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optical illusions

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albertus coro

on 11 January 2015

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Transcript of optical illusions

An optical or visual illusion is any effect on the sense of vision characterized by the visual perception of images that differ from objective reality.
optical illusions
Facts that make us understand optical illusions
• Physiological.
They are the effects of excessive stimulation of a specific type (brightness, colour, size, position, tilt, movement), such as the afterimages, that are the images that are apparently printed in our sight following bright lights.

Let's start...
The human brain is unique. It gives us the power to speak, imagine and problem solve. It is truly an amazing organ.
What does it do?
• It accepts information about the world around you from your various senses

• It lets you think, dream, reason and experience emotions.
All of these tasks are coordinated, controlled and regulated by an organ that is about the size of a small head of cauliflower.
The central nervous system regulates all the conscious and unconscious facets of your life.
• It handles your physical movement when walking, talking, standing or sitting.
• It controls body temperature, blood pressure, heart rate and breathing.
• Pathological.
They arise from a pathological exaggeration in physiological visual perception mechanisms causing the aforementioned types of illusions.

Also known as 6-frame illusion
It seems to be a moving image.
We could even consider magic as an illusion. And that's what it is, just an illusion.
Magicians make people see things which are just unreal. Even when people don´t believe in magic, they stare at it.
But... how do magicians trick us?
Will you be able to keep the secret?...
3 techniques
1. Psychological misdirection
The magician points at an object, a big gesture distracts, spectators fixate on a suddenly appearing dove. All are designed to distract from another movement that is vital for the trick.

3. Mental forcing

The simplest physical forcing is asking a spectator to pick a card from a special pack containing 52 aces of spades. But magicians consider this inelegant and prefer to use mental forcing to create their effects.

The spectator is put under pressure to choose but, at the same time the free choice is still emphasised.

2. Cognitive illusions

Magicians also use mental illusions which can fool our attention or play with the way we predict the future.

The most common example is where a coin is made to disappear after it is apparently passed from one hand to the other, when it has in fact been palmed. Because the mind is already working ahead, assuming the coin has been passed to the other hand, it’s as though it has disappeared when the other hand is revealed to be empty.
let's play
"A big movement hides a smaller one."
Our perception of images varies depending on factors such as visual acuity, colour blindness, astigmatism...
Look at this picture for 20 seconds. Then, blink quickly while looking at the wall. You will see the image in its real colours!
How many legs has this elephant?
• Cognitive.
They are the result of unconscious inferences.
They are commonly divided into:
Ambiguous illusions
are pictures or objects that elicit a perceptual "switch" between the alternative interpretations.
Necker cube on the left, impossible cube on the right
Rubin vase
Distorting or geometrical
optical illusions are characterized by distortions of size, length, position or curvature.
Café wall illusion
Ponzo illusion
Müller-Lyer illusion
Paradox illusions
are generated by objects that are paradoxical or impossible.
Penrose triangle
Impossible staircase
are optical illusions in which a figure is perceived even though it is not in the stimulus.
Some types of tricks
Sparkling or glowing grid
makes you believe that points at the intersections between two lines appear and disappear.

Hermann grid
makes you feel that there are "ghost" spots at the intersections of the lines.
It's an optical illusion in which distant objects are reflected in a smooth surface and it seems like you are seeing a liquid surface that actually does not exist.

It is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky.
Holography is an advanced technique of photography that consists on creating three-dimensional images based on the use of light. It is used a laser beam that records microscopically a photosensitive film. When this film receives light from the proper perspective, it projects a three dimensional image.
It is an illusion of visual perception in which a light area of the visual field looks larger than an otherwise identical dark area.
It is a graphical representation of three-dimensional objects on a flat space projecting them, using stereoscopy, so they seem to have volume.
art and optical illusions
Also known as optical art, it's a style of visual art that makes use of optical illusions to create an impression of movement, or hidden images and patterns.
It's an art technique that uses realistic imagery to create the optical illusion that the depicted objects exist in three dimensions.
It's a technique that employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is.

It is used primarily in
Some artists who have worked with optical illusions
M. C. Escher
Salvador Dalí
René Magritte
The human brain can only focus on one object, so when there are two different forms in a single image, the brain gets confused and we perceive a distinct view of reality.

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