Depth Perception Flashcards
Why is depth perception important?
3D perception is vital for interacting with the
world and recognising objects
Why is depth perception a problem?
How do we obtain a 3D
percept from two 2D
images on the retina?
Define the inverse problem
Any retinal image is consistent with infinitely
many possible configurations of the world
simply = The challenge of determining the objects and properties in the environment that produced a particular sensory input
Any retinal image is consistent with infinitely
many possible configurations of the world
simply = The challenge of determining the objects and properties in the environment that produced a particular sensory input
This is known as…?
The inverse problem
There are multiple sources of 3D information
List 4 types of 3D cues
- Binocular
- Motion
- Pictorial
- Oculomotor
- Binocular
- Motion
- Pictorial
- Oculomotor
What cues are these?
3D cues
Define binocular disparity
We have 2 eyes and each eye produces a different retinal image each
We have 2 different retinal images due to different views
Brain puts those 2 retinal images together, to see things in 3D
We have 2 eyes and each eye produces a different retinal image each
We have 2 different retinal images due to different views
Brain puts those 2 retinal images together, to see things in 3D
This is known as…?
Binocular disparity
Define motion cues
As we move, bits of the world move with our retina at different rates
As we move, bits of the world move with our retina at different rates
This is known as…?
Motion cues
What is motion parallax
Things in the distance move slowly in the retinal image to tell us about how far away things are
What is kinetic depth (KDE)
Due to object motion, bits at the side will move slower, bits in the middle will move faster and a lot more
Due to object motion, bits at the side will move slower, bits in the middle will move faster and a lot more
This is known as…?
kinetic depth (KDE)
Things in the distance move slowly in the retinal image to tell us about how far away things are
This is known as…?
Motion parallax
What are the 6 types of pictorial cues?
- Texture
- Elevation
- Relative size
- Perspective
- Shading
- Occlusion
What is occlusion pictorial cue?
If one object block the view of another object, it is closer to us
What is perspective pictorial cue?
Lines that are converging tend to move away from us
What are the 2 types of oculomotor cues?
- Convergence
- Accomodation
Lens changes shape to focus light into the retinal image
Fatter lens:
a. To focus on things far from you
b. To focus on things close to you
b. To focus on things close to you
Do our eyes converge more or less when the object is near?
More
Do our eyes converge more or less when the object is far?
Less
How do our eyes accommodate for a near object?
Lens becomes fatter
How do our eyes accommodate for a far object?
Lens becomes thinner
If we have so many different cues to depth what is the problem?
List 2 problems
- Many cues are ambiguous - 2D image compatible with infinite 3D worlds
- With multiple cues available – how do we
perceive a single unified world?
Many of the 3D cues (particularly the ____
cues) are ambiguous
Pictorial
The retinal image of ambiguity in perspective could have been created by 3 types of cues
image = a train track (parallel lines that look like they are converging at a distance) is a 2D retinal image
What are they?
- Parallel lines in the world receding away from you (e.g. A)
- Converging lines that are a constant distance from you (e.g. B)
- Infinite other 3D stimuli
The retinal image of ambiguity in shading could have been created by 3 types of cues
image = circle with a lighter top and darker bottom (shading)
What are they?
- A convex object that is lit from above (A)
- A concave object lit from below (B)
- It could be a flat surface with a pattern of light and
dark greys painted on it
Many of the 3D cues (particularly the pictorial
cues) are ambiguous
How do we overcome this ambiguity?
By using prior knowledge, or prior assumptions, to interpret the image
We can overcome ambiguity in depth perception by using prior knowledge, or prior assumptions, to interpret the image
How are these assumptions gained?
Through our knowledge and experience of the physical
properties of the world
We can overcome ambiguity in depth perception by using prior knowledge, or prior assumptions, to interpret the image
Is this bottom-up or top-down processing?
Top-down processing
We can overcome ambiguity in depth perception by using prior knowledge, or prior assumptions, to interpret the image
What approach to vision does this type of processing support?
Constructivist approach, we draw out knowledge about the world to make sense of things
We grew up in a world full of parallel lines, so we often interpret parallel lines as…?
Moving away from us
True or False?
We make the assumption
that lines in the world tend to be parallel
True
True or False?
