Choice and reinforcement delay.

Researchers let pigeons peck two keys in a two-step procedure. First, each key led to its own small chamber. Second, in that chamber, a delay timer ran before grain dropped. The team changed both the relative wait times and the actual clock seconds each side made the bird wait.

They wanted to see if choice followed the usual matching rule when absolute delays got long.

Birds still picked the key that paid off sooner, but the exact number of seconds on each clock also swayed them. Standard models that look only at the ratio of delays missed part of the story once waits stretched out.

Parmenter (1999) ran almost the same pigeon setup but added big versus small grain piles. The birds stayed just as sensitive to delay no matter the pile size, a clean conceptual replication that keeps the delay focus while ruling out amount effects.

Weil (1984) took the next step. He dropped the choice part and used one key only. Pigeons pecked less when the single grain delay grew, proving the absolute wait itself cuts response rate even without a second option. That finding extends D et al. by showing the delay punch holds in free-operant work.

Horner-Johnson et al. (2002) later moved the idea to humans picking between delayed dollars. Discounting curves matched the same hyperbolic shape first seen in the birds, showing the pigeon work scales up to people and money.

When you set up token boards, break cards, or any delayed reinforcement, think beyond which reward comes first. The actual seconds your learner waits on each side still color choice. Try keeping both absolute and relative delays short, or run a quick two-option probe if you see unexpected shifts in preference.