Care to join us in a cup of tea?

One of the functions of the brain is to identify the size and distance of objects and figures. To do this, it uses hints from the environment and knowledge it gained in the past. Experience teaches us that the farther we are from an object, the smaller it appears. But sometimes the brain's attempts to find logic in a picture end up confusing us, leading us to see things that aren't really there. Here, we're going to create a size illusion by playing with the relative distances of nearby and far-away objects.

To get your whole family inside a cup, you'll need:

• A camera
• A cup
• At least 3 members of your family (or a few friends)

The photographer will:

1. Place the entire group against a solid background (a wall, an ocean setting, etc.)
2. Position a chair about 4 meters in front of the group, and place a cup on the chair.
3. Close one eye. Give instructions to the group to move closer or further away, so that everyone "fits" inside the cup before you snap the picture.
4. Before pressing the button, be sure you haven't included any details that might spoil the illusion.
5. You can also take a picture of the family standing in the palm of someone's hand, or one person can be holding the sun or a ship in his hands. You can create all sorts of illusions!
6. Send a copy of your picture to the Science Museum [add a link to the "Send us an Illusion" page]

Where's the science here?
Our perception is not only determined by the picture our eyes see but also by what our brain "knows" and searches for in that picture. The brain interprets the picture based on the knowledge stored in our memories.

Our environment is filled with three-dimensional objects, but the picture they form on our eye's retina is two-dimensional. The brain uses the hints it gets and its past experience to "translate" the picture as three-dimensional. It reconstructs information about the object we see: its shape, size, distance, etc. In this illusion, the brain fails to properly judge distance. It confuses changes in distance with changes in size.

Size and distance illusions occur because of the brain's amazing capacity for perceptual constancy: the tendency to see objects, or characteristics of objects, as unchanging - despite changes in surrounding conditions (see also the Size Doesn't Matter illusion and the Ames Room). To achieve size consistency, the brain "fixes" the perceived size of objects using hints it receives about distance. Under certain conditions, hints from the environment lead the brain to judge the size of a person or object to be much larger or smaller than it really is. That is why the family appears to be a group of tiny people standing in a giant cup.

Related exhibits:

• Chairs from Wonderland
• Size Doesn't Matter
• Dr. Ames' Enchanted Room