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    有时候，右手可能不知道左手正在忙什么。事实证明每只手依赖各自不同的感觉系统来控制各自的运动。

    在一个右利手的小型研究中，人们发现优势手更依赖于视觉来指导它的运动，而左手——非优势手更依赖于来自身体肌肉、关节和皮肤的复合感觉。

    密歇根大学运动机能学运动科学系的副教授Susan Brown说，“我们觉得我们可以在一个右利手的人开瓶盖时体会这种情况，优势手通常在开瓶盖时受到视觉的监控与调整，而非优势手主要是根据肢体本身的感觉信息来掌握和稳定瓶子（罐子）的位置。”

    研究生Daniel Goble设计了一个实验，让右利手的成年人完成附着在杠杆系统上的两项任务，测量两侧肘关节的水平位置。

    在第一项任务中，主要是评估视觉对运动的控制情况。在不到一秒钟的时间内在受试者的左侧或右侧出示一个明亮的靶子（目标物）。然后，让受试者在一个附着在杠杆系统上的移动着的镭射指示器上标记目标物的位置。分别测试双手。目标物在同一方向出现，或从每一侧交叉出现。检查者发现在这项视觉任务中，右手（优势手）较少出现错误。

    在第二项任务中，让受试者蒙上眼睛，用左侧或右侧前臂向一个目标方向运动，在回到开始位置时停留3秒。然后告诉受试者返回同侧上肢或对侧上肢开始时的位置。在这项任务中，左手（非优势手）较少出现错误。

    Goble得出结论说，“在精确对比双侧上肢以后我们可以看到两侧明显的不同，这种区别主要取决于标识（瞄准）目标物时输入的感觉类型的不同。”

    传统意义上的优势手主要是在运动方面的区别——优势手在速度、力量与准确性方面比非优势手更胜一筹，这可能是人们更多的使用优势手的缘故。但在前面的实验中，Goble已经显示出这两侧上肢在感觉反馈方面也存在着不同。在完成任务时，非优势手显示更多的依赖于非视觉感觉输入。

    控制两侧上肢运动的是不同的大脑区域——这一事实或许可以解释人们为什么存在优势手的问题。这为一侧大脑半球损伤而造成偏侧身体活动障碍的患者进行康复运动时提供了一定的科学线索。如果两侧上肢确实使用不同的感觉系统，我们或许可以使用视觉任务锻炼优势手，而使用身体感觉任务来锻炼非优势手。

    Brown 和Goble计划进一步在更多类型的运动中探索这种感觉优势，诸如在存在或不存在视觉信息的情况下，在不同的运动速度、不同的上肢运动轨迹和不同的肌肉力量的情况下探讨这种感觉优势。他们也可能考虑应用脑部影象学检查来了解在不同的上肢运动时，中枢神经系统是如何活动的。

计算机模拟的实验设置：
http://www-personal.umich.edu/~dgoble/Vision%20Task.mov

消息来源：密歇根大学
http://www.physorg.com/news80536772.html

Left and Right Hands Rely on Different Senses

Sometimes, the right hand really may not know what the left hand is doing. It turns out that each of them relies on a different set of sensory inputs to control its movement.

In a small study of right-handed people, the dominant hand was found to be more dependent on vision for its guidance, while the left, non-dominant, hand was more attuned to body-based sensations from muscles, joints and skin.

"We think you can see this in the way a right-hander typically opens a jar," said Susan Brown, associate professor of movement science at the University of Michigan School of Kinesiology. "The preferred hand is usually monitored by vision as it twists off the lid while the non-preferred hand holds and stabilizes the jar's position using information from sensory receptors within the arm itself."

Graduate student Daniel Goble designed a study in which right-handed adults performed two tasks while attached to a lever system that measured the horizontal displacement of their elbow joints.

In the first task, which assessed visual control over movement, subjects were shown a lighted target to their left or right for less than a second. Then they were asked to mark the location the target had been in by moving a laser pointer attached to the lever system. The measurement was made with both hands, and with targets on the same side, or across from, each arm. Smaller errors were found for the preferred right arm in this visual task.

In the second task, the left or right forearm of blindfolded subjects was moved to a target position and held for three seconds before being returned to the start position. Then the subjects were told to return to that spot with either the same arm or the opposite arm. In this test, errors were smaller on the left, or non-preferred, side.

"We really saw marked differences in matching accuracy between arms, depending on what type of sensory input was used to present the target," Goble said.

Handedness and arm dominance have traditionally been attributed to differences in motor output, with the preferred arm demonstrating more speed, strength and efficiency than the non-preferred arm, perhaps because it gets more use. But in a previous study, Goble had shown that differences also exist in each arm's use of sensory feedback. The non-preferred left arm showed an enhanced ability to perform tasks based only on non-visual sensory inputs.

The fact that different parts of the brain primarily control each arm may shed some light on how handedness in humans evolved. It also may have implications for improving rehabilitation therapy for patients who have suffered damage to one side of the brain and have difficulty moving one side of the body. If the arms use different senses, perhaps vision-based tasks should be used to rehabilitate the preferred arm and body-based tasks for the non-preferred arm.

Brown and Goble plan to explore this sensory dominance further by looking at a wide range of movement tasks, such as differences in the ability to match different movement speeds, arm trajectories and muscle forces with and without visual information. They would also like to use brain imaging to see how neural activity compares with the observed behavior of the arms.

Computer animations of the experimental setup:
http://www-personal.umich.edu/~dgoble/Vision%20Task.mov

Source: University of Michigan

http://www.physorg.com/news80536772.html

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