Schedules using noxious stimuli. IV: An interlocking shock-postponement schedule in the squirrel monkey.

Scientists wired a lever to a mild shock circuit. Each press gave the monkey a little more time before the next shock.

The twist: every response also shortened the safety window. The schedule "interlocked" time and work.

They watched one squirrel monkey for many sessions. They tracked how fast it pressed as the clock ran down.

The monkey’s pressing sped up the closer it got to shock time. The curve looked just like a fixed-interval scallop.

Plain avoidance or shock-delivery schedules never made this smooth acceleration. Only the interlocking rule did.

Rider (1977) later saw the same break-and-run pattern in rats. Same rule, different species — a clean replication.

Zimmerman (1969) ran true fixed-interval shock sessions with the same monkeys. Those curves also scalloped, but the shocks were guaranteed, not avoided. The two papers show schedule shape can trump whether the stimulus is good or bad.

SIDMAN (1962) built an earlier "adjusting" avoidance schedule. It changed safety time too, yet it never produced the smooth scallop. T et al. refined the math and finally got the pattern, a clear case of one method superseding another.

You now know that a single schedule can turn avoidance into clock-like responding. If you ever shape safety behaviors — handwashing, checking, seat-belt use — think about tying the response cost to the time left. A brief, interlocking requirement may create steady acceleration instead of jerky all-or-none bursts. Try it when you want smooth, time-aware pacing from your learner.