Channel interaction in cochlear implant users evaluated using the electrically evoked compound action potential

One likely determinant of performance with a cochlear implant is the degree of interaction that occurs when overlapping subsets of nerve fibers are stimulated by various electrodes of a multielectrode array. The electrically evoked compound action potential (ECAP) can be used to assess physiological channel interaction. This paper describes results from two different methods of analysis of ECAP channel interaction measures made by the Nucleus neural response telemetry system. Using a forward-masking stimulus paradigm, masker and probe pulses are delivered through different electrodes. The response to the probe is then dependent on the extent of overlap in the stimulated neural populations. The amplitude of response to the probe as a function of masker electrode position then reflects the degree of overlap between the population of neurons responding to the masker and those stimulated by the probe. Results demonstrate large variations across individual implant users as well as across electrodes within an individual. In general, the degree of interaction is shown to be dependent on stimulus level.