Abstract
Our decisions are often swayed by a desire to avoid losses over a desire to acquire gains. While loss aversion has been confirmed for decisions about money or commodities, it is unclear how individuals generally value gains relative to losses in effort-based decisions. For example, do individuals avoid greater work more than they seek out less work? We examined this question in the context of physical effort, using an arm-reaching task in which decreased effort was framed as a gain and increased effort was framed as a loss. Subjects performed reaching movements against different levels of resistance that increased or decreased the effort demands of the reaches. They then chose to accept or reject various lotteries, each with a possibility of performing less effortful reaches and a possibility of performing more effortful reaches, compared to the certain outcome of performing reaches against a fixed reference level of effort. Subjects avoided higher effort conditions more than they sought lower effort conditions, demonstrating asymmetric valuation of gains and losses. Using prospect theory, we explored various model formulations to determine subject-specific valuation of effort in these mixed gambles. A nonlinear model of effort valuation demonstrating increasing sensitivity to absolute effort best described the effort lottery choices. In contrast to the loss-aversion observed in financial decisions, there was no evidence of loss aversion in effort-based decisions. Rather, we observed moderate relief-seeking behavior. This model confirms that gains and losses are valued asymmetrically. This is due to the combined effects of increasing sensitivity to absolute effort and moderate relief-seeking, leading to a net effect of greater avoidance of higher effort. Asymmetric valuation was magnified on a later day of testing. In contrast, subjects were loss-averse in a comparable financial task. We suggest that consideration of nonlinear effort valuation can inform future studies of sensorimotor control and exercise motivation.
Highlights
Loss aversion is a well-established phenomenon in human behavior
A curvilinear value function with 3 free parameters was used to describe the subjective value of an outcome X (SV = Xα, for X > 0; SV = −λ(−X)α for X < 0), where the value sensitivity parameter α describes the curvature of the function and the loss-aversion coefficient λ describes how losses are valued relative to gains
We tested a hybrid model combining a traditional prospect theory model with reference-dependent loss aversion, λ, that assumes an underlying linear absolute effort valuation function (i.e. X = Δb), with a model that allows for nonlinearities in the absolute encoding function, X = Δ(bγ)
Summary
Loss aversion is a well-established phenomenon in human behavior. Our desire to avoid negative outcomes (losses) often surpasses our desire to acquire positive outcomes (gains), notably affecting our financial and commodity-based decisions [1]. Imagine you have the opportunity to play a lottery with a 50:50 chance of winning $100 and losing $100. A rational decision maker would have no preference between playing the lottery
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