EFFECTS OF RATE OF REINFORCEMENT AND RATE OF CHANGE ON CHOICE BEHAVIOR IN TRANSITION

In two experiments with pigeons, a single variable-interval schedule a ssigned reinforcers to two response keys on a percentage basis. The pe rcentage of reinforcers assigned to each key was changed every few ses sions, and subjects' choice responses were recorded before and after e ach change. In Experiment 1, the overall rate of reinforcement was var ied across conditions. The pigeons' choice responses adapted more quic kly to a change in the reinforcement percentages when the overall rein forcement rates were higher, but acquisition rates varied by only abou t a factor of 3, whereas reinforcement rates were varied by about a fa ctor of 9. In Experiment 2, the reinforcement percentages changed abou t every 8 sessions in Phases 1 and 3, but every 1 or 2 sessions in Pha se 2. Pigeons' choice responses adapted to a change in reinforcement p ercentages more quickly in Phase 2 than in Phases 1 and 3. The results from both experiments pose difficulties for several prominent models of transitional choice behaviour. The results suggest that each succes sive reinforcer has more impact on a subject's subsequent choice behav iour when the overall rate of reinforcement is lower and when the rein forcement contingencies have changed frequently in the recent past.