Observer weighting of level and timing cues in bilateral cochlear implant users

The contribution of binaural level and timing cues available from each pulse in brief electrical pulse trains was determined in a lateralization task using an observer weighting paradigm. Four bilateral cochlear implant users were tested with randomized interaural time delays (ITDs) or, in a separate experimental condition, interaural level differences (ILDs) applied to each pulse at 100, 300, and 600 pulsess. To examine the effect of cue randomization, weights were also determined for stimuli with a common ITD applied to all postonset pulses. Listeners were further tested for the ability to restart binaural ITD sensitivity at a rate that produced onset dominance by reducing a single interpulse interval in the stimulus. Results showed that the onset always exerted a strong influence. At 100 pulsess, postonset ITDs and ILDs also contributed strongly. At 300 and 600 pulsess, contributions from postonset pulses remained substantial for ILDs but were much reduced for ITDs, particularly at 600 pulsess. Weights were similar with either independent or common ITD cues applied to postonset pulses, indicating that the cue randomization process itself did not affect weights. Restarting of ITD sensitivity at 300 pulsess by introducing a single reduced interpulse interval was not observed.