Kinesiology Program, School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ, 85004, USA,
Exp Brain Res. 2014 Feb;232(2):575-86. doi: 10.1007/s00221-013-3766-z. Epub 2013 Nov 21.
Directional preferences have previously been demonstrated during horizontal arm movements. These preferences were characterized by a tendency to exploit interaction torques for movement production at the shoulder or elbow, indicating that the preferred directions depend on biomechanical, and not on visual perception-based factors. We directly tested this hypothesis by systematically dissociating visual information from arm biomechanics. Sixteen subjects performed a free-stroke drawing task that required performance of fast strokes from the circle center toward the perimeter, while selecting stroke directions in a random order. Hand position was represented by a cursor displayed in the movement plane. The free-stroke drawing was performed twice, before and after visuomotor adaptation to a 30° clockwise rotation of the perceived hand path. The adaptation was achieved during practicing pointing movements to eight center-out targets. Directional preferences during performance of the free-stroke drawing task were revealed in ten out of the sixteen subjects. The orientation and strength of these preferences were largely the same in both conditions, showing no significant effect of the visuomotor adaptation. In both conditions, the major preferred directions were characterized by higher contribution of interaction torque to net torque at the shoulder as well as by relatively low inertial resistance and the sum of squared shoulder and elbow muscle torques. These results support the hypothesis that directional preferences are largely determined by biomechanical factors. However, this biomechanical effect can decrease or even disappear in some subjects when movements are performed in special conditions, such as the virtual environment used here.
先前已经在水平手臂运动中观察到了方向性偏好。这些偏好的特点是倾向于利用交互扭矩来产生肩部或肘部的运动，这表明首选方向取决于生物力学因素，而不是基于视觉感知的因素。我们通过系统地将手臂生物力学与视觉信息分离，直接检验了这一假设。16 名受试者执行了一项自由划动任务，要求他们从圆形中心快速向圆周方向划动，同时随机选择划动方向。手的位置由显示在运动平面中的光标表示。在进行了 30°顺时针手路径感知旋转的视动适应练习之后，完成了两次自由划动任务。适应是通过练习指向八个中心外目标的指向运动来实现的。在执行自由划动任务时，有 10 名受试者表现出了方向性偏好。在这两种情况下，这些偏好的方向和强度基本相同，没有视动适应的显著影响。在这两种情况下，主要的偏好方向表现为交互扭矩对肩部净扭矩的贡献较高，惯性阻力相对较低，肩部和肘部肌肉扭矩的平方和较低。这些结果支持了这样一种假设，即方向性偏好主要由生物力学因素决定。然而，当运动在特殊条件下进行时，例如这里使用的虚拟环境，这种生物力学效应可能会降低甚至消失。
