2. OPTICALOPTICAL
ILLUSIONSILLUSIONS

3. INDEXINDEX
 DEFINITION
 TYPES OF OPTICAL ILLUSIONS
 PERCIEVING OPTICAL ILLUSIONS-
1. Role of eye
2. Role of Brain
• FACTORS CAUSING OPTICAL
ILLUSIONS
• NATURAL OPTICAL ILLUSIONS

4. 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

5. 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.

6. TYPES OF OPTICALTYPES OF OPTICAL
ILLUSIONSILLUSIONS
There are 3 main types of optical
illusions
 LITERAL OPTICAL ILLUSIONS
 PHYSIOLOGICAL OPTICAL
ILLUSIONS
 COGNITIVE OPTICAL ILLUSIONS

7. I. LITERAL OPTICAL ILLUSIONS
Literal optical illusions are those illusions that create images
that are different from the objects that make them.

8. 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

11. 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

12. 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

13. RUBINVASEILLUSION

14. Distorting illusions offer distortions of size, length, or
curvature.Example:cafe wall illusion
2. DISTORTING ILLUSIONS

15. 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

16. PERCIEVINGPERCIEVING
OPTICAL ILLUSIONSOPTICAL ILLUSIONS

17. THE HUMAN EYETHE HUMAN EYE

18. 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

20. VISUAL PERCEPTION

21. ROLE OF BRAINROLE OF BRAIN
 Retina isresponsible 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

22. FACTORS CAUSING OPTICALFACTORS CAUSING OPTICAL
ILLUSIONSILLUSIONS
Following are the factors causing optical
illusions
1.Colour
2.Eye Structure
3.Depth and distance
4.Past experience
5.Lines and curves

23. 1) COLOUR

24. 2) EYE STRUCTURE
1.Arrangement of rods and cones on retina
2.Peripheral vision

25. 3) DEPTH AND DISTANCE

26. 4) PAST EXPERIENCE
African tribe

27. 5) LINES AND CURVES

28. NATURAL OPTICALNATURAL OPTICAL
ILLUSIONSILLUSIONS

29. RAINBOWS

30. Auroras are natural light displays in the sky, usually
observed at night, particularly in the polar zone. They
typically occur in the ionosphere
AURORAS

32. 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

34. SEEING ISSEEING IS
DECEIVINGDECEIVING

37. HOW MANY BLACK DOTS CAN YOU SEE IN THIS PICTURE

38. There are…..NONE
And….

39. BY THE WAY, HOW MANY LEGSBY THE WAY, HOW MANY LEGS
DOES THIS ELEPHANT HAS?DOES THIS ELEPHANT HAS?

41. 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