Human choices respond to added costs according to the energy budget rule

Abstract

The energy budget rule is a risk-sensitive optimal foraging model that predicts choice should be risk averse when need levels are relatively easy to meet within a foraging period (positive budget conditions), and risk prone when need levels are more difficult to meet (negative budget conditions). Although research with nonhumans has produced only limited support for the energy budget rule, analogue research with humans has shown that risky choice for monetary outcomes is typically consistent with the model’s predictions. Most human studies have tested the energy budget rule by manipulating minimum requirements, rates of gain, or reserves. The energy budget model also predicts, however, that energy expenditures (costs) can affect risk sensitivity. Two experiments therefore investigated whether monetary costs for choices would affect risk sensitivity. Adults were presented with choices between monetary options in blocks of five trials. Block earnings were paid only if earnings exceeded a minimum amount. Each trial, a monetary cost was subtracted from earnings when a choice was made. Cost magnitude was manipulated across conditions to generate one positive- (cost $0.00) and two negative-budget (cost $0.01 or $0.02) conditions. In Experiment 1, choice options produced the same mean earnings, with one producing a constant amount of money and the other a variable amount. In Experiment 2, both choice options produced the same mean amounts of money but different variances. Similar to previous earnings budget studies, choice varied as a function of budget condition. Trial-by-trial choice patterns were inconsistently predicted by a dynamic optimization model.