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