Mangalam Madhur, Yarossi Mathew, Furmanek Mariusz P, Tunik Eugene
Department of Physical Therapy, Movement and Rehabilitation Sciences, Northeastern University, Boston, MA, 02115, USA.
Department of Electrical and Computer Engineering, Northeastern University, Boston, MA, 02115, USA.
Exp Brain Res. 2021 May;239(5):1651-1665. doi: 10.1007/s00221-021-06079-8. Epub 2021 Mar 28.
Virtual reality (VR) has garnered much interest as a training environment for motor skill acquisition, including for neurological rehabilitation of upper extremities. While the focus has been on gross upper limb motion, VR applications that involve reaching for, and interacting with, virtual objects are growing. The absence of true haptics in VR when it comes to hand-object interactions raises a fundamentally important question: can haptic-free immersive virtual environments (hf-VEs) support naturalistic coordination of reach-to-grasp movements? This issue has been grossly understudied, and yet is of significant importance in the development and application of VR across a number of sectors. In a previous study (Furmanek et al., J Neuroeng Rehabil 16:78, 2019), we reported that reach-to-grasp movements are similarly coordinated in both the physical environment (PE) and hf-VE. The most noteworthy difference was that the closure phase-which begins at maximum aperture and lasts through the end of the movement-was longer in hf-VE than in PE, suggesting that different control laws might govern the initiation of closure between the two environments. To do so, we reanalyzed data from Furmanek et al. (J Neuroeng Rehabil 16:78, 2019), in which the participants reached to grasp three differently sized physical objects, and matching 3D virtual object renderings, placed at three different locations. Our analysis revealed two key findings pertaining to the initiation of closure in PE and hf-VE. First, the respective control laws governing the initiation of aperture closure in PE and hf-VE both included state estimates of transport velocity and acceleration, supporting a general unified control policy for implementing reach-to-grasp across physical and virtual environments. Second, the aperture was less informative to the control law in hf-VE. We suggest that the latter was likely because transport velocity at closure onset and aperture at closure onset were less independent in hf-VE than in PE, ultimately resulting in an aperture at closure onset having a weaker influence on the initiation of closure. In this way, the excess time and muscular effort needed to actively bring the fingers to a stop at the interface of a virtual object was factored into the control law governing the initiation of closure in hf-VE. Critically, this control law remained applicable, albeit with different weights in hf-VE, despite the absence of terminal haptic feedback and potential perceptual differences.
虚拟现实（VR）作为一种用于运动技能习得的训练环境已引起广泛关注，包括用于上肢的神经康复。虽然重点一直放在上肢的整体运动上，但涉及伸手抓取和与虚拟物体交互的VR应用正在不断增加。在手部与物体交互方面，VR缺乏真正的触觉，这引发了一个根本性的重要问题：无触觉的沉浸式虚拟环境（hf-VE）能否支持自然的伸手抓取动作协调？这个问题一直未得到充分研究，但在VR跨多个领域的开发和应用中却至关重要。在之前的一项研究（Furmanek等人，《神经工程与康复》16:78，2019）中，我们报告称，在物理环境（PE）和hf-VE中，伸手抓取动作的协调方式相似。最值得注意的差异是，闭合阶段（从最大孔径开始，持续到动作结束）在hf-VE中比在PE中更长，这表明在这两种环境中，可能有不同的控制规律来支配闭合动作的起始。为此，我们重新分析了Furmanek等人（《神经工程与康复》16:78，2019）的数据，在该研究中，参与者伸手抓取放置在三个不同位置的三个不同大小的物理物体以及匹配的3D虚拟物体渲染图。我们的分析揭示了与PE和hf-VE中闭合动作起始有关的两个关键发现。第一，在PE和hf-VE中，支配孔径闭合起始的各自控制规律都包括对运输速度和加速度的状态估计，这支持了一种在物理和虚拟环境中实施伸手抓取动作的通用统一控制策略。第二，在hf-VE中，孔径对控制规律的信息量较少。我们认为，后者可能是因为在hf-VE中，闭合起始时的运输速度和闭合起始时的孔径比在PE中关联性更小，最终导致闭合起始时的孔径对闭合起始的影响较弱。这样一来，在虚拟物体界面主动使手指停止所需的额外时间和肌肉努力就被纳入了hf-VE中支配闭合起始的控制规律。至关重要的是，尽管缺乏终端触觉反馈和潜在的感知差异，但这个控制规律在hf-VE中仍然适用，只是权重不同。
