Petreska Biljana, Billard Aude
Learning Algorithms and Systems Laboratory, Ecole Polytechnique Fédérale de Lausanne, EPFL-STI-I2S-LASA, Station 9, 1015, Lausanne, Switzerland.
Biol Cybern. 2009 May;100(5):331-50. doi: 10.1007/s00422-009-0300-2. Epub 2009 Apr 21.
Human motion studies have focused primarily on modeling straight point-to-point reaching movements. However, many goal-directed reaching movements, such as movements directed towards oneself, are not straight but rather follow highly curved trajectories. These movements are particularly interesting to study since they are essential in our everyday life, appear early in development and are routinely used to assess movement deficits following brain lesions. We argue that curved and straight-line reaching movements are generated by a unique neural controller and that the observed curvature of the movement is the result of an active control strategy that follows the geometry of one's body, for instance to avoid trajectories that would hit the body or yield postures close to the joint limits. We present a mathematical model that accounts for such an active control strategy and show that the model reproduces with high accuracy the kinematic features of human data during unconstrained reaching movements directed toward the head. The model consists of a nonlinear dynamical system with a single stable attractor at the target. Embodiment-related task constraints are expressed as a force field that acts on the dynamical system. Finally, we discuss the biological plausibility and neural correlates of the model's parameters and suggest that embodiment should be considered as a main cause for movement trajectory curvature.
人体运动研究主要集中在对直线点对点伸手动作进行建模。然而，许多目标导向的伸手动作，比如指向自身的动作，并非直线，而是沿着高度弯曲的轨迹。这些动作特别值得研究，因为它们在我们的日常生活中至关重要，在发育早期就出现，并且经常被用于评估脑损伤后的运动缺陷。我们认为，弯曲和直线伸手动作是由一个独特的神经控制器产生的，并且观察到的运动曲率是一种主动控制策略的结果，该策略遵循人体的几何形状，例如避免会撞到身体或产生接近关节极限姿势的轨迹。我们提出了一个数学模型来解释这种主动控制策略，并表明该模型在朝向头部的无约束伸手动作中能高精度地再现人体数据的运动学特征。该模型由一个在目标处具有单个稳定吸引子的非线性动力系统组成。与身体相关的任务约束被表示为作用于动力系统的力场。最后，我们讨论了该模型参数的生物学合理性和神经关联，并提出身体因素应被视为运动轨迹曲率的主要原因。
