Optical
Illusions
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The brain takes cues from images received from the eyes to help it
interpret what is being seen. Usually this is important for things like
depth perception, but occasionally it leads us astray. The cues deceive
us into thinking we see something that isn't true, or isn't even there.
In the pages that follow, you will see that we can arrange marks on the
paper or on the screen, that will fool your mind into seeing a false
reality. Identical lines will appear to be different lengths, ghostly
dark blobs appear where the screen or paper is white, black and white
patterns appear to move when they can't, etc. They can be so convincing
that you may have to check for your self that there's no trickery
involved.
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Some of the most powerful and well-known
illusions involve the distortion of reality, such that distances appear
longer or shorter than they really are, straight lines appear to bend, and
parallel lines seem to converge. |
Some two-dimensional figures can be interpreted
as solid objects in more than one way. A well-known example of this is the
flat representation of a wire-frame cube, which can be seen as if from
above, or below. |
These tiles create surprising optical illusions
when repeatedly copied to fill the screen. See if you can predict the
effect of each... |
Is the blue face in front or behind?
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Ghostly dots appear between the squares
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The word 'Liar' makes a face
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Necker cube- how is it oriented? Are
you seeing it as if from above, or below?
Click
here for animated Necker Cube
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Which of the two inner
circles is larger? They are both the same size
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The purple lines are
parallel but appear bent
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The diagonal lines
are in fact, parallel.
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The lines of the "V" are the same
length
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The top lines of the two quadrilaterals are the same length.
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The two inner circles are the same size.
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The single line if continued joins with the lower of the pair, not the
top.
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You can see the staircase as if looking from above - or from below.
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The lines appear to bend inwards but are actually straight.
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The lines appear to bend outwards but are actually straight.
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The lines appear to bend inwards but are actually straight.
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The farthest block appears larger than the nearer ones but is the same
height.
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You may see the slabs as if from above or
from below
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The shape is in fact a circle.
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Cube in a Corner
This picture is ambiguous in three ways:
- As a small cube in front of a larger cube;
- As a large cube with a corner cubelet cut out;
- As a small cube inside three perpendicular adjoining planes.
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A
wine goblet - or two faces in profile?
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The
white triangle looks very real, although there's no triangle, per se.
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Is
it a man playing a saxophone, or a girl's face?
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Do
you only see black shapes on white - or a word?
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A
very famous illusion - young lady or old hag? In 1915, a cartoonist named
W.E. Hill first published this drawing. It's hard to see what it's
supposed to be. Is it a drawing of a pretty young girl looking away from
us? Or is it an older woman looking down at the floor? Well, it's both.
The key is perception and what you expect to see. Here's a hint: The young
girl's necklace is the older woman's mouth. The young girl's chin and jaw
are the older woman's nose.
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Poggendorf
In 1860, J. C. Poggendorf, the editor of a journal of physics and
chemistry, received a monograph from Zöllner describing his illusion.
Poggendorff noticed and described another effect of the apparent
misalignment of the diagonal lines in Zöllner's figure. Thus the Poggendorff
illusion was discovered. |
It
is possible to build this - to be viewed from one special
position. However, the general object is impossible. |
An
elephantine variant of the impossible trident.
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Swedish artist Oscar Reutersvard is the
"father of impossible figures." He was the first to deliberately
make impossible figures |
Look at the image above. Move your eyes around
it. Do the dots at the intersection appear to scintillate? |
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http://www.hhmi.org/senses/a/a110.htm
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After
Images |
THINGS TO DO AND NOTICE
Steadily
fixate on the black light bulb for thirty seconds or more. Try not to
avert your gaze. Immediately turn your gaze to the white region on the
right adjoining the bulb (or a blank white sheet of paper). You should see
a glowing light bulb! |
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Stereo
Pictures |
To see the stereo view, fuse the image. If
you cross-fuse, use the right most two images, and if you diverge-fuse,
use the left-most two images. |
To see the stereo view, fuse the image. If
you cross-fuse, use the right most two images, and if you diverge-fuse,
use the left-most two images. |
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M.C.
Escher |
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Optical
Illusion Links |
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