Medendorp W P, Van Asselt S, Gielen C C
Department of Medical Physics and Biophysics, University of Nijmegen, The Netherlands.
Exp Brain Res. 1999 Mar;125(1):50-60. doi: 10.1007/s002210050657.
We studied pointing movements to remembered visual targets in a completely darkened room with and without self-made step movements in order to investigate in which coordinate system and to what extent target representations relative to the body are updated for self-induced egomotion. A small red-light-emitting diode on the fingertip provided visual feedback about fingertip position at all times. We asked subjects to make pointing movements that started 2 s after disappearance of a visual target. In this interval of 2 s the subject did or did not make a step. The pointing errors without a step showed that subjects undershot faraway targets in a systematic way, whereas they sometimes overshot nearby targets. We found that the step causes larger pointing errors both in amplitude and direction with a bias in the direction of the step. We explored three different versions of a descriptive model in which polar coordinates were used to describe the pointing movement, and in which either Cartesian or polar coordinates were used to update target position relative to the shoulder for the step. The results suggest that incorporation of the step displacement in the new target position relative to the subject is done in a Cartesian frame of reference. Moreover, the amplitude of the step displacement tends to be underestimated by subjects.
我们研究了在完全黑暗的房间中，有或没有自行做出的步移动作时，指向记忆中的视觉目标的动作，以便探究在自我诱导的自我运动中，目标相对于身体的表征是在哪个坐标系中更新的，以及更新的程度如何。指尖上的一个小型红色发光二极管随时提供关于指尖位置的视觉反馈。我们要求受试者在视觉目标消失2秒后开始做出指向动作。在这2秒的间隔内，受试者进行或不进行步移动作。没有步移动作时的指向误差表明，受试者会系统性地未够到远处目标，而有时又会超过近处目标。我们发现，步移动作在幅度和方向上都会导致更大的指向误差，且存在步移方向的偏差。我们探究了描述性模型的三种不同版本，其中使用极坐标来描述指向动作，并且对于步移动作，使用笛卡尔坐标或极坐标来更新相对于肩部的目标位置。结果表明，相对于受试者而言，在新的目标位置中纳入步移位移是在笛卡尔参考系中完成的。此外，受试者往往会低估步移位移的幅度。
