How do we know?
↻ One of the pages with a moving picture
A face illusion shows how the brain makes sense of what the eyes send.
- Light bounces off things and enters your eye. The clear cornea and the lens bend the light to make a sharp picture.
- The picture lands on the retina at the back of your eye. It is upside down and flipped left to right!
- Light-sensing cells in the retina turn the light into electrical signals. The optic nerve carries them to your brain.
- Your brain makes sense of the signals, and you see the world right side up.
Psychologist Peter Thompson of the University of York created a famous upside-down face illusion. A face with its eyes and mouth flipped looks normal upside down, but very strange the right way up!
Tricks like this help scientists learn how the brain makes sense of what the eyes send.
Scientists say there is no picture to spin around. The brain interprets the signals.
Wow number
120 million Each of your eyes has about 120 million rods, cells that see in black, white and gray and show you the shapes of things!
Myth or fact?
Your brain spins the upside-down picture around, like turning a photo. Myth. Scientists say there’s no picture to spin; the brain interprets signals.
Upside-down print is much harder to read. Fact. Try it with a book!
Think about it
Why do you think faces are harder to recognize when they are upside down?
Where in the world?
York, England where psychologist Peter Thompson of the University of York created a famous upside-down face illusion — 53.9591° N, 1.0815° W.
Where these facts come from
Every number on page 76, and who measured it
This page tells us about the parts of the eye and the rods that see shapes.
Eyes — KidsHealth, a health site for kids from Nemours Children's Health
kidshealth.org/en/kids/eyes.html
We checked it on 31 October 2026
This page tells us how light becomes signals that go to the brain.
How the Eyes Work — The U.S. National Eye Institute
nei.nih.gov/learn-about-eye-health/healthy-vision/how-eyes-work
We checked it on 31 October 2026
This page tells us that the picture on the back of the eye is upside down.
6.1 An Overview of the Visual System - Introduction to Behavioral Neuroscience — OpenStax, free college textbooks from Rice University
openstax.org/books/introduction-behavioral-neuroscience/pages/6-1-an-overview-of-the-visual-system
We checked it on 31 October 2026
This page tells us why the brain doesn't need to flip the picture.
Right-Side Up — Scientific American, a science magazine
scientificamerican.com/article/right-side-up
We checked it on 31 October 2026
Has this changed?
How eyes see is not going to change.
Scientists keep learning how the brain turns signals into what we see, and tricks like this one help.
Words from this page
- cornea
- The clear front window of the eye.
- retina
- The layer at the back of the eye that senses light.
- rod
- A cell in the retina that sees in black, white and gray.
Try it!
Draw an upside-down face illusion.
1. Draw a smiling face, but draw its eyes and smile upside down. 2. Turn the paper over so the whole face is upside down. Does it look OK? 3. Now turn it back the right way up. What do you notice?
What happens: the face may look almost normal upside down, but strange the right way up!
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