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Action & Perception > 6. Depth Perception > Flashcards

6. Depth Perception Flashcards

1
Q

Describe the Inverse Problem

A
  • Any retinal image is consistent (the same) with infinitely many possible configurations of the world
  • The visual system works out which is the correct configuration of the world
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2
Q

What are the Multiple sources of 3D information?

A

○ Binocular
○ Motion
○ Pictorial
○ Oculomotor

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3
Q

Why is Depth Perception Important?

A

3D perception is vital for interacting with the world and recognising objects

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4
Q

The prior assumption that lines in the world tend to be parallel or perpendicular to each other is used to disambiguate which depth cue?

A

Perspective

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5
Q

In what situation are we most likely to experience an illusion?

A

When our assumptions are invalid

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6
Q

When two cues are integrated by compromise the final percept will be what?

A

When two cues are integrated by compromise the final percept will be Biased towards the most reliable cue

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7
Q

Describe binocular cues.

A

○ It arises because we have 2 eyes that are in different positions in our heads. So they both have a slightly different view of the world = the retinal images will be different.

○ The visual system can match up the left and right eyes images and find the differences in the images (binocular disparities)
It uses these to work out the 3 dimension of the world must look like.

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8
Q

What is the most important Binocular Cue?

A

Binocular Disparity (Stero Vision)

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9
Q

What are the 2 motion cues?

A
  1. Motion parallax - We move around

2. Kinetic Depth - Objects move around

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10
Q

Describe Motion Parallax.

A
  • Cause motion on the retina
  • Things that are close to us move more and things further away will move less.
  • The visual system can use that different elements of an image are moving at different speeds to work out how fast they are
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11
Q

Describe Kinetic Depth (Kinetic Depth Effect/ KDE).

A
  • When objects move it creates motion in the retinal image.

- Because of the 3D shape of an object different parts of that object will appear to move at different speeds.

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12
Q

What do Pictorial cues tell us?

A
  • Can tell us how close or far away something is.
  • Perspective cue:
    ○ Lines converge as things move further away from us.
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13
Q

What are all the 6 Pictorial Cues?

A
  1. Texture
  2. Elevation
  3. Relative Size
  4. Perspective
  5. Shading
  6. Occlusion
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14
Q

Describe Oculomotor Cues.

A
  • Information that is not present in the retinal image. It is information we get due to the position of the eyes.
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15
Q

Describe the 2 types of the Oculomotor Cues.

A
  1. Convergence
    ○ Eyes converge when looking at a closer object
  2. Accommodation
    ○ The lens changes shape to focus an image of an object onto the retinal
    § Thinner retina = far away object
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16
Q

If we have so many different cues to depth what is the problem?

A
  1. Many cues are ambiguous – 2D image compatible with infinite 3D worlds
  2. With multiple cues available – how do we perceive a single unified world?
17
Q

Which type of depth cues are thought to be most ambiguous.

A

Pictorial Cues.

18
Q

What depth cues can create ambiguity?

A
  1. Perspective
  2. Shading
  3. Texture
  4. Elevation
19
Q

How does the visual system overcome ambiguity?

A
  • We can overcome this ambiguity by using prior knowledge, or prior assumptions, to interpret the image.
  • These assumptions are gained through our unconscious knowledge and experience of the physical properties of the world.
  • This is a type of top-down processing and supports the constructivist approach to vision
20
Q

What assumptions do we use about perspective?

A
  • make the assumption that lines in the world tend to be parallel.
  • We assume that since lines are parallel and the lines in the photo converges then they must be moving further away. It tells us about depths in a scene.
21
Q

What assumptions do we use about shading?

A

use an assumption that light comes from above.

22
Q

What assumptions do we use about texture?

A
  • we assume surface textures are isotropic (unbiased orientation) and homogeneous (uniform density)
  • Making this assumption means any changes in image texture orientation or density are attributed to changes in 3D surface orientation
23
Q

What assumptions do we use about Elevation?

A

we assume that objects rest on a ground plane (surface parallel to the ground)

24
Q

What is the problem with Depth Perception Assumptions?

A
  • Assumptions can lead to errors
  • Assumptions will be valid in most situations, but in some cases they will not be valid, which will lead to perceptual errors (illusions)
25
Q

What does the Ames Room Illusion show?

A
  • When we view the Ames room we assume lines are parallel or at right-angles, however this is not the case.
  • The perspective assumption of parallel lines is invalid which causes an erroneous (incorrect) percept.
  • Only works with one eye so there isn’t binocular disparity information.
26
Q

Describe the types of multi-cue integration.

A
  1. Compromise – take average, but take into account how reliable each cue is.
  2. Dominance – only trust one and ignore the other.
  3. Interaction – information incomplete or ambiguous, need one source to disambiguate the other
27
Q

Why is Multi-Cue Perception important?

A
  • Real-world scenes have multiple cues present
  • Cues must be integrated to achieve a single unified percept
  • Integration helps to overcome problems of:
    ○ Reliability
    ○ Ambiguity
    ○ Conflict
28
Q

What happens when two sources of depth information are conflicting?

A

-The brain will try to find a compromise between the two.
○ However the brain will take into account how reliable each source is.
- The perceived shape is biased towards motion cue

29
Q

What did Young et al (1993) study show?

A
  • Looks at how Ps combine two sources of 3D information.
  • Participants viewed computer generated cylinder defined by 2 cues:
    ○ Texture & Motion
30
Q

what is dominance?

A
  • When two cues define very different shapes or depths, the brain may choose to ignore one in preference for the other.
  • e.g. Elevations vs Relative size
31
Q

what happens in Richard Gregory’s Ames window illusion?

A
  • Motion (KDE) in conflict with perspective, again perspective wins.
32
Q

How does interaction help perception?

A
  • Some cues are ambiguous, but other cues can disambiguate them
    ○ e.g. binocular disparity can disambiguate ambiguous texture cues.
33
Q

what did Adams and Mamassian (2004) do?

A
  • introduced conflict between the texture and binocular disparity cues.
  • Texture disambiguated by binocular disparity (interaction) AND
  • Then 2 cues averaged (compromise)
34
Q

what did Adams and Mamassian (2004) conclude about the order of integration?

A
  • 2 stages
    1. interaction stage - where cues disambiguate each other
    2. compromise stage - where you average together disambiguated cues.
35
Q

What problems can cue integration overcome?

A

○ Unifying our percept of the world
○ Differences in cue reliability (compromise)
○ Conflicting information (compromise & dominance)
○ Cue ambiguities (interaction)

36
Q

What problems arise when there is conflict between binocular and oculomotor cue?

A

headaches
eye-strain
nausea

37
Q

What do cues tell us when we are looking at art & photography?

A

binocular, motion and oculomotor cues will all tell you these are 2D surfaces and yet we perceive vivid three-dimensionality due to pictorial information

38
Q

What do cues tell us when we are looking at Movies?

A

Pictorial and motion cues specify a 3D scene, but binocular cues and oculomotor cues define a flat surface

39
Q

What do cues tell us when we are looking at 3D Movies?

A

pictorial, motion and binocular cues all specify 3D scene, only oculomotor cues specify flat surface.
- problems can arise.

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