Visual areas in the brain. Image removed for copyright reasons.

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Megan West
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1 Visual areas in the brain Image removed for copyright reasons.

2 Image removed for copyright reasons. FOVEA OPTIC NERVE AQUEOUS HUMOR IRIS CORNEA PUPIL RETINA VITREOUS HUMOR LENS

3 What do you see? Why?

4 The world is a complicated place Image removed for copyright reasons.

5 Image removed for copyright reasons. FOVEA OPTIC NERVE AQUEOUS HUMOR IRIS CORNEA PUPIL RETINA VITREOUS HUMOR LENS

6 Courtesy of Peter Schiller. Used with permission.

7 Visual Cortex Outside view View from the middle Image removed for copyright reasons.

8 Flatten the brain (like making a map out of a globe, Only worse) Image removed for copyright reasons.

9 Do we really have center-surround receptive fields? The Hermann Grid

10 Do we really have center-surround receptive fields? The Hermann Grid

11 Do we really have center-surround receptive fields? Umm what is happening here?

12 The stimulus Bright Light Dim Light Bright Light Dim Light Time A neuron's response

13 % "I see it" Responses you want you get Light

14 Color How do you see color?

15 Wavelength 1 produces a response of size X Wavelength (nm)

16 Wavelength 2 produces a response of size X Wavelength (nm)

17 The problem of univariance univariance Wavelength (nm) Two wavelengths, one response.

18 So, we have a problem Wavelength (nm)

19 Here is a solution.add another cone type Wavelength (nm)

20 Two cones can give you color vision Y X Z Wavelength (nm) X/Y = red,, X/Z = green COMPARISONS ARE CRITICAL

21 Three cones give you Trichromacy M L S Wavelength (nm)

22 Three cones give you Trichromacy M L S Wavelength (nm) Any light = al + bm + cs

23 Let s add some patches together Wavelength (nm)

24 Let s take GREEN M 1 L 1 Wavelength (nm)

25 And add RED M 1 L 2 L 1 M 2 Wavelength (nm) Red + Green = (M1+M2)/(L1+L2) = 1

26 Compare that to YELLOW M 3 L 3 Wavelength (nm) Yellow = M3/L3 = 1

27 RED It follows that

28 It follows that plus RED GREEN

29 Yields Yellow R+G and Y are METAMERS This is ADDITIVE color mixture

30 But what about color paint in kindergarten? x x x x x x x x x x x x x x x x x x Blue paint Yellow paint

31 Mixing paint is SUBTRACTIVE x x x x x x x x x The intersection of Blue paint and Yellow paint looks Green

32 Recall Three cones give you Trichromacy M L S Wavelength (nm) Suppose: if S=M=L, then WHITE

33 Suppose that L gets tired? M L S Wavelength (nm) What does S=M>L look like?

34 Pretty boring

35 Pretty

36 Pretty, not boring

37 Try this Negative afterimage

38 Vertical and Horizontal look the same?

39 Go forward

42 Go back

43 Vertical and Horizontal look the same?

44 So, you found all these nice features what is the problem?

45 Which lines group together?

46 How about here? Why?

47 Which gray line is a likely continuation of the black line? not likely maybe not bad good bet

50 not bad good bet

51 Which gray line is a likely continuation of the black line? not likely maybe not bad good bet

52 WHAT IS THIS?

53 Does this seem likely?

54 This seems more likely Good continuation

55 One curved line or three? You know about occlusion

56 One curved line or three? You know about occlusion

57 Organized by columns or rows?

58 Now? Organized by columns or rows? Why? Proximity

59 Now? Organized by columns or rows? Why? Did Similarity trump Proximity?

61 Let s magnify the critical bit.

62 See that rectangle?

63 How about that rectangle?

64 How about that circle?

65 Not as good?

66 Edges are important

67 The visual system distinguishes real edges from shadows Image removed for copyright reasons. Remember: You want to know about the world, not your retina

68 COW

69 Minimal shadow can give you faces Images removed for copyright reasons. Faces from University of Bielefeld Cognitive Robot project.

70 Depth Cues From 2D-3D Image removed for copyright reasons.

71 Occlusion

72 Is this likely?

73 Size

74 Texture

75 Relative position (height in field)

76 Here is why it works

77 You don t need to recognize the objects

78 Areal Perspective (haze) The misty mountains far away

79 Linear Perspective Vanishing point

80 Linear Perspective? Image removed for copyright reasons. Where is the vanishing point?

81 Linear Perspective? These local bits don t add up

82 Linear Perspective? These add up ambiguously

83 Shadows Image removed for copyright reasons. But where is the sun?

84 And let s not forget Stereopsis, Vergence, and Motion parallax

Realtime 3D Computer Graphics Virtual Reality

Realtime 3D Computer Graphics Virtual Reality Human Visual Perception The human visual system 2 eyes Optic nerve: 1.5 million fibers per eye (each fiber is the axon from a neuron) 125 million rods (achromatic