Species differences in temporal control of behavior.

Lowe et al. (1977) compared how rats and pigeons act on fixed-interval and fixed-time schedules. The team watched lever presses from rats and key pecks from pigeons during the same timing task.

They recorded when each animal paused after food and how fast it responded later. The goal was to see if the two species use the same clock in their heads.

Rats stopped longer after food and then ran faster as the next reward got close. Pigeons pecked at a steady pace with only short breaks, making a smoother curve.

In other words, rats waited first and then worked hard, while pigeons worked the whole time. The shape of the response pattern depended on the species, not just the schedule.

Greene et al. (1978) extended the work to humans. Adults only showed the smooth scallop when a digital clock was on the screen; without it they looked more like rats with a clear break-and-run pattern.

McSweeney et al. (1993) later built the "linear waiting" model that explains why pigeon pauses grow with the interval. The model treats the pause as a direct read-out of the time just waited, backing up the steady pigeon data seen in 1977.

Frame et al. (1984) and Bauman et al. (1996) both found that rats can stretch their pauses when upcoming time cues are given, showing the rat pause is flexible, not fixed. These studies line up with the 1977 rat pattern and confirm that longer intervals yield longer waits.

If you use interval schedules in practice, remember that the learner's species and response style shape the pattern you will see. A child pressing a button may pause like a rat, while a child tapping steadily may look like a pigeon. Check whether external timers or clocks are present; removing them can flip the pattern. When shaping waiting behavior, pick cues and response topographies that match the learner's natural timing style.