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.

Animal procrastination: Pigeons choose to defer experiencing an aversive gap or a peck requirement.

When humans procrastinate, they delay completing a required relatively aversive task. In the present experiments with pigeons, we considered the possibility that completing the task close to the deadline results in the formation of a stronger conditioned reinforcer. In Experiment 1, pigeons were given a choice between two chains: (a) a signaled long period, followed by a dark gap, followed by a signaled short conditioned reinforcer, and food and (b) a signaled short period, followed by a dark gap, followed by a signaled long conditioned reinforcer, and food. We found a reliable preference for the delayed gap. In Experiment 2, we let pigeons choose between two chains: (a) walking to a near panel to peck a key, followed by a long walk to peck a key for reinforcement and (b) walking to a far panel to peck a key followed by a short walk to peck a key for reinforcement. When a single peck was required to either key, the pigeons were indifferent. When ten pecks were required to the near key but only one peck to the far key, the pigeons preferred the far key. When ten pecks were required to either key, the pigeons preferred the far key. The results of both experiments suggest that pigeons prefer to defer a relatively aversive event but, in keeping with Fantino's Delay Reduction Theory, this effect may result from the development of a strong conditioner reinforcer that occurs when the event (the gap or required pecking) comes close to reinforcement.

Midsession reversal learning by pigeons: Effect on accuracy of increasing the number of stimuli associated with one of the alternatives.

The midsession reversal task involves a simultaneous discrimination in which choice of one stimulus (S1) is correct for the first 40 trials and choice of the other stimulus (S2) is correct for the last 40 trials of each 80-trial session. When pigeons are trained on the midsession reversal task, they appear to use the passage of time from the start of the session as a cue to reverse. As the reversal approaches, they begin to make anticipatory errors, choosing S2 early, and following the reversal they make perseverative errors, continuing to choose S1. Recent research suggests that anticipatory errors can be reduced (while not increasing perseverative errors) by reducing the probability of reinforcement for correct S2 choices from 100% to 20%. A similar effect can be found by increasing the response requirement for choice of S2 from one peck to ten pecks. In the present experiments, we asked if a similar effect could be attained by increasing the number of stimuli that, over trials, could serve as S2. Instead, in both experiments, we found that increasing the number of S2 stimuli actually increased the number of anticipatory errors. Several interpretations of this result are provided, including the possibility that attention to the variable S2 stimuli may have interfered with attention to the S1 stimulus.