Sobell Department, Institute of Neurology, University College London, 33 Queen Square, London, WC1N 3BG, UK.
Exp Brain Res. 2010 Apr;202(1):181-8. doi: 10.1007/s00221-009-2125-6. Epub 2009 Dec 29.
Stepping down at a change of height is a fundamental part of human locomotion. At a novel step, this requires the transformation of visual information about a depth change into a stepping movement of appropriate size. However, little is known about this process or its development. We studied adults, 3- and 4-year-old children stepping down a single stair of variable height. We assessed how well stepping down was scaled to stair height using several kinematic measures. Of these, 'kneedrop' and 'toedrop' describe how far the leg has descended by the time it begins to 'swing in' in preparation for landing; and 'toeheight (speedpeak)' describes where the toe begins to decelerate. If visually controlled, their values should scale to the height of the stair. Under normal visual conditions, children scaled these movements to stair height as well as adults. In a second condition, participants closed their eyes just before stepping down to remove visual feedback during the step. Adults' steps were barely affected. For 4-year olds, only toeheight (speedpeak) decreased. For 3-year olds, both toedrop and toeheight (speedpeak) scaled less well to stair height than normal. The results suggest that visuomotor processes for fine-tuned stepping control develop remarkably early, but are initially dependent on visual feedback.
下台阶是人类行走的基本动作。在迈出新的一步时，这需要将关于深度变化的视觉信息转化为适当大小的台阶动作。然而，对于这个过程或其发展，我们知之甚少。我们研究了成年人和 3 至 4 岁的儿童下不同高度的单个台阶。我们使用了几种运动学测量方法来评估下台阶动作与台阶高度的匹配程度。其中，“屈膝下降”和“脚尖下降”描述了腿在开始“摆动”准备落地之前下降的距离；“脚尖高度（速度峰值）”描述了脚尖开始减速的位置。如果是受视觉控制的，那么这些值应该与台阶的高度成比例。在正常的视觉条件下，儿童和成年人一样，根据台阶的高度调整这些动作。在第二种情况下，参与者在下台阶前闭上眼睛，以在台阶上行走时消除视觉反馈。成年人的脚步几乎没有受到影响。对于 4 岁的儿童，只有脚尖高度（速度峰值）降低了。对于 3 岁的儿童，脚尖下降和脚尖高度（速度峰值）与台阶高度的匹配程度都不如正常情况下那么好。研究结果表明，精细的踏台控制的视觉运动过程发展得非常早，但最初依赖于视觉反馈。
