Superstitious key pecking after three peck-produced reinforcements.

The first three pecks on a response key by experimentally naive pigeons produced grain reinforcements. Thereafter, for approximately 50 experimental sessions and under a variety of schedule conditions, grain was presented independently of the subjects' behaviors. The pigeons continued to peck the response key "superstitiously" throughout the 50 sessions. The results suggest that superstitions are commonplace-not relatively infrequent or abnormal events-in the behavior of pigeons.