Contrast and induction in multiple schedules of discrete-trial concurrent reinforcement.
Choice between two reinforced options produces induction or contrast in the unchanged option, proving schedule interactions show up in discrete trials, not just free-operant rate counts.
01Research in Context
What this study did
Researchers ran a two-key box with pigeons. Each trial gave the bird a choice: peck the white key or the red key.
They changed two things across trials. Sometimes the white key paid off in a new spot. Sometimes it paid off less often. The red key always stayed the same.
What they found
When the white key moved, birds followed it. Their red-key rate moved the same way. This is induction.
When the white key simply paid less, red-key rate jumped the opposite way. This is contrast.
Both effects were bigger when the red key was already thin on payoff.
How this fits with other research
Hamilton et al. (1978) ran the same year with the same birds and got the same split: induction or contrast depending on what changed. The pattern repeats.
Hineline et al. (1969) and Maltz (1981) show the next component, not the last one, sets contrast size. The 1978 data fit that rule; the white-key drop makes the upcoming red key look richer, so contrast appears.
McSweeney (1975) used concurrent VI treadles and still saw contrast. The effect is not tied to discrete trials or key pecks.
Why it matters
If you run multiple schedules with kids, remember that changing payoff in one slot moves behavior in the other. To get more work on the target task, slightly lower the payoff in the alternate task and keep the target payoff steady. Watch for induction when you move the reward spot; watch for contrast when you thin the rate.
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02At a glance
03Original abstract
Three pigeons were exposed to two-key discrete-trial concurrent schedules of reinforcement. Red and white key colors alternated irregularly and the assignment of reinforcers depended on key color. The red-key schedules were held constant, with the scheduled relative frequency of reinforcement for left-key pecks set at 0.75, while the white-key schedules varied. When the location of white-key reinforcement was changed from one side to the other, while its overall frequency was constant, red-key choices shifted in the same direction as white-key choices, an induction effect. When the overall frequency of white-key reinforcement was changed while its location remained constant, red key choices shifted in a direction opposite to white-key choices, a contrast effect. Both induction and contrast effects were clearer when the overall frequency of red-key reinforcement was reduced. These data demonstrate that the allocation of responding may exhibit schedule interaction effects similar to those commonly reported for response rate.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.30-53