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Monkeys choose as if maximizing utility compatible with basic principles of revealed preference theory

Pastor-Bernier, Alexandre and Plott, Charles R. and Schultz, Wolfram (2017) Monkeys choose as if maximizing utility compatible with basic principles of revealed preference theory. Proceedings of the National Academy of Sciences of the United States of America, 114 (10). E1766-E1775. ISSN 0027-8424. PMCID PMC5347590.

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Revealed preference theory provides axiomatic tools for assessing whether individuals make observable choices “as if” they are maximizing an underlying utility function. The theory evokes a tradeoff between goods whereby individuals improve themselves by trading one good for another good to obtain the best combination. Preferences revealed in these choices are modeled as curves of equal choice (indifference curves) and reflect an underlying process of optimization. These notions have far-reaching applications in consumer choice theory and impact the welfare of human and animal populations. However, they lack the empirical implementation in animals that would be required to establish a common biological basis. In a design using basic features of revealed preference theory, we measured in rhesus monkeys the frequency of repeated choices between bundles of two liquids. For various liquids, the animals’ choices were compatible with the notion of giving up a quantity of one good to gain one unit of another good while maintaining choice indifference, thereby implementing the concept of marginal rate of substitution. The indifference maps consisted of nonoverlapping, linear, convex, and occasionally concave curves with typically negative, but also sometimes positive, slopes depending on bundle composition. Out-of-sample predictions using homothetic polynomials validated the indifference curves. The animals’ preferences were internally consistent in satisfying transitivity. Change of option set size demonstrated choice optimality and satisfied the Weak Axiom of Revealed Preference (WARP). These data are consistent with a version of revealed preference theory in which preferences are stochastic; the monkeys behaved “as if” they had well-structured preferences and maximized utility.

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Additional Information:© 2017 National Academy of Sciences. Freely available online through the PNAS open access option. Edited by Charles R. Gallistel, Rutgers University, Piscataway, NJ, and approved January 23, 2017 (received for review July 21, 2016). We thank Aled David for invaluable help with animal training and Matt Shum, Kim Border, and three anonymous reviewers for helpful comments on the manuscript. This work was supported by The Wellcome Trust, the European Research Council, and National Institutes of Health Caltech Conte Center. Author contributions: A.P.-B., C.R.P., and W.S. designed research; A.P.-B. performed research; A.P.-B. analyzed data; and A.P.-B., C.R.P., and W.S. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
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European Research Council (ERC)UNSPECIFIED
Subject Keywords:marginal rate of substitution; optimal choice; reward; transitivity; axiom
Issue or Number:10
PubMed Central ID:PMC5347590
Record Number:CaltechAUTHORS:20170215-165607567
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Official Citation:Alexandre Pastor-Bernier, Charles R. Plott, and Wolfram Schultz Monkeys choose as if maximizing utility compatible with basic principles of revealed preference theory PNAS 2017 114 (10) E1766-E1775; published ahead of print February 15, 2017, doi:10.1073/pnas.1612010114
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74354
Deposited By: George Porter
Deposited On:16 Feb 2017 16:38
Last Modified:03 Oct 2019 16:37

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