Effort-based decisions, in which people weigh potential future rewards against effort costs required to achieve those rewards, have largely been studied separately for cognitive or physical effort, yet most real world actions incur both cognitive and physical effort costs. What is the relationship between cognitive and physical effort costs? Here we attempt to formalize the mechanisms underlying effortbased decisions and address methodological challenges to isolate and measure the factors contributing to such decisions (including sensitivity to reward and effort costs).
Patch foraging is an ecologically valid reward rate maximization problem with well developed theoretical tools to understand choices. We developed the Effort Foraging Task to isolate and quantify the cost of both cognitive and physical effort using a computational model. We embedded cognitive or physical effort costs into a patch foraging sequential decision task. Participants chose between harvesting a depleting patch, or traveling to a new patch that was costly in time and effort. Participants exit thresholds (reflecting the reward they expected to receive by harvesting when they chose to travel to a new patch) were sensitive to cognitive and physical effort demands, allowing us to quantify the perceived effort cost in monetary terms. Individual differences in cognitive and physical effort costs were positively correlated, suggesting that these are perceived and processed in common terms across different domains. We found patterns of correlation of both cognitive and physical effort costs with self-reported cognitive function, anhedonia, depression, anxiety, and fatigue. This suggests that our task captures decision mechanisms closely associated with real-world motivation, and can be used to study individual variation in effort-based decisions across different domains of cost.
