Reaching movements are subject to noise arising during the sensing, planning and execution phases of movement production, which contributes to movement variability. When vision of the moving hand is available, reaching variability appears to be strongly influenced by noise occurring during the specification and/or online updating of movement plans in visual coordinates. In contrast, when vision of the hand is unavailable, variability appears more dependent upon hand movement direction, suggesting a greater influence of execution noise. Given that execution noise acts in part at the muscular level, we hypothesized that reaching variability should depend not only on movement direction but initial arm posture as well. Moreover, given that the effects of execution noise are more apparent when movements are performed without vision of the hand, we reasoned that postural effects would be more evident when visual feedback was withheld. To test these hypotheses, subjects planned memory-guided reaching movements to three frontal plane targets, using either an 'adducted' or 'abducted' initial arm posture. Movements were then executed with and without hand vision. We found that the effects of initial arm posture on movement variability were idiosyncratic in both visual feedback conditions. In addition, without visual feedback, posture-dependent differences in variability varied with movement extent, growing abruptly larger in magnitude during the terminal phases of movement, and were moderately correlated with differences in mean endpoint positions. The results emphasize the role of factors other than noise (i.e. biomechanics and suboptimal sensorimotor integration) in constraining patterns of movement variability in 3D space.

中文翻译：

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姿势对手臂运动变异性的影响是特质的，并且依赖于反馈

到达动作易受动作产生的感测，计划和执行阶段产生的噪声的影响，这会导致动作变化。当有活动的手的视觉可用时，到达范围的可变性似乎受到在视觉坐标中的运动计划的指定和/或在线更新期间发生的噪声的强烈影响。相反，当手的视力不可用时，可变性似乎更依赖于手的移动方向，这表明执行噪声的影响更大。鉴于执行噪声部分地在肌肉水平上起作用，我们假设达到可变性不仅应取决于运动方向，而且还应取决于手臂的初始姿势。此外，如果在没有视力的情况下执行运动时执行噪声的影响更加明显，我们认为，如果不提供视觉反馈，则姿势效应会更加明显。为了检验这些假设，受试者计划使用“内收”或“外收”的初始手臂姿势，以记忆为指导，达到三个额叶平面目标的移动。然后在有或没有手视觉的情况下执行动作。我们发现，在两种视觉反馈条件下，初始手臂姿势对运动变异性的影响都是特质的。此外，在没有视觉反馈的情况下，与姿势有关的差异性随运动程度的不同而变化，在运动的末期阶段幅度突然增大，并且与平均终点位置的差异适度相关。结果强调了噪声以外因素的作用（即