Examining the effect of context on the watercolor illusion
Hale, Ralph Griffin
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The watercolor illusion (WCI) occurs when a physically non-colored region surrounded by an outer contour and an inner fringe appears filled in with a pale tint the same hue as the fringe (see Figures 2 and 3). Previous literature investigating the WCI has focused primarily on stimulus parameters affecting illusion magnitude and the likely neural mechanisms responsible, rarely discussing how this phenomenon may be affected by global context. The present experiments are the first to explore the effect of global context on the WCI. Experiment 1 examined the WCI using pictures of a variety of three-dimensional solid surfaces and objects as compared to more traditional two-dimensional stimuli. By keeping the local information nearly identical across conditions we evaluated how the global context influenced the magnitude and spatial extent of the illusion. Experiment 2 examined the influence of global context further using images of three-dimensional wireframe versions of the solid looking objects used in Experiment 1. Experiment 3 examined how the perception of WCI stimuli were affected when split into two parts. This allowed us to explore how global stimulus changes impact color spreading as it relates to previous literature showing the WCI spreads in the absence of a border. The fact color failed to spread outside of these now physically unenclosed configurations demonstrates global configuration is an important factor in how color spreading manifests. This study is one of the first to demonstrate the global configuration of WCI stimuli can influence color spreading and color spreading may not occur with unenclosed stimuli depending on this global context.