Kinesiology Program, Arizona State University, P.O. Box 870701, Tempe, AZ 85287-0701, USA.
Exp Brain Res. 2011 Mar;209(2):299-309. doi: 10.1007/s00221-011-2547-9. Epub 2011 Jan 29.
Previous research has revealed directional biases (preferences to select movements in specific directions) during horizontal arm movements with the use of a free-stroke drawing task. The biases were interpreted as a result of a tendency to generate motion at either the shoulder or elbow (leading joint) and move the other (subordinate) joint predominantly passively to avoid neural effort for control of interaction torque. Here, we examined influence of vision, movement speed, and attention on the directional biases. Participants performed the free-stroke drawing task, producing center-out strokes in randomly selected directions. Movements were performed with and without vision and at comfortable and fast pace. A secondary, cognitive task was used to distract attention. Preferred directions remained the same in all conditions. Bias strength mildly increased without vision, especially during fast movements. Striking increases in bias strength were caused by the secondary task, pointing to additional cognitive load associated with selection of movements in the non-preferred directions. Further analyses demonstrated that the tendency to minimize active interference with interaction torque at the subordinate joint matched directional biases in all conditions. This match supports the explanation of directional biases as a result of a tendency to minimize neural effort for interaction torque control. The cognitive load may enhance this tendency in two ways, directly, by reducing neural capacity for interaction torque control, and indirectly, by decreasing capacity of working memory that stores visited directions. The obtained results suggest strong directional biases during daily activities because natural arm movements usually subserve cognitive tasks.
先前的研究表明，在使用自由 stroke 绘图任务进行水平手臂运动时，存在方向偏向（即选择特定方向运动的偏好）。这些偏向被解释为产生运动的倾向，要么在肩部或肘部（主导关节），要么主要被动地移动另一个（从属）关节，以避免神经努力控制交互扭矩。在这里，我们研究了视觉、运动速度和注意力对方向偏向的影响。参与者执行自由 stroke 绘图任务，以随机选择的方向进行中心向外的 stroke。在有和没有视觉的情况下，以舒适和快速的速度进行运动。使用次要的认知任务来分散注意力。在所有条件下，首选方向保持不变。在没有视觉的情况下，偏向强度略有增加，尤其是在快速运动时。次要任务导致偏向强度显著增加，表明与选择非首选方向的运动相关的额外认知负荷。进一步的分析表明，在从属关节上最小化交互扭矩的主动干扰的趋势与所有条件下的方向偏向相匹配。这种匹配支持将方向偏向解释为最小化交互扭矩控制的神经努力的结果。认知负荷可以通过两种方式增强这种趋势，直接地通过减少交互扭矩控制的神经容量，以及间接地通过降低存储访问方向的工作记忆容量。所得结果表明，在日常活动中存在强烈的方向偏向，因为自然手臂运动通常为认知任务服务。
