Pii: S0376-6357(98)00052-7

This study reexamined the processes of acquisition and extinction under periodic reinforcement. During the first phase of the experiment, pigeons were exposed to a fixed-interval schedule either 40 or 80 s long. During the second phase, each session started with the fixed-interval schedule but changed to extinction at an unpredictable moment. The results showed that during phase 1 the curve for the average rate of pecking along the interval rotated across sessions, that is, the rate immediately after food decreased, whereas the rate at the end of the interval increased. The initial and terminal rates approached their steady state at different speeds. During the extinction trials of phase 2, behavior was characterized by pause-peck oscillations with a period slightly longer than the fixed-interval duration. These findings concerning acquisition and extinction under periodic reinforcement were then compared with the predictions of some current theories of timing. © 1998 Elsevier Science B.V. All rights reserved.