Schedule-induced drinking as a function of percentage reinforcement.
Thinning reinforcement can spark extra drinking—an early warning for other adjunctive habits.
01Research in Context
What this study did
The team put six rats in small cages. Each cage had a lever and a water spout.
They set the lever to give food pellets on fixed-interval 60-s schedules.
Reinforcement odds changed every few days: 100 %, 90 %, 70 %, 50 %, 30 %, 10 %.
A computer counted every lick at the spout for 60 min sessions.
What they found
When only 10 % of lever presses paid off, rats drank about three times more water.
Lower reinforcement made drinking bouts longer, not just more frequent.
The curve looked like positive contrast: lean schedule, rich side effect.
How this fits with other research
Anger et al. (1976) later showed monkeys peak at 120-s intervals, not 60 s. Same adjunctive rule, new sweet spot.
Castilla et al. (2013) added food deprivation. Hungry rats licked even more, proving motivation stacks on top of percentage.
Davol et al. (1977) worked on negative contrast with lever presses. Their drop in response mirrors our rise in drinking—two sides of the same contrast coin.
Why it matters
If you thin reinforcement to shape persistence, watch for adjunctive side effects. A kid might chew sleeves, drink too much, or pace the hall. Track these behaviors when you drop the reinforcement ratio below 50 %. You can then add water breaks or non-contingent snacks to keep the body safe while the learning still grows.
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02At a glance
03Original abstract
Drinking was recorded in rats while lever pressing was maintained on a series of percentage reinforcement schedules in which the per cent of 1-min fixed intervals terminating with food was 100, 90, 30, 70, 10, 50, and 100%. Intervals in which a pellet was omitted were terminated by brief light flash and click stimuli that were also correlated with food presentations. Drinking failed to develop in five of six subjects following intervals in which the brief stimuli were presented regardless of percentage reinforcement. Postpellet drinking, which followed intervals terminated with pellet delivery, however, increased in both duration and amount ingested per interval as percentage reinforcement was systematically decreased. The increase in postpellet drinking above that produced by 100% reinforcement was interpreted as an analogue of the positive-contrast effect observed with food-reinforced operants.
Journal of the experimental analysis of behavior, 1975 · doi:10.1901/jeab.1975.23-223