Types of Illusions
Illusion (lat. Illusion - deception, mistake) - the distorted perception of a real object or a scene. Illusions may appear at a morbid (physical, physiological illusions, metamorphopsia).
Physical - dealing with the real-world laws of Physics (EG: optical illusion: a spoon, partially sunk in a glass of water seems to be broken);
Optical Illusions - eye perception errors, caused by inexactness or inadequacy of subconscious image correction processes.
Sound Illusions, EG Shepard's tones.
Physiological - caused by the features of the peripheral or central analyzer cells (sense organs) of a human (for example: if you rise two items of different mass at the same time with your both hands several times and then repeat it with another couple of items of equal mass, the item in the hand where there was the easier one before, will seem heavier than the item in another hand).
Affective - appear under the influence of mood change or caused by emerging effect of fear or anxiety;
Verbal - appear as a result of distorted perception of other people's talks.
Limited (Matamorphospia) - distorted visual perception of shape, size, color, position in space, static or moving state of a real object; there are autometamorphospia (you feel your own body parts' size or shape change) and exometamorphospia (wrong perception of surrounding objects); this disorder may happen not only to a morbid but also to healthy people with view organs pathology;
Illusion of understanding (embodied understanding) - A feeling that there's someone near you; this illusion was found by C. Jaspers; the author thought that this type of illusions was the sign of hallucinations and delirium.
Pareidolic (functional illusions) - a special kind of illusions where at complex patterns (on a carpet or winter glass) you can see different fantastic images with time.
Optical illusions (or visual illusions in the narrow meaning) - visual perception errors, caused by inexactness or inadequacy of the processes of subconscious correction of a visible image (the Moon illusion, the wrong estimation of length, angles or color of the pictured object, motion illusions, illusion of object absence - the banner blindness etc.) and physical reasons ("The oblate Moon", "The broken spoon" in a glass of water). The reasons of optical illusions are being researched both in the field of sight physiology, and the psychology of view perception.
Optical illusions show that you can't always believe what you see. Many people think that reality is only what you see. Optical illusions show the existence of unobvious things in our life - the illusory phenomenon.
Playing with optical illusions can help you change your conscious. We trick our brain to lure it at the new levels of perception. And then we can see things that don't exist.
Color Perception Illusions
We know for about one hundred years that when there appears an image on our retina, that has bright and dark parts, the light of the bright zones seems to overflow to the darker parts. This phenomenon is called the Optical Irradiation.
Depth perception illusions are the inadequate reflection of the perceptible object and its properties. Today the most studied are the illusory effects that happen during 2D contour images perception. Subconsciously our brain sees only one-convex (one-concave) images. Our perception depends on the direction of the outer (real or supposed) light.
Illusions often cause the wrong quantity evaluations of the real geometric values. It turns out that you can be mistaken for even more that 25% if you don't re-check your EST ratings with a ruler.
The ESTs of the real geometric values depend much on the image background character. This applies to lengths (the Ponzo Illusion), squares and radiuses of curvature. It's also may be applied to angles, shapes and so on.
- Static image seems to move.
- When watching two moving balls they might seem to be of different size.
- The same rotating image might rotate in different directions or even perform oscillation moves.
Flipover - a kind of optical illusion where the character of the perceived object depends on view direction. One of them is the "duck-rabbit": the image may be treated both as a duck and as a rabbit.
The Stereopairs put on a periodical structure (Bela Julesz, Hungary) allow to see a stereo-image just like an ordinary stereopair. Periodical image makes eye-splitting easier for us (as a rule - to the infinity), so after focusing at some centimeters you can see a stereo-image. Partially this method allows combine the stereopair images removing the limits of their size but putting another limit about the content of the picture and is calculated by computers.
Optical illusion - the impression about the visible object or a scene that doesn't match the reality, i.e. optical deception. Some visual deceptions have scientific basis; others still can't find the explanation. Why do the optical deceptions appear?
Human visual apparatus is a very complicated system that has definite abilities and limits. We meet optical illusions very often in our every-day life.
First of all these are the ordinary optical illusions you've read about -mirages. You can often find light deceptions dealing with color of the Sun at sunrise or sunset and illusions dealing with the size of celestial orbs at the skyline.
Lots of illusions can be explained by the construction of a human's eye and its limited abilities. There are so many car accidents on crossroads with traffic-lights at twilight when your eyes adapt the new conditions or at night when drivers think the traffic-light to be just a street-light. When you chose the right pattern for your wallpapers you can visually enlarge a small room. When you chose the right fabrics color you can hide the lacks of your figure. Though, visual illusion is not always just the play of light and shadow or a natural perception of an object. There are lots of specially invented optical puzzles, having amazing effects.