A good time to leave?: the sunk time effect in pigeons

•Like humans, pigeons do not know when is a good time to leave – they commit the sunk time effect.•Pigeons persist in responding during a long time interval, which ends with no reward, instead of making an escape response which might return them to a short interval ending in reward.•Whether they escape depends on their discrimination of the ratio of short to long intervals. Persistence in a losing course of action due to prior investments of time, known as the sunk time effect, has seldom been studied in nonhuman animals. On every trial in the present study, pigeons were required to choose between two response keys. Responses on one key produced food after a short fixed interval (FI) of time on some trials, or on other trials, no food (Extinction) after a longer time. FI and Extinction trials were not differently signaled, were equiprobable, and alternated randomly. Responses on a second Escape key allowed the pigeon to terminate the current trial and start a new one. The optimal behavior was for pigeons to peck the escape key once the duration equivalent to the short FI had elapsed without reward. Durations of the short FI and the longer Extinction schedules were varied over conditions. In some conditions, the pigeons suboptimally responded through the Extinction interval, thus committing the sunk time effect. The absolute duration of the short FI had no effect on the choice between persisting and escaping. Instead, the ratio of FI and Extinction durations determined the likelihood of persistence during extinction