Preference for fixed-interval schedules of reinforcement.

Killeen (1970) let pigeons pick between two fixed-interval schedules.

The birds could peck either key. Both gave the same total food, just on different timers.

The goal was to see if shorter waits felt better when pay stayed equal.

The birds almost always chose the key with the shorter interval.

They also pecked faster right after picking the short timer, a clue they expected food sooner.

Even though daily food never changed, the shorter wait felt more valuable.

Duncan et al. (1972) later showed the same thing with chained schedules. Pigeons picked a simple FI over a chained FI of the same length, proving simpler is better.

Wacker et al. (1985) added that breaking the interval into chained segments hurts preference even more. Together these papers say: any added step lowers value.

Catania et al. (1974) looked like a contradiction. In a three-key set-up the birds stopped following the matching rule. The difference is key count: two keys keep choices clean; three keys overload the bird.

Token boards and cash-in periods are fixed-interval schedules. Kids will gravitate toward the shorter wait if the prize is the same. Keep your intervals as short as the task allows and skip extra steps. One clear timer beats a pretty chain.