Schedules of food postponement: II. Maintenance of behavior by food postponement and effects of the schedule parameter.
Delaying food after a response cuts behavior just like delaying shock avoidance, so keep reinforcers immediate.
01Research in Context
What this study did
Clark et al. (1977) asked if food can keep a lever-pressing habit alive even when it never comes right after the response. They set up a food-postponement schedule with squirrel monkeys. Each lever press delayed the next food pellet by 20 seconds. Food could also arrive on its own every 10 seconds if the monkey did nothing.
The team then removed food completely to see if the behavior would stop. Finally, they put the schedule back to check if the lever pressing would bounce back.
What they found
Lever pressing stayed strong while food was postponed. When food stopped, the behavior quickly died out. The moment the postponement schedule returned, the monkeys pressed again at once.
Changing the delay between response and food changed how fast the monkeys pressed. Shorter or longer intervals produced clear, orderly shifts in response rate.
How this fits with other research
Vos et al. (2013) later saw the same delay effect under fixed-ratio schedules with pigeons. Longer delays still meant fewer responses, showing the 1977 pattern holds across species and schedules.
Buriticá et al. (2017) added that even brief delays or lower food deprivation cut response rates on fixed-interval schedules. Their work extends the 1977 finding into timing tasks and shows the rule is general: delayed food weakens behavior.
Cowie et al. (2011) seemed to disagree. They claimed food works mainly as a signal for the next food, not as a response strengthener. Yet C et al. showed behavior rose and fell with the delay parameter, a clean dose-response curve. The two studies simply ask different questions: parametric control versus signal function. Both can be true.
Why it matters
If you use edible reinforcers, remember that any wait time—whether from your hands, a peer, or a vending device—immediately weakens the response you want to keep. Keep food delivery instant or buffer the delay with a bridging stimulus. When thinning schedules, shorten the response-to-food gap before you stretch the ratio; the delay, not the extra work, is what dampens behavior.
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02At a glance
03Original abstract
In Experiment I, food-deprived, feeder-trained squirrel monkeys pressed a lever to postpone brief electric shocks (Response-Shock=Shock-Shock interval=30 seconds). Forty-one three-hour sessions of shock postponement were followed by 120 sessions of concurrent shock and food postponement. The shock schedule was unchanged and the food schedule was Response-food interval-20 seconds, Food-food interval 10 seconds. After concurrent shock and food postponement, the shock schedule was discontinued and 40 sessions of food postponement ensued, followed by 53 sessions of extinction. After extinction, food postponement was resumed for 11 sessions. Stable responding with low food rates was maintained under food-postponement after the concurrent schedule. Responding decreased to low levels under extinction and recovered immediately to previous levels when the food-postponement schedule was re-instated. In Experiment II, a parameter of the food-postponement schedule was studied sequentially. Using the same subjects, the Response-food-Food-food interval was manipulated from four seconds to 80 seconds with several orders of presentation. Relations of response rates and food rates to the parameter were similar to those seen under shock postponement. Exposure to very short postponement times (four seconds), resulting in very high food rates, decreased but did not abolish subsequent responding at longer postponement times. Results are discussed from the point of view that reinforcing functions of stimuli consequent on responding depend on a prior history of scheduled contact with those stimuli.
Journal of the experimental analysis of behavior, 1977 · doi:10.1901/jeab.1977.28-253