Ambiguity aversion in capuchin monkeys
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An ambiguous event happens at multiple probability levels or within a range of probability levels; a risky event happens at a single probability level. Expected utility theory, subjective expected utility theory, and prospect theory from human economics predict no difference in choice of risky vs ambiguous events. Stimulus response models applied to choice behavior of nonhuman animals predict risk aversion. Contrary to these predictions, three tufted capuchin monkeys (Sapajus apella) were averse to ambiguous events over risky events. Our results are partially explained by our novel behavioral economic model, Pan-Fragaszy Softmax model. Our results are the first to show ambiguity aversion in monkeys, and because they are contrary to the prediction of the stimulus-response model, they strengthen the evidence for meta-cognition in nonhuman animals.