Effects of variations in the temporal distribution of reinforcements on interval schedule performance.

The team changed how often food arrived. Sometimes it came on a fixed clock. Sometimes it came at random times.

They watched how the timing of the animal’s pecks or lever presses changed.

The goal was to see which schedule gives the most clock-like control over behavior.

Fixed-interval schedules created the clearest time pattern. Animals waited, then worked fastest just before the next reward.

As the schedule moved toward random timing, the neat pause-and-run shape faded.

The closer the schedule looked like fixed-interval, the stronger the time control.

DeVellis et al. (1979) added a ruler to the finding. They showed the pause after food grows as a power law: double the FI, multiply the pause by a set factor.

Bauman et al. (1996) stretched the idea further. They used steadily longer intervals and still saw the pause grow step by step.

Greene et al. (1978) moved the test to college students. People only showed the classic scallop when a visible clock was on the wall. Without it, the tidy time pattern fell apart.

Killeen (2023) wrapped all these facts into one math frame. The 1976 pattern is now viewed as momentum building: predictable food makes behavior heavier and harder to stop.

You now know that schedule shape, not just rate, drives timing. If you want tight temporal control, pick fixed-interval or add a visible timer. If you want looser responding, vary the interval and drop cues. Use this when shaping wait behavior, teaching delay tolerance, or thinning reinforcement in classrooms and clinics.