Same color illusion
The same color illusion (also known as Adelson's checker shadow illusion, checker shadow illusion and checker shadow) is an optical illusion in which identical shades of gray appear to be different.
Discovery
The same color illusion was first published in 1995 by Edward H. Adelson, Professor of Vision Science at Massachusetts Institute of Technology (MIT).[1]
Description
The same color illusion shows what appears to be a checkerboard made of dark and light gray squares. Resting in one corner of the checkerboard is a green cylinder that casts a shadow diagonally across the middle of the board. Two of the squares on the board are labeled "A" and "B". When studying the image, square A appears markedly darker than square B, even though they are the exact same shade of gray. If one removes the image surrounding the two squares (or covers it over with a paper), it is clear that they are the same shade.
Explanation
When looking at the image, the brain and visual system interprets it as a three dimensional image. When interpreting scenes in real life, the visual system has techniques that compensate for different lighting and shadows, enabling us to better interpret objects as they actually exist. There are several specific aspects that contribute to the remarkable success of this illusion.
First, lighter squares surrounded by darker squares appear lighter than average based on local contrast. Conversely, darker squares surrounded by lighter squares appear darker for the same reason. Second, the shadow of the cylinder has soft edges. The visual system tends to ignore gradual changes in light level, focusing instead on sharp edges. Additionally, certain colors such as gray, green, and yellow are more difficult for the visual system to judge accurately. Often, cues for these colors are taken from the surrounding context. As can be seen in the same color illusion, when the context is removed, it is obvious that the two gray squares are the same shade.[2]
Applications
The same color illusion aptly demonstrates why it is so important to verify what may seem like obvious assumptions when conducting scientific experiments. The human eye and brain can be easily fooled into misinterpretations, which could affect the results of any number of scientific inquiries.
Notes
- ↑ Adelson, Edward H. (2005). Checkershadow Illusion. Retrieved 2007-04-21.
- ↑ Robert Nemiroff and Jerry Bonnell. "The same color illusion" Bangkok Post. July 24, 2007. Retrieved October 26, 2007.
External links
All links Retrieved November 16, 2007.
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