|You Are Here: HOME >> science mysteries » illusions & brain teasers >> cognitive illusions|
The way you look at an object can affect how you see it. Sometimes there are two images in the same picture, but you can only see one at a time so your brain chooses one (when it deals with too much information).
Cognitive “illusions” rely on stored knowledge about the world (depth, rabbits, women) and are also under some degree of conscious control (we can generally reverse the perception at will).
Cognitive Illusions - Examples
Ambiguous figures demonstrates our
ability to shift between figure and ground which provides the
basis for the two interpretations of these figures.
The Reversible Figures
Look at the red dot. Is it located in the upper right front
This reversible figure is called the Schroder
Are you looking at this cylinder from left to right or right to left?
Rabbit or a Duck?
A young lady or an old woman?
Click on 3 images above to enlarge.
There are 9 people in this picture, which is a
For more, please visit Official Website of Octavio Ocampo
Mysterious Figures: Dark Angel
Tessellations in art can be mainly linked to M.C. Escher, a Dutch artist, born in 1898. After being a graphic artist, he traveled to Spain and did sketches of the art he saw at the Alhambra, a Morrish temple. He became interested in tilings and started to incorporate geometric designs into his art. Escher created hundreds, maybe thousands, of tessellating shapes in the forms of fish, dogs, crabs, and other beasts.
Completion figures are figures which the mind rather unambiguously interprets in a particular way despite the fact that the input is incomplete relative to what is typically "seen". Illusory contours may be partly accounted for by low level contrast effects, partly by more cognitive processes inferring the existence of occluding objects.
These two Kanizsa figures shown above illustrate the mind's willingness to see an equilateral triangle despite the fact that no border information about the center triangle is in the picture.
Do you see the letter "E" or just black lines?
Paradox Illusions: Impossible Figures and Objects
Version by Penrose
Another version of the
Another version of the
More Impossible Objects
Impossible wheels - by M.C. Escher
Instructions from hell
Near the ground, you can count five different elephant
M.C. Escher was very clever at representing impossible
Follow the stairs on the castle terrace.
M.C. Escher "Drawing Hands", 1948 (lithography)
Stereograms - 3D illusions
Stereograms are 3D images hidden within another picture. In order to view the 3-D images, simply stare at the picture until the image starts to take shape.
Zen Spiral. Can you see the hidden image?
Geometric illusions are examples of how our mind attempts to find
orderly representations out of sometimes ambiguous and disorderly 2d
images. The images transmitted from our retina to our brain are imperfect
representation of reality (for example 2d images cannot accurately
represent 3d space). Our visual system is capable of performing complex
processing of information received from the eyes in order to extract
meaningful perceptions. Sometimes, however, this process can lead to faulty
The Café Wall Illusion. Are the lines crooked are straight? If you stare at a single cube, do the adjacent lines appear to slide past each other?
Some visual stimuli cannot be perceived in a way that accords with what we can measure (with a ruler or similar) e.g. The Café Wall Illusion Even if we know that the lines of mortar are all straight, we see them as sloping. Illusions are cases where we find significant differences between perceived and measured reality (a very broad definition).
The center connecting line is seen as shorter
The figure above shows both figures superimposed on one another in order to demonstrate in yet another way that the center line is of equal length in both figures.
Which line is longer, AB or BC?
You probably perceive the middle circle as smaller in the figure on the left than the circle in the center of the second figure. They are actually the same size.
Perspective, Depth and Distance
Your eyes judge distance based on the size of objects and where the objects are positioned. For example, if you don’t know the size of two objects, you may see one as smaller because it is farther away. In reality, the objects are the same size. An easy way to think about this is by using train tracks. Train tracks appear to get smaller as they get farther away, but as you move along them, you see they are the same. Lines that appear to come together in the distance make you have a distorted perception of distance.
Version of Ponzo Illusion.
The variation in the apparent size of the Moon (smaller when overhead, larger when near the horizon) is another natural illusion; it is not an optical phenomenon, but rather a cognitive or perceptual illusion.
Moon Illusion. The moon illusion is one of the most famous of all illusions. Stated simply, the full moon, when just above the horizon, appears much larger than when it is overhead. Yet the moon, a quarter of a million miles away from the earth, always subtends the same angle wherever it is in the sky, roughly 0.5 degrees.
