Takahashi Chie, Azad Morteza, Rajasekaran Vijaykumar, Babič Jan, Mistry Michael
School of Computer Science, University of Birmingham, Birmingham, United Kingdom.
Edinburgh Centre for Robotics, School of Informatics, University of Edinburgh, Edinburgh, United Kingdom.
Front Neurosci. 2022 Jun 6;16:841901. doi: 10.3389/fnins.2022.841901. eCollection 2022.
Humans are capable of adjusting their posture stably when interacting with a compliant surface. Their whole-body motion can be modulated in order to respond to the environment and reach to a stable state. In perceiving an uncertain external force, humans repetitively push it and learn how to produce a stable state. Research in human motor control has led to the hypothesis that the central nervous system integrates an internal model with sensory feedback in order to generate accurate movements. However, how the brain understands external force through exploration movements, and how humans accurately estimate a force from their experience of the force, is yet to be fully understood. To address these questions, we tested human behaviour in different stiffness profiles even though the force at the goal was the same. We generated one linear and two non-linear stiffness profiles, which required the same force at the target but different forces half-way to the target; we then measured the differences in the learning performance at the target and the differences in perception at the half-way point. Human subjects learned the stiffness profile through repetitive movements in reaching the target, and then indicated their estimation of half of the target value (position and force separately). This experimental design enabled us to probe how perception of the force experienced in different profiles affects the participants' estimations. We observed that the early parts of the learning curves were different for the three stiffness profiles. Secondly, the position estimates were accurate independent of the stiffness profile. The estimation in position was most likely influenced by the external environment rather than the profile itself. Interestingly, although visual information about the target had a large influence, we observed significant differences in accuracy of force estimation according to the stiffness profile.
人类在与顺应性表面交互时能够稳定地调整姿势。他们的全身运动可以被调节以响应环境并达到稳定状态。在感知不确定的外力时，人类会反复推它并学习如何产生稳定状态。人类运动控制的研究提出了这样的假设：中枢神经系统将内部模型与感觉反馈相结合以产生准确的运动。然而，大脑如何通过探索运动来理解外力，以及人类如何根据对力的体验准确估计力，仍有待充分理解。为了解决这些问题，我们测试了人类在不同刚度分布下的行为，尽管目标处的力是相同的。我们生成了一种线性和两种非线性刚度分布，它们在目标处需要相同的力，但在到达目标的中途需要不同的力；然后我们测量了目标处学习性能的差异以及中途点感知的差异。人类受试者通过重复运动到达目标来学习刚度分布，然后分别指出他们对目标值一半（位置和力）的估计。这种实验设计使我们能够探究在不同分布中所经历的力的感知如何影响参与者的估计。我们观察到三种刚度分布的学习曲线的早期部分是不同的。其次，位置估计是准确的，与刚度分布无关。位置估计最有可能受外部环境而非分布本身的影响。有趣的是，尽管关于目标的视觉信息有很大影响，但我们观察到根据刚度分布，力估计的准确性存在显著差异。
