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"Reality": Construction,
Deconstruction, and Reconstruction


Spiral "Illusion"
Visual "illusions" aren't "tricks" but rather windows into how the brain makes informed guesses.

Take a look at the spiral pattern below. How many colors do you see? Maybe four? Green, blue, purple, and orange? What if someone told you there were only 3 colors in the pattern? If so, two of the "colors" must be the same.

How about the "blue" and "green"? Try clicking with your mouse and dragging the two stripes indicated by the arrows onto white space on the page.

Here are the two pieces. They look the same. Are you surprised? This observation tells us something important about color and about the brain. "Color" is actually not something "out there in the world". Instead, color is constructed by your brain, based not only on light coming from a particular place but on the entirety of the information it gets from your eyes. And what your eyes detect is not color, but wavelengths of light (see Variations in Perception and their Significance).

In the case of the spiral pattern, the "blue" and the "green" portions are sending to your eye the same combination of wavelengths and intensities of light. It is the context, or the surrounding patterns of purple and orange stripes that contributes to the perception that the two are not the same color.

Let's look at what other colors might appear given this surrounding environment of orange and purple stripes. The draggable pattern below consists of everything except the "blue" and "green" parts. That is, the image contains only the orange and purple pattern on a transparent background. Drag the pattern onto the different swatches of colors below. How does the orange and purple pattern affect the background? What two additional colors do you see in each case?

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