Across‐channel sensitivity to temporal asynchrony in cochlear implantees

Five post‐lingually deafened users of the LAURAflex cochlear implant detected temporal asynchronies between two 400‐ms, 100‐Hz trains of 40‐μs biphasic pulses, applied to two ‘‘target’’ electrode pairs. The pulses in the signal stimulus of each 2IFC trial were delayed by between 0.3 and 4.8 ms on either the basal or apical target, relative to those on the other target. The pulses in the standard stimuli were nearly synchronous, containing a 0.1 ms‐delay to the electrode whose pulses were not delayed in the signal. All listeners performed substantially above chance over a wide range of delays. Four were more sensitive to basal delays than to apical delays; one showed the opposite trend. Presenting a ‘‘masking’’ 1000‐Hz pulse train to electrode(s) between the two targets did not substantially affect the results. This finding, combined with the wide (6–10 mm) separation between the targets suggests that performance was not mediated by neurons responding to both target electrodes. Rather, it is argued that they represent a genuine sensitivity to differences in timing between discrete auditory channels.