Contrast and induction in rats on multiple schedules.
Contrast from schedule shifts is brief and may vanish without signals or the right reinforcer.
01Research in Context
What this study did
Researchers placed rats on two alternating schedules. One side gave steady food for lever presses. The other side gave no food at all.
They watched how fast the rats pressed when food suddenly stopped. They wanted to see if the animals would work harder in the still-paid side.
What they found
Most rats did press faster in the paying side at first. This 'positive contrast' faded after a while.
The team never saw slower pressing when food returned. Negative contrast simply did not show up. Induction effects came and went, just like positive contrast.
How this fits with other research
Aragona et al. (1975) ran almost the same setup and also got mixed results. They swapped milk for pellets and still saw contrast appear and then vanish. The two papers together tell us the fade-out is real, not a fluke.
Marcucella (1976) added a twist: signal the food or not. Full signals kept contrast alive, partial signals killed it. That explains why the 1971 contrast died—no extra cues told the rats food was coming back.
Honig et al. (1988) pushed further, using both food and alcohol. Contrast showed up for food but not for alcohol under multiple schedules. Reinforcer type matters, so do not assume every reward will behave the same way.
Why it matters
If you use schedule changes to boost client motivation, expect a short-lived jump. Plan quick probes right after the shift and do not wait for lasting gains. Add clear signals if you want the boost to stick around. And remember—what serves as the reinforcer (food, praise, tokens) can decide whether contrast even appears.
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02At a glance
03Original abstract
Eight rats were trained on a variable-interval schedule in the presence of a light (Phase I). Responding was then extinguished in the presence of darkness that alternated with the light (Phase II). Reinforcement was then introduced in the presence of darkness (Phase III). Several rats were then returned to the condition of Phase II (Phase IV) and then to that of Phase III (Phase V). The responding of most rats showed clear behavioral contrast in Phase II-i.e., an increase in responding in the presence of the light. When, for three rats, Phase III was introduced early after the occurrence of positive contrast, either positive induction occurred, i.e., an increase in responding in the presence of the light, or there was little change. Negative contrast did not occur. It was further shown that positive contrast dissipates over time, thus replicating a result previously obtained with pigeons and that the positive induction effect seems also to dissipate over time. The introduction of reinforcement in the presence of darkness (Phases III and V) after the dissipation of positive contrast seemed to have little consistent effect.
Journal of the experimental analysis of behavior, 1971 · doi:10.1901/jeab.1971.15-289