Detection of small across-channel timing differences by cochlear implantees

Five post-lingually deafened users of the LAURA cochlear implant were prese nted with two trains of biphasic pulses applied concurrently to two widely separated channels. They could all discriminate between stimuli where pulse s on the two channels were nearly synchronous (inter-channel delay = 0.1 ms ) and those where there was a longer delay applied to one channel. All show ed an asymmetry, being more sensitive when the longer delay was on either t he more basal or, depending on the listener, the more apical channel. For f our out of the five listeners this asymmetry could be at least partly attri buted to one stimulus, with a 0.1-ms delay in either the apical (three list eners) or basal tone listener) channel, sounding markedly different from al l other stimuli used in the experiment. Both the overall sensitivity of lis teners and the general pattern of results survived the presentation of mask ers on intermediate channels, and did not vary markedly with changes in the polarity of the pulses applied to one channel. Although the results varied substantially across listeners, it is concluded that they demonstrate a ge nuine sensitivity to the relative timing of stimulation applied to discrete populations of auditory nerve fibers. (C) 2000 Elsevier Science B.V. All r ights reserved.