Laboratory of Neuromotor Physiology, Santa Lucia Foundation, Rome, Italy.
J Neurophysiol. 2010 Mar;103(3):1673-84. doi: 10.1152/jn.00945.2009. Epub 2010 Jan 20.
In adults, locomotor movements are accommodated to various support surface conditions by means of specific anticipatory locomotor adjustments and changes in the intersegmental coordination. Here we studied the kinematic strategies of toddlers at the onset of independent walking when negotiating various support surface conditions: stepping over an obstacle, walking on an inclined surface, and on a staircase. Generally, toddlers could perform these tasks only when supported by the arm. They exhibited strategies very different from those of the adults. Although adults maintained walking speed roughly constant, toddlers markedly accelerated when walking downhill or downstairs and decelerated when walking uphill or upstairs. Their coordination pattern of thigh-shank-foot elevation angles exhibited greater inter-trial variability than that in adults, but it did not undergo the systematic change as a function of task that was present in adults. Thus the intersegmental covariance plane rotated across tasks in adults, whereas its orientation remained roughly constant in toddlers. In contrast with the adults, the toddlers often tended to place the foot onto the obstacle or across the edges of the stairs. We interpret such foot placements as part of a haptic exploratory repertoire and we argue that the maintenance of a roughly constant planar covariance--irrespective of the surface inclination and height--may be functional to the exploratory behavior. The latter notion is consistent with the hypothesis proposed decades ago by Bernstein that, when humans start to learn a skill, they may restrict the number of degrees of freedom to reduce the size of the search space and simplify the coordination.
在成年人中，通过特定的预期运动调整和节段间协调的变化，运动适应各种支撑面条件。在这里，我们研究了幼儿在开始独立行走时在各种支撑面条件下的运动策略：跨过障碍物、在倾斜表面上行走和在楼梯上行走。通常，幼儿只有在手臂支撑的情况下才能完成这些任务。他们表现出的策略与成年人非常不同。尽管成年人保持行走速度大致不变，但幼儿在下坡或下楼时明显加速，在上坡或上楼时减速。他们的大腿-小腿-脚抬高角度的协调模式表现出比成年人更大的试验间可变性，但不像成年人那样随着任务的变化而发生系统变化。因此，成年人的节段间协方差平面在任务之间旋转，而幼儿的协方差平面的方向大致保持不变。与成年人相比，幼儿经常倾向于将脚放在障碍物上或放在楼梯的边缘。我们将这种脚部放置解释为触觉探索行为的一部分，并且我们认为，无论表面倾斜度和高度如何，大致恒定的平面协方差的维持可能对探索行为是有用的。这个概念与 Bernstein 几十年前提出的假设是一致的，即当人类开始学习一项技能时，他们可能会限制自由度的数量，以减少搜索空间的大小并简化协调。
