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Optical Illusions. Seeing Is Deceiving. Christopher Landauer Science of Art March 9, 2000. What is an Illusion?. il·lu·sion ( î -l ¡¹ zh e n ) noun 1. a. An erroneous perception of reality. b. An erroneous concept or belief.

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optical illusions

Seeing Is Deceiving

Christopher Landauer

Science of Art

March 9, 2000

what is an illusion
What is an Illusion?

il·lu·sion (î-l¡¹zhen) noun

1. a. An erroneous perception of reality.

b. An erroneous concept or belief.

2.The condition of being deceived by a false perception or belief.

3.Something, such as a fantastic plan or desire, that causes an erroneous belief or perception.

4.Illusionism in art.

  • Latin root of illusion is illudere which means “to mock”
  • Optical illusions mock our trust in our senses
  • Suggest that the eye is not a passive camera; rather,
  • perception is an active process that takes place in the
  • brain and is not directly predictable from simple
  • knowledge of physical relationships
what s the big deal
What’s the big deal?
  • Human reliance on correspondence between conscious experience and physical reality
  • Continual verification of our senses
  • Cultural Heritage
    • “Seeing is Believing”
    • “See it with my own two eyes”
history of illusions
History of Illusions


  • Afterimage caused by glancing at the sun
  • A stick half in and half out of water
history of illusions5
History of Illusions
  • 500 B.C. - Height of the Greek Period
  • “The eyes and ears are bad witnesses when they are at the service of minds that do not understand their language”
  • -Parmenides
  • Two Viewpoints on Perception:
    • 1. Sensory inputs are inaccurate. Mind corrects these inaccuracies to
    • provide an accurate representation of the environment.
    • Illusions: Senses are relied on more than the Mind
    • 2. Senses are inherently accurate and produce a true picture of the
    • environment. Mind is limited.
    • Illusions: Mind interferes with the Senses
history of illusions6
History of Illusions

c. 450 B.C.

“The mind sees and the mind hears. The rest is blind and deaf.”


“Man is nothing but a bundle of sensations”


c. 300 B.C.

“We must perceive objects through the senses but with the mind”


384 - 322 B.C.

“Each sense has one kind of object which it discerns, and never errs

in reporting that what is before it is color or sound; Although, it

may err as to what it is that is colored or where it is, or what it is

that is sounding, or where it is.”


history of illusions7
History of Illusions

A. Ideal Parthenon

B. Architrave Illusion


C. Illusionary Distortion

D. Alterations made to offset illusion

history of illusions8
History of Illusions

“For the sight follows gracious contours; and unless we flatter its pleasure by proportionate alterations of the modules--so that by adjustment there is added the amount to which suffers illusion--an uncouth and ungracious aspect will be presented to the spectators.”


history of illusions9
History of Illusions


Convexing of column to overcome parallel lines appearing concave

Irradiation Illusion:

Bright objects appear larger

history of illusions10
History of Illusions


“More of an Art than a Science”

Early Preparadaigmatic Science

-Trial and error

-Aesthetic, not scientific

-No factual understanding

-No treatsies

-No schools of thought

history of illusions11
History of Illusions

1596 - 1650Descartes:

There is both a registration stage and an interpretation stage in the perceptual process. Perceptual error or illusion may intrude at either of these two steps along the road to consciousness.

1700 - 1800Given at Birth vs. Learned through Experience

Reid & Kant:

All knowledge of the external world comes directly

through the senses and is interpreted by innate mechanisms

Berkeley & Hume:

All perceptual qualities are learned through experience with the environment

history of illusions12
History of Illusions
  • 1800 - 1870Experimental Foundations
  • Mueller, E.H. Weber, Helmholtz, Baldwin, Hering use Physics, Physiology, Philosophy to form treatises
  • Specialist and Non-specialist working in area of visual geometric illusions carrys on to the present
  • 1922 - Luckiesh: lighting engineer 1964 - Tolansky: physicist 1972 - Robinson: psychologist
  • 1900s Revolution and Rebirth
    • Behaviorists vs. Gestalt
    • Methodology vs. Theoretical
    • Percepual response & Brain wave patterns
current state of illisions
Current State of Illisions


Paradigmatic Science (Psychology)


Normal Sciences => Anomoly => Crisis => Revolution

Current status: Normal Science

- mopping up

- puzzle solving

- guidelines for research

ambiguous figures
Ambiguous Figures

Face or Vase?

ambiguous figures15
Ambiguous Figures


Nels Isralson

L'Amour de Pierrot c.1905

Gossip and Satan

Geo. A. Wotherspoon

ambiguous figures16

Bust of Voltaire

- Houdon, 1781

Ambiguous Figures

Slave Market With the Disappearing Bust of Voltaire

- Salvadore Dali, 1940

ambiguous figures17
Ambiguous Figures

The Great Panoramic

- Salvadore Dali, 1936

ambiguous figures18
Ambiguous Figures

Multiple Figures





ambiguous figures19
Ambiguous Figures

Mask Concavity

ambiguous figures20
Ambiguous Figures

Mach’s Figure

ambiguous figures21
Ambiguous Figures

Schroder’s Staircase

ambiguous figures22
Ambiguous Figures

Oscillating Cubes

ambiguous figures25
Ambiguous Figures

Cube looks like a cube.

“Equal sides and right angles.”

Eye: Perspetive projection

Reverse: Topless pyramid change of shape

Cube looks distorted, on face smaller than the other.

Depth is paradoxical

Reverse: No Change

ambiguous figures26
Ambiguous Figures

Cube does not look like a cube.

Eye: Near face is same size as far face

Reverse: Topless pyramid further face always looks larger

Necker Cube. No face is front or back by perspective

Depth is paradoxical

Reverse: No change

ambiguous figures27
Ambiguous Figures
  • Possible views:
  • Cube with corner missing
  • Box in corner of room
  • Small cube infront of large cube

3 in 1 Illusion

ambiguous figures28
Ambiguous Figures

Cube / Room

  • Possible views:
  • 3D Cube
  • Corner of Room