This pair of talks integrates two extensive sets of Adelson-like experiments on lightness. In Part 2 it is argued that modification of the diamonds experiments demonstrate an early-vision explanation, without reliance on illumination, transparency, apparent depth, and junctions.
Grays ordinarily look darker on light backgrounds.
Adelson showed that two rows of diamonds looked the same on different backgrounds when the diamond tips crossed into the other background. Adelson added different grey tips, consistent with illumination changes, thus releasing the rest of the diamonds to no longer match. Grays on light backgrounds reverted to looking darker. New experiments show that the introduction of any edge along the light - dark background boundary releases the diamonds to look different in different surrounds. Adelson's tips and all of our edges produce essentially the same magnitude of lightness shifts.