Income maximizing in concurrent interval-ratio schedules.

Scientists watched mice choose between two levers. One lever paid off on a variable-ratio schedule. The other paid on a variable-interval schedule.

The twist: the length of each food pellet changed across sessions. The team wanted to see if longer pellets would push the mice toward the interval lever.

When the food lasted longer, the mice spent more time on the interval lever. The result matched a simple rule: pick the side that gives the most food per minute.

Wallander et al. (1983) ran a near-copy study with rats and got the same lean toward the interval side once leisure time was ruled out.

Davison et al. (1989) also tested maximization in 1989, but with pigeons and a different cue. They saw no effect, which looks like a clash. The difference is species and what was changed: pellet length here, feedback lights there.

Savastano et al. (1994) moved the setup to human adults. People only partly followed the maximization rule. They split the difference between matching and optimal, showing the animal result does not always scale up to humans.

The study reminds us that reinforcer size, not just rate, steers choice. When you run concurrent schedules in a classroom or clinic, keep each reward the same length. If one side gives longer play time or bigger bites, clients will drift that way even if the pay rate is lower. Check duration first before you tweak rate.