Towards increasing timing sensitivity in electric hearing

Abstract

Sensitivity of bilateral cochlear-implant (CI) listeners to interaural time differences (ITDs) in electric pulse trains is degraded compared to normal-hearing (NH) listeners presented with ITDs in pure tones. This degradation manifests both as an elevated ITD threshold and upper perceptual limit of stimulation rates. Similar limitations were observed for temporal pitch, despite the difficulty to disentangle temporal and place pitch cues in NH listeners. We tested the hypothesis that ITD and monaural rate-pitch sensitivity of CI listeners at high rates of electric stimulation can be improved by introducing extra pulses with short inter-pulse intervals (SIPIs) at low rates in amplitude modulated high-rate pulse trains. Results show that SIPIs significantly improved ITD and monaural rate-pitch sensitivity at low modulation depths. These similar improvements suggest a possible overlapping benefit of SIPIs for CI listeners in everyday environments requiring high rates for encoding speech. Considering the documented effects of neural deprivation, its potential reversal by training, and the potential for NH-like timing sensitivity as observed in exceptional CI listeners, we began to investigate the effects of vision-induced ITD training in CI listeners. Preliminary results will be discussed in the light of the timing sensitivity limitations in electric hearing.