PATIENT PERFORMANCE WITH THE COCHLEAR-CORPORATION 20-IMPLANT - BIPOLAR VERSUS MONOPOLAR ACTIVATION(2)

A within-subjects comparison of monopolar versus bipolar stimulation w as performed using a modified version of the Nucleus mini-22 cochlear implant, the Nucleus ''20 + 2'' implant. Six subjects underwent implan tation with this device, which is identical to the Nucleus 22 cochlear implant with the addition of two extracochlear indifferent electrodes . These electrodes provide two monopolar modes of stimulation in addit ion to the standard bipolar modes used with the Nucleus 22 device. One of the indifferent electrodes is a ball placed under the temporalis m uscle (MP1), whereas the second electrode is mounted on the lateral as pect of the receiver-stimulator (MP2). After a pre-experimental phase, subjects used each of three stimulation modes (BP + 1, MP1 and MP2) f or a total of 4 weeks each. Variables tested with each mode included e lectric thresholds, comfort levels, dynamic ranges, and speech recogni tion. Both the MP1 and MP2 modes of stimulation required significantly less current than the bipolar mode (BP + I)to reach threshold and com fort level. Analysis of dynamic range data also indicated a significan t stimulation mode effect. However, stimulation in the various modes d id not significantly affect speech recognition scores, although two su bjects demonstrated significantly improved speech recognition scores w hen programmed in a monopolar mode.