Effects of Dual-Electrode Asynchrony on Temporal Pitch Discrimination With Amplitude Modulation and Short Inter-Pulse...

Cochlear-implant listeners show impaired pitch perception compared to normal-hearing listeners. One of the factors limiting pitch sensitivity in multi-electrode as compared to single-electrode stimulation can be intracochlear interactions of electrode signals (i.e., channels). We measured temporal-pitch discrimination sensitivity for loudness-balanced dual-electrode stimuli with various spatio-temporal configurations in listeners with MED-EL implants. We hypothesized a link between pitch sensitivity and tonotopic separation as well as (monaural) temporal electrode asynchrony, the latter resulting in various combinations of inter-pulse intervals in the compound stimuli received by the auditory nerve. Per-electrode stimulus types were high-rate (i.e., 1,000-pps) pulse trains with a 100-Hz amplitude modulation and both with and without additional pulses inserted with short inter-pulse intervals at modulation peaks. The temporal asynchrony had a detrimental effect for tonotopic separations below 2.2 mm but not for separations of 7.1 mm and more. This pattern was largely consistent across stimulus types and can be attributed to spectro-temporal channel interactions. When compared with sensitivity to unmodulated 100-pps pulse trains [Lindenbeck et al., Trends in Hearing, 28, Article 23312165241271340 (2024)], stimuli without short inter-pulse interval pulses yielded lower sensitivity while stimuli with short inter-pulse interval pulses approached low-rate sensitivity for some tonotopic separations. Despite lower sensitivity overall, high-rate pitch cues seemed to be integrated (i.e., improved) more across the two electrodes than low-rate pitch cues when compared to single-electrode stimulation. These results suggest that short inter-pulse interval pulses are beneficial for temporal-pitch sensitivity in dual-electrode configurations.