Discriminability of frequency of food or stimulus presentations in variable-time schedules.

Researchers used pigeons to test if the birds could tell how often food was coming.

The birds got grain on a variable-time schedule. No peck was needed.

A light or sound came on each time food arrived. Later the birds saw the same light without food. The team watched if the birds acted as if food was due.

The pigeons pecked more when the light had signaled a high food rate.

Control faded if the signal came long before food. The birds also pecked when new food rates matched the old one.

Coe et al. (1997) extends this work. They showed pigeons can also pick the least frequent stimulus, but accuracy drops the longer ago it appeared. Together the two studies say birds track both how often and how recently events happen.

HERRNSTEIN (1961) is a predecessor. That paper showed pigeons spread their pecks to match how often each key paid off. Mandell (1984) goes further by proving the birds notice the rate itself, not just where to peck.

Wildemann et al. (1973) is methodologically similar. Both used pigeons to study schedule cues; they found birds can tell when food does not depend on responding, while Mandell (1984) shows they can also tell how often it comes.

If animals can feel the rhythm of reinforcement, you can use that in your programs. Pair a brief song or light with dense reinforcement, then use the same cue during thin schedules to keep behavior strong while you fade goodies. Check that the cue stays close in time to the last reinforcer so control stays tight.