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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

            Prehistory:

            • 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”
                                          -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 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
History of Illusions

        A. Ideal Parthenon

        B. Architrave Illusion
        (Jastrow-Lipps)

        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.”

                                  -Vitruvius
History of Illusions

   Entasis:
          Convexing of column to overcome
          parallel lines appearing concave

   Irradiation Illusion:
           Bright objects appear larger
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
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
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
 Illisions

    Conclusion:
          Paradigmatic Science (Psychology)

    1900s

    Normal Sciences => Anomoly => Crisis => Revolution

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


Face or Vase?
   Ambiguous Figures
                                           RetroActive
                                           Nels Isralson
L'Amour de Pierrot
c.1905




                     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



2


              2
 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
                                other.
   angles.”
                                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
                               perspective
   Eye:   Near face is same
          size as far face     Depth is paradoxical
   Reverse: Topless pyramid    Reverse: No change
   further face always looks
   larger
 Ambiguous Figures

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




3 in 1 Illusion
Ambiguous Figures
                      Cube / Room


   Possible views:
   • 3D Cube
   • Corner of Room

				
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