Pigeons can learn a difficult discrimination if reinforcement is delayed following choice.

Delaying reinforcement typically has been thought to retard the rate of acquisition of an association, but there is evidence that it may facilitate acquisition of some difficult simultaneous discriminations. After describing several cases in which delaying reinforcement can facilitate acquisition, we suggest that under conditions in which the magnitude of reinforcement is difficult to discriminate, the introduction of a delay between choice and reinforcement can facilitate the discrimination. In the present experiment, we tested the hypothesis that the discrimination between one pellet of food for choice of one alternative and two pellets of food for choice of another may be a difficult discrimination when choice consists of a single peck. If a 10-s delay occurs between choice and reinforcement, however, the discrimination is significantly easier. It is suggested that when discrimination between the outcomes of a choice is difficult and impulsive choice leads to immediate reinforcement, acquisition may be retarded. Under these conditions, the introduction of a brief delay may facilitate acquisition.