Fig. 4. Effect of conditioning time. (A) Short trains of stimuli. Root-mean-square voltage (Vrms) values (mean ± S.D., N=6) of 200 ms following the due-time of the first missing flash at the end of trains of various numbers of flashes at 10 Hz (squares and circles) and 15 Hz (asterisks). Since omitted stimulus potentials (OSPs) cannot confidently be identified after trains of only three or four flashes, Vrms values for such trains measure essentially the spontaneous activity. Values are higher for trains containing more than five flashes and reach a maximum at around eight flashes. In this preparation, the values increase again after 12–14 flashes. (B) Longer trains of stimuli. Trains of 9 Hz of various durations, showing only the last three flashes. This recording locus showed a late spike burst type of visual evoked potential (VEP) and a more vigorous OSP, essentially uninfluenced by the duration. The OSP after 30 s is anomalous.
