Color and lightness

Gating of remote effects on lightness

Paola Bressan, Peter Kramer

Abstract
In various versions of the dungeon illusion (P. Bressan, 2001), we show that grouping between targets and contextual disks determines whether remote luminances affect target lightness or not. In the dungeon illusion, target disks surrounded by contextual disks contrast with them rather than with the immediate background. We formally establish the existence of this illusion and show that it reverses when the luminance of the targets is either lower (double decrement) or higher (double increment) than the luminances of both the background and the contextual disks rather than in between them. On the basis of the double-anchoring theory of lightness (P. Bressan, 2006a), we predict and show that grouping gates the effects of remote luminances in such a way that they go in opposite directions in the double-decrement and double-increment inverted-dungeon illusions. Our results support the double-anchoring theory and demonstrate that luminances that are far away from the targets are irrelevant in some conditions but critical in others.

Bressan, P., & Kramer, P. (2008). Gating of remote effects on lightness. Journal of Vision, 8(2):16, 1-8.

See original paper on the Journal of Vision website (the pdf can be downloaded for free)

The central eight disks in each panel look either bluish or greenish, but they are all actually grey.

Dungeons, gratings, and black rooms: a defense of double-anchoring theory and a reply to Howe et al. (2007)

Paola Bressan

Abstract
The double-anchoring theory of lightness (Bressan, 2006) assumes that any given region belongs to a set of frameworks, created by Gestalt grouping principles, and receives a provisional lightness within each of them; the region’s final lightness is a weighted average of all these values. In their critique, Howe, Sagreiya, Curtis, Zheng, and Livingstone (2007) (a) show that the target’s lightness in the dungeon illusion (Bressan, 2001) and in White’s effect is not primarily determined by the region with which the target is perceived to group, and (b) claim that this is a challenge to the theory. I argue that Howe et al. misinterpret grouping for lightness by equating it with grouping for object formation, and by ignoring that lightness is determined by frameworks’ weights and not by what appears to group with what. I show that Howe et al.’s empirical findings, together with those on grating induction and all-black rooms that they cite as problematic, actually corroborate rather than falsify the theory.

Bressan, P. (2007). Dungeons, gratings, and black rooms: a defense of double-anchoring theory and a reply to Howe et al. (2007). Psychological Review, 114, 1111-1115.

The place of white in a world of grays: a double-anchoring theory of lightness perception

Paola Bressan

Abstract
The specific gray shades in a visual scene can be derived from relative luminance values only when an anchoring rule is followed. The double-anchoring theory I propose in this paper, as a development of the anchoring theory of Gilchrist et al. (1999), assumes that any given region (a) belongs to one or more frameworks, created by Gestalt grouping principles, and (b) is independently anchored, within each framework, to both the highest luminance and the surround luminance. The region’s final lightness is a weighted average of the values computed, relative to both anchors, in all frameworks. The new model not only accounts for all lightness illusions that are qualitatively explained by the anchoring theory, but also for a number of additional effects; and it does so quantitatively, with the support of mathematical simulations.

Bressan, P. (2006). The place of white in a world of grays: a double-anchoring theory of lightness perception. Psychological Review, 113, 526-553.