1. DEPTH PERCEPTION
© Wesner, M. F.

2. Cue vs. Ecological Theory
(1950)
(1979)
Cue Theories
Feature extraction process (i.e., the computational construction of components)
Ecological (James J. Gibson, 1950’s on)
Gestalt-like approach - all items in environment are directly & contextually processed (i.e., the optic array of textures, shadows and edges are all processed directly to constitute depth and movement)
Gibson challenged the idea that the nervous system actively constructs conscious visual perception, and instead promoted ecological psychology, in which the mind directly perceives environmental stimuli without additional cognitive construction or processing. He claimed the environment decides perception, and meaning is in what the environment "affords" the observer (Theory of Affordance=what can I gain from the object, not what are all the possible permutations of the object’s quality). No distinction between sensation and perception! No information processing! What is available to us from the environment is based on our prior experiences and we act on those. Some consider Gibson the first post cognitivist – an intuitive understanding of context in a situation without the need of symbolic representations of all possible permutations.

3. Four Groups of Depth Cues
Pictorial
Oculomotor (accommodation & convergence*)
Kinetic (motion-produced cues)
Binocular Disparity*
*Binocular Depth Cues

4. Monocular Depth Cues
Pictorial

5. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size

7. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size
Interposition (overlap)

8. Law of Prägnanz in operation here !B A
Law of Prägnanz in operation here !

9. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size
Interposition (overlap)
Lighting & Shadowing

12. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size
Interposition (overlap)
Lighting & Shadowing
Elevation -position of objects relative to the horizon

15. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size
Interposition (overlap)
Lighting & Shadowing
Elevation -position of objects relative to the horizon
Linear Perspective - “carpentered environment”

16. Linear Perspective - Geometric cues using converging lines and vanishing points
Renaissance architect Leon Battista Alberti (1435) published an artist manual that systemized drawing in linear perspective.
Vanishing point
Alberti was also involved with systemizing color layers, dark-to-full saturation-to-white, chiaroscuro.

18. Leonardo Da Vinci capitalized on the
vanishing point concept..

19. ..at the end of a communal dining hall.
Santa Maria delle Grazie in Milano.. at the end of a refectory hallway..

21. Monocular Depth Cues Pictorial
Size of image - usually involves a familiar size
Interposition (overlap)
Lighting & Shadowing
Elevation -position of objects relative to the horizon
Linear Perspective - “carpentered environment”
Aerial Perspective - Rayleigh scatter

22. Titian - Vecellio Tiziano (1488/1490 – 1576) Bacchus & Ariadne (1520-3)

23. Monocular Depth Cues Pictorial
*Size of image - usually involves a familiar size
Interposition (overlap)
Lighting & Shadowing
Elevation -position of objects relative to the horizon
Linear Perspective - “carpentered environment”
Aerial Perspective - Rayleigh scatter
Detail Perspective - Texture gradient (Size cue*)

24. Simple line textons:

25. Simple line textons with size cues:

26. Illusions are the result of depth cue conflicts

30. B is closer than A

31. flip the ambiguous linear depth cue. New B is still closer than A.

32. Familiar size helps reduce the linear cue ambiguity

33. Familiar Size vs. linear perspective - “forced perspective”
Size constancy gone awry..

34. Linear perspective conflicting with size
Demo

35. Müeller Lyer Illusion

36. Linear Perspective vs. Size

37. Ponzo Illusion

38. Linear Perspective with Size, elevation..
..& texture

40. Monocular Depth Cues Pictorial
Accommodation (kinesthetic sense in ciliary muscles)
optical ∞
diverging light (within ∞)

42. ..although accommodation is considered a monocular depth cue, it does have a close link (or synkinesis) with binocular convergence or divergence (i.e., the accommodation/vergence ratio).
convergence
divergence

43. Monocular Depth Cues Pictorial
Accommodation (kinesthetic sense in ciliary muscles)
Kinetic Cues (movement-produced cues

