Credit assignment between body and object probed by an object transportation task

Gaiqing Kong,Qining Wang,Zhihao Zhou,Kunlin Wei,Konrad Kording

doi:10.1038/s41598-017-13889-w

Abstract

It has been proposed that learning from movement errors involves a credit assignment problem: did I misestimate properties of the object or those of my body? For example, an overestimate of arm strength and an underestimate of the weight of a coffee cup can both lead to coffee spills. Though previous studies have found signs of simultaneous learning of the object and of the body during object manipulation, there is little behavioral evidence about their quantitative relation. Here we employed a novel weight-transportation task, in which participants lift the first cup filled with liquid while assessing their learning from errors. Specifically, we examined their transfer of learning when switching to a contralateral hand, the second identical cup, or switching both hands and cups. By comparing these transfer behaviors, we found that 25% of the learning was attributed to the object (simply because of the use of the same cup) and 58% of the learning was attributed to the body (simply because of the use of the same hand). The nervous system thus seems to partition the learning of object manipulation between the object and the body.

Highlights

Humans excel at using tools and manipulating objects
Given that the learning was about transporting a weight, the initial trajectory height of this ballistic movement is a direct indicator of participants’ feedforward prediction of object weight
If the transfer action does not share the same effector and the same object as the original action, the motor system exhibits little transfer of learning obtained during object manipulation even when the participant explicitly knows two objects are identical

Summary

Introduction

Humans excel at using tools and manipulating objects. Our dexterous manipulation of objects owes to efficient construction of an internal representation of object property through trial-by-trial learning[1,2,3]. Studies with reaching perturbation paradigms (albeit with a hand-held object) examine how motor learning transfers between limbs[16,17] or how learning aftereffect is affected when people disengage the object[5,10]. In these studies, between-limb transfer and the reduction in aftereffect by disengaging the object have been hypothesized to be caused by the learning attributed to the object. Though both object manipulation paradigm and reaching paradigm have found that learning is related to the specific object the learner interacts with, none of the studies quantifies the partitioning of learning between the body and the object within a single experimental framework

Methods

Results

Conclusion