Pii: S0304-3940(02)00935-7

Simultaneous lightness contrast is a classical visual illusion, which has been the focus of research for several generations of visual scientists. Still, there is no agreement on its mechanisms. There are two main competing accounts. The first is descended from ideas of Ewald Hering [Hering, E., Outline of a Theory of the Light Sense, (1874), translated from the German by L. Hurvich and D. Jameson, Harvard University, Cambridge, MA (1964)]. It is based on low-level retinal mechanisms processing the local luminance contrast between the target and the background. The second, originally proposed by Herman von Helmholtz [von Helmholtz, H., Handbuch der Physiologischen Optik, Leipzig, Voss, (1867).] suggests that the illusion is the result of a misjudgement of the illumination. We present a new demonstration, which challenges both explanations. It suggests that simultaneous lightness contrast is not specifically a lightness illusion, being a particular case of a more general phenomenon known as the ‘anchoring effect’. q 2002 Elsevier Science Ireland Ltd. All rights reserved.