Sperandio Irene, Lak Armin, Goodale Melvyn A
The Brain and Mind Institute and the Department of Psychology, The University of Western Ontario, London, Ontario, Canada.
J Vis. 2012 Feb 21;12(2):18. doi: 10.1167/12.2.18.
Traditionally, the perceived size of negative afterimages has been examined in relation to E. Emmert's law (1881), a size-distance equation that states that changes in perceived size of an afterimage are a function of the distance of the surface on which it is projected. Here, we present evidence that the size of an afterimage is also modulated by its surrounding context. We employed a new version of the Ebbinghaus-Titchener illusion with flickering surrounding stimuli and a static inner target that generated a vivid afterimage of the latter but not the former. Observers were asked to give an initial manual estimate of the size of the inner target during the adaptation phase followed by another manual estimate of the size of the afterimage during the test phase. Manual estimates were affected by the size-contrast illusion both when the surrounding contextual elements were present during afterimage induction and when the surrounding elements were absent during the viewing of the afterimage (Experiment 1). Such a modulation in perceived size, however, did not occur when observers viewed only the flickering surrounding context for a prolonged period of time and then estimated the size of a static target presented on the monitor afterward, demonstrating that flickering stimuli by themselves did not produce any aftereffect on perceived size (Experiment 2). Furthermore, in a final experiment, we showed that the modulation observed in the test phase of Experiment 1 was not due to memory of the manual estimates that had been performed during the adaptation phase (Experiment 3). These findings provide clear evidence for the role of high-level cognitive processes on the perceived size of an afterimage beyond the retinal level. Thus, although retinal stimulation is required to induce an afterimage, post-retinal factors influence its perceived size.
传统上，负后像的感知大小是根据E. 埃默特定律（1881年）进行研究的，该定律是一个大小-距离方程，表明后像感知大小的变化是其投射表面距离的函数。在此，我们提供证据表明，后像的大小也会受到其周围环境的调节。我们采用了一种新版本的艾宾浩斯-铁钦纳错觉，其中周围刺激闪烁，内部目标静止，内部目标会产生生动的后像，而周围刺激则不会。在适应阶段，要求观察者对内部目标的大小进行初步手动估计，随后在测试阶段对后像的大小进行另一次手动估计。当后像诱导期间存在周围环境元素时，以及在后像观察期间周围元素不存在时，手动估计均受大小对比错觉的影响（实验1）。然而，当观察者长时间仅观察闪烁的周围环境，然后估计随后出现在显示器上的静止目标的大小，这种感知大小的调节并未发生，这表明闪烁刺激本身不会对感知大小产生任何后效（实验2）。此外，在最后一个实验中，我们表明实验1测试阶段观察到的调节并非由于对适应阶段所进行的手动估计的记忆（实验3）。这些发现为高级认知过程在视网膜水平之上对后像感知大小的作用提供了明确证据。因此，虽然诱导后像需要视网膜刺激，但视网膜后因素会影响其感知大小。
