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The ephemeral-reward task involves providing subjects a choice between two distinctive stimuli, A and B, each containing an identical reward. If A is chosen, the food associated with A is obtained ...

Animals choose suboptimally when provided with cues that signal whether reinforcement is coming or not. For example, pigeons do not prefer an alternative that always provides them with a signal for reinforcement over an alternative that provides them with a signal for reinforcement only half of the time and a signal for the absence of reinforcement the rest of the time. In the present research, we tested the hypothesis that if the results of the choice are delayed, pigeons will choose less suboptimally. We tested this hypothesis by forcing pigeons to wait following their choice, requiring them to complete a fixed-interval 20-s schedule prior to receiving the signals for reinforcement. In Experiment 1, we gave the pigeons a choice between (a) a 50% chance of receiving a signal for reinforcement or a 50% chance of receiving a signal for the absence of reinforcement and (b) a 100% chance of receiving a signal for reinforcement. When the signal for reinforcement was delayed, most of the pigeons chose optimally. When it was not delayed, most of the pigeons chose suboptimally. In Experiment 2, we gave the pigeons a choice between (a) a 25% chance of receiving a signal for reinforcement or a 75% chance of receiving a signal for nonreinforcement and (b) a 100% chance of receiving an unreliable signal for reinforcement (predicting reinforcement 75% of the time). When the signal was not delayed, the pigeons showed a strong tendency to choose suboptimally but they chose suboptimally much less when the signal was delayed.

In the Monty Hall dilemma, humans are initially given a choice among three alternatives, one of which has a hidden prize. After they have chosen, but before revealing whether they have won the prize, subjects are shown that one of the remaining alternatives does not have the prize, and they are asked whether they want to stay with their original choice or switch to the remaining alternative. Switching results in obtaining the prize two thirds of the time, but even after considerable training, humans fail to consistently adopt the optimal strategy of switching. Pigeons, however, show closer-to-optimal switching performance with this task. One of the reasons that humans choose suboptimally is their mistaken assumption that with two alternatives, the probabilities of winning the prize are the same for staying and switching, and staying may be preferred because of a sense of endowment (ownership of the initial response). When we tried to produce an endowment effect in pigeons by requiring 20 pecks (rather than one peck) for the initial choice, it actually resulted in faster acquisition of the switching response. In the present research with pigeons, we examined the finding from human research that subjects are more likely to switch if they are not responsible for making the initial choice (another approach to the endowment effect). Inconsistent with the findings with humans, we found that when the initial choice was made for the pigeons, they actually showed less of a tendency to switch than did pigeons that made the initial choice themselves.

Pigeons show relatively poor memory when trained on 0-s delayed matching and tested with longer delays. We hypothesized that one reason for the effect of delay may be a loss of association between sample responding and reinforcement. To test this hypothesis, we compared the effect of standard delays inserted between the offset of the sample and the onset of the comparison stimuli with similar delays inserted between the comparison response and reinforcement. We also manipulated whether the delay was dark or lit because there is some evidence that lit delays are disruptive but filled intervals may also help bridge delays. In Experiment 1, pigeons were trained with a 0-s delay and were tested with longer delays. When both delays and delay illumination were novel, we found no effect of delay of reinforcement and only a small effect of delay illumination. In Experiment 2, to eliminate the effect of the novelty of the delay and delay illumination, pigeons were trained with delays from the start. Results indicated once again that delay of reinforcement had little effect on matching accuracy. However, in Experiment 2, delay illumination produced a general decline in matching accuracy and when it preceded comparison choice its effect increased with increasing delay. The results indicate that the rate of forgetting seen in the typical delayed matching experiment is not due to delay of reinforcement for attention to the sample. The results also confirm that lighting the delay after the sample is detrimental to delayed matching. Surprisingly perhaps, lighting the delay after the comparison response is also detrimental to delayed matching. Finally, it was concluded that a more accurate assessment of the rate of forgetting in delayed matching can be obtained by training with variable delays from the outset.