ANTICIPATORY CONTRAST AND DIET SELECTION BY PIGEONS

The effect of future rate of reinforcement on choice and rate of respo nding was examined in three experiments in all of which pigeons perfor med on an operant simulation of diet selection followed by either a hi gh or low rate of reinforcement. In Experiment 1 the duration of the p rey selection task was 20 min. A within-subjects design was used: in o ne operant chamber a high rate of reinforcement followed the session o f diet selection, and in another chamber, a low rate of reinforcement followed. In Experiment 2 a between-subjects design was used with 8 mi n of diet selection and a stronger manipulation of rate of reinforceme nt. In Experiment 3, a within-subjects design was used with more highl y discriminable operant chambers. The results on rate of responding we re consistent with what is known about contrast: A weak contrast effec t during the diet selection task was obtained in Experiment 1, a large r contrast effect in Experiment 3, and a conditioning effect was found in Experiment 2. The effect on choice was examined in Experiments 1 a nd 3 but was weak in both cases. The results suggest that the mechanis m underlying contrast in choice and rate of responding are not one and the same. Foraging implications are discussed.