Internal clock and memory processes in animal timing.

Temporal control of behavior was investigated within the framework of an internal clock model. Pigeons were exposed to signaled fixed-interval 30-s trials mixed with extended unreinforced (baseline) trials. On unreinforced break trials, the signal was interrupted for a period of time after trial onset. In Experiment 1, comparisons between the peak time obtained on baseline and on break trials produced peak time shifts that were longer than those expected if the clock had stopped during the break but shorter than if the clock had reset. In Experiment 2, systematic manipulations of duration and location of breaks produced peak time shifts that were nonlinear functions of break duration and that varied linearly with break location. The obtained peak times were more consistent with a continuous memory decay model than with the stop-retain or the reset hypotheses.