Observing behavior during interval schedules.

P et al. watched pigeons peek at a colored key during fixed-interval schedules. The birds could peck a separate key to open a tiny window and see the color.

The team tracked when the birds looked. They wanted to know if looking matched the moment food arrived or some other part of the interval.

Looking peaked halfway through the interval, then dropped before food arrived. The birds were not staring right at payoff time.

The color itself kept the peeking alive. Schedule stimuli can drive extra behavior even when they do not deliver food.

DEWS (1965) saw the opposite: pigeons looked most right after food, then stopped once pecking started. The difference is timing. B used mixed FI-FR, so food came at unpredictable moments and looking stayed tied to payoff.

Roper (1978) later showed that FI schedules spark other collateral acts like drinking or running, and the form changes with interval length. P et al. fit this pattern: schedule time itself can evoke responses.

Okouchi (2003) extended the idea, proving that past interval lengths still sway current FI rate. Together these papers say the interval clock controls more than just the final operant response.

When you run FI or FI-like programs, remember that clients may engage in extra watching, tapping, or talking at mid-interval. These collateral acts are not off-task; they are schedule-induced. You can track them as a built-in measure of temporal control or use them as prompts to teach waiting skills.