Explanation: Is the Moon larger when near the horizon? No -- as shown above, the Moon appears to be very nearly the same size no matter its location on the sky. Oddly, the cause or causes for the common Moon Illusion are still being debated. Two leading explanations both hinge on the illusion that foreground objects make a horizon Moon seem farther in the distance. The historically most popular explanation then holds that the mind interprets more distant objects as wider, while a more recent explanation adds that the distance illusion may actually make the eye focus differently. Either way, the angular diameter of the Moon is always about 0.5 degrees. In the above time-lapse sequence taken near the end of last year, the Moon was briefly re-imaged every 2.5 minutes, with the last exposure of longer duration to bring up a magnificent panorama of the city of Seattle.
Moonrise Over Seattle. Credit & Copyright: Shay
How does this illusion come about? Since the moon always subtends an
angle of 0.5 degrees, the image on the retina must always be the same.
Clearly the problem is one of interpretation. One simple experiment shows
this to be so. A full moon just above the horizon will not appear so large
to the human eye if a piece of paper is held up to that eye with a hole in
it, so that only the moon can be seen through the hole and not the
horizon. If the other eye is open at the same time, viewing both the moon
and the horizon, the two eyes will each see different sized moons!
The explanation is believed to be as follows. We 'know' that a cloud that is overhead will be larger than when it moves towards the horizon. And an airplane that is a mere speck on the horizon becomes large when it is overhead. And we are all familiar with standing under a tree which seems enormous, yet at a couple of hundred paces seems insignificant. It would seem that so much of our world is interpreted this way that we are ill-equipped to cope with an object like the moon, that subtends the same angle at the eye, whatever position it occupies in the sky. And so our brain 'interprets' the image that it 'sees', and tells us that the moon is larger than it really is.
People have thought that the thicker atmosphere along the horizon could
act as a magnifying glass enlarging the image of the full Moon when it is
on the horizon. That could not be the case as there is not enough
atmosphere around the Earth to cause a dramatic lens effect. Anyway,
according to the laws of physics, if the atmosphere was really refracting
the image of the Moon, it would appear smaller!
Regardless of its elevation, the distance between an
observer (at the center of the horizontal line) and the moon remains
constant (unfilled circles). However, a moon perceived as growing closer
as its elevation increases (filled circles), must appear as growing
Some scientists have proposed that the Moon Illusion effect depends on
our perception of the sky as a flat-topped dome the rim of which appears
further away than the top of the dome. The effect of this error in
perspective is for the Moon overhead to appear smaller than the horizon
Moon. The diagram (fig. 2) opposite shows the apparent location of the
Moon at various points as it travels across the sky. This is the diagram
commonly seen in books promoting this hypothesis… But the diagram can be
misleading! The hemispherical flat-topped dome in the picture is not of
proven relevance to the effect and ought to be omitted as it falsely
suggests a mental process of "projecting" the moon onto that dome.
Others have proposed that the Moon Illusion had to do with the fact
that the eye-brain system is designed to work on the horizontal plane, not
the vertical plane. On the horizon we process the Moon image in the
optimal orientation giving us its true apparent size. Tipping our head
back to view the high Moon, we see a non-optimal image. The illusion is
not that the horizon Moon is larger, but that the overhead Moon is smaller
in size than it "ought" to be. Others have argued that comparisons with
buildings and other objects on the horizon are responsible for the
differences between the Moon’s apparent size when looking horizontally and
looking vertically (this explanation is contradicted by the fact that the
Moon Illusion also occurs over open water).
Finally, here is an explanation that is sufficiently satisfactory. The effect of this illusion is due mainly to the fact that our brain interprets the sky as being farther away near the horizon, and closer near the zenith (directly overhead, see fig. 3 opposite). This isn’t surprising; look at the sky on a cloudy day and the clouds overhead may be a few kilometers above you, but near the horizon they might be hundreds of kilometers away. The Moon, when it’s on the horizon, is interpreted by your brain as being farther away. Since it’s the same apparent size as when it’s high up, your brain figures it must be physically bigger (as illustrated in fig. 4 further below). Otherwise, the distance would make it look smaller. This effect is the well-known Ponzo Illusion (fig. 5.a). Actually, the Moon Illusion effect is the result of a mix of Ebbinghaus size illusion (fig. 5.b) plus Ponzo illusion (see resulting fig. 6).
_ _ _
Moon Illusion Links:
Click on the image below for the solution of this puzzle.
Copyright 2003-2011 by www.World-Mysteries.com
Illusions and Brain Teasers. Explore
Ambiguous Figures, Reversible Figures, Impossible Figures and Objects,
Contrast and Color effects, Illusion Artists.