Let’s look at this picture. There are two circles around the black dot. Now move your head forwards and backwards. Then you will see that the two circles seem to move when your head is moving forwards and backwards while looking at the black dot. Now stop. They don’t move anymore. (It’s only a two-dimensional space: this magazine!) Is this picture kidding you? The answer is ‘No.’ It is an ‘optical illusion.’
The Egocentric Study, Optical Illusion
An optical illusion is characterized by visually perceived images that are deceptive or misleading. A normal human being learns an object’s objective characteristics like figure, size, and volume through repeated study. The source of this study remains the human’s brain. When this study faces the real object with a human’s eyes, the learned data and the optical action create an impact, and our eye perceives a ‘difference’ between them. This difference is continual, but we usually designate optical illusion when the differential gap is especially large. Let’s look at some examples of optical illusion. We have already learned perspective. (The background object looks smaller than the object in the foreground than in reality) Therefore we infer that the object in the background is bigger than that in the foreground. But you know that each bar’s length is actually same in the following pictures. * Measure their lengths with a ruler. They are the same.*
The other reason for optical illusion is mainly the afterimage effect. The human brain keeps a picture’s image even if the subject has only looked at the picture for a short while. This afterimage is put together so that it appears to be moving. The principle of animation is similar to this, the afterimage effect.
Geometrical Illusions
Geometrical and distorted illusions are also optical illusions; the geometrical relationship such as length, angle, direction, or size looks distorted. Look at the Ebbinghouse Illusion. When you compare the picture on the left, you can see that the size of each concentric circle is the same. Other circles obstruct you from seeing the concentric circles. Observe the other picture, the Müller-Lyer optical illusion. The segments which are actually the same length look different according to the arrows’ direction; the upper segment appears longer than the lower segment. This is because our brain judges length with form. In this sentence, ‘length’ means segment, ‘form’ means the total length of these objects. Namely, comparing their whole length, the upper object is longer than the lower, so we perceive that the upper segment is longer.
*Which concentric circle looks smaller? Their length is the same.*
Light and Shade Illusions
We have learned about light and shade in art class. A white area surrounded by a black area looks bright than other areas, while a black area surrounded by a white area looks darker than other areas. Look at the lower picture, named ‘Hermann Grid Illusion.’ If you examine it carefully, you can see many gray spots at the points where the grids cross. The reason is also in our eyes. Let’s enlarge this picture. Part ‘B’ is closer to the black area than part ‘A’, so part ‘B’ looks brighter. But part ‘A’ is relatively further from the black area than part ‘B’, therefore you see gray spots. * Hermann grid illusion*
Ambiguous Illusions
Ambiguous illusions are pictures or objects that elicit a perceptual 'switch' between the alternative interpretations. They arise from the human perception that if one part of an object is focused on, the other part appears to be in the background. The Rubin Vase is a well known example.
* What is this picture? A vase or two faces? * My Wife and My Mother-In-Law*
Use of Optical Illusions
These days optical illusions are used for interest in constructions like theme parks. However it is made use of in real life. A good example of optical illusion is clothing. The vertical emphasizes length by taking down our view, and makes the wearer look longer and thinner than they really are. Optical illusions are also utilized in golf course design. If the distance to the hole is shorter, the designer makes fewer undulations, so the golfer feels that the distance is longer than it really is.
All sources from Wikipedia (http://en.wikipedia.org/wiki/Optical_illusion)