This page illustrates that our senses cannot always be trusted. Our mind is the final arbiter of truth.

Perpetually ascending staircase.

How can the man go up all the time and come back to the same place over and over?

The red squares are the same color in the upper part
and in the lower part of the "X"

The diagonal lines are parallel.

There are no gray spots at the corners of the squares.

The rows of black and white squares are all parallel.

Impossible triangle.

Parallel lines at sunrise.

The center circles are both the same size.

The Vertical lines are both the same length.

Three-prong fork.

Ambiguous cubes

There are only white circles at the intersections

All the bumps are identical.
The one in the lower right corner is upside-down,
The image to the right is rotating.

Wavy Squares? No!
The background of concentric circles makes the squares appear distorted.

Rotating Wheels
The circles appear to rotate when you move your head closer and further away from the screen while looking at the dot in the center.

Warped Square?
There are no curved lines in this figure.

Blind Spot Experiment

The retina is the part of the eye covered with receptors that respond to light. A small portion of the retina where the optic nerve connects to the brain has no receptors. An image that falls on this region will not be seen. Close your right eye. With your left eye, look at the L below. Slowly move your head closer or further away from the screen while looking at the L. The R will disappear when your head is approximately 50 cm (20 in) from the screen. You can repeat the experiment with your right eye by looking at the R.

Pinhole Experiment

Take two pieces of heavy paper. On one of them make three holes with a pin spaced about 2 mm apart (1/16 inch) from each other. On the other one, make a single hole with the pin. Place the card with the three holes next to your eye and look through the holes at the card with one hole. You will see three holes instead of one.

Stereoscopic Vision

Stereoscopic vision makes depth perception possible. By crossing your eyes while looking at these two pictures, the brain perceives a combined image with a central section on a different plane. (Hint: Keep your eyes level with the pictures. Place your fingertip between the pictures on the line that says "BOA" and look at your fingertip while you bring your finger toward your eyes. When your fingertip is approximately 7 inches (20 cm) from your eyes, the pictures in the background will combine into a 3-dimensional picture.)

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Two-keyboard Pipe Organ