Liebermann Dario G, Krasovsky Tal, Berman Sigal
Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Israel.
J Mot Behav. 2008 Nov;40(6):516-31. doi: 10.3200/JMBR.40.6.516-531.
The article characterizes hand paths and speed profiles for movements performed in a nonplanar, 2-dimensional workspace (a hemisphere of constant curvature). The authors assessed endpoint kinematics (i.e., paths and speeds) under the minimum-jerk model assumptions and calculated minimal amplitude paths (geodesics) and the corresponding speed profiles. The authors also calculated hand speeds using the 2/3 power law. They then compared modeled results with the empirical observations. In all, 10 participants moved their hands forward and backward from a common starting position toward 3 targets located within a hemispheric workspace of small or large curvature. Comparisons of modeled observed differences using 2-way RM-ANOVAs showed that movement direction had no clear influence on hand kinetics (p < .05). Workspace curvature affected the hand paths, which seldom followed geodesic lines. Constraining the paths to different curvatures did not affect the hand speed profiles. Minimum-jerk speed profiles closely matched the observations and were superior to those predicted by 2/3 power law (p < .001). The authors conclude that speed and path cannot be unambiguously linked under the minimum-jerk assumption when individuals move the hand in a nonplanar 2-dimensional workspace. In such a case, the hands do not follow geodesic paths, but they preserve the speed profile, regardless of the geometric features of the workspace.
本文描述了在非平面二维工作空间（恒定曲率的半球体）中执行运动时的手部轨迹和速度分布。作者在最小急动模型假设下评估了端点运动学（即轨迹和速度），并计算了最小幅度轨迹（测地线）和相应的速度分布。作者还使用2/3幂定律计算了手部速度。然后，他们将模型结果与实证观察结果进行了比较。共有10名参与者将手从一个共同的起始位置向前和向后移动，朝向位于小曲率或大曲率半球形工作空间内的3个目标。使用双向重复测量方差分析对模型观察到的差异进行比较表明，运动方向对手部动力学没有明显影响（p < 0.05）。工作空间曲率影响手部轨迹，手部轨迹很少遵循测地线。将轨迹限制在不同曲率下并不影响手部速度分布。最小急动速度分布与观察结果紧密匹配，并且优于2/3幂定律预测的结果（p < 0.001）。作者得出结论，当个体在非平面二维工作空间中移动手部时，在最小急动假设下，速度和轨迹不能明确关联。在这种情况下，手部不遵循测地线路径，但无论工作空间的几何特征如何，它们都保持速度分布。
