Aversive aspects of a fixed-interval schedule of food reinforcement.
Fixed-interval pay can spark aggression right after you deliver the reinforcer.
01Research in Context
What this study did
The team put six food-deprived pigeons in a box. A key lit up every 60 seconds. The first peck after the light paid food.
They counted how often each bird struck a nearby stuffed toy. Baseline had no schedule. Then they ran 30 daily FI sessions.
What they found
Attack jumps the moment food arrives. Birds bit the toy most right after eating. Pauses grow longer across days, and so does the biting.
The schedule itself, not the food, drives the anger. When food stops, aggression fades.
How this fits with other research
Duker et al. (1996) later showed bigger food portions make the biting worse. Same FI, same birds, just more grain per payoff.
Dardano (1970) saw the same spike under high fixed-ratio and extinction. Different schedules, same angry birds. Together the papers say: any lean or unpredictable pay can breed aggression.
Arnett (1972) ran FI with a clock cue. The cue stretched the pause and cut key pecks but never tested attack. Their longer quiet time could be the safest window—an idea worth checking.
Why it matters
Your client may not bite a toy, but post-reinforcement pauses are risky moments. Watch for SIB, property destruction, or peer hits right after you deliver a token, snack, or praise on an FI schedule. Add brief prompts or differential reinforcement of other behavior during that pause to block the first strike.
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02At a glance
03Original abstract
The key pecking of pigeons was reinforced according to a fixed-interval schedule of reinforcement. The pigeons were also given the opportunity to attack a restrained target pigeon. The attack rates during the sessions of fixed-interval reinforcement were higher than during the operant level sessions in four of the five pigeons. Most attack occurred during the post-reinforcement pause in key pecking. It was suggested that a fixed-interval schedule of positive reinforcement possesses aversive properties, the most aversive of which are located during the post-reinforcement pause.
Journal of the experimental analysis of behavior, 1972 · doi:10.1901/jeab.1972.17-405