Within-channel gap detection using dissimilar markers in cochlear implant listeners.

Temporal gap detection thresholds were measured between perceptually dissimilar electrical markers in cochlear implant listeners. Both markers were presented to the same electrode pair. The amplitude and pulse rate of the first marker were fixed, and gap thresholds were measured as a function of either the pulse rate or the amplitude of the second marker. In either case, U-shaped functions were obtained, with lowest gap thresholds occurring when the two markers were similar in both amplitude and pulse rate. Because the two markers were presented to the same electrode pair, the data cannot be accounted for on the basis of across-channel interactions. It is hypothesized that when different markers are used, the perceptual discontinuity from the first marker to the second is similar to the sensation of a brief gap, and dominates the gap detection process. Thus, gap threshold functions with electrically dissimilar markers serve more as indicators of perceptual distance between the markers and less as measures of temporal resolution.