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Does Your Brain Do Flips?

Normal Sight: Normal ray tracing of light to the retina. Shows image will 'flip'.

With Pinhole: Ray tracing of pin through pinhole; a shadow is cast on the retina. You may not be aware of it, but when you look at the world, the image projected on your retina is upside down. This is due to the optics used by our eyes. Our brain compensates for this upside down view and everything seems perfectly normal to us.

Don't believe it? Do this simple experiment. Take a metal straight pin with a head, just like the one shown in the picture, and poke a hole in a 3x5 index card. Hold the hole in the index card very close to your eye and look through it. While looking through the hole, position the head of the pin very close to the card so you can see it through the hole. Can you see it? Isn't the pin upside down? Voila! What you are seeing is a shadow of the pin on your retina. Normally, when we see an object, light passes through our cornea and an image is formed on the retina. When you look at the pin through the pinhole, your cornea cannot focus the image because it's not designed to work over such short distances. You merely see a shadow image that appears on your retina right side up. Since your brain is trained to flip things you see, it flips the shadow of the pin upside down.

Interestingly enough, if you wear special glasses that invert the images you see, within a few days your brain will compensate and the world will appear right side up again!


About the Author

Willa LarsenWilla Larsen, MS
Willa Larsen writes on a wide array of topics for ScienceIQ. Willa received a BS in physics from University of Colorado and a MS in materials science and engineering from UCLA. She previously worked making infrared detectors for the Hubble, missiles and surveillance equipment. Willia is the publisher of which helps fund animal rescue.

Further Reading
The Eye and Visual Optical Instruments
by George Smith, David A. Atchison

Related Web Links
Tricks of the Eye, Wistom of the Brain
by Paul Grobstein, Serendip

The Living Camera: How do eyes make images?
by BioMedia Associates

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