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Cochlear implant systems are based on stimulation of the auditory nerve fibers by electrical current with implanted electrodes. In the clinical tests, based on stimulation by electrical current and recording the evoked compound action potential (CCAP) same as neural response telemetry (NRT), electrical behavior and population distribution of the nerve fibers can be evaluated. Stimulation parameter in mimicking the normal hearing can be determined by the results of these tests. Condition of these tests is different from the actual stimulation for hearing, both in amplitude and time sequence of the stimulation current pulses. Therefore, there are some problems in the mapping the test results to stimulation parameters. At this paper, we have presented a new selective nonsimultaneous multi-electrode stimulation (NSMES) method based on applying the inhibitory pre-pulses by lateral electrodes that changes the initial conditions of the fibers to focus on the target fibers. The results of simulations show that this method will penalize undesired population distribution of the remained excitable fibers and it has been distinguished from the desired one. To estimate the electrical behavior of the fibers in normal use of the system for hearing, which has much more pulse rate than the test condition, we assumed a probabilistic function for recovery time of the fibers to map the test results to hearing condition parameters. Simulation results show that the stimulation electrode array parameters can be determined more accurately by the presented modification qualitatively and quantitatively.
Date of Conference: 1-5 Sept. 2004