Worth the Work? Monkeys Discount Rewards by a Subjective Adapting Effort Cost

Area of Science:

• Behavioral economics
• Neuroscience
• Primate cognition

Background:

• Life requires allocating limited energy resources to maximize benefits from scarce opportunities.
• Economic theory suggests optimizing choices via reward utility minus effort disutility.
• The subtractive model of effort disutility needs further testing for its ability to account for experience-dependent trade-offs.

Purpose of the Study:

• To test the subtractive model of effort disutility in nonhuman primates (Macaca mulatta).
• To investigate how experience influences reward-effort trade-offs.
• To develop and validate a reference-dependent effort disutility model.

Main Methods:

• Binary choice task with varied reward quantity and physical effort.
• Random utility modeling to estimate reward utility and effort disutility.
• Comparison of subtractive, parabolic, and exponential effort discounting models.

Main Results:

• The subtractive effort model provided better out-of-sample predictions than alternative models.
• Effort disutility was dependent on prior experience with effortful options.
• A reference-dependent effort disutility model explained increased effort expenditure after experience.

Conclusions:

• Monkeys discount rewards by subtracting a subjective effort cost, which is relative to learned expected effort.
• Subjective effort costs are context- and experience-dependent.
• Accurate measurement of subjective effort costs is crucial for understanding brain mechanisms of effort-based decision-making.