Learning from the value of your mistakes: evidence for a risk-sensitive process in movement adaptation

Alaa A Ahmed,Michael C Trent

doi:10.3389/fncom.2013.00118

Abstract

Risk frames nearly every decision we make. Yet, remarkably little is known about whether risk influences how we learn new movements. Risk-sensitivity can emerge when there is a distortion between the absolute magnitude (actual value) and how much an individual values (subjective value) a given outcome. In movement, this translates to the difference between a given movement error and its consequences. Surprisingly, how movement learning can be influenced by the consequences associated with an error is not well-understood. It is traditionally assumed that all errors are created equal, i.e., that adaptation is proportional to an error experienced. However, not all movement errors of a given magnitude have the same subjective value. Here we examined whether the subjective value of error influenced how participants adapted their control from movement to movement. Seated human participants grasped the handle of a force-generating robotic arm and made horizontal reaching movements in two novel dynamic environments that penalized errors of the same magnitude differently, changing the subjective value of the errors. We expected that adaptation in response to errors of the same magnitude would differ between these environments. In the first environment, Stable, errors were not penalized. In the second environment, Unstable, rightward errors were penalized with the threat of unstable, cliff-like forces. We found that adaptation indeed differed. Specifically, in the Unstable environment, we observed reduced adaptation to leftward errors, an appropriate strategy that reduced the chance of a penalizing rightward error. These results demonstrate that adaptation is influenced by the subjective value of error, rather than solely the magnitude of error, and therefore is risk-sensitive. In other words, we may not simply learn from our mistakes, we may also learn from the value of our mistakes.

Highlights

Effective movement relies largely on adaptation: the process of correcting control from movement to movement, which, critically, is driven by movement error (Topka et al, 1998; Smith and Shadmehr, 2005; Bastian, 2008; Rabe et al, 2009)
In summary, our results provide evidence for a risk-sensitive process underlying movement adaptation
Adaptation can be altered by modulating an individual’s subjective error value function. The implications of these findings are far-reaching and could potentially lead to new and improved rehabilitation therapies that are tailored to each and every patient at an individual level. We hope they can lead to significant advances in our understanding of the neural mechanisms by which risk influences the learning process in both motor and non-motor tasks

Summary

Introduction

Effective movement relies largely on adaptation: the process of correcting control from movement to movement, which, critically, is driven by movement error (Topka et al, 1998; Smith and Shadmehr, 2005; Bastian, 2008; Rabe et al, 2009). Investigations of adaptation have largely overlooked the fact that not all movement errors of the same magnitude necessarily have the same subjective value. The error magnitude is equivalent, the subjective value is drastically different. One would respond to each error very differently on the shot. Most movements involve similar decisions, where the subjective value of an error must be considered. The fact that people respond differently demonstrates that the magnitude of the error and the subjective value of the error, are not always the same. This raises the question of whether adaptation may depend on the subjective value, rather than the magnitude, of an error

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