Reinforcement duration and the peak shift in post-discrimination gradients.
A simple cue that marks the richer reward sharpens stimulus control and produces reliable peak shift.
01Research in Context
What this study did
Researchers worked with pigeons in a small lab chamber. The birds pecked a colored key for grain.
Some trials paid 6 seconds of grain. Other trials paid only 2 seconds. A bright hopper light signaled the longer payoff.
What they found
When the hopper light marked the 6-sec grain, pigeons learned fast. Their pecking shifted away from the short-pay color.
Later tests showed a clear peak shift. Birds pecked most on a color slightly past the rich one, proof of sharp stimulus control.
How this fits with other research
Brinker et al. (1975) later showed that even a 3-min break after extinction can create peak shift. Schmidt et al. (1969) adds that salient duration cues make the shift stronger and faster.
Van Houten et al. (1980) shaped the length of the key peck itself. Both studies prove that timing features—of either reward or response—can be brought under tight stimulus control.
Locurto et al. (1980) found that local contrast shoulders fade with longer training. The 1969 cueing method may help those early errors disappear sooner by making the payoff difference obvious.
Why it matters
If you run discrimination programs, flag the better payoff with a distinct signal—an extra light, a special sound, a longer click. The change acts like a billboard and speeds up learning. You should see fewer errors and a cleaner peak shift during probe tests. Try it next time you shape two-option requesting or visual matching.
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02At a glance
03Original abstract
Pigeons were trained to key-peck for food, first with single-stimulus training and then with successive discrimination (multiple schedule) training. In the multiple schedule, two different wavelengths were each correlated with equally frequent variable-interval reinforcement but different durations (6 sec vs. 2 sec) of access to grain. For some birds, the different durations of feeding cycle were cued by different intensities of the food hopper light. For some of these "cued" birds, single-stimulus training had been carried out with 6-sec feedings and when multiple-schedule training was introduced, the novel stimulus was correlated with 2-sec feedings. For the others, 2-sec feedings were originally used, and the novel stimulus was then present during the 6-sec reinforcement duration. The cueing procedure enhanced discrimination performance, and was necessary for the consistent production of a peak shift. In addition, the condition in which original training had been carried out with 6-sec feedings, and thus reinforcement duration was reduced in the presence of the novel stimulus, led to the best performance.
Journal of the experimental analysis of behavior, 1969 · doi:10.1901/jeab.1969.12-759