Exploring watercolor illusion spreading between dissected stimulus parts.

The article focuses on how global stimulus configuration influences the watercolor illusion (WCI), a visual phenomenon where an achromatic region surrounded by an outer contour and inner chromatic fringe appears tinted with the fringe's hue. Through experiments dissecting WCI-inducing stimuli into parts with varying gaps and contour removals, the study found that color spreading does not always extend beyond unenclosed borders; instead, global perceptual organization constrains the illusion. Participants often perceived dissected stimuli as either amodally completed behind an illusory white occluding surface or as separate objects, with color spreading confined within these perceptual boundaries. These findings highlight the importance of global context and figure-ground organization in determining the spatial extent of color spreading in the WCI, supporting models that integrate boundary and surface processing in visual perception.