Henriques D Y P, Crawford J D
Centre for Vision Research, York University, Toronto, Ontario M3J 1P3, Canada.
J Neurophysiol. 2002 Apr;87(4):1677-85. doi: 10.1152/jn.00509.2001.
Eye-hand coordination requires the brain to integrate visual information with the continuous changes in eye, head, and arm positions. This is a geometrically complex process because the eyes, head, and shoulder have different centers of rotation. As a result, head rotation causes the eye to translate with respect to the shoulder. The present study examines the consequences of this geometry for planning accurate arm movements in a pointing task with the head at different orientations. When asked to point at an object, subjects oriented their arm to position the fingertip on the line running from the target to the viewing eye. But this eye-target line shifts when the eyes translate with each new head orientation, thereby requiring a new arm pointing direction. We confirmed that subjects do realign their fingertip with the eye-target line during closed-loop pointing across various horizontal head orientations when gaze is on target. More importantly, subjects also showed this head-position-dependent pattern of pointing responses for the same paradigm performed in complete darkness. However, when gaze was not on target, compensation for these translations in the rotational centers partially broke down. As a result, subjects tended to overshoot the target direction relative to current gaze; perhaps explaining previously reported errors in aiming the arm to retinally peripheral targets. These results suggest that knowledge of head position signals and the resulting relative displacements in the centers of rotation of the eye and shoulder are incorporated using open-loop mechanisms for eye-hand coordination, but these translations are best calibrated for foveated, gaze-on-target movements.
眼手协调需要大脑将视觉信息与眼睛、头部和手臂位置的持续变化进行整合。这是一个几何上复杂的过程，因为眼睛、头部和肩部有不同的旋转中心。因此，头部旋转会导致眼睛相对于肩部平移。本研究考察了这种几何结构在头部处于不同方位的指向任务中对规划精确手臂运动的影响。当被要求指向一个物体时，受试者会调整手臂方向，将指尖置于从目标到注视眼睛的连线上。但是，当眼睛随着每个新的头部方位平移时，这条眼 - 目标连线会发生移动，从而需要一个新的手臂指向方向。我们证实，当注视目标时，受试者在闭环指向过程中会在各种水平头部方位上使指尖与眼 - 目标连线重新对齐。更重要的是，在完全黑暗中执行相同范式时，受试者也表现出这种依赖头部位置的指向反应模式。然而，当注视不在目标上时，对这些旋转中心平移的补偿会部分失效。结果，受试者相对于当前注视往往会超过目标方向；这或许可以解释先前报道的将手臂指向视网膜周边目标时出现的误差。这些结果表明，头部位置信号以及由此产生的眼睛和肩部旋转中心的相对位移信息是通过开环机制用于眼手协调的，但这些平移对于中央凹注视目标的运动进行校准最为有效。
