Fig. 2. (A) An example of single novelty response (NR) from a single rotation of the stimulus object. The dotted line is the instantaneous electric organ discharge (EOD) rate in pulses s^–1. The green line is the spike density function (SDF) derived from this single sequence of pulses. Notice how closely the SDF follows the instantaneous EOD rate, except for the four shortest intervals that compose the `scallop' signature but contribute very little to the overall area of the NR. The time of minimum object distance is shown by the broken red line. (B) EOD rate during a session of 10 stimulus object rotations. The black dots are 10 sequences of instantaneous EOD frequency, and the green line is their SDF. (C) SDF from the same session, showing start time and end time as well as the threshold EOD rate and the baseline period. (D) Spike density derivative (SDD) showing how start time and end time are determined by zero-crossings relative to maximum. Notice how the first post-maximum, negative-to-positive zero-crossing does not register as end time because the corresponding SDF value is above threshold.