Abstract
Expected utility theory (EUT), the first axiomatic theory of risky choice, describes choices as a utility maximization process: decision makers assign a subjective value to the choice options, and choose the option with the highest subjective value. This description can be obtained for every subject that complies with the four axioms of EUT. The continuity axiom, central to EUT and to its modifications, requires decision makers to be indifferent between a gamble and a specific probabilistic combination of a more preferred and a less preferred gamble. Compliance with the axiom is necessary for the definition of numerical subjective values. We experimentally tested the continuity axiom for a broad class of gamble types in four monkeys, showing that their choice behavior complied with the existence of numerical subjective values. We used the numerical quantity defined by the continuity axiom to characterize subjective preferences in a magnitude-probability space. This mapping highlighted a trade-off relation between reward magnitudes and probabilities, compatible with the existence of a utility function underlying subjective value computation. These results support the existence of a numerical utility function able to describe choices, allowing for the investigation of the neuronal substrates responsible for coding such rigorously defined numerical quantities.
Footnotes
Email addresses Wolfram Schultz: Wolfram.Schultz{at}protonmail.com