SUCCESSIVE DISCRIMINATION-TRAINING WITH EQUATED REINFORCEMENT FREQUENCIES - FAILURE TO OBTAIN BEHAVIORAL-CONTRAST

Pigeons were trained on 2 component multiple schedules in which responding in 1 component (S1) was always maintained by a variable-interval schedule. In Experiment I, low response rates were reinforced in the 2nd (S2) component for 6 master subjects. This schedule was adjusted to equate reinforcement frequencies in the 2 components. These subjects were compared to yoked partners, for which reinforcement in the S2 component was made available on a variable-interval schedule whose value was determined by the master subjects. A similar procedure was used in Experiment II, where the S2 schedule for master subjects made reinforcers contingent on the absence of responding. No evidence was found in either experiment for a behavioral contrast effect in the S1 component attributable to response reduction in the S2 component. A reliable contrast effect was obtained from a group of pigeons given extinction conditions in the S2 component, which was compared to a group maintained throughout on a multiple variable-interval schedule. The results suggest that previous indications of behavioral contrast in similar situations were probably caused by uneven reinforcement distributions or reflect uncontrolled fluctuations in response rates.