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Document Type

Article

Abstract

Studies have shown that rats' rates of levE3r pressing for lowconcentration liquid-sucrose reinforcers in the first half of an experimental session are higher if food-pellet, rather than the same sucrose, reinforcement will be delivered in the second half. Experiment 1 investigated whether this induction effect would be altered if subjects were provided with an external "clock" (i.e ., stimuli that changed as the period of food-pellet reinforcement approached). Induction was not altered by the clock. Experiment 2 investigated whether subjects' might be internally timing the upcoming food pellets. Subjects responded in sessions in which pressing the left and right lever was reinforced in the first and second half, respectively, of the session and the switch in reinforcement between halves was unsignaled. Delivering foodpellet reinforcement in one half of the session altered the timing functions, but induction in responding for 1 % sucrose was still observed. Experiment 3 investigated whether induction might then be the result of a disruption in timing. It partially replicated the procedure of Experiment 2, but also had subjects respond in conditions in which timing the switch in reinforcement between halves was not necessary. Similar results were observed across conditions in which timing was and was not required. These results question the idea that timing is involved in the appearance of induction. They suggest that some other mechanism, such as a change in the value of the sucrose, is behind the effect.

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