A model of a Nucleus 24 cochlear implant fitting protocol based on the electrically evoked whole nerve action potential

Objective: The goal of this study was to model a cochlear implant fitting protocol based on the electrically evoked whole nerve action potential (EAP) measured using the Neural Response Telemetry capabilities of the Nucleus CI24M cochlear implant. The model and data were based on the significant correlations found between the EAP threshold and growth function slope and psychophysical threshold and dynamic range, respectively, in 12 subjects (Franck, Reference Note 3; Franck & Norton, 2001). Design: Using a retrospective split-half study design, these correlations found between psychophysical mapping levels and EAP data from six of the subjects were used in a model to predict psychophysical mapping levels from EAP data of the other six subjects. Results: Predicted psychophysical mapping levels from the model of the EAP-based fitting protocol closely approximated measured cochlear implant fitting psychophysics. Conclusions. The close approximation of the measured data to the model data indicates the feasibility of the clinical use of an EAP-based cochlear implant fitting protocol. The realization of this model would only require two loudness judgments from the patient, whereas traditional fitting requires 44, and would be fit in a live-voice mode, accounting for across-electrode loudness summation.