Speaker
Description
Pitch perception by cochlear-implant (CI) users is generally poor both due to technical limitations as well as biological constraints. Nevertheless, delivering sufficient information to provide the best possible pitch percept is important. Here we explore the feasibility of CI processing strategies that aim to improve pitch perception by presenting information on the stimulus temporal fine structure (TFS) in low-frequency channels to the corresponding apical electrodes. Eight users of the MED-EL CI took part in a pitch-ranking experiment with stimuli presented through direct stimulation and consisting of isochronous pulse trains presented concurrently to the four most apical electrodes. When the same pulse rate was applied to all electrodes, pitch ranks increased until about 300 pulses per second (pps). Presenting different rates (100, 200, 300, and 400 pps) to each electrode produced a pitch percept that was ranked between 100 and 200 pps, irrespective of the rate-to-electrode allocation. For both same- and mixed-rate conditions, maximizing the delay between individual pulses on different electrodes generally produced a higher pitch rank compared to when the delay was kept short. Our results show no evidence that CI users can combine the rates of TFS applied to different apical channels so as to estimate the fundamental frequency but do show that the pitch can be affected by the between-electrode delay, likely due to electrical current spread. We conclude that presenting different temporal patterns to adjacent electrodes is unlikely to produce a robust and clear pitch.