Rats’ Response Rates for 1 % Sucrose When Food-Pellet Reinforcement is Upcoming: Effect Of Upcoming Reinforcement Contingency

Previous research has demonstrated that rats' rates of lever pressing for 1% liquid-sucrose reinforcers in the first half of a 50mm session increase when food-pellet, rather than the same sucrose, reinforcement will be delivered in the second half of the session. The present study investigated whether this increase (i.e., induction) would be influenced by alterations to the response-reinforcer relationship in the second half of the session. Experiment 1 manipulated this relationship by delaying reinforcers in the second half of the session by 0.1,1.0, or 10.0 s, in different conditions. Induction was little affected by the delays. Experiment 2 provided reinforcers in the second half of the session on a different schedule of reinforcement (fixed ratio, fixed interval, or differential reinforcement of low rates) across conditions. Induction was large when the fixed-ratio schedule was upcoming and small or absent when the differential-reinforcement-of-low-rates schedule was upcoming. These differences, however, covaried with differences in obtained reinforcement. Experiment 3 eliminated the response-reinforcer relationship in the second half of the session by, in some conditions, delivering reinforcers on a variable-time schedule. Doing so reduced the size of, but did not eliminate, the observed induction. The present results increase the generality of induction and suggest that both the type of upcoming reinforcer and the contingency that will deliver that reinforcer can contribute to its appearance.