Variable-ratio conditioning history produces high- and low-rate fixed-interval performance in rats.
Even brief VR exposure can erase the normal FI scallop, so always factor past ratio history into your data interpretation.
01Research in Context
What this study did
The team gave rats 20-response variable-ratio (VR 20) training. Later they switched the same rats to a 30-second fixed-interval (FI 30-s) schedule.
They wanted to see if the earlier VR experience changed the way the animals later responded under the interval schedule.
What they found
Rats with the VR past no longer showed the smooth scallop that FI usually produces. Instead the same rats split into two clear styles: some responded very fast and steady, others responded very little.
Naïve rats that had only known FI kept the normal within-interval acceleration curve.
How this fits with other research
Dews (1978) first mapped the classic FI scallop in monkeys. The new data say that one brief VR history can wipe that pattern out, so the scallop is not fixed.
Meuret et al. (2001) also showed that VR parameters carry forward: pigeons tracked changing VR minimums and the control lingered. Both papers agree that ratio history stays in the behavior.
Van Houten et al. (1980) moved the VR versus fixed-schedule question into children and found VR tokens raised attention. The rat lab and the classroom studies together tell us the VR effect crosses species and settings.
Why it matters
If you put a client on a FI schedule, remember any earlier ratio work—even a short one—can flip the picture you expect. Check baseline shape before you decide the program is not working; the learner may simply be showing history, not failure.
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02At a glance
03Original abstract
Four rats were exposed to an A-B-A-B series of 30 sessions each of variable-ratio 20 (A) and fixed-interval 30-s (B) schedules. Four other rats received 120 sessions of fixed-interval 30 s. The rats with a history of variable-ratio responding subsequently showed primarily high or low response-rate patterns on the fixed-interval schedule without evidence of classical scalloping (i.e., increased rates of responding throughout the interreinforcement interval), except infrequently in 1 rat. The rats exposed to only the fixed-interval 30-s schedule displayed the expected sequence of scalloping giving way to lower rate break-run or simply low-rate responding over time. This experiment shows that when naive rats are exposed to even a simple history of reinforcement (in this case, a variable-ratio 20), their subsequent fixed-interval performance is very different from comparable performance in naive rats, and might be said to be more similar to the responding of adult humans. The argument is made that care should be taken in comparing the fixed-interval performance of humans and nonhumans because humans have a complex history of reinforcement, whereas laboratory nonhumans are typically naive.
Journal of the experimental analysis of behavior, 1989 · doi:10.1901/jeab.1989.52-167