Temporal pitch perception of multi-channel stimuli by cochlear-implant users

Some cochlear-implant (CI) processing strategies aim to improve pitch perception by presenting information on the stimulus temporal fine structure (TFS) in low-frequency channels to the corresponding apical electrodes. To explore the feasibility of such strategies we asked eight users of the MED-EL CI to pitch-rank stimuli consisting of isochronous pulse trains presented concurrently to the four most apical CI electrodes. When the same rate was applied to all electrodes pitch ranks increased with increasing rate up to 200-300 pulses-per-second (pps), consistent with previous research. Presenting rates of 100, 200, 300, and 400 pps to one electrode per rate produced a pitch rank between that of the 100- and 200-pps same-rate stimuli. The assignation of pulse rate to electrode did not have a consistent effect on pitch ranks. However, maximizing the delay between pulses on the different electrodes generally produced higher pitch ranks compared to when the between-electrode pulse delay was very short. Our results show no evidence that listeners combine the rates of TFS applied to different channels so as to estimate the fundamental frequency, but do show that pitch can be affected by between-electrode delays. We conclude that presenting different temporal patterns to adjacent electrodes is unlikely to produce a clear and robust pitch, and propose an alternative method for conveying the F0 of complex sounds on multiple electrodes of a CI.