A clarification of continuous repertoire development.

Researchers taught pigeons to peck at two different speeds.

One tone meant peck fast. Another tone meant peck slow.

Then they played brand-new tones that sat between the two trained speeds.

They watched to see if the birds would peck at an in-between speed.

The birds did not peck in the middle.

They still pecked either fast or slow, nothing else.

The new tones got sorted into one of the two old boxes.

Fantino (1967) saw the same thing years earlier. Pigeons on fixed-interval schedules also ignored small time changes.

Périkel et al. (1974) showed the opposite. When a light told the bird exactly how long to work, the birds hit the time goal.

The difference is the signal. J’s birds got a clear cue that meant "time is up." V’s birds only got tones that already meant "fast" or "slow," so nothing told them "middle is okay.

Allen et al. (1989) add that pigeons can reproduce many durations, but only when each duration is first linked to its own cue. Without those links, the birds stay all-or-none.

If you want smooth, graded behavior, give a unique cue for each level.

Without clear middle cues, learners jump between the two trained ends.

Next time you shape duration—like staying at a desk or waiting in line—add a special signal for the in-between step. A color change, a click, or a word can stand for "just right," so the child does not bounce between too-short and too-long.