Department of Mechanical Engineering, Polytechnique Montreal, Montreal, Quebec, Canada.
Department of Biomedical Engineering, McGill University, Montreal, Quebec, Canada.
J Neurophysiol. 2022 Apr 1;127(4):1159-1170. doi: 10.1152/jn.00283.2021. Epub 2022 Mar 30.
Human upright balance is maintained through feedback mechanisms that use a variety of sensory modalities. Vision senses information about the position and velocity of the visual surround motion to improve balance by reducing the sway evoked by external disturbances. This study characterized the effects of visual information on human anterior-posterior body sway in upright stance by presenting perturbations through a virtual reality system. This made it possible to use a new visual perturbation signal, based on trapezoidal velocity pulses, whose amplitude and velocity could be controlled separately. To date, the influences of visual field position and velocity have only been studied independently due to the experimental limitations. The hip displacement, ankle torques, shank angles, and surface EMGs of four major ankle muscles were measured bilaterally as outputs. We found that the root mean square (RMS) hip displacement (body angle) increased systematically with visual input amplitude. However, for each amplitude, the RMS body angle increased when input velocity was changed from 2 to 5 degrees per second (dps) and then decreased from 5 to 10 dps. Spectral analysis was used to compute frequency response over a frequency range from 0.04 to 0.6 Hz. The gain of body sway relative to the perturbation increased with frequency, whereas the coherence declined. Moreover, as the stimulus amplitude increased, the gain generally decreased, whereas the mean coherence values always increased. The mean gains and mean coherence values were greatest for the velocity of 5 dps. This study presents a novel experimental approach to study human postural control and augments our knowledge of how visual information is processed in the central nervous system to maintain balance. In this paper, we developed a new methodological approach to study the effects of visual information on dynamic body sway. We used VR to apply visual perturbations to induce AP body sway. We designed a new visual stimulus waveform based on trapezoidal velocity pulses whose peak-to-peak amplitude and velocity could be modulated independently. Subsequently, we investigated how the amplitude and velocity of visual field motion influence the postural responses evoked in healthy adults.
人类的直立平衡是通过使用多种感觉模式的反馈机制来维持的。视觉感知有关视觉环境运动的位置和速度的信息，通过减少外部干扰引起的摆动来改善平衡。本研究通过虚拟现实系统呈现扰动，来描述视觉信息对人体直立姿势前后方向身体摆动的影响。这使得基于梯形速度脉冲的新视觉扰动信号成为可能，该信号的幅度和速度可以单独控制。迄今为止，由于实验限制，仅独立研究了视野位置和速度的影响。作为输出，双侧测量了髋关节位移、踝关节转矩、小腿角度和四个主要踝关节肌肉的表面肌电图。我们发现，均方根（RMS）髋关节位移（身体角度）随着视觉输入幅度的增加而系统增加。然而，对于每个幅度，当输入速度从 2 到 5 度每秒（dps）变化时，RMS 身体角度增加，然后从 5 到 10 dps 减少。频谱分析用于计算从 0.04 到 0.6 Hz 的频率范围内的频率响应。相对于扰动，身体摆动的增益随频率增加而增加，而相干性降低。此外，随着刺激幅度的增加，增益通常降低，而平均相干值总是增加。对于 5 dps 的速度，平均增益和平均相干值最大。本研究提出了一种新的实验方法来研究人体姿势控制，并增加了我们对视觉信息在中枢神经系统中如何处理以维持平衡的认识。在本文中，我们开发了一种新的方法学方法来研究视觉信息对动态身体摆动的影响。我们使用 VR 来施加视觉扰动以引起 AP 身体摆动。我们设计了一种基于梯形速度脉冲的新视觉刺激波形，其峰峰值幅度和速度可以独立调节。随后，我们研究了视场运动的幅度和速度如何影响健康成年人引起的姿势反应。
