Electrical field interactions in different cochlear implant systems.

The goal of this study was to evaluate electrical field interactions produced by the stimulation of different types of intracochlear electrodes in 12 adult subjects (three Ineraid, four Clarion S-Series, three S-Series with the electrode positioning system-EPS and two Clarion HiFocus-I with the EPS). Psychophysical measurements were conducted with biphasic stimuli (813 pulse per second, 153.8 micros/phase). "Perturbation" signals (300 ms) were applied to one electrode chosen at the middle of the array and their effects on detection thresholds of "probe" signals (30 ms) were measured on the neighbor basal electrode. Perturbation levels were set below the detection threshold of the perturbation electrode (-2 dB re threshold). Measurements were first conducted for simultaneous stimulation of the probe and of the perturbation electrodes, for monopolar for all subjects and for bipolar stimulus configurations for both Clarion HiFocus-I subjects. The tested Clarion electrodes did not present lower monopolar interactions than the Ineraid electrodes. Nevertheless, considering the shorter distance between electrodes for the Clarion than for the Ineraid, the tested Clarion electrodes might be more selective than the Ineraid. We did not find any significant monopolar electrical field-interaction differences between subjects who received the S-Series array with and without the EPS. We did not find lower interactions for both subjects who received the HiFocus-I array than for subjects who received the S-Series. Electrical field interactions were lower for bipolar than for monopolar configurations for both HiFocus-I subjects. A second set of measurements was conducted for nonsimultaneous stimulation similar to the one used in continuous interleaved sampling sound strategy. These measurements showed that interactions evaluated for simultaneous biphasic stimuli were larger than for nonsimultaneous stimulation.