1. 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.
2. Bezold Effect
The Bezold Effect is an optical illusion, named after a German professor of meteorology, Wilhelm von Bezold (1837-1907), who discovered that a color may appear different depending on its relation to adjacent colors. In the above example, the red seems lighter combined with the white, and darker combined with the black.
3. Café Wall Illusion
The cafĂ© 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 cafĂ© at the bottom of St Michaelâs Hill, Bristol. This optical illusion makes the parallel straight horizontal lines appear to be bent. To construct the illusion, alternating light and dark âbricksâ are laid in staggered rows. It is essential for the illusion that each âbrickâ is surrounded by a layer of âmortarâ (the grey in the image). This should ideally be of a color in between the dark and light color of the âbricksâ.
4. The Chubb Illusion
The Chubb illusion is an optical illusion wherein the apparent contrast of an object varies dramatically, depending on the context of the presentation. Low-contrast texture surrounded by a uniform field appears to have higher contrast than when it is surrounded by high-contrast texture. This was observed and documented by Chubb and colleagues in 1989.
5. Ebbinghaus Illusion
The Ebbinghaus illusion is an optical illusion of relative size perception. In the best-known version of the illusion, two circles of identical size are placed near to each other and one is surrounded by large circles while the other is surrounded by small circles; the first central circle then appears smaller than the second central circle.
6. Fraser Spiral Illusion
The illusion is also known as the false spiral, or by its original name, the twisted cord illusion. The overlapping black arc segments appear to form a spiral; however, the arcs are a series of concentric circles.
7. Hermann Grid Illusion
The Hermann grid illusion is an optical illusion reported by Ludimar Hermann in 1870 while, incidentally, reading John Tyndallâs Sound. The illusion is characterised by âghostlikeâ 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.
8. 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.
9. 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 eyeâs interpretation of two-dimensional pictures as three-dimensional objects.
10. Isometric Illusion
An isometric illusion (also called an ambiguous figure or inside/outside illusion) is a type of optical illusion, specifically one due to multistable perception. In the image above, the shape can be perceived as either an inside or an outside corner.
11. 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.
12. Kanizsa Triangle
The Kanizsa triangle is an optical illusion first described by the Italian psychologist Gaetano Kanizsa in 1955. In the image above, a white equilateral triangle is perceived, but in fact none is drawn.
13. 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.
14. Poggendorff Illusion
The Poggendorff Illusion is an optical illusion that involves the brainâs perception of the interaction between diagonal lines and horizontal and vertical edges. It is named after Johann Poggendorff (1796-1877), a German physicist who first described it in 1860. In the image above, a straight black and red line is obscured by a grey rectangle. The blue line appears, instead of the red line, to be the same as the black one, which is clearly shown not to be the case in the second picture.
15. 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.
