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OpticalIllusions

Seeing Is Deceiving

Christopher Landauer

Science of Art

March 9, 2000

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?

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

Prehistory:

Afterimage caused by glancing at the sun
A stick half in and half out of water

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

c. 450 B.C.

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

-Epicharmus

“Man is nothing but a bundle of sensations”

-Protagoras

c. 300 B.C.

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

-Plato

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.”

-Aristotle

A. Ideal Parthenon

B. Architrave Illusion

(Jastrow-Lipps)

C. Illusionary Distortion

D. Alterations made to offset illusion

“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.”

-Vitruvius

Entasis:

Convexing of column to overcome parallel lines appearing concave

Irradiation Illusion:

Bright objects appear larger

Conclusion:

“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

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

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