The document discusses optical illusions and the history of their study. It explains that optical illusions reveal that perception is an active process in the brain rather than a direct reflection of physical reality. The history of illusions is then reviewed from ancient Greece to modern times, showing different viewpoints on the relationship between senses and mind over time. Various types of illusions are also presented including ambiguous figures that can be seen in more than one way.

1. Optical Illusions Seeing Is Deceiving By Rizwan

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

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

9. History of Illusions Entasis : Convexing of column to overcome parallel lines appearing concave Irradiation Illusion : Bright objects appear larger

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

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

14. Ambiguous Figures Face or Vase?

15. Ambiguous Figures L'Amour de Pierrot c.1905 Gossip and Satan Geo. A. Wotherspoon RetroActive Nels Isralson

16. Ambiguous Figures Slave Market With the Disappearing Bust of Voltaire - Salvadore Dali, 1940 Bust of Voltaire - Houdon, 1781

17. Ambiguous Figures The Great Panoramic - Salvadore Dali, 1936

18. Ambiguous Figures 2 2 2 3 Multiple Figures

19. Ambiguous Figures Mask Concavity

20. Ambiguous Figures Mach’s Figure

21. Ambiguous Figures Schroder’s Staircase

22. Ambiguous Figures Oscillating Cubes

23. Ambiguous Figures Necker Cube

24. Ambiguous Figures

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