Pigeons and other animals sometimes deviate from optimal choice behavior when given informative signals for delayed outcomes. For example, when pigeons are given a choice between an alternative that always leads to food after a delay and an alternative that leads to food only half of the time after a delay, preference changes dramatically depending on whether the stimuli during the delays are correlated with (signal) the outcomes or not. With signaled outcomes, pigeons show a much greater preference for the suboptimal alternative than with unsignaled outcomes. Key variables and research findings related to this phenomenon are reviewed, including the effects of durations of the choice and delay periods, probability of reinforcement, and gaps in the signal. We interpret the available evidence as reflecting a preference induced by signals for good news in a context of uncertainty. Other explanations are briefly summarized and compared.

In a baseline condition, pigeons chose between an alternative that always provided food following a 30‐s delay (100% reinforcement) and an alternative that provided food half of the time and blackout half of the time following 30‐s delays (50% reinforcement). The different outcomes were signaled by different‐colored keylights. On average, each alternative was chosen approximately equally often, replicating the finding of suboptimal choice in probabilistic reinforcement procedures. The efficacy of the delay stimuli (keylights) as conditioned reinforcers was assessed in other conditions by interposing a 5‐s gap (keylights darkened) between the choice response and one or more of the delay stimuli. The strength of conditioned reinforcement was measured by the decrease in choice of an alternative when the alternative contained a gap. Preference for the 50% alternative decreased in conditions in which the gap preceded either all delay stimuli, both delay stimuli for the 50% alternative, or the food stimulus for the 50% alternative, but preference was not consistently affected in conditions in which the gap preceded only the 100% delay stimulus or the blackout stimulus for the 50% alternative. These results support the notion that conditioned reinforcement underlies the finding of suboptimal preference in probabilistic reinforcement procedures, and that the signal for food on the 50% reinforcement alternative functions as a stronger conditioned reinforcer than the signal for food on the 100% reinforcement alternative. In addition, the results fail to provide evidence that the signal for blackout functions as a conditioned punisher.

Pigeons chose between an (optimal) alternative that sometimes provided food after a 10-s delay and other times after a 40-s delay and another (suboptimal) alternative that sometimes provided food after 10 s but other times no food after 40 s. When outcomes were not signaled during the delays, pigeons strongly preferred the optimal alternative. When outcomes were signaled, choices of the suboptimal alternative increased and most pigeons preferred the alternative that provided no food after the long delay despite the cost in terms of obtained food. The pattern of results was similar whether the short delays occurred on 25% or 50% of the trials. Shortening the 40-s delay to food sharply reduced suboptimal choices, but shortening the delay to no food had little effect. The results suggest that a signaled delay to no food does not punish responding in probabilistic choice procedures. The findings are discussed in terms of conditioned reinforcement by signals for good news.

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Many studies have shown that pigeons will sometimes behave suboptimally by choosing an option that provides food less frequently over one that provides food more frequently. The critical factor in driving suboptimal behavior in these procedures is that the delayed outcomes are differentially signaled on the suboptimal alternative, but not the optimal alternative. Although this procedure is frequently cited as potentially analogous to human gambling, there is little empirical data to evaluate this assertion. The present study tested both pigeon (Experiment 1) and human (Experiment 2) subjects with a suboptimal choice task. Subjects chose between a suboptimal alternative that provided a large reinforcer 20% of the time and an optimal alternative that always provided a small reinforcer. Stimuli presented during the delays signaled the outcomes on the suboptimal alternative in some conditions. When outcomes were signaled, pigeons chose the suboptimal alternative more frequently than did humans. When the outcomes were not signaled, pigeons' choices became more optimal, but humans' choices did not. Humans' suboptimal choice was unrelated to performance on a probability discounting task. Overall, these findings suggest that although both pigeons and humans can choose suboptimally, more research is needed in order to determine whether non-human performance on this task can serve as a model for human gambling.