Amblard B, Crémieux J, Marchand A R, Carblanc A
Exp Brain Res. 1985;61(1):21-37. doi: 10.1007/BF00235617.
The differential contributions of static versus dynamic visual cues to postural control were studied in human subjects. Lateral body oscillations were measured with accelerometers located at head, hips and ankle levels, while subjects righted their balance under various mechanical conditions: on either a soft (foam rubber) support or a hard one, and in either the classical or the sharpened Romberg stance. The visual pattern (horizontal or vertical rectangular grating) was illuminated with either a stroboscopic bulb or a normal one, and control measurements were also taken in darkness for each mechanical condition. Acceleration signals were processed into their frequency power spectra, the mean area and shape of which were taken to characterize the postural skills involved and the effects of either the visual suppressions or the mechanical destabilizations. Although dynamic visual cues have already been found to play a major role in the control of lateral body sway (Amblard and Crémieux 1976), we demonstrate here that static visual cues, the only ones available under stroboscopic illumination, also make a clear though minor contribution. Hence we suggest the existence of two modes of visual control of lateral balance in man, which are well separated in terms of the frequency range of body sway: the first mechanism, which operates below 2 Hz and is strobe-resistant, seems to control the orientation of the upper part of the body; the second mechanism, which operates above 4 Hz, centers on about 7 Hz and is strobe-vulnerable, seems to immobilize the body working upwards from the feet. Thus static visual cues may slowly control re-orientation or displacement, whereas dynamic visual cues may contribute to fast stabilization of the body. In between the frequency ranges at which these two visuomotor mechanisms come into play, at about 3 Hz, there is what we call a "blind frequency", a visually neutral sway frequency which may arise from the incompatibility of visual reorientation with visual stabilization, and where vision appears unable to reduce postural sway to any marked extent. Transmission of the destabilization produced by suppression of visual cues or by mechanical methods from one anatomical level to another is also briefly discussed in terms of bio-mechanical constraints, and the correlations between various pairs of levels are considered.
研究了静态与动态视觉线索对人体姿势控制的不同贡献。使用位于头部、臀部和脚踝水平的加速度计测量身体的横向摆动，同时让受试者在各种机械条件下恢复平衡：在软（泡沫橡胶）支撑或硬支撑上，以及在经典或锐化的罗姆伯格姿势下。视觉图案（水平或垂直矩形光栅）用频闪灯泡或普通灯泡照亮，并且在每种机械条件下也在黑暗中进行对照测量。加速度信号被处理成其频率功率谱，其平均面积和形状被用来表征所涉及的姿势技能以及视觉抑制或机械不稳定的影响。尽管已经发现动态视觉线索在控制身体横向摆动中起主要作用（安布拉德和克雷米厄，1976年），但我们在此证明，在频闪照明下唯一可用的静态视觉线索也做出了明显但较小的贡献。因此，我们认为人类存在两种横向平衡视觉控制模式，就身体摆动的频率范围而言，它们有明显区分：第一种机制在2赫兹以下起作用且抗频闪，似乎控制身体上部的方向；第二种机制在4赫兹以上起作用，以约7赫兹为中心且易受频闪影响，似乎从脚部向上使身体保持稳定。因此，静态视觉线索可能缓慢控制重新定向或位移，而动态视觉线索可能有助于身体的快速稳定。在这两种视觉运动机制起作用的频率范围之间，约3赫兹处存在我们所谓的“盲频”，即视觉中性摆动频率，它可能源于视觉重新定向与视觉稳定的不兼容性，并且在该频率下视觉似乎无法在任何显著程度上减少姿势摆动。还根据生物力学限制简要讨论了通过抑制视觉线索或通过机械方法产生的不稳定从一个解剖水平传递到另一个解剖水平的情况，并考虑了各对水平之间的相关性。
