Schedule-induced escape from fixed-interval reinforcement.

Brown et al. (1972) asked pigeons to peck a key on fixed-interval schedules. The interval length changed across sessions: short, medium, or long.

After each food delivery the birds could stay and wait or hop to a second key that ended the trial early. The team counted these escape hops.

Escape peaked at middle-length intervals and dropped at very short or very long ones. The curve looks like an upside-down U.

The birds did not flee because the work was hard; they fled when the wait felt just long enough to be annoying.

Dove et al. (1974) saw the same upside-U for attack under variable-interval schedules. Both papers show adjunctive behavior rising then falling as time-to-food stretches.

Kono (2017) kept the fixed-interval plan but watched where pigeons pecked. Longer intervals made the birds drift around the key, echoing the restless "I want out" mood G et al. captured with escape.

Shull (1971) tracked post-reinforcement pauses on a single long FI. Pauses alternated long-short-long, hinting that birds feel time in chunks. G et al. add the escape lever, proving those chunks can feel aversive enough to quit.

If you run FI schedules in token boards or DRL programs, watch for escape signs at mid-length waits. Break the interval, offer a brief stretch, or let the learner choose a shorter cycle. You can keep the reinforcement plan while removing the sweet spot where frustration peaks.