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.

Funding: Austrian Academy of Sciences: A-25606 Austrian Academy of Sciences: A-100315