An optical illusion is always characterized by visually perceived
images that, at least in common sense terms, are deceptive or
misleading. Therefore, the information gathered by the eye is processed
by the brain to give, on the face of it, a percept that does not tally
with a physical measurement of the stimulus source. This is a list of
twenty amazing illusions.
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 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”.
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 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.
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 eye’s 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. Lilac Chaser
Lilac chaser is a visual illusion, also known as the Pac-Man
illusion. It consists of 12 lilac (or pink or magenta-like), blurred
disks arranged in a circle (like the numbers on a clock), around a
small, black, central cross on a grey background. One of the disks
disappears briefly (for about 0.1 second), then the next (about 0.125
second later), and the next, and so on, in a clockwise direction. When
one stares at the cross for about 20 seconds or so, one first sees a gap
running around the circle of lilac disks, then a green disk running
around the circle of lilac disks, then a green disk running around on
the grey background, the lilac disks appearing to have disappeared or to
have been erased by the green disk.
14. 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.
15. Necker Cube
The Necker cube is an ambiguous line drawing. It is a wire-frame
drawing of a cube in isometric perspective, which means that parallel
edges of the cube are drawn as parallel lines in the picture. When two
lines cross, the picture does not show which is in front and which is
behind. This makes the picture ambiguous; it can be interpreted two
different ways. When a person stares at the picture, it will often seem
to flip back and forth between the two valid interpretations (so-called
multistable perception).
16. 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.
17. Poggendorff Illusion
The Poggendorff Illusion is an optical illusion that involves the
brain’s 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.
18. Adelson’s Checker Shadow Illusion
The image shows what appears to be a black and white checker-board
with a green cylinder resting on it that casts a shadow diagonally
across the middle of the board. The black and white squares are actually
different shades of gray. The image has been constructed so that
“white” squares in the shadow, one of which is labeled “B,” are actually
the exact same gray value as “black” squares outside the shadow, one of
which is labeled “A.” The two squares A and B appear very different as a
result of the illusion.
19. White Illusion
White’s illusion is an optical illusion illustrating the fact that
the same target luminance can elicit different perceptions of brightness
in different contexts. Note, that although the gray rectangles are all
of equal luminance, the ones seen in the context with the dark stripes
appear brighter than the ones seen in the context with the bright
stripes. Note that this effect is opposite to what would be expected
from a simple physiological explanation on the basis of simultaneous
contrast (in that case the rectangles sharing the long borders with the
dark stripes should appear brighter).
20. 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.
source : http://listverse.com/2007/09/16/20-amazing-optical-illusions/
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