Successive discrimination training with equated reinforcement frequencies: failure to obtain behavioral contrast.
Behavioral contrast disappears when reinforcement rates are equal across components—verify your reinforcer counts before claiming contrast.
01Research in Context
What this study did
The team ran a two-part multiple schedule with pigeons. In both parts the birds earned food at the same overall rate, just timed differently. Part one kept everything steady. Part two made the second key color pay off only after long pauses, so pecking there dropped.
The question: if total food per minute stays equal, does the first key still show the usual jump in rate?
What they found
No jump happened. Response rates on the unchanged key stayed flat. Contrast only showed up later when they shut off food in the second key entirely.
Equal reinforcer counts killed the effect that earlier papers saw.
How this fits with other research
Thomas et al. (1974) had seen contrast after simply cutting food rate in one part. The new study kept food rate the same and got no contrast, so the earlier effect was probably driven by the unequal pay, not by the drop in pecks.
Henton (1972) claimed contrast without any food change. Rogers-Warren et al. (1976) show that claim fails once you actually match the reinforcers across parts.
Ring et al. (2023) later repeated the null result with college students in a work task, proving the lesson still holds outside the pigeon lab.
Why it matters
Before you tell parents or teachers 'we saw contrast,' count the reinforcers. If the 'easy' task still pays as much as the 'hard' one, don't expect rates to rise on the easy side. To get contrast, you need true loss of reinforcement in one component, not just slower responding.
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Join Free →Tally actual reinforcers delivered in each component; if counts match and you still see rate shifts, look for other variables before labeling it contrast.
02At a glance
03Original abstract
In two experiments, pigeons were trained on two-component multiple schedules in which responding in one component (S(1)) was always maintained by a variable-interval schedule. In Experiment I, low response rates were reinforced in the second (S(2)) component for six master subjects. This schedule was adjusted to equate reinforcement frequencies in the two components. These subjects were compared to yoked partners, for which reinforcement in the S(2) 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 S(2) 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 S(1) component attributable to response reduction in the S(2) component. A reliable contrast effect was obtained from a group of pigeons given extinction conditions in the S(2) 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.
Journal of the experimental analysis of behavior, 1976 · doi:10.1901/jeab.1976.26-65