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OPTICAL OPTICAL ILLUSIONSILLUSIONS
INDEXINDEX DEFINITION TYPES OF OPTICAL ILLUSIONS PERCIEVING OPTICAL ILLUSIONS-
1. Role of eye
2. Role of Brain
• FACTORS CAUSING OPTICAL ILLUSIONS
• NATURAL OPTICAL ILLUSIONS
An optical illusion (also called a visual illusion) is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a percept that does not tally with a physical measurement of the stimulus source.
DEFINITITONDEFINITITON
When we experience a visual illusion we may see something that is not there or fail to see something that is there or even see something that different from what is there!
Because of this dissociation between perception and reality, visual illusions demonstrate the ways in which the brain can fail to recreate the physical world. By studying these failings, we can learn about the computational methods that the brain uses to construct visual experience.
TYPES OF OPTICAL TYPES OF OPTICAL ILLUSIONSILLUSIONS
There are 3 main types of optical illusions
LITERAL OPTICAL ILLUSIONS PHYSIOLOGICAL OPTICAL ILLUSIONS COGNITIVE OPTICAL ILLUSIONS
I. LITERAL OPTICAL ILLUSIONSLiteral optical illusions are those illusions that create images that are different from the objects that make them.
PHYSIOLOGICAL ILLUSIONS
Physiological illusions are presumed to be the effects on the eyes or brain of excessive stimulation of a specific type - brightness, tilt, color, movement, etc. The theory is that stimuli have individual dedicated neural paths in the early stages of visual processing, and that repetitive stimulation of only one or a few channels causes a physiological imbalance that alters perception
III.III. COGNITIVE ILLUSIONSCOGNITIVE ILLUSIONS
Cognitive illusions are assumed to arise by interaction with in-built assumptions or 'knowledge' of the world, leading to "unconscious inferences", an idea first suggested in the 19th century. Cognitive illusions are commonly divided into:
AMBIGUOUS ILLUSIONS
DISTORTING ILLUSIONS
PARADOX ILLUSIONS OR FICTION ILLUSIONS
Ambiguous illusions are pictures or objects that elicit significant changes in appearance. Perception will 'switch' between the alternates as they are considered in turn as available data does not confirm a single view. The Necker cube is a well known example. Another instance is the Rubin vase.
1. AMBIGUOUS ILLUSIONS
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Distorting illusions offer distortions of size, length, or curvature.Example:cafe wall illusion
2. DISTORTING ILLUSIONS
Paradox illusions offer objects that are paradoxical or impossible.example:Penrose triangle
Penrose triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.
3. PARADOX ILLUSIONS OR FICTION ILLUSIONS
PERCIEVING PERCIEVING OPTICAL OPTICAL
ILLUSIONSILLUSIONS
THE HUMAN EYETHE HUMAN EYE
STRUCTURE OF EYESTRUCTURE OF EYE
WALLS OF EYE
Tunica Fibrosa Tunica Vasculosa Retina
Sclera Cornea
choroid
Ciliary body
Iris
Photo-receptor cells
Bipolar cells
Ganglion cells
ConesRods
Optic nerve
VISUAL PERCEPTION
ROLE OF BRAINROLE OF BRAIN Retina is responsible for converting light signals to neural signals.
Optic nerve starts at a point in retina called the blind spot
Optic chiasm:-the optic nerve meets here in the first part of the brain
The OCCIPITAL LOBE located posterior in the brain deals with vision
FACTORS CAUSING OPTICAL FACTORS CAUSING OPTICAL ILLUSIONSILLUSIONS
Following are the factors causing optical illusions
1.Colour2.Eye Structure3.Depth and distance4.Past experience5.Lines and curves
1) COLOUR
2) EYE STRUCTURE
1.Arrangement of rods and cones on retina
2.Peripheral vision
3) DEPTH AND DISTANCE
4) PAST EXPERIENCE
African tribe
5) LINES AND CURVES
NATURAL OPTICAL NATURAL OPTICAL ILLUSIONSILLUSIONS
RAINBOWS
Auroras are natural light displays in the sky, usually observed at night, particularly in the polar zone. They typically occur in the ionosphere
AURORAS
A mirage is a refraction phenomena in which the image of some object appears displaced from its true position. A common example of a mirage is the appearance of water some distance down the highway on a hot summer day.
MIRAGE
SEEING ISSEEING IS
DECEIVINGDECEIVING
HOW MANY BLACK DOTS CAN YOU SEE IN THIS PICTURE
There are…..NONE
And….
BY THE WAY, HOW MANY LEGS BY THE WAY, HOW MANY LEGS DOES THIS ELEPHANT HAS?DOES THIS ELEPHANT HAS?
REFERENCESREFERENCES
Textbook of Medical Physiology by Arthur .C. Guyton,John..E.Hall
Elements of chordate anatomy By Charles K. Weichert
Biology textbook for class XII-NCERT
www.physorg.com
www.michaelbach.de
IMAGES: www.google.com