Document Type



Two experiments examined whether differential resistance to change would occur under identical variable-interval schedules as a function of a differential behavioral history. In Experiment 1, each of 3 pigeons first pecked at different rates under a multiple variable-ratio differential-reinforcement-of-Iow-rate schedule. In a subsequent condition, a multiple variable-interval variable··interval schedule operated in the presence of the same training stimuli, during which there were three 4-session prefeeding probes each occurring during a different stage of training. Pecking generally was more resistant to change in the presence of the stimulus previously correlated with the differential-reinforcement-of-Iow-rate schedule, and this result was more reliable during the earlier probes. In Experiment 2, each of 3 pigeons first was exposed to a multiple variable-interval extinction schedule, after which a variable-interval schedule replaced extinction. During 3 probes, each conducted during a different stage of multiple variable-interval variable-interval schedule training, food was delivered response independently between components. In the first probe, pecking was more resistant to change for each pigeon under the variable-interval schedule that had been in effect longer, but during the final 2 probes this differential resistance was absent. The present results, therefore, show that under identical schedules a behavioral history can influence resistance to chan~~e differentially, but that these history effects tend to dissipate with continued exposure to the identical schedules.