FI length and performance of an FI FR chain schedule of reinforcement.

The team chained a fixed-interval (FI) schedule to a fixed-ratio (FR) schedule. Pigeons had to wait through the FI, then finish the FR to get food.

They changed only the FI length across conditions. Everything else stayed the same.

Longer FIs flattened the scallop. Birds paused more after food and ran longer at the end.

Total responses per reinforcer rose as the FI grew. The pause after food became the easiest way to see the change.

Glynn (1970) later stripped the chain to a pure FI. The pause still tracked the interval, proving the pause is interval-driven, not chain-driven.

Harzem et al. (1978) seems to disagree. They paid birds for holding long pauses and saw pauses shrink. The twist: extra reinforcement for pausing adds a new rule, so pause length follows the tightest contingency, not just the clock.

Byrd (1972) pushed the idea further. Even when only 7% of intervals paid off, the scallop and its pause stayed intact, showing the pattern is tough once learned.

When you run FI or FI-FR blends, watch the post-reinforcement pause. It is a quick, no-math gauge of schedule control. If the pause stretches, the learner feels the interval as longer. If you add extra rules like paying for waiting, expect the pause to shrink. Use this to fine-tune token boards, work-break cycles, or any timing-based intervention.