Simultaneous intracochlear stimulation based on channel interaction compensation: analysis and first results.

A simultaneous paradigm for electric stimulation of the acoustic nerve based on a monopolar electrode configuration and sign-correlated pulses is presented. Simultaneous pulse amplitudes are determined by taking into account parameters of spatial channel interaction. The computation of simultaneous amplitudes requires the solution of linear systems of equations in an iterative procedure. The computation amount can be reduced significantly, if the spatial impulse responses in individual electrodes can be approximated by two exponentially decaying branches with decay constants alpha toward apex and beta toward base. Generally, the associated inverse of the channel interaction matrix is tridiagonal. Preliminary vowel and consonant identification tests with four cochlear implant patients have been conducted for sequential and simultaneous processor settings. For equal overall pulse repetition rates, comparable speech perception scores were obtained, when the decay constants alpha and beta were set accordingly. Theoretically, the pulse rate of an N-channel system can be increased up to a factor of N as compared to the standard sequential paradigm, and pulses with technically reasonable phase durations can be utilized.