van Donkelaar P, Franks I M
Human Performance and Motor Control Laboratory, University of British Columbia, Vancouver, Canada.
Exp Brain Res. 1991;83(3):618-32. doi: 10.1007/BF00229840.
If movement control is afforded through the advance planning, or preprogramming, of upcoming actions, then one of the behavioral outcomes should be an increase in reaction time (RT) as the movement becomes more complex. In some situations, however, RT does not increase across levels of complexity, rather it remains invariant. In these cases, on-line preparation is typically inferred. That is, the sequence is said to be prepared in parts throughout the movement, as opposed to entirely beforehand. Given that there is some planning occurring during the sequence, then evidence of this process should be apparent within the movement itself. Three such dependent variables appear to provide such evidence. Specifically, the number of times the underlying accelerations cross the zero line within the movement, the number of 'significant deviations' within the acceleration trace, and the length of time for which the muscles are active (as measured by EMG) in relation to the duration of the movement. In the present experiment, then, these variables were measured in addition to the time required to prepare and initiate a movement performed under conditions conducive to either preprogramming or online preparation. Specifically, the movements were either completed as fast as possible, or at a considerably slower, more controlled speed. Each of the dependent variables displayed evidence of preprogramming in the movements completed at the fast velocity, and on-line preparation in the slower paced movements. Thus, in the slow condition, subjects appeared to rely more heavily on on-line prepared adjustments to produce an accurate outcome. The convergence attained between the various dependent measures lends power to the conclusions regarding hypothesized modes of control within the different speeds of movement.
如果动作控制是通过对即将发生的动作进行预先规划或预编程来实现的，那么行为结果之一应该是随着动作变得更加复杂，反应时间（RT）会增加。然而，在某些情况下，RT并不会随着复杂度的增加而增加，而是保持不变。在这些情况下，通常推断存在在线准备。也就是说，序列被认为是在整个动作过程中逐步准备的，而不是完全提前准备。鉴于在序列执行过程中会进行一些规划，那么这一过程的证据应该在动作本身中显现出来。有三个这样的因变量似乎能提供这样的证据。具体来说，是动作中潜在加速度穿过零线的次数、加速度轨迹内“显著偏差”的数量，以及肌肉活动的时长（通过肌电图测量）与动作持续时间的关系。在本实验中，除了测量在有利于预编程或在线准备的条件下准备和启动一个动作所需的时间外，还对这些变量进行了测量。具体而言，动作要么尽可能快地完成，要么以相当慢、更可控的速度完成。每个因变量在快速完成的动作中都显示出预编程的证据，在较慢节奏的动作中则显示出在线准备的证据。因此，在慢速条件下，受试者似乎更依赖在线准备的调整来产生准确的结果。不同因变量测量结果之间的一致性，为关于不同动作速度下假设控制模式的结论提供了有力支持。
