct identification of vowels, consonants, and words in sentences was measured with two speech strategies: one which used simultaneous stimulation and another which used sequential stimulation. Speech recognition scores were correlated with measured electrical-field interaction for the strategy which used simultaneous stimulation but not the strategy which used sequential stimulation. Higher speech recognition scores with the simultaneous strategy were generally associated with lower levels of electrical-field interaction. Electrical-field interaction accounted for as much as 70% of the variance in speech recognition scores, suggesting that electrical-field interaction is a significant contributor to the variability found across patients who use simultaneous strategies.