Wang Wei, Yang Kaiming, Zhu Yu
Beijing Key Laboratory of Precision and Ultra-Precision Manufacturing Equipment and Control, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
Entropy (Basel). 2021 Apr 28;23(5):541. doi: 10.3390/e23050541.
Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.
诱发被称为自运动错觉的视动现象对于改善在虚拟环境（VE）中的行走感觉至关重要。在VE中，在恒定的向前速度上叠加视点振荡对于在静态条件下提高视动强度是有效的。然而，在跑步机行走条件下，振荡频率和振幅对视动强度的影响仍不清楚。此外，由于视运动夹带机制，如果设计不当，这些视觉振荡会影响步态模式并对实现自然行走产生不利影响。本研究旨在确定垂直视点振荡的最佳频率和振幅，以提高视动强度并减少步态限制。七名受试者在跑步机上行走时观看视觉场景。视觉场景呈现出与跑步机速度相等的恒定向前速度，并添加了不同的垂直视点振荡。测试了五种频率和振幅不同组合的振荡模式。受试者对视动强度进行口头评分。计算左右（M-L）压力中心（CoP）的复杂度以指示步态限制。实验结束后，要求受试者根据他们的行走体验给出最佳和最差的振荡模式。振荡频率和振幅与视动强度呈强正相关。在低频振荡下，M-L CoP复杂度降低。中等振荡幅度的M-L CoP复杂度大于小幅度和大幅度。此外，受试者更喜欢那些步态复杂度高的振荡模式。我们建议首先应选择M-L CoP复杂度最大的振荡幅度以减少步态限制。然后，增加振荡频率以提高视动强度，直到达到个人偏好或晕动病的界限。这些发现为促进在VE中自然行走的感觉提供了重要指导。
