Error Correction and the Structure of Inter-Trial Fluctuations in a Redundant Movement Task.

Joby John,Jonathan B Dingwell,Joseph P Cusumano,Jörn Diedrichsen

doi:10.1371/journal.pcbi.1005118

Joby John, Jonathan B Dingwell + Show 2 more

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https://doi.org/10.1371/journal.pcbi.1005118

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Abstract

We study inter-trial movement fluctuations exhibited by human participants during the repeated execution of a virtual shuffleboard task. Focusing on skilled performance, theoretical analysis of a previously-developed general model of inter-trial error correction is used to predict the temporal and geometric structure of variability near a goal equivalent manifold (GEM). The theory also predicts that the goal-level error scales linearly with intrinsic body-level noise via the total body-goal sensitivity, a new derived quantity that illustrates how task performance arises from the interaction of active error correction and passive sensitivity properties along the GEM. Linear models estimated from observed fluctuations, together with a novel application of bootstrapping to the estimation of dynamical and correlation properties of the inter-trial dynamics, are used to experimentally confirm all predictions, thus validating our model. In addition, we show that, unlike “static” variability analyses, our dynamical approach yields results that are independent of the coordinates used to measure task execution and, in so doing, provides a new set of task coordinates that are intrinsic to the error-regulation process itself.

Highlights

During the repeated execution of goal-directed movements, statistical variability is always observed from one trial to the and this motor variability has long been a major focus of movement neuroscience [1,2,3]
It is becoming clear that these two challenges are not merely impediments to be overcome, but rather hold a key to understanding how humans maintain motor performance under changing circumstances, such as those caused by fatigue, injury, or aging
We focus on skilled performance, and, starting with a previously-developed general model for inter-trial error correction [21, 26, 28], we present a theoretical analysis using the shuffleboard task as an illustrative example

Summary

Introduction

During the repeated execution of goal-directed movements, statistical variability is always observed from one trial to the and this motor variability has long been a major focus of movement neuroscience [1,2,3]. It is generally believed that these inter-trial fluctuations contain crucial information about how the neuromotor system organizes itself to meet task requirements in the face of physical constraints, external perturbations, and motor noise [4,5,6,7,8,9]. There is an excess of body-level degrees of freedom over those needed to specify the outcome of a typical goal-directed movement, and it is natural to expect this redundancy to affect the structure of observed variability. Every point in a task manifold corresponds to a body state that results in perfect task execution, and so, as a consequence, only body-level deviations away from the manifold result in error at the goal level

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