Department of Biomedical Engineering, Marquette University and Medical College of Wisconsin, P.O. Box 1881, Milwaukee, WI, 53201-1881, USA.
Department of Neurology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
J Neuroeng Rehabil. 2022 Aug 17;19(1):90. doi: 10.1186/s12984-022-01060-0.
People with multiple sclerosis (PwMS) have balance deficits while ambulating through environments that contain moving objects or visual manipulations to perceived self-motion. However, their ability to parse object from self-movement has not been explored. The purpose of this research was to examine the effect of medial-lateral oscillations of the visual field and of objects within the scene on gait in PwMS and healthy age-matched controls using virtual reality (VR).
Fourteen PwMS (mean age 49 ± 11 years, functional gait assessment score of 27.8 ± 1.8, and Berg Balance scale score 54.7 ± 1.5) and eleven healthy controls (mean age: 53 ± 12 years) participated in this study. Dynamic balance control was assessed while participants walked on a treadmill at a self-selected speed while wearing a VR headset that projected an immersive forest scene. Visual conditions consisted of (1) no visual manipulations (speed-matched anterior/posterior optical flow), (2) 0.175 m mediolateral translational oscillations of the scene that consisted of low pairing (0.1 and 0.31 Hz) or (3) high pairing (0.15 and 0.465 Hz) frequencies, (4) 5 degree medial-lateral rotational oscillations of virtual trees at a low frequency pairing (0.1 and 0.31 Hz), and (5) a combination of the tree and scene movements in (3) and (4).
We found that both PwMS and controls exhibited greater instability and visuomotor entrainment to simulated mediolateral translation of the visual field (scene) during treadmill walking. This was demonstrated by significant (p < 0.05) increases in mean step width and variability and center of mass sway. Visuomotor entrainment was demonstrated by high coherence between center of mass sway and visual motion (magnitude square coherence = ~ 0.5 to 0.8). Only PwMS exhibited significantly greater instability (higher step width variability and center of mass sway) when objects moved within the scene (i.e., swaying trees).
Results suggest the presence of visual motion processing errors in PwMS that reduced dynamic stability. Specifically, object motion (via tree sway) was not effectively parsed from the observer's self-motion. Identifying this distinction between visual object motion and self-motion detection in MS provides insight regarding stability control in environments with excessive external movement, such as those encountered in daily life.
多发性硬化症（MS）患者在穿过包含移动物体或视觉运动以感知自身运动的环境时，存在平衡缺陷。然而，他们解析物体与自身运动的能力尚未得到探索。本研究的目的是使用虚拟现实（VR）检查 MS 患者和年龄匹配的健康对照组在视场的内外侧摆动和场景内的物体对步态的影响。
14 名 MS 患者（平均年龄 49±11 岁，功能步态评估评分为 27.8±1.8，伯格平衡量表评分为 54.7±1.5）和 11 名健康对照组（平均年龄：53±12 岁）参与了这项研究。参与者在跑步机上以自我选择的速度行走时，佩戴 VR 耳机，耳机投射出一个沉浸式森林场景，同时评估动态平衡控制。视觉条件包括（1）无视觉处理（速度匹配的前后光流），（2）场景的 0.175 米内外侧平移摆动，包括低频对（0.1 和 0.31Hz）或（3）高频对（0.15 和 0.465Hz），（4）低频对（0.1 和 0.31Hz）时虚拟树的 5 度内外侧旋转摆动，（5）（3）和（4）中树和场景运动的组合。
我们发现，MS 患者和对照组在跑步机行走时，对模拟视场（场景）的内外侧平移均表现出更大的不稳定性和视觉运动同步。这表现为平均步幅和变异性以及质心摆动的显著增加（p<0.05）。视觉运动同步表现为质心摆动与视觉运动之间的高相干性（幅度平方相干性=~0.5 至 0.8）。只有 MS 患者在场景中的物体移动时（即摆动的树木）表现出明显更大的不稳定性（更高的步幅变异性和质心摆动）。
结果表明，MS 患者存在视觉运动处理错误，降低了动态稳定性。具体来说，物体运动（通过树木摆动）不能有效地从观察者的自身运动中分离出来。在 MS 中识别这种视觉物体运动和自身运动检测之间的区别，可以深入了解在日常生活中遇到的具有过多外部运动的环境中的稳定性控制。
