FIG. 2.

Examples of spikes evoked by 5,000-pulse/s trains from three fibers of three cats. Superimposed responses to the first 10 ms of repeated pulse trains are shown. In the spikes shown in the left column, two distinctly different ISIs are evident in response to the two highest stimulus levels, consistent with a two-peaked IH. Spikes from a second fiber (middle column) demonstrate somewhat different timing, with smaller differences between the first and second ISIs. That fiber also demonstrates a cumulative effect of increasing temporal variation within successive volleys of spikes. That pattern should not be interpreted simply as increased “jitter” but also as greater uncertainty in the stimulus pulse number that causes spike initiation. In the case of fiber D58-7-1 (right column), two-stage artifact reduction (box-car filtering followed by template subtraction) was required to reduce the impact of a relatively large ECAP potential that occurred across the first 1.5 ms of each trace. The ECAP subtraction resulted in distorted first spikes; specifically, those spikes had a large preceding negative peak (single asterisk) and a narrowed action potential (double asterisks). In this case of poor artifact subtraction, the occurrence of spike failures (i.e., relatively flat lines over the 0–1.5-ms epoch) reinforce the fact that the distorted spikes are, indeed, action potentials.