Remote effects on lightness

With the help of the double-anchoring theory of lightness (Bressan, 2006 Psychological Review 113 526 - 553), we investigated the occurrence and reversal of simultaneous contrast in the dungeon illusion (Bressan, 2001 Perception 30 1031 - 1046). In this display, target disks surrounded by contextual disks contrast with them rather than with the immediate background. We show that the dungeon illusion reverses if the luminance of the target is either lower (double decrement) or higher (double increment) than the luminances of both the background and contextual disks, rather than in-between them. We also show that remote luminances outside the display of primary interest affect these inverted-dungeon displays in ways that depend on the strength of grouping between target and contextual disks. As a consequence, the double-decrement inverted-dungeon illusion decreases, and the double-increment inverted-dungeon illusion increases, with remote luminance. We conclude that far-away luminances that are normally ignored as of marginal importance can play a critical role in lightness.