It's too quick to blame myself-the effects of fast and slow rates of change on credit assignment during object lifting.

Kelene Fercho,Lee A Baugh

doi:10.3389/fnhum.2014.00554

Abstract

Although there have been substantial research efforts examining the effect of various rates of change in reaching movements, there has been little to no research devoted to this issue during object manipulation tasks. In force-field and visuomotor adaptation studies, two parallel processes have been identified: first, a fast process that adapts and de-adapts quickly is thought to enable the actor to deal with potentially transient perturbations. Second, a slower, but longer lasting process adapts if these initial perturbations persist over time. In a largely separate body of research, the role of credit assignment has been examined in terms of allotting the cause of errors to changes in the body vs. changes in the outside world. Of course, these two processes are usually linked within the real world, with short lasting perturbations most often being linked to external causes and longer lasting perturbations being linked to internal causes. Here, we demonstrate that the increases in load forces associated with a gradual increase in object weight during a natural object lifting task are transferred when lifting a novel object, whereas a sudden increase in object weight is not. We speculate that gradual rates of change in the weight of the object being lifted are attributed to the self, whereas fast rates of change are more likely to be attributed to the external environment. This study extends our knowledge of the multiple timescales involved in motor learning to a more natural object manipulation scenario, while concurrently providing support for the hypothesis that the multiple time scales involved in motor learning are tuned for different learning contexts.

Highlights

Our motor system is finely tuned to generate accurate movements when interacting with our environment, we inevitably make many mistakes on a daily basis when manipulating our surroundings
To examine the longevity of this effect, planned comparisons between the last three lifts of the large red block for the DISCUSSION temporal credit assignment has been examined in a number of different scenarios, little to no research has examined these issues during natural object lifting tasks, despite such scenarios requiring a solution to the credit assignment problem
In order to maximize future lifting performance with an object, the ability to accurately predict the forces necessary to lift said object is an essential component of dexterous object manipulation (Johansson and Westling, 1988; Johansson and Flanagan, 1999; Wolpert and Flanagan, 2001; Flanagan et al, 2006), and the temporal nature of the errors applied is likely to be an important factor within this prediction, as has been demonstrated in other tasks

Summary

Introduction

Our motor system is finely tuned to generate accurate movements when interacting with our environment, we inevitably make many mistakes on a daily basis when manipulating our surroundings. The motor system is capable of adapting future movement based on the errors experienced in previous interactions with the world. To fully-benefit from this type of error-based learning, the underlying cause of experienced errors must be identified. Suppose you are playing a round of golf, and on the 10th hole your drive off the tee falls much shorter than you had predicted. When the swing is made, the sensorimotor system is capable of comparing the movement’s outcome to a desired and/or predicted state. This error-based learning could be used to adjust the motor commands for the following swing. Errorbased learning is well-understood, having been examined in many variants of adaptation paradigms including saccadic adaptation (Pélisson et al, 2010), reaching in force fields (Thoroughman and Shadmehr, 2000), and grip force modulation (Flanagan and Wing, 1997)

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