The power of nothing: Risk preference in pigeons, but not people, is driven primarily by avoidance of zero outcomes
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Description: When making risky decisions, people and pigeons often show similar choice patterns. When people learn the reward probabilities through repeated exposure to the outcomes, their preference is disproportionately influenced by the extreme (highest and lowest) outcomes occurring in the decision context. Overweighting of these extremes increases preference for risky alternatives that lead to the highest outcome and decreases preference for risky alternatives that lead to the lowest outcome, termed the extreme-outcome rule. This rule predicts greater risk seeking for choices between safe and risky high-value outcomes than for choices between safe and risky low-value outcomes, when both choices occur in the same context. In a series of studies, we examine how this extreme-outcome rule generalizes within and across two evolutionary distant species: pigeons (Columba livia) and humans (Homo sapiens). Both species showed risky choices consistent with the extreme-outcome rule when a low-value risky option could yield an outcome of zero. When all outcome values were increased such that none of the options could lead to zero, people but not pigeons were still consistent with the extreme-outcome rule. Unlike people, pigeons no longer avoided a low-value risky option when it yielded a non-zero food outcome. These results suggest that, despite some similarities, different mechanisms underlie risky choice in pigeons and people.