PITCH PERCEPTION FOR DIFFERENT MODES OF STIMULATION USING THE COCHLEAR MULTIPLE-ELECTRODE PROSTHESIS

Numerical estimations of pitch were obtained from nine postlinguistica lly deafened adults using the 22-electrode cochlear implant manufactur ed by Cochlear Pty. Limited. A series of electrodes on the array were stimulated using three modes of stimulation: Bipolar (BP), common grou nd (CG), and monopolar (MONO). In BP stimulation, an electric current was passed between two electrodes separated by one electrode for eight patients and two electrodes for one patient. In CG stimulation, a sin gle electrode was activated and the other electrodes on the array were connected together to serve as the return path for the current. In MO NO stimulation, an electric current was passed between a single electr ode and the most basal electrode on the array. Pitch estimations were generally consistent with the tonotopic organization of the cochlea. T here was a marked reversal in pitch for electrodes in the middle of th e array using CG stimulation for three patients. A reduced range of pi tch using MONO stimulation was recorded for patients where the most ba sal electrode was internal to the cochlea. There were also individual differences in pitch estimations between the three modes of stimulatio n for most patients. The current levels required to elicit threshold ( T) and comfortable listening (C) levels were, in general, higher for B P stimulation than for CG stimulation and were lowest for MONO stimula tion. For CG stimulation, there was a tendency for T and C levels to b e higher for electrodes in the middle of the array than at the basal o r apical ends. For MONO stimulation, T and C levels uniformly increase d in an apical to basal direction for the majority of patients. There was no consistent pattern in T and C levels for BP stimulation. The si ze of the range of usable hearing using CG stimulation tended to be si milar to that using BP stimulation and was usually higher than that us ing MONO stimulation.