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					Optical Illusions

               Christopher Landauer
               Science of Art
               March 9, 2000
What is an Illusion?

       il·lu·sion (-lzhen) 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


            • Afterimage caused by
              glancing at the sun

            • A stick half in and half out
              of water
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”

   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 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 Illusions

        A. Ideal Parthenon

        B. Architrave Illusion

        C. Illusionary Distortion

        D. Alterations made to
          offset illusion
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 Illusions

          Convexing of column to overcome
          parallel lines appearing concave

   Irradiation Illusion:
           Bright objects appear larger
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 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

   Berkeley & Hume:
               All perceptual qualities are learned through
               experience with the environment
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
Current State of

          Paradigmatic Science (Psychology)


    Normal Sciences => Anomoly => Crisis => Revolution

    Current status: Normal Science
                         - mopping up
                         - puzzle solving
                         - guidelines for research
 Ambiguous Figures

Face or Vase?
   Ambiguous Figures
                                           Nels Isralson
L'Amour de Pierrot

                     Gossip and Satan
                     Geo. A. Wotherspoon
                                         Bust of Voltaire
Ambiguous Figures                        - Houdon, 1781

   Slave Market With the Disappearing Bust of Voltaire
                - Salvadore Dali, 1940
Ambiguous Figures

    The Great Panoramic
                 - Salvadore Dali, 1936
Ambiguous Figures

             Multiple Figures

     2                    3


 Ambiguous Figures

Mask Concavity
   Ambiguous Figures

Mach’s Figure
Ambiguous Figures

        Schroder’s Staircase
Ambiguous Figures

            Oscillating Cubes
  Ambiguous Figures

Necker Cube
Ambiguous Figures
Ambiguous Figures

   Cube looks like a cube.      Cube looks distorted, on
                                face smaller than the
   “Equal sides and right
                                Depth is paradoxical
   Eye: Perspetive projection
                                Reverse: No Change
   Reverse: Topless pyramid
            change of shape
Ambiguous Figures

   Cube does not look like a   Necker Cube. No face is
   cube.                       front or back by
   Eye:   Near face is same
          size as far face     Depth is paradoxical
   Reverse: Topless pyramid    Reverse: No change
   further face always looks
 Ambiguous Figures

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

3 in 1 Illusion
Ambiguous Figures
                      Cube / Room

   Possible views:
   • 3D Cube
   • Corner of Room