Overmatching in rats: the barrier choice paradigm.

The team built two levers for rats. One lever sat behind a low wall. The other sat behind a taller wall. Rats could press either lever for food.

The walls made one lever harder to reach. The scientists watched how often rats pressed each lever and how long they stayed at each side.

When the tall wall got even taller, rats pressed the easy lever far more than the food rate alone predicted. Their response ratio shot past the perfect match line.

Yet the time they spent on each side still matched the food rate. Effort changed how many presses, not how long they stayed.

Older rat studies said high effort kills response rate. Anonymous (1995) and Lowe et al. (1995) both showed harder lever presses drop rates. Those studies used force, not a wall, and looked at single levers.

Aparicio (2001) used a choice set-up. The rats could still leave the hard side, so total behavior did not fall. Pinkston et al. (2017) later argued force looks punishing only if you ignore weak presses. The barrier study fits that view: effort steers choice, it does not suppress it.

Llewellyn et al. (1976) saw pigeons actually increase reinforced presses when force went up. The new rat data echo this: effort can raise reinforced output if the contingency stays clear.

When you add work to one task, clients may flock to the easier one even if pay is equal. Check both response counts and time spent. If you want balance, raise the reinforcement rate on the hard side or lower the effort. Do not assume effort is a punisher—give an escape route and behavior will redistribute, not disappear.