Discrimination and emission of temporal intervals by pigeons.

Pigeons pecked a red key on a DRL schedule. After each pause, the key turned blue.

Pecks on the blue key paid off only if the prior red pause had lasted a set time. The birds had to learn which pause length 'unlocked' food.

Researchers then tested whether the birds would stretch their pauses when the key color changed. They wanted to see if the birds could both notice and produce longer pauses.

The pigeons clearly noticed the pause length. When the prior red pause was long, blue-key pecking shot up.

But they did not stretch their own pauses. Red-key IRTs stayed short even after weeks of training.

Discrimination and emission came apart. The birds could tell time without using that skill to earn more food.

de Villiers (1980) later used a free-operant method and got the same clean temporal discrimination, showing the result holds across setups.

Rutter et al. (1987) pushed further. They varied the payoff for different IRTs and found bias shifted while sensitivity stayed flat. This confirms the 1966 split: birds sense time but bias their response separately.

Stancliffe et al. (2007) added a memory load—birds had to remember both sample color and elapsed time. Early sessions looked messy, yet timing re-emerged. Together these papers trace a line: pigeons always discriminate time, but extra task demands can mask the skill until practice irons out the noise.

When you shape waiting or self-control, do not assume the client can produce the delay just because they can notice it. Build separate repertoires: one for detecting the passage of time (clocks, signals, rules) and another for emitting the longer wait. Use prompts, DRL schedules, or rule statements to bridge the gap the 1966 birds never closed.