School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona.
Mechanical and Aerospace Engineering, University of Central Florida, Orlando, Florida.
J Neurophysiol. 2023 Feb 1;129(2):380-391. doi: 10.1152/jn.00329.2022. Epub 2023 Jan 11.
The human sensorimotor system can adapt to various changes in the environmental dynamics by updating motor commands to improve performance after repeated exposure to the same task. However, the characteristics and mechanisms of the adaptation process remain unknown for dexterous manipulation, a unique motor task in which the body physically interacts with the environment with multiple effectors, i.e., digits, in parallel. We addressed this gap by using robotic manipulanda to investigate the changes in the digit force coordination following mechanical perturbation of an object held by tripod grasps. As the participants gradually adapted to lifting the object under perturbations, we quantified two components of digit force coordination. One is the direction-specific manipulation moment that directly counteracts the perturbation, whereas the other one is the direction-independent internal moment that supports the stability and stiffness of the grasp. We found that trial-to-trial improvement of task performance was associated with increased manipulation moment and a gradual decrease of the internal moment. These two moments were characterized by different rates of adaptation. We also examined how these two force coordination components respond to changes in perturbation directions. Importantly, we found that the manipulation moment was sensitive to the extent of repetitive exposure to the previous context that has an opposite perturbation direction, whereas the internal moment did not. However, the internal moment was sensitive to whether the postchange perturbation direction was previously experienced. Our results reveal, for the first time, that two distinct processes underlie the adaptation of multidigit force coordination for dexterous manipulation. Changes in digit force coordination in multidigit object manipulation were quantified with a novel experimental design in which human participants adapted to mechanical perturbations applied to the object. Our results show that the adaptation of digit force coordination can be characterized by two distinct components that operate at different timescales. We further show that these two components respond to changes in perturbation direction differently.
人类感觉运动系统可以通过更新运动指令来适应环境动力学的各种变化，从而提高在重复暴露于相同任务后的性能。然而，对于灵巧操作，即身体与环境通过多个效应器（即数字）并行进行物理交互的独特运动任务，其适应过程的特征和机制仍不清楚。我们使用机器人操纵器来解决这个差距，研究了在使用三脚架抓取器抓取的物体受到机械干扰后，数字力协调的变化。随着参与者逐渐适应在干扰下提起物体，我们量化了数字力协调的两个组成部分。一个是直接抵消干扰的方向特定操作力矩，另一个是支持抓握稳定性和刚度的方向独立内部力矩。我们发现，任务性能的逐次改进与操作力矩的增加以及内部力矩的逐渐减小有关。这两个力矩的适应速度不同。我们还研究了这两个力协调组件如何响应干扰方向的变化。重要的是，我们发现操作力矩对重复接触具有相反干扰方向的先前环境的程度敏感，而内部力矩则不敏感。然而，内部力矩对变化后的干扰方向是否以前经历过敏感。我们的研究结果首次揭示了在灵巧操作中，多数字力协调的适应由两个不同的过程支撑。通过一种新的实验设计，我们量化了多数字物体操作中数字力协调的变化，在该设计中，人类参与者适应施加在物体上的机械干扰。我们的结果表明，数字力协调的适应可以通过两个不同的组件来描述，这些组件在不同的时间尺度上运行。我们进一步表明，这两个组件对干扰方向的变化有不同的反应。
