Department of Biomedical Engineering, University of Southern California, 1042 Downey Way, DRB 140, Los Angeles, CA 90089, USA.
Neuroscience. 2013 Feb 12;231:61-9. doi: 10.1016/j.neuroscience.2012.11.043. Epub 2012 Dec 2.
We tested a hypothesis that the classical relation between movement time and index of difficulty (ID) in quick pointing action (Fitts' Law) reflects processes at the level of motor planning. Healthy subjects stood on a force platform and performed quick and accurate hand movements into targets of different size located at two distances. The movements were associated with early postural adjustments that are assumed to reflect motor planning processes. The short distance did not require trunk rotation, while the long distance did. As a result, movements over the long distance were associated with substantial Coriolis forces. Movement kinematics and contact forces and moments recorded by the platform were studied. Movement time scaled with ID for both movements. However, the data could not be fitted with a single regression: Movements over the long distance had a larger intercept corresponding to movement times about 140 ms longer than movements over the shorter distance. The magnitude of postural adjustments prior to movement initiation scaled with ID for both short and long distances. Our results provide strong support for the hypothesis that Fitts' Law emerges at the level of motor planning, not at the level of corrections of ongoing movements. They show that, during natural movements, changes in movement distance may lead to changes in the relation between movement time and ID, for example when the contribution of different body segments to the movement varies and when the action of Coriolis force may require an additional correction of the movement trajectory.
我们检验了一个假设，即在快速指向动作（菲茨定律）中，运动时间与难度指数（ID）之间的经典关系反映了运动规划层面的过程。健康受试者站在力台上，进行快速准确的手部动作，进入位于两个距离的不同大小的目标。这些动作与早期姿势调整有关，这些调整被认为反映了运动规划过程。短距离不需要躯干旋转，而长距离则需要。因此，长距离的运动与相当大的科里奥利力有关。研究了平台记录的运动动力学和接触力和力矩。两种运动的运动时间都与 ID 成比例。然而，数据不能用单个回归拟合：长距离运动的截距较大，对应的运动时间比短距离运动长约 140 毫秒。运动起始前的姿势调整幅度与短距离和长距离的 ID 成比例。我们的结果为菲茨定律在运动规划层面而不是在正在进行的运动的校正层面出现的假设提供了强有力的支持。它们表明，在自然运动中，运动距离的变化可能导致运动时间和 ID 之间的关系发生变化，例如当不同身体部位对运动的贡献发生变化时，或者当科里奥利力的作用可能需要对运动轨迹进行额外校正时。
