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Understanding Optical Illusions Mohit Gupta. Truth: But this is an ! What are optical illusions? Light (Sensing) Oracle Perception: I see.

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Presentation on theme: "Understanding Optical Illusions Mohit Gupta. Truth: But this is an ! What are optical illusions? Light (Sensing) Oracle Perception: I see."— Presentation transcript:

1 Understanding Optical Illusions Mohit Gupta

2 Truth: But this is an ! What are optical illusions? Light (Sensing) Oracle Perception: I see

3 Optical Illusion in Nature Image Courtesy:

4 A Brightness Illusion

5 Different kinds of illusions Brightness and Contrast Illusions Twisted Cord Illusions Color Illusions Perspective Illusions Relative Motion Illusions Illusions of Expressions

6 Lightness Constancy Our Vision System tries to compensate for differences in illumination

7 Why study optical illusions? Studying how brain is fooled teaches us how it works It makes us happy : Al Seckel Illusions of the senses tell us the truth about perception [Purkinje]

8 Simultaneous Contrast Illusions

9 Low-level Vision Explanation Receptive Fields in the Retina Negative Photo-receptors Positive Photo-receptors Inhibitory Light Excitatory Light

10 Low-level Vision Explanation Positive Gradient Negative Gradient

11 High-level Vision Explanation: Context Less Incident Illumination More Incident Illumination Brightness = Reflectance * Incident Illumination Higher Perceived Reflectance Lower Perceived Reflectance

12 The Hermann grid illusion

13 The Hermann grid: Low level Explanation Lateral Inhibition

14 The Hermann grid illusion Focus on one intersection

15 Why does the illusion disappear? Receptive fields are smaller near the fovea (center) of the eye

16 The Waved Grid: No illusion!

17 Scintillating Grids: Straight and Curved

18 Adelsons checkerboard illusion

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20 Where is the illusion?

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22 Rubiks Cube Color Illusion Same Color?

23 Rubiks Cube Color Illusion

24 Todorovics Gradient Chessboard Illusion Are all the dots the same color?

25 Craik-OBrien-Cornsweet Illusion Actual Profile Perceived Profile

26 Whites Illusion

27 Footstep Illusion Click Contrast affecting Perception of speed

28 Twisted Cord Illusions

29 Are the lines parallel? Straight?

30 Café Wall Illusion

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32 A variant of the Café Wall Illusion

33 The Fraser Spiral Illusion

34 Pinnas Intertwining Illusion

35 Illusions involving perspective

36 Shepards table-top illusion Which is bigger?

37 Shepards table-top illusion Which is bigger?

38 Shadow Illusions

39 Shape-from-Shading Shadows influence the perception of shape

40 Click Kerstens Ball and Shadow Illusion Shadows influence the perception of motion and position

41 Relative Motion Illusions

42 Out of Focus Illusion

43 Spinning Wheel Illusion

44 Motion Induced Blindness Click

45 Anamorphoses Leonardos Eye [Leonardo Da Vinci, 1485]

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47 Image Courtsey: Good things come to those who wait

48 Why study optical illusions? Studying how brain is fooled teaches us how it works It makes us happy : Al Seckel Click Illusions of the senses tell us the truth about perception [Purkinje]

49 Have fun with Optical Illusions Then think about them! Eschers Waterfall

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51 Mach Band Illusions

52 Intrinsic Image Separation

53 Footstep Illusion: Contrast affecting Perception of speed Kick-back Illusion Stepping feet Illusion Reverse-phi phenomenon[Howe et al, Journal of Vision]

54 Levels of Processing Low-level Vision Mid-level Vision High-level Vision Light receptive cells at the retina level Surfaces, contours, grouping Cognition – knowledge about materials, objects, scenes, illumination

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