Contrast and reallocation of extraneous reinforcers between multiple-schedule components.
Contrast can be just reinforcers sneaking to the lean side—watch the extras, not just the main schedule.
01Research in Context
What this study did
Pigeons pecked two keys under a multiple schedule. One key paid off at a steady rate. The other key paid off at two different rates that alternated every few minutes.
Extra grain sometimes dropped no matter which key the bird hit. The team tracked where those free grains landed. They wanted to know if the birds moved the free food toward the leaner component.
What they found
When the main key became stingy, response rates on that key shot up—classic positive contrast.
The surprise: extra-key reinforcers shifted into the lean component. The birds didn’t earn more total food; they simply moved the free pieces to where pay was low.
How this fits with other research
Smith et al. (1975) saw no contrast on the main key and said contrast came from summing two peck types. Szatmari (1992) still finds contrast, but shows the driver is reinforcer reallocation, not extra pecks.
Green et al. (1975) caught a late-component response surge that old theories missed. P’s data add a second hidden process: birds quietly steer free food toward the lean side.
Davol et al. (1977) trimmed negative contrast by reinforcing long pauses. P flips the problem: instead of changing what you reinforce, watch where the subject moves the extras.
Why it matters
If you run multiple schedules in practice, remember that ‘extra’ reinforcers—praise, tokens, even accidental attention—may slide toward the leaner component. Track these side payments. You might see contrast vanish once the extras are pinned down, saving you from needless schedule tweaks.
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02At a glance
03Original abstract
Four pigeons responded in components of multiple schedules in which two responses were available and reinforced with food. Pecks on the left key ("main" key) were reinforced at a constant rate in one component and at a rate that varied over conditions in the other component. When reinforcer rate was varied, behavioral contrast occurred in the constant component. On the right key ("extra" key), five variable-interval schedules and one variable-ratio schedule, presented conjointly, arranged reinforcers for responses in all conditions. These conjoint schedules were common to both multiple-schedule components-rather than unique to particular components-and reinforcers from these schedules could therefore be arranged in one component and obtained during the other component. In this way, the additional reinforcers were analogous to the "extraneous" reinforcers thought to maintain behavior other than pecking in conventional multiple schedules. Response rate on the extra key did not change systematically over conditions in the constant component, and in the varied component extra responding was inversely related to main-key reinforcement. All subjects obtained more extra-key reinforcers in whichever component arranged fewer main-key reinforcers. Consistent with the theory that reallocation of extraneous reinforcers may cause behavioral contrast, absolute reinforcer rate for the extra key in the constant component was low in conditions that produced positive contrast on the main key and high in those that produced negative contrast. Also consistent with this theory, behavioral contrast was reduced in two conditions that canceled extra-key reinforcers that had been arranged but not obtained at the end of components. Thus, a constraint on reallocation markedly reduced the extent of contrast.
Journal of the experimental analysis of behavior, 1992 · doi:10.1901/jeab.1992.58-497