虽然无约束运动的研究揭示了神经控制的重要特征,将这些见解推广到更复杂的对象操纵是具有挑战性的。人类擅长与物体的物理互动,即使这些对象引入复杂的动力学和运动学约束。这项研究检查了人类以他们喜欢的和三个指示的速度(带有视觉反馈)转动水平平面曲柄(半径10.29厘米),在顺时针和逆时针方向。探讨神经力学动力学的作用,指示的速度涵盖了很宽的范围:快速(接近性能极限),中等(接近首选速度),和非常慢(渲染动态效果可以忽略不计)。因为运动学受限的运动涉及重要的物理相互作用,从生物力学的影响中解开神经控制是一个挑战。为了解决这个问题,我们对交互动力学进行建模,以从观察到的力和运动学数据中“减去”外围生物力学,从而估计可能以运动表示的潜在神经动作的各个方面。我们证明了这种方法的价值:值得注意的是,一条近似椭圆形的路径出现了,速度最小值与曲率最大值一致,类似于在不受约束的运动中看到的,即使手以几乎恒定的速度沿着恒定的曲率路径移动。这些发现表明神经控制器利用外围生物力学来简化物理相互作用。因此,即使物理相互作用阻止了它们在手运动学中的表达,在不受约束的运动中看到的模式也会持续存在。速度-曲率关系的重新出现表明这是应该的,至少在某种程度上,强调平滑性和可预测性的神经过程。新的和注意身体与运动学约束的相互作用在日常行为中是司空见惯的。我们报告了一项关于人类转动曲柄的研究,施加恒定手路径曲率的圆形约束,因此应抑制手速的变化,这是由于广泛报道的无约束运动的幂律速度-曲率关系。值得注意的是,我们发现,当外周生物力学因素被去除时,速度-曲率关系再次出现,表明它是,至少在某种程度上,神经起源。
While the study of unconstrained movements has revealed important features of neural control, generalizing those insights to more sophisticated object manipulation is challenging. Humans excel at physical interaction with objects, even when those objects introduce complex dynamics and kinematic constraints. This study examined humans turning a horizontal planar crank (radius 10.29 cm) at their preferred and three instructed speeds (with visual feedback), both in clockwise and counterclockwise directions. To explore the role of neuromechanical dynamics, the instructed speeds covered a wide range: fast (near the limits of performance), medium (near preferred speed), and very slow (rendering dynamic effects negligible). Because kinematically constrained movements involve significant physical interaction, disentangling neural control from the influences of biomechanics presents a challenge. To address it, we modeled the interactive dynamics to \"subtract off\" peripheral biomechanics from observed force and kinematic data, thereby estimating aspects of underlying neural action that may be expressed in terms of motion. We demonstrate the value of this method: remarkably, an approximately elliptical path emerged, and speed minima coincided with curvature maxima, similar to what is seen in unconstrained movements, even though the hand moved at nearly constant speed along a constant-curvature path. These findings suggest that the neural controller takes advantage of peripheral biomechanics to simplify physical interaction. As a result, patterns seen in unconstrained movements persist even when physical interaction prevents their expression in hand kinematics. The reemergence of a speed-curvature relation indicates that it is due, at least in part, to neural processes that emphasize smoothness and predictability.NEW & NOTEWORTHY Physically interacting with kinematic constraints is commonplace in everyday actions. We report a study of humans turning a crank, a circular constraint that imposes constant hand path curvature and hence should suppress variations of hand speed due to the power-law speed-curvature relation widely reported for unconstrained motions. Remarkably, we found that, when peripheral biomechanical factors are removed, a speed-curvature relation reemerges, indicating that it is, at least in part, of neural origin.