The power of nothing: Risk preference in pigeons, but not people, is driven primarily by avoidance of zero outcomes.

Both human and nonhuman animals regularly need to make choices where the outcomes of their actions are unpredictable or probabilistic in some way. These are often termed "risky" choices. Faced with uncertain rewards, people () and pigeons () often show similar choice patterns. When the reward probabilities of risky choices are learned through experience, preferences in both species seem to be disproportionately influenced by the extreme (highest and lowest) outcomes 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. In a series of studies, we systematically examine how this overweighting of extreme outcomes in risky choice generalizes across 2 evolutionary distant species: pigeons and humans. Both species showed risky choices consistent with an overweighting of extreme outcomes when the low-value risky option could yield an outcome of 0. When all outcome values were increased such that none of the options could lead to 0, people but not pigeons still overweighted the extremes. Unlike people, pigeons no longer avoided a low-value risky option when it yielded a nonzero food outcome. These results suggest that, despite some similarities, different mechanisms underlie risky choice in pigeons and people. (PsycINFO Database Record (c) 2019 APA, all rights reserved).