Gilster R, Kuhtz-Buschbeck J P, Wiesner C D, Ferstl R
Institute of Physiology, Christian-Albrechts-University, Olshausenstrasse 40, 24098, Kiel, Germany.
Exp Brain Res. 2006 May;171(3):416-20. doi: 10.1007/s00221-006-0463-1. Epub 2006 Apr 25.
The assumption that the Ebbinghaus/Titchener illusion deceives perception but not grasping, which would confirm the two-visual-systems hypothesis (TVSH) as proposed by Milner and Goodale (The visual brain in action, 1995), has recently been challenged. Franz et al. (Exp Brain Res 149:470-477, 2003) found that the illusion affects both perception and grasping, and showed that the effect of the illusion on the peak grip aperture (PGA) cannot be accounted for by different sizes of the gap that separates the central target disk from the surrounding flankers. However, it is not yet clear if the presence of flankers per se influences grasping. We therefore compared kinematic parameters of prehension, using the Ebbinghaus illusion, and a neutral control condition where normal subjects grasped a disk without any flankers. In accordance with the well-known effects of the illusion on perceived size, the PGA was smaller when the target disk was surrounded by large flankers, and larger when it was encircled by small flankers. However, the largest PGA values were reached in the neutral control condition. Hence the presence of flankers leads to a general reduction of the PGA, possibly because the flankers are regarded as obstacles. This 'reduction effect' casts doubts on how appropriate it is to directly compare perceptual measures and PGA values when using the Ebbinghaus illusion. Even smaller effects of the illusion on the PGA compared to larger perceptual effects cannot be unequivocally interpreted.
埃宾浩斯/铁钦纳错觉会欺骗感知但不会影响抓握，这一假设若得到证实，将支持米尔纳和古德尔提出的双视觉系统假说（TVSH）（《行动中的视觉大脑》，1995年），但该假设最近受到了挑战。弗兰兹等人（《实验脑研究》149:470 - 477，2003年）发现这种错觉会同时影响感知和抓握，并表明错觉对峰值握距孔径（PGA）的影响不能用分隔中央目标圆盘与周围侧翼的间隙大小差异来解释。然而，侧翼本身的存在是否会影响抓握尚不清楚。因此，我们使用埃宾浩斯错觉以及正常受试者抓握无任何侧翼圆盘的中性对照条件，比较了抓握的运动学参数。与错觉对感知大小的众所周知的影响一致，当目标圆盘被大侧翼包围时，PGA较小，而当被小侧翼包围时，PGA较大。然而，在中性对照条件下达到了最大的PGA值。因此，侧翼的存在导致PGA普遍减小，可能是因为侧翼被视为障碍物。这种“减小效应”让人质疑在使用埃宾浩斯错觉时直接比较感知测量值和PGA值是否合适。与较大的感知效应相比，错觉对PGA的影响甚至更小，这也无法得到明确的解释。