44. A B A B
Slight move to the right

45. With..
AA’ > BB’
Nodal point
..we perceive object A closer than B because object A moves faster than object B (i.e., equal time for image to sweep the arcs). A B’ A’ B

46. cornea Lens Nodal Point (~7 mm behind corneal apex)
Thin lens system equivalent

47. Binocular Depth Cues
Vergence
convergence
divergence

48. Binocular Depth Cues Vergence
Binocular Disparity (true depth perception - stereopsis)

49. Image correspondence - when the image is projected onto similar regions of the retinas in both eyes.
foveas

50. Image noncorrespondence (disparity) - when the image is projected onto dissimilar regions of the retinas in both eyes.
Nodal points
Nodal points
foveas

51. Image disparity
Left eye
Right eye

52. Stereopsis makes use of image disparity:

54. Front Screen Finger RE LE If objects are in line with one another:
Crossed = image of nearer object projects to temporal side of fixation image; results in movement direction opposite that of open eye.
Uncrossed = image of further object projects to nasal side of fixation image; results in movement direction that is the same as that of open eye. RE LE

55. Crossed vs. Uncrossed Disparity
Rays project to temporal hemiretinas
foveas

56. Crossed vs. Uncrossed Disparity
Rays project to nasal hemiretinas
foveas

57. Note: The magnitude of the disparity defines the distance from the fixation plane..
Greater crossed disparity

58. NOTE: Objects do NOT have to lie in visual alignment to establish a crossed or uncrossed disparity. Retinal image (non)correspondence has to do with a fixation point plane (or arc).

59. The geometry of stereoscopic depth
The geometry of stereoscopic depth. Begins with the Vieth-Müller (1862) horopter surface..

62. F
Correspondence along
the horopter surface

63. F
Crossed disparity - fusion into one brain image

64. F
Crossed diplopia - seeing double

65. F
Uncrossed disparity - fusion into one brain image

66. F
Uncrossed diplopia - seeing double

67. F Uncrossed Diplopia Uncrossed Diplopia Panum’s Fusion Area

69. or anglyphs

70. Figure 12.31
This is a stereogram of Lake Palanskoye, located in northern Kamchatka peninsula of Russia.
Merging the images through free fusion generates a stunning three-dimensional view of this region.

76. The middle line produces uncrossed disparity, which will push it “behind” the flanking lines. That’s all you need. The brain does the rest.

79. F Uncrossed Diplopia Uncrossed Diplopia Panum’s Fusion Area

80. A cortical binocular cell could be composed of disparate, monocular receptive fields that represent fusional space!

81. by definintion, within Panum’s Fusion Area

82. Size and Shape Constancy
© Wesner, M. F.

85. Size constancy involves high-end processing
Size constancy involves high-end processing. Yet, perceptual grouping (Prägnanz) can be achieved on a post-constancy representation (top-down influence).

86. A B

87. Post-constancy
grouping
Size grouping
Notice that the central column of shapes is physically identical to those in the 3 left columns. However, using linear perspective, the central column appears as an in-depth surface. Thus, the perceived shape of these items are of a circle, not an ellipse, much like the circles in the 3 right-hand columns. Subjects will be more likely to group the central column with the circles ( post-constancy grouping).

88. Size (shape) constancy are based on depth cues.
Classic study by Boring done in the “hallowed halls” of Harvard University..

89. Monocular view
Constant visual angle

90. Size (shape) constancy are often the culprits for many visual illusions..

91. Linear perspective in conflict with size..

92. Shape and size constancy in conflict..

94. Sky is perceived as a flattened dome..
Shallow bowl effect

96. Kaufman & Rock (1962) Shallow bowl effect
The perceived difference in distance to the moon (registered distance) establishes the perceived size of the moon.
The judged distance to the moon is influenced by the perceived size of the moon (i.e., horizon is bigger than zenith.
Kaufman & Rock (1962)
Shallow bowl effect
Problem: How is it that something that is registered far away (in the horizon) is judged to be closer because its apparent size is misperceived as bigger? A “top-down” nightmare.