Every movement is a reflection of a person’s subjective values, manifested as a willingness to expend energy to achieve a desired outcome. Economically speaking, a person should maximize the utility of their movements by acquiring as much reward as early as possible with the least amount of effort. However, effort alone paints an incomplete picture of the costs associated with movement. There are other factors at play, such as error, time, and risk, that can modulate how much and when effort is expended. Here, I explore how the subjective valuation of effort relative to other costs can influence movement decisions.

The first study investigates the effect of age on preference for error over effort during motor learning. Older adults performed an arm-reaching adaptation task with greater error than younger adults, which is traditionally interpreted as a deficit in learning. However, I show that a difference in subjective cost of effort can manifest these same larger errors while still learning as much as younger adults.

The second study investigates the interaction of time and effort on preference. The traditional view of effort is that we should be agnostic to when periods of high effort are performed—only total energy matters so long as the goal is accomplished. Using an isometric arm-pushing task, I show that subjects preferred earlier high physical effort to later and that the strength of their preference is also reflected in how they indicated their preference.

The third study pilot tests how a virtual reality system could be used to investigate the effect of reward on walking speed. The fourth and final study builds and extends this pilot study to investigate how immediate reward, a history of reward, and baseline effort costs influence walking speed. I find that subjects walked faster not only for higher immediate reward but also when they experienced a history of higher reward. In addition, subjects walked slower when effort costs were higher.

Collectively, these studies deepen our understanding of how subjective effort cost interacts with error, time, and reward, and how these interactions manifest in our movement decisions.