Mechanisms underlying the effects of unsignaled delayed reinforcement on key pecking of pigeons under variable-interval schedules.
Unsignaled delays over four seconds kill response rates because animals switch to watching for the reinforcer.
01Research in Context
What this study did
Researchers worked with four pigeons on a variable-interval schedule.
Each peck could earn grain, but the food hopper only rose after an unsignaled delay.
They tracked key pecks and time spent staring at the empty hopper.
What they found
Peck rates dropped sharply when delays reached four seconds or more.
The birds spent more time looking at the hopper instead of pecking.
Watching the hopper, not the key, explained the lost responses.
How this fits with other research
Davis et al. (1972) saw the same drop, but they used a light to signal the delay.
Both studies show delays hurt rates; the new twist is that unsignaled delays make birds switch to hopper watching.
Barnard et al. (1977) first showed the four-second cliff in autoshaping.
The current work proves the same limit holds under standard VI schedules.
Why it matters
If you use delayed reinforcement, keep the delay under four seconds and give a clear signal. Without a signal, clients may stop the target behavior and just watch for the reward.
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02At a glance
03Original abstract
Three experiments were conducted to test an interpretation of the response-rate-reducing effects of unsignaled nonresetting delays to reinforcement in pigeons. According to this interpretation, rates of key pecking decrease under these conditions because key pecks alternate with hopper-observing behavior. In Experiment 1, 4 pigeons pecked a food key that raised the hopper provided that pecks on a different variable-interval-schedule key met the requirements of a variable-interval 60-s schedule. The stimuli associated with the availability of the hopper (i.e., houselight and keylight off, food key illuminated, feedback following food-key pecks) were gradually removed across phases while the dependent relation between hopper availability and variable-interval-schedule key pecks was maintained. Rates of pecking the variable-interval-schedule key decreased to low levels and rates of food-key pecks increased when variable-interval-schedule key pecks did not produce hopper-correlated stimuli. In Experiment 2, pigeons initially pecked a single key under a variable-interval 60-s schedule. Then the dependent relation between hopper presentation and key pecks was eliminated by arranging a variable-time 60-s schedule. When rates of pecking had decreased to low levels, conditions were changed so that pecks during the final 5 s of each interval changed the keylight color from green to amber. When pecking produced these hopper-correlated stimuli, pecking occurred at high rates, despite the absence of a peck-food dependency. When peck-produced changes in keylight color were uncorrelated with food, rates of pecking fell to low levels. In Experiment 3, details (obtained delays, interresponse-time distributions, eating times) of the transition from high to low response rates produced by the introduction of a 3-s unsignaled delay were tracked from session to session in 3 pigeons that had been initially trained to peck under a conventional variable-interval 60-s schedule. Decreases in response rates soon after the transition to delayed reinforcement were accompanied by decreases in eating times and alterations in interresponse-time distributions. As response rates decreased and became stable, eating times increased and their variability decreased. These findings support an interpretation of the effects of delayed reinforcement that emphasizes the importance of hopper-observing behavior.
Journal of the experimental analysis of behavior, 1998 · doi:10.1901/jeab.1998.69-103