Optical Illusions

A blivet 

A blivet, also known as a poiuyt, is an undecipherable figure, an optical illusion and an impossible object. It appears to have three cylindrical prongs at one end which then mysteriously transform into two rectangular prongs at the other end.

The Café Wall Illusion

The café wall illusion is an optical illusion, first described by Doctor Richard Gregory. He observed this curious effect in the tiles of the wall of a café at the bottom of St Michael’s Hill, Bristol. This optical illusion makes the parallel straight horizontal lines appear to be bent. To construct the illusion, alternating light and dark “bricks” are laid in staggered rows. It is essential for the illusion that each “brick” is surrounded by a layer of “mortar” (the grey in the image). This should ideally be of a color in between the dark and light color of the “bricks”.

The Hermann Grid Illusion

The Hermann grid illusion is an optical illusion reported by Ludimar Hermann in 1870 while, incidentally, reading John Tyndall’s Sound. The illusion is characterised by “ghostlike” grey blobs perceived at the intersections of a white (or light-colored) grid on a black background. The grey blobs disappear when looking directly at an intersection.

 The Hering Illusion

The Hering illusion is an optical illusion discovered by the German physiologist Ewald Hering in 1861. The two vertical lines are both straight, but they look as if they were bowed outwards. The distortion is produced by the lined pattern on the background, that simulates a perspective design, and creates a false impression of depth.

Impossible Cube Illusion

The impossible cube or irrational cube is an impossible object that draws upon the ambiguity present in a Necker cube illustration. An impossible cube is usually rendered as a Necker cube in which the edges are apparently solid beams. This apparent solidity gives the impossible cube greater visual ambiguity than the Necker cube, which is less likely to be perceived as an impossible object. The illusion plays on the human eye’s interpretation of two-dimensional pictures as three-dimensional objects.

Jastrow Illusion

The Jastrow illusion is an optical illusion discovered by the American psychologist Joseph Jastrow in 1889. In this illustration, the two figures are identical, although the lower one appears to be larger.

Motion Illusion

One type of motion illusion is a type of optical illusion in which a static image appears to be moving due to the cognitive effects of interacting color contrasts and shape position. To properly view this effect, click the image above to see the full sized version.

 Up down Stairs Illusion

This is a simple, enjoyable optical illusion. Just stare at the picture for awhile, and at first you’ll think that the stairs go up. A fairly simple illusion. But as your eyes look around the picture, and especially if they glance to the left corner, it helps your brain think of the stairs in a different way.
They start to flip perspective and it looks like you’re looking UP at the stairs instead. Then your brain will flip it back. It appears to be impossible to imagine the stairs going both ways at the same time. The picture doesn’t flip the picture, it’s how your brain interprets it.

This red spiral appears to move

This is a great demonstration of illusory movement. It seems the bigger the image and the bigger the screen, the more it appears to work. It also helps if you try to count the objects inside this moving red spiral. As your eyes move around, you'll see the red "dots" flicker.

Start with the outer circle and just move your eyes around as if you are counting the dots. Then try to freeze your eyes and as you don't move them, see if the rest of the image is moving. As with all of our moving pictures, you may want to print them out to prove that they're really not moving, it just looks like they are! Personally, I think it looks like a school of fish, all moving together in quick waves with the ocean. 

Zöllner Illusion

In this figure the black lines seem to be unparallel, but in reality they are parallel. The shorter lines are on an angle to the longer lines. This angle helps to create the impression that one end of the longer lines is nearer to us than the other end. This is very similar to the way the Wundt illusion appears. It may be that the Zöllner illusion is caused by this impression of depth.

Orbison Illusion

The Orbison illusion is an optical illusion that was first described by the psychologist William Orbison in 1939. The bounding rectangle and inner square both appear distorted in the presence of the radiating lines. The background gives us the impression there is some sort of perspective. As a result, our brain sees the shape distorted. This is a variant of the Hering and Wundt illusions.

Source:- Wikipedia