We make the assumption that light comes from below
False
We make the assumption that light comes from above
e.g. At home, lights are on the ceiling, sunlight comes from above
The higher up the object looks in the image, the ___ it is from us
a. Closer
b. Further
b. Further
How do we resolve ambiguity in elevation?
We assume the object rests on a ground plane (parallel to the ground)
We grew up in the world with gravity, everything rests on a ground plane
The retinal image of ambiguity in elevation could have been created by 2 types of cues
What are they?
- Objects sitting on a surface (A)
- Objects floating in the air (B)
This retinal image could have been created by:
- Objects sitting on a surface (A)
- Objects floating in the air (B)
What type of ambiguous retinal image does this apply to?
a. Ambiguity in elevation
b. Ambiguity in perspective
c. Ambiguity in shading
a. Ambiguity in elevation
This retinal image could have been created by:
- Parallel lines in the world receding away from you (e.g. A)
- Converging lines that are a constant distance from you (e.g. B)
- Infinite other 3D stimuli
What type of ambiguous retinal image does this apply to?
a. Ambiguity in elevation
b. Ambiguity in perspective
c. Ambiguity in shading
b. Ambiguity in perspective
This retinal image could have been created by:
- Aconvex object that is lit from above (A)
- A concave object lit from below (B)
- A flat surface with a pattern of light and dark greys painted on it
What type of ambiguous retinal image does this apply to?
a. Ambiguity in elevation
b. Ambiguity in perspective
c. Ambiguity in shading
c. Ambiguity in shading
We assume the object rests on a ground plane (parallel to the ground)
We grew up in the world with gravity, everything rests on a ground plane
We use this assumption/knowledge to resolve what type of ambiguity?
a. Ambiguity in shading
b. Ambiguity in perspective
c. Ambiguity in elevation
c. Ambiguity in elevation
We make the assumption that light comes from above
e.g. At home, lights are on the ceiling, sunlight comes from above
We use this assumption/knowledge to resolve what type of ambiguity?
a. Ambiguity in shading
b. Ambiguity in perspective
c. Ambiguity in elevation
a. Ambiguity in shading
We make the assumption
that lines in the world tend to be parallel
We grew up in a world full of parallel lines, so we often interpret parallel lines as moving away from us
We use this assumption/knowledge to resolve what type of ambiguity?
a. Ambiguity in shading
b. Ambiguity in perspective
c. Ambiguity in elevation
b. Ambiguity in perspective
True or False?
Assumptions are always accurate
False
Assumptions can lead to errors
What is the term used for errors made by assumptions to resolve ambiguous retinal images?
Perceptual errors (illusions)
List 2 types of perceptual errors (illusions) that resulted from making erroneous assumptions
- Ames room
- Convex illusion
What is the ames room illusion?
A room that is built with both the floor and ceiling at an angle, creating forced perspective and tricking your eye into thinking both sides of the room are the same
Person in the left corner of the room looks tiny compared to the person standing in the right corner of the room
A room that is built with both the floor and ceiling at an angle, creating forced perspective and tricking your eye into thinking both sides of the room are the same
Person in the left corner of the room looks tiny compared to the person standing in the right corner of the room
This is known as…?
Ames room
Why do we experience the Ames room illusion?
We make assumptions that the room is like any other regularly shaped room so the walls and floors are parallel or at right angles to each other
When we view the Ames room we assume lines are
____ or ____, however this is not the case
Parallel or at right-angles
What causes the illusion in the Ames room?
The perspective assumption of parallel lines is invalid
What is the convex illusion?
When a concave image (e.g. a footprint on mud) looks convex (e.g. like a bump/hill)
When a concave image (e.g. a footprint on mud) looks convex (e.g. like a bump/hill)
This is known as…?
Convex illusion
A footprint looks convex (a hill) even though it is concave
What causes this illusion?
Because we assume light comes from above
The image is concave but light is coming from below
An ammonite looks convex (a hill) even though it is concave because we assume …?
Light comes from above
Instead, it is concave but light is coming from below
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
What is multi-cue perception?
When we are exposed to multiple cues in real-world scenes
When we are exposed to multiple cues in real-world scenes
This is known as…?
Multi-cue perception
How do we achieve a single unified concept when we are exposed to multiple cues at once?
