An Optical Illusion

Do you trust your eyes? If so, how can you trust your eyes?  The picture is famous for optical illusion.  Can you believe the square marked A and the one marked B are exactly same colour?  You may say "A is much darker than B"; however, they are same.  This is called an optical illusion (or visual illusion), which is characterized by visually perceived images that differ from objective reality.  There are three main types: literal optical illusions, physiological optical illusions, and cognitive optical illusions.


Initially, literal optical illusions create images that are different from the objects that make them.  For example, the lines in following picture are actually parallel, but we somehow feel they have angles.
Zollner, who were Geman, found this optical illusion.  I don't know why our eyes are deceived in this case.  According to Zollner, oblique lines in each parallel lines influence our brain, and the bigger the angle of oblique line is, the more effective it is.  I have a lot of examples about this kind of simple optical illusion, so if you  guys want me to introduce them, let me know!



The second type of optical illusions is physiological one.  This one is the effects on the eyes and brain of excessive stimulation of a specific type such as brightness, colour, size, position, tilt, or  movement. For example, look at the left picture.  Although there are only white dots on the cross, we can see black dots there.  The theory is that a stimulus follows its individual dedicated neural path in the early stages of visual processing, and that intense or repetitive activity in that or interaction with active adjoining channels cause a physiological imbalance that changes perception, according to the literature on this subject.


The third type is cognitive optical illusion.  This type is  called "unconscious inferences". This idea was suggested in the 19th century by Hermann Helmholtz.  For example, look at the right picture.  What do you think this picture looks like?  Some people might say this is two faces which gaze at each other.  The other people might say this is vase.  If we change the way to see it, we can find other shape in a same picture.


What are optical illusions teaching us?  What I wanted to say with using those example is a very simple but important thing. That is, nobody can say "what I see is absolutely correct".  People usually believe only what they can see; however, sometimes truth is hidden.  If we change the way to see, we may be able to see what we haven't seen or what other people usually see.


P.S.
I put the picture which clearly explains the first picture because some of you may be still doubtful.