Force and rate relations in responding during variable-interval reinforcement.

Llewellyn et al. (1976) tested how hard you have to press a lever to get food. They used a variable-interval schedule. That means food could drop at any time, but only if the press was strong enough.

They slowly raised the force rule. First 0.1 N, then higher. They counted every press, even the soft ones that failed.

When the force rule went up, the animals did not quit. They pressed just as often, but most presses now met the new force rule.

Soft, lazy presses almost disappeared. Total output stayed the same. The schedule kept working.

Two later rat studies saw the opposite. Anonymous (1995) and Lowe et al. (1995) raised force from 0.25 N to 2.00 N. Response rates dropped and pauses grew long. The difference: they used fixed-ratio schedules, not variable-interval.

Pinkston et al. (2017) re-examined the old data and added new counts. They found the same pattern as E et al.: once you count every press, total rate stays flat. The drop was a measurement illusion.

Stancliffe et al. (2007) repeated the test with mice. Higher force cut official presses but raised near-threshold presses. Again, the animals worked around the rule instead of giving up.

Before you add effort to a task, check the schedule. On variable-interval or other time-based plans, clients may simply try harder and meet the new rule. On ratio schedules, extra effort can slow them down. Count every response, even the weak ones, before you decide effort is punishing.