Channel interactions have less impact on temporal-pitch than ITD sensitivity in dual-electrode cochlear implant stimulation

Timing cues, i.e., interaural time differences (ITDs) and temporal pitch, are pivotal for sound localization and source segregation, but their perception is impaired in cochlear-implant (CI) listeners compared to normal-hearing listeners. Interactions between channels (i.e., electrodes) are assumed to be an important limiting factor, being responsible for pronounced differences in performance between single- and multi-electrode stimulation. To unveil the origin of these performance differences and the role of channel interactions, dual- and single-electrode monaural temporal-pitch and ITD sensitivity was measured in a total of eight CI listeners. The use of matched experimental setups for ITD and pitch enabled us to directly compare the effects of between-electrode delay, tonotopic separation of electrodes, and stimulus type (low vs. high carrier rate).

Our results demonstrate the important role of channel interactions in timing-cue sensitivity for both temporal pitch and ITD. For pitch, the lack of a delay effect for wide tonotopic separations suggests perceptual independence of electrodes approximately 7 to 10 mm apart, regardless of the stimulus type (i.e., of its intrinsic potential for channel interaction). For ITD, a pitch-like effect of tonotopic spacing was only found for low-rate stimulation (i.e., conditions having a low channel interaction potential). The impact of channel interactions appears to be distinct in monaural vs. binaural processing, i.e., pitch seems to be less susceptible to channel interactions than ITD.