AN INTRODUCTION TO ILLUSIONS

This section is devoted to the magic of illusions, and contained here are a selection of illusions ranging from very basic art illusions to animation-based eye-teasers. Some of these will leave you dumbfounded while others will make your brain hurt as you try to understand how they could have been created in a world governed by fundamental physics. Of course, the illusions you see aren't breaking the laws of the universe - though it is these rules which help to make the illusions work.

Each human eye takes in a two dimensional (2D) image - this is a flat picture of whatever you are looking at. As we have two eyes, we cope with a dual-2D image of the world around us. By combining the pictures from both eyes, our brain is able to determine "perspective", and thus create a 3D image in the mind. A 3D image is one with depth to it, which enables us to determine relative distances of objects from ourselves, and contributes to our overall spatial awareness (awareness of where you are in relation to everything around you). To make our lives a lot easier, our brains do not try to logically determine everything we see - instead, they apply these rules of thumb to the images and make a reasonable judgment based upon what we already know.

If you look at a car approaching you as you cross the road with both eyes, your brain uses the focal distance (the point at which the images from both your eyes convene on the car) to determine how far away the car is. As your focal point changes, you are able to estimate the speed of the car.. which is obviously more accurate as the car gets closer (since your eyes would move a greater amount in relation to the distance the car moves in order to track it). If you closed one eye you would only see a 2D image, meaning you would not be able to judge the distance or speed of the vehicle.

However, as you know, you would be able to look at a car with one eye and guess how far away it was. This is because your brain applies a number of other assumptions when assessing the situation. You know roughly how big a car is, and so if the car you see is small, you know that it is far away. You determine the size of something by comparing it to it's surroundings. By removing the surroundings you lose all perspective of the car, and judging it's distance would be impossible.

You might encounter this situation if you saw a picture of a car in a magazine against a white background. With only a 2D image and no scenery to compare the car to, you do not know how big it is. Your brain copes with this situation by applying the final rule of thumb, and also the most random - memory. You know how big a car is, and it looks like other cars so you "expect" it to have the same proportions. In fact you may be looking at a 1:4 scale model, but you would never be able to determine that. Your brain has filled in the blanks.

The creators of optical illusions play on this fact alone.. If a computer eye looked at any of these images, it would see only the lines, it would not see the "impossible" shape or image, it would simply interpret only the data it has to work with. Your brain sees an image and misinterprets it according to what it expects to be seeing

The following pages explore a number of different types of illusion, and provide a short explanation of how the illusion works. Please note that these pages may take a while to load on a slow modem, due to the graphical content.