Most of the deceptions of view, as already mentioned, depends on what we do not only look, but also unconsciously in this talk. "We look not with the eyes and the brain," say psychologists. You will readily agree with this, when you get acquainted with illusions, where the imagination of the beholder consciously involved in the process of vision.
Take a look at Fig. 1. If you will show this picture to others, you will get a threefold answer the question of what it depicts. Some will say that this staircase; others say it's a niche, recessed in the wall; the third, finally, will see it as a paper strip, bent "harmonic" and extended obliquely in the white box square.
Figure 1. What you see here, the stairs, niche or strip bent "harmonic"?
Oddly enough, all three answers are correct! You can see all these things, if, looking at the figure , you do in a different way.
Namely, looking at the drawing, try first of all to look at the left part of the picture, you will see stairs. If your opinion will slip on the picture from right to left, you will see a niche. If your opinion should be slanted towards the diagonal from the lower right edge to the top left, you will see a folded "accordion" paper strip.
However, during prolonged viewing the attention be weary, and you will see alternately one, then another, then a third, already regardless of your desire.
Figure 2. How are there in Cuba? Where two cube - top or bottom?
A curious illusion Fig. 3; we unwittingly give the impression that the distance AB is shorter than AC. Meanwhile, they are equal.
Figure 3. Which is longer, AB or AC?