Lackner J R, Rabin E, DiZio P
Ashton Graybiel Spatial Orientation Laboratory and Volen Center for Complex Systems, Brandeis University, Waltham, MA 02454-9110, USA.
Exp Brain Res. 2001 Aug;139(4):454-64. doi: 10.1007/s002210100775.
Light touch of the index finger with a stationary surface at non-mechanically supportive force levels (<100 g) greatly attenuates the body sway of standing subjects. In three experiments, we evaluated the properties of finger contact and of the contacted object necessary to produce postural stabilization in subjects standing heel-to-toe with eyes closed, as well as how accurately hand position can be controlled. Experiment 1 involved finger contact with flexible filaments of different bending strengths, a flat surface, and an imagined spatial position. Contact with the flat surface was most effective in attenuating sway; the flexible filaments were much less effective but still significantly better than imagined contact. Experiment 2 compared the effectiveness of finger contact with a flexible filament, a rigid filament of the same diameter, a flat surface, and an imagined spatial position. The rigid filament and flat surface conditions were equally effective in attenuating body sway and were greatly superior to contact with the flexible filament, which was superior to imagined contact. Experiment 3 included five conditions: arms by sides; finger "contact" with an imagined spatial position; finger contact with a flat surface; finger contact with a flexible filament attempting to maintain it bent; and contact with the flexible filament attempting not to bend it. The arms by sides and finger "contact" with an imagined position conditions did not differ significantly; all three conditions involving actual finger contact showed significantly less center of pressure and hand sway, but contact with the flat surface was most effective in attenuating both postural and hand displacement. In all three experiments, the level of force applied in fingertip contact conditions was far below that necessary to provide mechanical stabilization. Our findings indicate that: (1) stimulation of a small number of receptors in the fingertip is adequate to allow stabilization of sway, (2) fingertip force levels as low as 5-10 g provide some stabilization, (3) contact with a stationary spatial referent is most effective, and (4) independent control of arm and torso occurs when finger contact is allowed.
在非机械支撑力水平（<100克）下，食指与固定表面的轻轻触碰能极大地减弱站立受试者的身体摇摆。在三个实验中，我们评估了在闭眼脚跟对脚尖站立的受试者中产生姿势稳定所需的手指接触和被接触物体的特性，以及手部位置能被控制的精确程度。实验1涉及手指与不同弯曲强度的柔性细丝、平面以及想象中的空间位置的接触。与平面的接触在减弱摇摆方面最有效；柔性细丝的效果要差得多，但仍明显优于想象中的接触。实验2比较了手指与柔性细丝、相同直径的刚性细丝、平面以及想象中的空间位置接触的效果。刚性细丝和平面对减弱身体摇摆的效果相同，且都大大优于与柔性细丝的接触，而柔性细丝又优于想象中的接触。实验3包括五个条件：双臂垂于身体两侧；手指“接触”想象中的空间位置；手指接触平面；手指接触柔性细丝并试图使其弯曲；以及接触柔性细丝并试图不让其弯曲。双臂垂于身体两侧和手指“接触”想象位置的条件没有显著差异；所有涉及实际手指接触的三个条件下，压力中心和手部摇摆都明显更小，但与平面的接触在减弱姿势和手部位移方面最有效。在所有三个实验中，指尖接触条件下施加的力水平远低于提供机械稳定所需的力水平。我们的研究结果表明：（1）刺激指尖的少量感受器就足以实现摇摆的稳定，（2）低至5 - 10克的指尖力水平就能提供一定的稳定作用，（3）与固定的空间参考物接触最有效，（4）当允许手指接触时，手臂和躯干能独立控制。
