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Understanding Optical Illusions

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Understanding Optical Illusions Mohit Gupta Context lightness constancy is at work here. From the context, our brain thinks that the left part of the image is ... – PowerPoint PPT presentation

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Title: Understanding Optical Illusions


1
Understanding Optical Illusions
Mohit Gupta
2
What are optical illusions?
Perception I see
Light (Sensing)
Truth But this is an !
Oracle
3
Optical Illusion in Nature
Image Courtesy http//apollo.lsc.vsc.edu/classes/
met130/notes/chapter19/graphics/infer_mirage_road.
jpg
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

Illusions of the senses tell us the truth about
perception Purkinje
  • It makes us happy ? Al Seckel

8
Simultaneous Contrast Illusions
9
Low-level Vision Explanation
Negative Photo-receptors
Positive Photo-receptors
Receptive Fields in the Retina
-
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
Higher Perceived Reflectance
Lower Perceived Reflectance
Brightness Reflectance Incident Illumination
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
19
Adelsons checkerboard illusion
20
Where is the illusion?
21
Where is the illusion?
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
Contrast affecting Perception of speed
Click
28
Twisted Cord Illusions
29
Are the lines parallel? Straight?
30
Café Wall Illusion
31
Café Wall Illusion
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
Kerstens Ball and Shadow Illusion
Click
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
46
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47
Good things come to those who wait
Image Courtsey http//www.apprendre-en-ligne.net/
blog/images/guinnessbase.jpg
48
Why study optical illusions?
  • Studying how brain is fooled teaches us how it
    works

Illusions of the senses tell us the truth about
perception Purkinje
  • It makes us happy ? Al Seckel

Click
49
Have fun with Optical Illusions
Eschers Waterfall
Then think about them!
50
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51
Mach Band Illusions
52
Intrinsic Image Separation
53
Footstep Illusion Contrast affecting Perception
of speed
Stepping feet Illusion
http//www.michaelbach.de/ot/mot_feet_lin/index.ht
ml
http//journalofvision.org/6/12/5/images/Figure_2a
_Demo.html
http//journalofvision.org/6/12/5/images/Figure_8b
_Demo.html
http//journalofvision.org/6/12/5/images/Figure_8d
_Demo.html
Kick-back Illusion
http//journalofvision.org/6/12/5/images/Figure_7b
_Demo.html
http//journalofvision.org/6/12/5/images/Figure_8a
_Demo.html
http//journalofvision.org/6/12/5/images/Figure_8c
_Demo.html
Reverse-phi phenomenon
Howe et al, Journal of Vision
54
Levels of Processing
  • Low-level Vision
  • Light receptive cells at the retina level
  • Mid-level Vision
  • Surfaces, contours, grouping
  • High-level Vision
  • Cognition knowledge about materials, objects,
    scenes, illumination

55
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57
http//www.michaelbach.de/ot/
58
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