The effect of second-half reinforcer type on responding for sucrose in the first half of the session

• Published in: Behavioural processes 2000-03, Vol.49 (1), p.43-60
• Main Authors: Weatherly, Jeffrey N, Stout, Jason E, Rue, Hanna C, Melville, Cam L
• Format: Article
• Language: English
• Subjects: Animal; Biological and medical sciences; Contrast; Fundamental and applied biological sciences. Psychology; Induction; Learning; Learning. Memory; Lever press; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Rats; Reinforcer type; Variable-interval schedule
• ISSN: 0376-6357; 1872-8308
• DOI: 10.1016/S0376-6357(00)00072-3

The present study investigated whether the sucrose-reinforced lever pressing of rats in the first half of a 50-min session would be sensitive to upcoming food-pellet reinforcement in the second half. In Experiment 1, the type of reinforcer in the first half of the session was always liquid sucrose and type of reinforcer in the second half (liquid sucrose or food pellets) varied across conditions. Sucrose concentration varied across groups (1, 5, or 25%). Results showed that rates and patterns of responding for 1%, and sometimes for 5%, sucrose reinforcers in the first half of the session were higher and steeper, respectively, when food-pellet, rather than sucrose, reinforcement occurred in the second half. Responding for 25% sucrose was not similarly affected. Experiment 2 replicated the results of Experiment 1 using a within-subjects design. Although the present results represent induction (i.e. the opposite of contrast), they are consistent with some results on consummatory contrast. They also further demonstrate that responding on interval schedules of reinforcement can be altered prospectively. By doing so, however, they pose potential problems for current theories for why operant response rates change within the session.