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. Author manuscript; available in PMC: 2020 Jun 26.

Published in final edited form as: Exp Clin Psychopharmacol. 2019 May 23;28(2):181–195. doi: 10.1037/pha0000300

Figure 1. — Schematic illustrating two trials in the concurrent-chains procedure for one rat. For this particular rat, the left lever is associated with the large, uncertain reinforcer, and the right lever is associated with the small, certain reinforcer. During the initial link, the lever that allows the rat to advance to the terminal link is determined by the program (this is the dependent schedule). In trial 1, responses on the left lever are recorded during the initial link but have no programmed consequence. In this case, the rat has to complete the response requirement (FR 5) on the right lever to end the initial link. After a 2-s delay, the terminal link begins. Responses on the left lever are recorded but have no programmed consequence. Completing the response requirement (FR 3) on the right lever results in delivery of one sucrose-based pellet. In trial 2, responses on the right lever during the initial link are recorded but have no programmed consequences. The rat has to respond on the left lever to advance to the terminal link. During the terminal link, responses on the right lever are recorded but have no programmed consequences. Completing the response requirement on the left lever results in probabilistic delivery of four sucrose-based pellets. For each rat, the active lever (i.e., the lever that ends the initial link and the lever that leads to reinforcement) is pseudo-randomized across trials, such that each lever leads to reinforcement on an equal number of trials (5 trials each per block; 25 total trials across the session). Abbreviations: HL = house light; ITI = inter-trial interval; LL = left lever; LSL = left stimulus light; OA = odds against (note: odds against = [1/probability]-1); RR = right lever; RSL = right stimulus light.

Figure 1. — Schematic illustrating two trials in the concurrent-chains procedure for one rat. For this particular rat, the left lever is associated with the large, uncertain reinforcer, and the right lever is associated with the small, certain reinforcer. During the initial link, the lever that allows the rat to advance to the terminal link is determined by the program (this is the dependent schedule). In trial 1, responses on the left lever are recorded during the initial link but have no programmed consequence. In this case, the rat has to complete the response requirement (FR 5) on the right lever to end the initial link. After a 2-s delay, the terminal link begins. Responses on the left lever are recorded but have no programmed consequence. Completing the response requirement (FR 3) on the right lever results in delivery of one sucrose-based pellet. In trial 2, responses on the right lever during the initial link are recorded but have no programmed consequences. The rat has to respond on the left lever to advance to the terminal link. During the terminal link, responses on the right lever are recorded but have no programmed consequences. Completing the response requirement on the left lever results in probabilistic delivery of four sucrose-based pellets. For each rat, the active lever (i.e., the lever that ends the initial link and the lever that leads to reinforcement) is pseudo-randomized across trials, such that each lever leads to reinforcement on an equal number of trials (5 trials each per block; 25 total trials across the session). Abbreviations: HL = house light; ITI = inter-trial interval; LL = left lever; LSL = left stimulus light; OA = odds against (note: odds against = [1/probability]-1); RR = right lever; RSL = right stimulus light.