An analysis of contrast effects in multiple schedules.
Reinforcement history causes brief response-rate swings, but lasting contrast needs an extra push.
01Research in Context
What this study did
Baron et al. (1966) watched pigeons peck a key under two back-to-back VI schedules. One schedule paid off often. The other paid rarely or not at all.
The team switched the order each day. They counted pecks minute-by-minute to see if the birds sped up or slowed down right after a switch.
What they found
Response rates jumped or dipped for a few minutes when the schedule changed. These bumps faded before the session ended.
The short-lived bumps did not explain why birds kept different overall speeds across entire sessions. Something else must drive the long-term contrast.
How this fits with other research
Green et al. (1975) ran the same VI-to-extinction swap and saw the same quick spike. They also caught a late-component surge that the 1966 paper missed. The two studies agree that contrast starts fast; the newer one simply looked closer at the final minutes.
Innis (1978) replaced VI with fixed-interval schedules and still found transient contrast. The effect is real across schedule types, not just VI.
Szatmari (1992) added a second key that gave extra food. Birds moved extra pecks to the key that paid less on the main key. This reallocation idea gives a reason for the long-term contrast the 1966 paper could not explain.
Why it matters
When you alternate rich and lean reinforcement, expect a quick burst or drop in responding right after the change. Do not assume this early bump tells you the whole story. Track responding across the full component and watch for extra sources of reinforcement that may keep the contrast alive.
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Join Free →Plot minute-by-minute responding after you switch from rich to lean VR; note if the dip fades or stays, then check for hidden reinforcers.
02At a glance
03Original abstract
Some phenomena of behavioral contrast in multiple schedules are reviewed, and three accounts of contrast are considered. Rate changes within a constant schedule component (transient contrasts) are distinguished from rate changes across successive schedule cycles (sustained contrasts). Pigeons were exposed to a three-component multiple schedule, in which a stimulus correlated with a constant variable interval schedule of reinforcement was preceded by a stimulus correlated with more frequent variable interval reinforcement, or by an extinction stimulus. If the preceding stimulus was correlated with more frequent reinforcement, the response rate in the constant component was low and increased with time. If the preceding stimulus was correlated with extinction, the rate in the constant component was high and decreased with time. Similar transient contrasts were observed in a two-component multiple schedule with different variable interval schedules in the two components. The transient contrast effects in the three-component schedule were shown to depend on differential reinforcement frequency rather than differential response rate in the preceding component. Such transient contrasts were not sufficient to account for sustained contrast effects observed in these experiments. The relation of these findings to the concepts of excitation and inhibition is discussed.
Journal of the experimental analysis of behavior, 1966 · doi:10.1901/jeab.1966.9-305