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Adam Reeves, Rebecca Grayhem; Reversing the watercolor effect. Journal of Vision 2009;9(8):329. doi: 10.1167/9.8.329.
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© ARVO (1962-2015); The Authors (2016-present)
In Pinna's watercolor effect, a boundary line is drawn on a white field to enclose a central region. When the line is colored purple on the outside and yellow on the inside, an illusory yellow color wash is propogated throughout the enclosed region, which then appears figure-like. Naïve observers rated the strength of this illusion as a function of the number of frames the boundary line was displayed; pre- and post- frames were a uniform white of the same mean illuminance (80 cd/m2). The illusion grew steadily until 10 frames (100 ms) were presented, after which no further increase was noted. We wonderd whether the illusion developed before, or after, the boundary signal created a figure. The bounding contour colors were reversed. The illusory yellow now spread into the background, not into the interior. The amplitude and time course of the illusion were hardly affected. We speculate that the watercolor illusion develops at a stage of color processing which occurs before that which distinguishes foreground from background.
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