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.

中文翻译：

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提高矢量强度和减少步态神经约束的垂直视点振荡的最佳频率和幅度

诱发称为矢量的自运动错觉对于改善虚拟环境 (VE) 中行走的感觉至关重要。在 VE 中将视点振荡添加到恒定的前向速度对于提高静态条件下的矢量强度非常有效。然而，跑步机行走条件下振荡频率和振幅对矢量强度的影响仍不清楚。此外，由于视觉运动牵引机制，如果设计不当，这些视觉振荡会影响步态模式，不利于实现自然行走。本研究的目的是确定垂直视点振荡的最佳频率和幅度，以提高矢量强度并减少步态限制。七名受试者在跑步机上行走，同时观看视觉场景。视觉场景呈现出等于跑步机速度的恒定前进速度，并添加了不同的垂直视点振荡。测试了具有不同频率和幅度组合的五种振荡模式。受试者对矢量强度进行口头评价。计算内侧 (ML) 压力中心 (CoP) 复杂性以指示步态限制。实验结束后，受试者被要求根据他们的步行经验给出最好和最差的振荡模式。振荡频率和振幅与矢量强度有很强的正相关性。ML CoP 复杂性在低频振荡下降低。中等振幅比小振幅和大振幅具有更大的 ML CoP 复杂性。此外，受试者更喜欢那些步态复杂性较大的振荡模式。我们建议首先选择具有最大 ML CoP 复杂度的振荡幅度以减少步态约束。然后，增加振荡频率以提高矢量强度，直至个人喜好或晕动病的边界。这些发现为促进 VE 中自然行走的感觉提供了重要指导。