Responding under discrete-trial fixed-interval schedules of reinforcement.

Researchers ran pigeons on a fixed-interval schedule that was chopped into short trials. Each trial gave the bird a few seconds to peck. If the interval had not ended, the trial simply ended and a new one began. This let the team watch how responding grew as the interval neared its end, but without the messy, free-flow pecking seen in the usual setup.

The birds still shifted from almost no pecks to rapid pecking, but the jump was cleaner. There was less scatter in the data. The tidy trial breaks made the classic FI scallop easier to see and to measure.

Nevin (1969) first drew the two-state picture: pigeons wait, then switch to fast pecking about two-thirds of the way through a normal, free-operant FI. The 1972 study keeps that same switch, proving the pattern is not an artifact of free access to the key.

Gibbon (1967) and Gardner et al. (1977) later showed the FI shape can be held up by brief lights or even cocaine instead of food. Together these papers widen the lens: the scallop appears across reinforcer types and across procedural tweaks.

Kodera et al. (1976) probed the pause phase itself, finding that extra food during the wait barely stretches it. Their result fits the 1972 data: once the FI clock starts, the schedule, not momentary treats, drives the bird's timing.

If you need a rock-stable baseline for a study or a client assessment, slice the session into brief response windows. Discrete trials cut the noise, so rate changes, pauses, or drug effects stand out faster. You save time and need fewer data points to see a real effect.