Reward value revealed by auction in rhesus monkeys

Economic choice is thought to involve the elicitation of the private and subjective values of various choice options. Thus far, the estimation of subjective values in animals has relied upon repeated choices and was expressed as an average from dozens of stochastic decisions. However, decisions are made moment-to-moment, and their consequences are usually felt immediately. Here we describe a Becker-DeGroot-Marschak (BDM) auction-like mechanism that encourages animals to truthfully reveal their subjective value in individual choices. The monkeys reliably placed well-ranked BDM bids for up to five juice volumes while paying from a water budget. The bids closely approximated the average subjective values estimated with conventional binary choices, thus demonstrating procedural invariance and aligning with the wealth of knowledge acquired with these less direct estimates. The feasibility of BDM bidding in monkeys encourages single-trial neuronal studies and bridges the gap to the widely used BDM method in human neuroeconomics.