Soranzo Alessandro, Galmonte Alessandra, Agostini Tiziano
School of Social Science and Law, University of Teesside, Middlesbrough TS1 3BA, UK.
Perception. 2010;39(5):592-605. doi: 10.1068/p6462.
Lightness contrast and lightness assimilation are opposite phenomena: in contrast, grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in assimilation, the opposite occurs. The question is: which visual process favours the occurrence of one phenomenon over the other? Researchers provided three answers to this question. The first asserts that both phenomena are caused by peripheral processes; the second attributes their occurrence to central processes; and the third claims that contrast involves central processes, whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT system equipped with goggles for stereo vision was run. Observers were asked to evaluate the lightness of a grey target, and two variables were systematically manipulated: (i) the apparent distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept constant throughout, so that the peripheral processes remained the same. The results show that the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we conclude that central mechanisms are involved in both lightness contrast and lightness assimilation.
在对比中，灰色目标在与明亮表面（诱导物）相邻时比与黑暗表面相邻时显得更暗；在同化中，则会出现相反的情况。问题是：哪种视觉过程更有利于其中一种现象而非另一种现象的发生？研究人员对这个问题给出了三个答案。第一个答案认为，这两种现象都是由外周过程引起的；第二个答案将它们的发生归因于中枢过程；第三个答案则声称，对比涉及中枢过程，而同化涉及外周过程。为了检验这些假设，在一个配备了用于立体视觉的护目镜的IT系统上进行了一项实验。要求观察者评估一个灰色目标的明度，并系统地操纵两个变量：（i）诱导物的表观距离；以及（ii）诱导物的亮度。整个过程中视网膜刺激保持恒定，以便外周过程保持不变。结果表明，目标的明度取决于这两个变量。由于视网膜刺激保持恒定，我们得出结论，中枢机制参与了明度对比和明度同化。
