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Risky choice: Probability weighting explains independence axiom violations in monkeys.

Simone Ferrari-Toniolo1, Leo Chi U Seak1, Wolfram Schultz1

  • 1Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK.

Journal of Risk and Uncertainty
|January 19, 2023
PubMed
Summary
This summary is machine-generated.

Monkeys exhibit graded preference changes, not outright reversals, when faced with risky choices, challenging Expected Utility Theory. Cumulative Prospect Theory better explains their decision-making, aligning with human behavior in similar studies.

Keywords:
ChoiceGamblePreference reversalProbability

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Area of Science:

  • Behavioral Economics
  • Decision Neuroscience
  • Animal Cognition

Background:

  • Expected Utility Theory (EUT) is a foundational model for rational decision-making under risk, based on several axioms.
  • The Independence Axiom (IA) is a critical EUT axiom, stating preferences should remain invariant to common probabilistic mixtures.
  • Violations of the IA, such as common consequence (CC) and common ratio (CR) effects, are well-documented in human decision-making.

Purpose of the Study:

  • To rigorously test violations of the Independence Axiom (IA) in a non-human primate model.
  • To compare the explanatory power of Expected Utility Theory (EUT) and Cumulative Prospect Theory (CPT) in predicting choice behavior.
  • To investigate the nature of preference changes in risky choice, distinguishing between outright reversals and graded shifts.

Main Methods:

  • Conducted thousands of stochastic choice trials with three monkeys over several months, using diverse binary gamble sets.
  • Administered common consequence (CC) and common ratio (CR) tests to probe violations of the Independence Axiom (IA).
  • Employed Linear Discriminant Analysis (LDA) and Akaike Information Criterion (AIC) to model choice data and compare theoretical predictions.

Main Results:

  • Monkeys demonstrated few outright preference reversals (8%) but significant graded preference changes (46%) when gambles were altered.
  • Gamble probabilities were strong predictors of preference changes in both CC (72%) and CR (88%) tests.
  • Cumulative Prospect Theory (CPT), incorporating probability weighting, provided a superior account of choices compared to Expected Value (EV) or EUT models.

Conclusions:

  • Monkeys' decision-making under risk exhibits graded preference changes, consistent with violations of the Independence Axiom (IA).
  • CPT's framework, including nonlinear probability weighting, better captures the observed choice patterns than traditional EUT or EV models.
  • These findings in primates offer valuable insights into the fundamental mechanisms of risky decision-making, with implications for understanding human behavior and neural correlates.