Tool Use and Generalized Motor Programs: We All Are Natural Born Poly-Dexters

François Osiurak,Ludovic Delporte,Mathieu Lesourd,Yves Rossetti

doi:10.1038/s41598-018-28759-2

Abstract

For most people, human tool use is inextricably entwined with manual dexterity. This folk belief is widespread among scientists too. In this line, human tool use is based on motor programs about how the hand interacts with tools, implying that the use of end-effectors other than the hand should generate motor control difficulties (e.g., inability to reproduce a specific tool-use action over time), because these so-called programs characterize the spatiotemporal parameters of hand movements, but not of other end-effectors. To test this, we asked participants to perform three tool-use actions (e.g., pounding a nail) with four end-effectors (i.e., right foot, right elbow, left hand, right hand). We show that participants not only spontaneously performed the tool-use actions effectively, but also crucially kept tools’ spatiotemporal parameters constant among the end-effectors. This phenomenon, which we call poly-dexterity, is at odds with the view that the human brain stores hand-centered motor programs for tool use. Poly-dexterity is instead consistent with the idea that, once the tool-use action is formed mentally, general motor programs can be applied to a variety of end-effectors. Reversing the usual evolutionary perspective, our findings support that, in the course of evolution, manual dexterity has come after tool-use skills.

Highlights

The manipulation-based approach is somewhat inconsistent with the frequent observation that individuals born without arms can use many tools with their feet in everyday life
Our analyses focused on four classical kinematic landmarks[14,15] (Cycle duration; Maximum velocity of the forth movement; Peak acceleration of the forth movement; Peak deceleration of the forth movement) and one relevant spatial attribute (Vertical movement amplitude)
As expected, each tool was characterized by specific spatiotemporal parameters, even if these were slightly modified by the biomechanical constraints of each end-effector

Summary

Introduction

The manipulation-based approach is somewhat inconsistent with the frequent observation that individuals born without arms can use many tools with their feet in everyday life (e.g., eating with a fork) While this observation may be interpreted as evidence that manual dexterity is not a prerequisite for tool use, it could be argued that such atypical behavior results from idiosyncratic neural plasticity and/or extended practice using uncommon end-effectors. This suggests that, when an individual is born without arms, the tool-specific motor programs usually used by ordinary people to specify the hand-centered spatiotemporal parameters are ontogenetically recycled for the use of feet[12]. Our analyses focused on four classical kinematic landmarks[14,15] (Cycle duration; Maximum velocity of the forth movement; Peak acceleration of the forth movement; Peak deceleration of the forth movement) and one relevant spatial attribute (Vertical movement amplitude)

Methods

Results

Conclusion