Response Characteristics of Nerve Fibers to Patterned Electrical Stimulation

Abstract

The main interest of our group is the establishment of optimal coding strategies for cochlear implant patients, based on data gained in animal experiments. Obviously two features of normal auditory nerve performance have to be offered to the patient’s brain: an adequate time structure of the discharge pattern in the nerve fibers and a sufficient place-frequency coding. Correct time structure will be most important for single-channel devices, as it is the only means of information transfer in this type of prosthesis. Multichannel implants are capable of a certain place-frequency coding. Yet it may be difficult to obtain good place coding because of channel interaction and resrictions in the correct placement of the electrodes. Therefore, preserving the signal time structure in the impulse pattern will also be important for multichannel devices. In addition, there are even more difficulties, as the performance of any device will depend on the particular status of the patient, e.g., survival of nerve fibers, preservation of central synapses, competence of language (prelingually or postlingually deafened), and so on. Thus there may be patients in whom a perfect imitation of peripheral mechanisms will still not lead to sufficient speech comprehension. Entirely different approaches, such as preprocessing of speech and feature extraction, may have to be used in such cases.