Darling W G, Hondzinski J M, Harper J G
Department of Exercise Science, University of Iowa, Iowa City, IA 52242, USA.
Exp Brain Res. 2000 Dec;135(3):360-72. doi: 10.1007/s002210000526.
The effects of varying gaze direction on perceptions of the upper limb kinesthetic coordinate system axes and of the median plane location were studied in nine subjects with no history of neuromuscular disorders. In two experiments, six subjects aligned the unseen forearm to the trunk-fixed anterior-posterior (a/p) axis and earth-fixed vertical while gazing at different visual targets using either head or eye motion to vary gaze direction in different conditions. Effects of support of the upper limb on perceptual errors were also tested in different conditions. Absolute constant errors and variable errors associated with forearm alignment to the trunk-fixed a/p axis and earth-fixed vertical were similar for different gaze directions whether the head or eyes were moved to control gaze direction. Such errors were decreased by support of the upper limb when aligning to the vertical but not when aligning to the a/p axis. Regression analysis showed that single trial errors in individual subjects were poorly correlated with gaze direction, but showed a dependence on shoulder angles for alignment to both axes. Thus, changes in position of the head and eyes do not influence perceptions of upper limb kinesthetic coordinate system axes. However, dependence of the errors on arm configuration suggests that such perceptions are generated from sensations of shoulder and elbow joint angle information. In a third experiment, perceptions of median plane location were tested by instructing four subjects to place the unseen right index fingertip directly in front of the sternum either by motion of the straight arm at the shoulder or by elbow flexion/extension with shoulder angle varied. Gaze angles were varied to the right and left by 0.5 radians to determine effects of gaze direction on such perceptions. These tasks were also carried out with subjects blind-folded and head orientation varied to test for effects of head orientation on perceptions of median plane location. Constant and variable errors for fingertip placement relative to the sternum were not affected by variations in gaze direction or head orientation. Thus, the perceived position of the trunk-fixed median plane is not altered by varying gaze direction. The implications of these results for mechanisms underlying kinesthetic perceptions and their potential roles in programming of upper limb movements to visual targets are discussed.
在九名无神经肌肉疾病病史的受试者中，研究了不同注视方向对上肢运动觉坐标系轴和正中面位置感知的影响。在两个实验中，六名受试者在不同条件下通过头部或眼睛运动改变注视方向，注视不同视觉目标，同时将看不见的前臂与躯干固定的前后（a/p）轴和地球固定的垂直方向对齐。还在不同条件下测试了上肢支撑对感知误差的影响。无论头部还是眼睛移动以控制注视方向，不同注视方向下与前臂与躯干固定的a/p轴和地球固定的垂直方向对齐相关的绝对恒定误差和可变误差相似。当与垂直方向对齐时，上肢支撑可减少此类误差，但与a/p轴对齐时则不然。回归分析表明，个体受试者的单次试验误差与注视方向相关性较差，但在与两个轴对齐时均显示出对肩部角度的依赖性。因此，头部和眼睛位置的变化不会影响上肢运动觉坐标系轴的感知。然而，误差对手臂配置的依赖性表明，此类感知是由肩部和肘关节角度信息的感觉产生的。在第三个实验中，通过指示四名受试者通过肩部伸直手臂的运动或在肩部角度变化时通过肘部屈伸，将看不见的右手食指尖直接放在胸骨前方，测试正中面位置的感知。注视角度左右各变化0.5弧度，以确定注视方向对此类感知的影响。这些任务也在受试者蒙眼且头部方向改变的情况下进行，以测试头部方向对正中面位置感知的影响。相对于胸骨的指尖放置的恒定误差和可变误差不受注视方向或头部方向变化的影响。因此，改变注视方向不会改变躯干固定的正中面的感知位置。讨论了这些结果对运动觉感知潜在机制及其在上肢向视觉目标运动编程中的潜在作用的影响。
