Sequential effects of interval duration on fixed-interval performance.

Pigeons pecked a key for food on fixed-interval (FI) schedules. The schedule length changed every session: 30 s, 60 s, or 120 s. The order was random, so a 30 s interval could follow a 120 s interval.

The researcher recorded response rate and pause length in each interval. He asked: does the length of the last interval change how the bird acts in the new one?

Yes. After a long interval, birds paused longer at the start of the next interval. After a short interval, they started pecking sooner.

The effect was small but steady. It showed that the bird’s “clock” carries memory of the last interval into the new one.

Fantino (1969) saw the same carry-over and called it “transient contrast.” Short runs made pauses shrink; long runs made them grow. Dougan (1987) narrowed the cause to just the single previous interval.

Born et al. (1974) showed that contrast comes from different reinforcement rates across components. Dougan (1987) proves the effect still appears even when reinforcement rate stays the same; only the prior interval length changed.

Okouchi et al. (2006) pushed further. They held response rate constant and still got history effects. Together the three papers build a timeline: 1969 finds the pattern, 1987 trims the cause to duration alone, 2006 shows pure reinforcement history can do it too.

Your client’s past FI schedule can nudge their timing now. If yesterday’s interval was long, expect a longer pause today. When you shorten FI to shape faster work, do it across several sessions so the old long interval does not slow the new one. Check pause data session-to-session; a blip may be history, not failure to learn.