Preference reversal and delayed reinforcement

Pigeons chose, in a two-key discrete-trial procedure, between 2- and 4-sec access to grain, with the larger amount always presented 4 sec later than the smaller. As the delay between the choice and the availability of the smaller reinforcement was varied from .01 to 12 sec, all subjects reversed preference from the small-early to the large-late reinforcement. The values of delay at which preference reversed were approximately consistent with the matching law as adapted for delayed reinforcement.