||Achromatic form perception is based on luminance, not brightness.
Two figures were observed by the authors, one a subjective disk and the other a cup whose shape was revealed by shadows. The figures were presented in a single color on a background of a different color, and the observers adjusted the radiance of one color until, in the first case, the vividness of the subjective contour reached a minimum subjective contour or, in the second case, the impression of depth that is due to shadows disappeared. Results followed the data for minimum flicker matches (made with the same stimuli) much more closely than those for direct brightness matching. Achromatic form perception in general and subjective contour and shadow perception in particular appear to be based on the intensity dimension measured by flicker photometry, not on that measured by brightness matching. (PsycINFO Database Record (c) 2007 APA, all rights reserved)