Laboratoire d'Etude des Mécanismes Cognitifs, Université de Lyon, 5, avenue Pierre Mendès-France, 69676, Bron Cedex, France.
Institut Universitaire de France, 103, Boulevard Saint-Michel, 75005, Paris, France.
Sci Rep. 2018 Jul 11;8(1):10429. doi: 10.1038/s41598-018-28759-2.
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.
对于大多数人来说，人类工具的使用与手的灵巧性是密不可分的。这种民间信念在科学家当中也很普遍。在这种观点中，人类工具的使用是基于手部与工具相互作用的运动程序，这意味着使用手以外的末端效应器应该会产生运动控制困难（例如，无法随着时间的推移再现特定的工具使用动作），因为这些所谓的程序特征化了手部运动的时空参数，但不是其他末端效应器的。为了验证这一点，我们要求参与者使用四个末端效应器（即右脚、右肘、左手和右手）执行三个工具使用动作（例如，钉钉子）。我们表明，参与者不仅自发有效地执行了工具使用动作，而且关键是在末端效应器之间保持了工具的时空参数不变。这种现象我们称之为多灵巧性，与认为大脑为工具使用存储以手为中心的运动程序的观点相悖。多灵巧性与这样一种观点是一致的，即一旦形成了心理上的工具使用动作，通用的运动程序就可以应用于各种末端效应器。与通常的进化观点相反，我们的发现支持了这样一种观点，即在进化过程中，手的灵巧性是在工具使用技能之后出现的。
