This project idea comes to you from Folie Technique in Montreal, Quebec.

To understand the principles of perception by looking at optical illusions.

Your eyes are optical instruments, like the microscope and the telescope, but they can adjust more easily. Your eyes can tell different colours apart, they can adapt very quickly to variations in the amount of light they're receiving, and they can focus themselves automatically.

The iris controls the quantity of light entering the eye. The lens focuses the light. Each retina is composed of 7 million cone cells that detect colours and 12 million rod cells that detect black and white shapes as well as movement. The eye forms a reversed image on the retina. Right at the beginning of your development as a baby, your brain learned to turn the reversed image right-side up and to interpret it.

Your perception of the world is a translation, a transposition under another form of reality; it is not loyal to reality because your brain adds to, removes from, reorganizes, and interprets the sensory clues it receives. And your senses can trick you. This is what we call an optical illusion.

If you want to look at the optical illusions on your computer screen, just keep reading. If you want to show them to friends or bring them to school, however, you'll have to save them and print them.

1. Each of us has a dominant eye; this eye is privileged by the brain to process information.

EX 1. Stretch your arm out and stare at one of your fingers while you alternately close each of your eyes. Your finger will seem to move more with one eye closed; this is your dominant eye. Scientists who use telescopes or microscopes prefer to use their dominant eye.

2. Tendency to perceive objects:
   Perception is global, which means that it is easier for your brain to perceive objects rather than infinite groups of points.

EX 2. If you draw a line, you see a line and not a quantity of lined-up points.

1. Rule of proximity:
   Tendency to "put together" elements that are the closest together.



According to the placement of the dots, you see rows or columns, but each figure contains the same number of points and has a comparable surface.

2. Rule of resemblance:
   Tendency to "put together" elements that are similar or that are repeated.



You see rows or columns according to whether the black dots are placed in rows or in columns.



Three zones are delimited according to the same principle.

3. Rule of symmetry:
   Tendency to perceive as objects things that are symmetrical rather than things that are asymmetrical.



On the left, you see white columns while on the right, you see black columns. And yet they are the same pattern only with the colours reversed.

4. Rule of good continuation:
   Tendency to follow the appearance of the general alignment of the elements of a figure. This is the basis of all camouflage.



You see a circle covered by an X rather than pieces of pie with the separating lines going beyond the pie.

5. Rule of closure:
   Tendency to complete the missing parts of an object.



According to the rule of closure, you see squares instead of the columns which the proximity of the lines suggests. You also complete the square delimited by the black dots even though it doesn't exist. Same for the triangle.

6. Sense:
   Tendency, after having perceived the essence of a drawing, to not be able to see it as you had seen it before.



A hunter walking with his dog behind a fence.



Person squatting, washing the floor, with a bucket on the left. The letter B or the number 13.



A cup or the hips of a child.

3. Figure-ground perception:
   Tendency to detach a figure from its background, and vice versa. You can't organize all the information in one idea, or see the object suggested by the background at the same time as the one suggested by the figure.



An old woman with a hood in black or the profile of Scrooge with a long nose in white. You also see a cup or two figures facing each other.

4. Perceptual constancy:
   Things remain the same in your mind in spite of important modifications in their presentation on the retina.
1. Size constancy:
   Size varies with distance, but you perceive it as constant.



2. Shape constancy:
   In spite of variations caused by changes in angle and orientation, you perceive form as constant. See FIG 11.





You perceive the rhombus as a square when it is placed on the cube.



You see the pyramid differently depending on the angle.

3. Colour constancy:
   Colour varies with lighting, but you perceive it as the same. Look at the shirt you are wearing in the dark and then in the light.



4. Brightness constancy:
   Tendency to see the environment around a dark object brighter than normal.



Notice the brightness near the black spots.

Continue to more optical illusions.