Choice and delay of reinforcement.

Azrin et al. (1967) let pigeons peck two keys. One key gave food after a short wait. The other key gave food after a longer wait. The birds could switch keys at any time.

The team changed the delays many times. They counted how many pecks happened on each key. They wanted to see if the birds matched their pecks to the speed of payoff.

The birds pecked the key that paid faster about twice as much. When the left key paid twice as fast, two-thirds of the pecks landed there.

This "matching" pattern held across many delay pairs. The study gave the first clean lab proof that immediacy, not just amount, steers choice.

Kydd et al. (1982) seems to disagree. They also used two keys and varied delays, but the birds did not favor the faster side. The twist: R et al. kept the average wait the same on both sides. Once the overall wait is equal, birds stop caring which side is quicker.

Singh et al. (1982) widened the picture. They added a "search" period before the choice. After longer searches, birds accepted longer delays. The lesson: past wait time re-sets what counts as "too slow."

Steege et al. (1989) took the setup to humans. People picked the side that gave more money per minute, not the side that cut the wait. Species matters: pigeons track immediacy; humans track overall gain.

When you design reinforcement schedules, immediacy is power. Deliver the functional reinforcer as soon as the target response occurs. If you must add wait time, balance it across options or the client will drift to the faster payoff. Check past wait history too; a long task earlier can make later delays more acceptable.