Capturing Temporal and Spectral Response Properties of Auditory Nerve Fibers for a Cochlear Implant Coding Strategy

Background

Temporal response properties of auditory nerve fibers (ANFs) and spatial spread of neural excitation impose limitations for electrical stimulation of cochlear implants (CIs). Thus, a CI coding strategy that utilizes such neurophysiological characteristics would be beneficial. Neural response characteristics (recovery, facilitation, and spread of excitation) can be explored by recording electrically evoked compound action potentials (ECAPs).

Objective

The aim of this study was to extract ANFs characteristics via NRT (Neural Response Telemetry) and integrate them in a novel CI coding strategy for the selection of stimulation channels.

Methods

CI users implanted with Cochlear® Nucleus™ implants took part in the study and amplitude growth functions were recorded for 3 stimulation electrodes (apical, middle, and basal). The probe CL for each test electrode varied from visually detected ECAP threshold to the current level which yielded a response amplitude of 100 µV. The masker to probe intervals varied between 13 µs to 6000 µs. Spread of excitation was measured for the test electrodes with the standard forward masking artefact cancellation technique.

The outcomes of these electrophysiological recordings were integrated in a bio-inspired coding strategy for a better selection of channels with highest energy content. Two versions of this novel strategy were compared with the conventional ACE coding strategy using speech in noise sentence and melody contour identification tests.

Results

Objective measures as well as performance data obtained with CI recipients will be presented and discussed in relation to previous studies.