Food-deprived rats in Experiment 1 responded to one of two tandem schedules that were, with equal probability, associated with a sample lever. The tandem schedules' initial links were different random-interval schedules. Their values were adjusted to approximate equality in time to completing each tandem schedule's response requirements. The tandem schedules differed in their terminal links: One reinforced short interresponse times; the other reinforced long ones. Tandem-schedule completion presented two comparison levers, one of which was associated with each tandem schedule. Pressing the lever associated with the sample-lever tandem schedule produced a food pellet. Pressing the other produced a blackout. The difference between terminal-link reinforced interresponse times varied across 10-trial blocks within a session. Conditional-discrimination accuracy increased with the size of the temporal difference between terminal-link reinforced interresponse times. In Experiment 2, one tandem schedule was replaced by a random ratio, while the comparison schedule was either a tandem schedule that only reinforced long interresponse times or a random-interval schedule. Again, conditional-discrimination accuracy increased with the temporal difference between the two schedules' reinforced interresponse times. Most rats mastered the discrimination between random ratio and random interval, showing that the interresponse times reinforced by these schedules can serve to discriminate between these schedules.
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