Fig. 2.

Cumulative interresponse time (IRT) distributions from the variableinterval differential-reinforcement-of-low-rate (VI-DRL) evaluation, experiment 1. The upper panel illustrates the similarity of baseline temporal-patterning across the two portions (VI and DRL) of the conjunctive schedule. The lower panel shows the effect of repeated nicotine dosing on the temporal patterning of responses; repeated 0.3 mg/kg dosing produced an increased frequency of short IRTs (a leftward shift in the distribution) compared with initial dosing.