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Rudiger von der Heydt, Rachel Pierson; Dissociation of color and figure-ground effects in the watercolor illusion. Journal of Vision 2005;5(8):500. doi: 10.1167/5.8.500.
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© ARVO (1962-2015); The Authors (2016-present)
The watercolor illusion occurs when figures are defined by a double contour consisting of lines of different colors and contrasts. Two phenomena are observed, illusory color spreading (Pinna et al., Vision Res. 41:2669–76, 2001) and figure-ground organization (Pinna et al., Vision Res. 43:43–52, 2003). The purpose of the present study was to distinguish whether the figure-ground effect is a consequence of the color illusion or due to an independent mechanism. Subjects were tested with displays consisting of six adjacent stripes outlined by dark purple lines in which alternating stripes were lined orange inside to produce the watercolor illusion. In experiment 1, the illusory color was measured by finding the matching physical color in the alternate stripes. Figureness (probability of ‘figure’ responses, 2AFC) of the watercolor stripes was then determined with and without the matching color in the alternate stripes. The color match reduced figureness by 46%, but did not abolish it. There was a range of colors in which the watercolor stripes dominated as figures over the alternate stripes although the latter appeared more saturated in color. In experiment 2, the effect of tinting alternate stripes was measured in displays without watercolor illusion (no orange lining). Figureness increased with color contrast, but its value at the corresponding contrast fell short of the figureness value obtained for the watercolor pattern. Thus, both experiments indicate that figureness produced by the watercolor pattern is stronger than expected from the color effect, suggesting independent mechanisms. We conjecture that part of the figure-ground effect of the watercolor pattern results from the double lines stimulating neurons that are selective for asymmetric edge profiles. Such neurons may signal border ownership and thus contribute to figure-ground segregation (Zhou et al., J. Neurosci. 20:6594–6611, 2000).
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