Exploiting the geometry of the solution space to reduce sensitivity to neuromotor noise.

Zhaoran Zhang,Se-Woong Park,Meghan E Huber,Dena Guo,Dagmar Sternad

doi:10.1371/journal.pcbi.1006013

Zhaoran Zhang, Se-Woong Park + Show 3 more

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https://doi.org/10.1371/journal.pcbi.1006013

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Abstract

Throwing is a uniquely human skill that requires a high degree of coordination to successfully hit a target. Timing of ball release appears crucial as previous studies report required timing accuracies as short as 1-2ms, which however appear physiologically challenging. This study mathematically and experimentally demonstrates that humans can overcome these seemingly stringent timing requirements by shaping their hand trajectories to create extended timing windows, where ball releases achieve target hits despite temporal imprecision. Subjects practiced four task variations in a virtual environment, each with a distinct geometry of the solution space and different demands for timing. Model-based analyses of arm trajectories revealed that subjects first decreased timing error, followed by lengthening timing windows in their hand trajectories. This pattern was invariant across solution spaces, except for a control case. Hence, the exquisite skill that humans evolved for throwing is achieved by developing strategies that are less sensitive to temporal variability arising from neuromotor noise. This analysis also provides an explanation why coaches emphasize the “follow-through” in many ball sports.

Highlights

As evolutionary biologists have noted, the primary advantage of human upright gait is that it frees the hands to hunt, fight, explore, and exploit the environment [1, 2]
While throwing by itself requires the coordination of the multi-segmented body in an egocentric reference frame, aiming to a target requires orienting one’s own bodily actions to an allocentric reference frame [33, 34]. It is the fine-tuning of the arm trajectory and creating a longer window for successful ball releases that critically determine a dexterous throw
Our results showed that the error and successful hits critically depended on the geometry of the solution space defined by the target location relative to the thrower (Hypothesis 1)

Summary

Introduction

As evolutionary biologists have noted, the primary advantage of human upright gait is that it frees the hands to hunt, fight, explore, and exploit the environment [1, 2]. Humans have developed the ability to throw a projectile to hit a target, which significantly extended man’s area of influence [3,4,5,6]. The ability to throw, together with other forms of tool use, has co-evolved with, or even been instrumental to the development of cognitive abilities that have given humans their evolutionary advantage [6]. While non-human primates can throw objects, humans are vastly superior when accurately aiming at a target, as can be seen in ball sports. This disparity indicates an essential difference between coordinating one’s own movements and coordinating one’s body with respect to external reference points [7]. Numerous studies in comparative and evolutionary biology, sports biomechanics, and motor neuroscience have tried to understand this quintessentially human skill [4, 8,9,10,11]

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