2. What is an Illusion?
il·lu·sion (-lzhen) 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
3. 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”
5. 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
6. History of Illusions
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
7. History of Illusions
A. Ideal Parthenon
B. Architrave Illusion
(Jastrow-Lipps)
C. Illusionary Distortion
D. Alterations made to
offset illusion
8. 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.”
-Vitruvius
10. History of Illusions
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
11. History of Illusions
1596 - 1650 Descartes:
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 - 1800 Given 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
12. History of Illusions
1800 - 1870 Experimental 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
13. Current State of
Illisions
Conclusion:
Paradigmatic Science (Psychology)
1900s
Normal Sciences => Anomoly => Crisis => Revolution
Current status: Normal Science
- mopping up
- puzzle solving
- guidelines for research
25. 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
26. 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
