Restoring sensitivity to interaural timing differences in bilateral cochlear implant listeners using multi-electrode stimulation

Abstract

Identification and discrimination of sound sources in complex auditory environments is facilitated for normal-hearing listeners from access to interaural time differences (ITDs). For patients fitted with bilateral cochlear implants (BiCI), binaural sensitivity is harder to achieve due to several factors, including asynchronous interaural processing. BiCI listeners have shown good ITD sensitivity with low rates of electrical stimulation; however, low-rate delivery of ITD cues is unrealistic for the high-rate pulsatile stimulation required to achieve good speech understanding. One solution is to present a mix of high- and low-rate stimulation on different electrodes, preserving both speech recognition and sound localization ability. In the present study, a binaural benefit was observed in a mixed-rate strategy under direct electrical stimulation: ITD sensitivity was measured in a two-alternative forced-choice discrimination task, using seven multi-electrode conditions. We hypothesized that by introducing low-rate ITDs at a few electrodes alongside high-rate ITDs at remaining electrodes provides sufficient ITD cues for sound localization. The present data suggests the binaural system of BiCI listeners can extract pertinent cues to achieve ITD sensitivity even when high-rate ITD information is presented at the majority of the cochlear locations. This lends to a possibility in implementation of ITD cues to current processing strategies.