Is Seeing Believing? 
Illusions and Lightness Perception from Helmholtz to the 21st Century

The perception of surface albedo (lightness) is one of the most basic aspects of visual awareness. It has been recognized from as early the 19th century that the apparent lightness of a region depends on the context in which it is embedded. Does the visual system explicitly disentangle surface reflectance from the prevailing illumination and atmospheric conditions? Or can lightness be estimated using shortcuts, without generating layered representations? This question has been hotly debated for over a hundred years. A review of historical perspectives will be presented, as well as dramatic new visual illusions that unequivocally demonstrate the impact that layered image representations can play in lightness perception.