An Adaptive Response to Uncertainty Generates Positive and Negative Contrast Effects

Choice in Changing Environments Animals, including humans, generally tend to judge the world on relative, rather than absolute, terms. For example, the value of a particular object or reward is generally determined based on comparison to other rewards we have received in the past or to those that others have received. Such contrast effects can have negative or positive impacts on our behavior. McNamara et al. (p. 1084) used an optimality model to show that contrast effects could evolve as an adaptive response to environmental instability and unpredictability. Contrast effects, in which current behavior depends on past conditions, may be an adaptive response to uncertainty. Successive contrast effects, in which behavior is dependent on whether conditions are currently better or worse than they were before, are a striking illustration of the fact that animals evaluate the world in relative terms. Existing explanations for these effects are based on descriptive models of psychological and physiological processes, but little attention has been paid to the factors promoting their evolution. Using a simple and general optimality model, we show that contrast effects can result from an adaptive response to uncertainty in a changing, unpredictable world. A wide range of patterns of environmental change will select for sensitivity to past conditions, generating positive and negative contrast effects. Our analysis reveals the importance of incorporating uncertainty and environmental stochasticity into models of adaptive behavior.