Interaural-time-difference discrimination as a measure of place of stimulation for cochlear-implant listeners with single-sided deafness

Recently, some patients with single-sided deafness (SSD) have received a cochlear implant (CI), with the goal of improving their spatial-hearing abilities. Because electrode arrays typically do not reach the cochlear apex, standard frequency-to-electrode allocations are likely to create a substantial interaural cochlear place-of-stimulation mismatch, and might not optimize binaural function for SSD-CI listeners. As a first step, we evaluated whether a test of interaural-time-difference (ITD) discrimination could be used to identify the cochlear place of stimulation for individual electrodes. Six SSD-CI listeners were presented with 500-ms bursts of 100-pps electrical pulse trains on a single electrode, and bandlimited pulse trains with variable carrier frequencies in the acoustic ear. Listeners discriminated between two “static” intervals (each containing four bursts with constant ITD) and a “moving” interval (four bursts with variable ITD). For most listeners and electrodes, performance peaked at a particular acoustic carrier frequency, which was on average 0.57 octaves higher (range = -0.2-1.1 octaves) than the standard clinically allocated center frequency. These results demonstrate that an ITD-discrimination task can identify the optimal frequency allocation required for a given CI electrode to maximize binaural function for SSD-CI listeners. The opinions and assertions presented are the private views of the authors and are not to be construed as official or as necessarily reflecting the views of the Department of Defense.