Strawberry Fields

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SA Mind

Nothing is real about the colors you see here

Illusory blues and reds: The car image is composed of red and gray tones. Each strawberry in the fruit plate image is composed of tones of grey. The strawberries will still look red if they are replaced with gray blobs. Credit: Akiyoshi Kitaoka (left and top right): Michael Bach (bottom right)

Every object we see is a mirror in some way. A perfect mirror is a lake with a glassy surface on a sunny day. It reflects all light accurately and without scattering. A red strawberry is also a mirror, even though it is imperfect. Strawberry’s red color is due to the fact that they absorb and reflect bluish wavelengths. Sometimes, the light that falls on strawberries does not contain any red. How can we see red strawberries when there are no red wavelengths?

In the late 19th century German physiologist Ewald Hering showed that our experience of color is partly the result of our brain interpreting blue as opposite to yellow and red as opposite to green. Our perception of a strawberry as red is far from the original light wavelengths. Instead, our visual system determines what the strawberry’s surface color is based upon a process that detects the source of light and then discounts it.

This perceptual result is known as color constancy. It allows us to perceive an object’s colour as constant regardless of its illumination conditions. Color constancy is why strawberries appear red at sunset and noon under cloudy skies at your local farmer’s market and flooded with fluorescent lighting in your supermarket’s produce aisle.

The car photograph was created by Akiyoshi kitaoka, a vision scientist, using free online software. It exemplifies a kind of color constancy known as the Land effect. This is Edwin H. Land’s invention of the Polaroid camera. Although we see the car as being blue, the image actually contains only red and grey wavelengths.

Another form of color constancy is illustrated by Kitaoka’s plate of strawberries. Your brain may disagree with the fact that every berry is actually gray. You don’t see strawberries as red because you know their color. Michael Bach, a vision scientist, modified the original image by replacing each berry in the original photo with a gray blob. The result shows that no prior knowledge of fruit color is necessary: even blobs that are not shapeless will take on the color our visual system assigns them, based on our implicit assumptions regarding the light source.

This article was originally published with the title “Strawberry Fields” in SA Mind 33, 4, (July 2022)

ABOUT THE AUTHOR(S)

    Susana Martinez-Conde and Stephen Macknik are professors of ophthalmology at the State University of New York and the organizers of the Best Illusion of the Year Contest. They have co-authored Sleights of Mind: What the Neuroscience of Magic Reveals about Our Ev

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