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Perception and Action > 6 -Depth Perception > Flashcards

6 -Depth Perception Flashcards

1
Q

why is depth perception important?

A

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

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2
Q

why is depth perception a problem

A

How do we obtain a 3D
percept from two 2D
images on the retina?

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3
Q

what is the inverse problem

A

Any retinal image is consistent with infinitely many possible configurations of the world

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4
Q

what are binocular cues

A

– Binocular disparity (Stereo vision)

Two eyes looking at stimulus from different locations
Visual system matches left and right image
Different images - use binocular disparities differences to see what the depth looks like

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5
Q

what are motion cues

A

we move objects move
Things that are close to us will move more and things further away will move less
In the opposite direction to direction were travelling
motion parallax - due to self-motion
kinetic depth (KDE) - due to object motion

When an object is moving will cause motion in the retinal image
Different parts of surface will move at different speeds, texture closest moves fast but texture at side moving slower and less

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6
Q

what is kinetic depth

A

due to object motion
When an object is moving will cause motion in the retinal image
Different parts of surface will move at different speeds, texture closest moves fast but texture at side moving slower and less

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7
Q

what is motion parallax

A

due to self-motion
Things that are close to us will move more and things further away will move less
In the opposite direction to direction were travelling

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8
Q

what are the 6 pictorial cues

A 
texture
elevation
relative size
perspective
shading 
occlusion
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9
Q

what is texture

A

change in density and size

higher density further away

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10
Q

what is relative size

A

big image closer

smaller image gurther away

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11
Q

what is perspective

A

lines converge as they get further away from us

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12
Q

what is shading

A

patterns of light and dark can give an impression of cavities and convexities

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13
Q

convergence for a far target and near target

A

Info we get bc of eyes
Converge towards each other to fixate on certain objects
Converge more when closer
Distance - parallel
sends to visul system how far away the thing were fixating on is

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14
Q

what is accomodation

A

Focused image on retina

Depending on how far away things is lens changes to focus light

Lens fat when thing close to you to bend image

Further away thinner stretched out more to bring far away object

Send signals to higher up in visual system to say how far away the thing is

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15
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?
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16
Q

ambiguity in depth perception

A

many of the 3D cues (particularly the pictorial

cues) are ambiguous

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17
Q

ambiguity in shading

A

This retinal image could have been created by: • a convex object that is lit from above (A) • a concave object lit from below (B) • (or it could be a flat surface with a pattern of light & dark greys painted on it)

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18
Q

how can we overcome ambiguity in depth perception

A
  • Many of the 3D cues (particularly the pictorial cues) are ambiguous
  • We can overcome this ambiguity by using prior knowledge, or prior assumptions, to interpret the image.
  • These assumptions are gained through our 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
(see week 1)

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19
Q

e.g. interpreting train tracks

A

To interpret this image we can make the assumption that lines in the world tend to be parallel.

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20
Q

e.g. shading in image

A

To interpret this retinal image we use an assumption that light comes from above
convex chape

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21
Q

ambiguity in texture

A

This retinal image could have
been created by either:
1. A 2D square with a pattern of ellipses (ovals) that change shape
2. A 3D cylinder with a 3D pattern of circles wrapped around

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22
Q

to interpret ambiguity in texture

A

To interpret these retinal images 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

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23
Q

isotropic

A

no bias in its orientation

24
Q

homogenous

A

surface texture have same elements

25
Q

ambiguity in elevation

A

To interpret this image we assume that objects rest on a ground plane

26
Q

what assumptions are we using

A

Perspective cue - lines converging

Make assumption lines in world parallel - converging in order for us to work out theyre further away

Lighter at top darker on bottoms - eg. Onions - light coming from above - convex

Texture on walls increasing in density further away - make assumption its isotopic and homogeneous

Elevation cue - towards closer further away higher - assumption resting on aa ground plane - higher up in image

27
Q

Assumptions can lead to errors

A

Assumptions will be valid in most situations,

but in some cases they will not be valid, which will lead to perceptual errors (illusions)

28
Q

what is an example of an erroneous assumption

A

Ames room
Assume is a regular shaped room - left side of scene is much further away
Assumption is invalid - experience an illusion - innacuarate perception cue

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 percept

29
Q

how to we overcome ambiguity in depyh perception

A

Many of the 3D cues (particularly the pictorial cues) are ambiguous
• We can overcome this ambiguity by using prior assumptions based on physical
properties of the world
• In situations where our assumptions are not valid we will make perceptual errors

30
Q

multi-cue perception

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

31
Q

integration of cues helps to overcome problems of …

A

reliability
ambiguity
conflict

32
Q

what are the 3 types of integration

A

compromise
dominance
interaction

33
Q

when multiple cues are available what happens

A

When multiple cues are available the visual system will try to integrate cues in order to obtain a unified percept

34
Q

what happens in compromise

A

When two sources of depth information are conflicting, the brain will try to find a compromise between the two.
try to average

35
Q

what did young et al do

A

Participants viewed computer generated cylinder defined by 2 cues in conflict:
– Texture – Motion
does the cylinder look flattened circular or stretched?

Change texture - stretched can see on side

Motion -
each define a different shape
texture - flattened
motion - stretched

36
Q

texture and motion conflict - What shape do participants perceive?

A

Perceived shape is a compromise between the two cues

37
Q

what if one cue is more reliable than the other

A

When texture made less regular (hence less reliable) perceived shape is biased towards motion cue

When motion made less smooth (hence less reliable) perceived shape is biased towards texture cue

38
Q

summary of compromise

A
  • When 2 cues are conflicting the brain will try to average them
  • Final percept of shape will be biased towards most reliable cue
39
Q

what happens in dominance of cues

A

when two cues define very different shapes or depths the brain may choose to ignore one in preference for the other
large cue-conflicts tend to arise when ones assumptions are invalid
usually the cue with valid assumptions will dominate

40
Q

when an invalid cue dominates what happens

A

it creates an illusion

41
Q

what happens in when cues are in conflict

A

When conflict between 2 cues is too great, the

brain will choose one cue and ignore the other

42
Q

how to disambiguate texture

A

could be convex or concave
usually percieved as convex bc we have a bias for convex objects
binocular disparity can disambiguate

43
Q

binocular disparity and texture interaction

A

Adams and Mamassian (2004)
introduced conflict between cues
•Texture disambiguated by binocular disparity (interaction)
then 2 cues averaged

44
Q

what is the order of integration

A

interaction stage - cues disambiguate each other

compromise stage - join together

45
Q

summary of interaction

A
  • Ambiguous cues such as texture and shading can be disambiguated by other less ambiguous cues
  • Evidence suggests this stage occurs prior to cue compromise.
46
Q

what are the 3 types of cue integration

A

Three types of cue integration

  1. Compromise
  2. Dominance
  3. Interaction
47
Q

Cue integration helps to overcome problems of:

A

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

48
Q

Do cue conflicts apply in the real world?

A 
yes
Cue conflicts arise in a number of everyday
stimuli e.g.
– Art & Photography 
– Movies 
– 3D Movies
49
Q

movies - cue conflicts

A

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

50
Q

3D movies

A

3D movies – pictorial, motion and binocular cues all specify 3D scene, only oculomotor cues specify flat surface

51
Q

art and photography - cue conflicts

A

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

52
Q

Depth cues must be integrated to:

A

– achieve a unified percept
– take account of differences in reliability
– overcome conflict and ambiguity

53
Q

what is an inverse problem

A

recoving depth drom 2D retinal images

54
Q

what are the 3 types of integration

A

compromise dominance interaction

55
Q

how is ambiguity overcome

A

by the use of prior assumptions

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