The cues must be integrated (combined)
What problems can cue integration (combining cues) overcome?
List 3
- Reliability
- Ambiguity
- Conflict
What are the 3 types of multi-cue integration?
- Compromise
- Dominance
- Interaction
Image being blindfolded and trying to shoot a hoop in basketball
Since your eyesight is blocked, you rely on your two friends behind you to provide an estimate of the distance from where you are standing and where the hoop is
Describe how you would use compromise integration on the multiple cues given by your two friends
You would take the average between the two friends but take into account how reliable each friend is
e.g. Trusting Friend 1 over Friend 2 because they play basketball, biased towards more reliable info
You would take the average between the two friends but take into account how reliable each friend is
e.g. Trusting Friend 1 over Friend 2 because they play basketball, biased towards more reliable info
What multi-cue integration is this?
a. Interaction
b. Compromise
c. Dominance
b. Compromise
Image being blindfolded and trying to shoot a hoop in basketball
Since your eyesight is blocked, you rely on your two friends behind you to provide an estimate of the distance from where you are standing and where the hoop is
Describe how you would use dominance integration on the multiple cues given by your two friends
You would trust one friend and ignore the other
Assume one of them is getting the estimate really wrong, choose whichever one is more trustworthy/reasonable
You would trust one friend and ignore the other
Assume one of them is getting the estimate really wrong, choose whichever one is more trustworthy/reasonable
What multi-cue integration is this?
a. Interaction
b. Compromise
c. Dominance
c. Dominance
Image being blindfolded and trying to shoot a hoop in basketball
Since your eyesight is blocked, you rely on your two friends behind you to provide an estimate of the distance from where you are standing and where the hoop is
Describe how you would use interaction integration on the multiple cues given by your two friends
Information incomplete or ambiguous, need one
source to disambiguate the other
simply = You would use the information from Friend 1 to disambiguate the information given by Friend 2
Information incomplete or ambiguous, need one
source to disambiguate the other
simply = You would use the information from Friend 1 to disambiguate the information given by Friend 2
What multi-cue integration is this?
a. Interaction
b. Compromise
c. Dominance
a. Interaction
When multiple cues are available the visual
system will try to integrate cues in order to obtain a …?
Unified percept
Define compromise
When two sources of depth information are conflicting, the brain will try to find a
compromise between the two
When two sources of depth information are conflicting, the brain will try to find a
compromise between the two
This is known as…?
Compromise
Describe Young et al’s (1993) study on compromise integration
List 5 points
- Participants viewed computer generated cylinder defined by 2 cues:
- Texture
- Motion (These objects will move, at different rates, bits at the side move less and slower, bits in the middle move faster and a lot more)
- Task: Apparently circular cylinder task
- Judgement: Does the cylinder look flattened, circular or stretched?
- Experimenters manipulated the texture cue; they changed the compression around the side
- Less compression = Cylinder looked flattened
- More compression = Cylinder looked stretched
- Experimenters put the 2 cues into conflict (e.g. texture was flattened, motion was stretched)
- Middle surface moving a lot faster and a lot more than the surface on the side = Cylinder appeared more stretched
- Middle surface moving a lot slower and a lot less than the surface on the side = Cylinder appear more flat
- Texture and motion conflict: What shape do
participants perceive?
Texture and motion conflict: What shape do participants perceive?
Perceived shape is a
compromise between
the two cues
The brain averaged together the cues defined by texture and by motion
The brain averaged together the cues defined by texture and by motion
This is evidence supporting…?
Compromise multi-cue integration
Describe the Young et al.’s (1993) 2nd study on compromise integration
List 2 points
- Made texture cues less regular (less reliable) in one condition
e.g. Distorted circles on the surface = less reliable cue
- Made motion cues less regular (less reliable) in another condition
e.g. Made motion jerky, motion cue is not perceived as moving smoothly
When texture cues are made less regular (less reliable) in one condition
e.g. Distorted circles on the surface = less reliable cue
What is the perceived shape of the cylinder based on?
The perceived shape is biased towards motion cue because it is more reliable
When motion cues less regular (less reliable) in another condition
e.g. Made motion jerky, motion cue is not perceived as moving smoothly
What is the perceived shape of the cylinder based on?
The perceived shape is biased towards texture cue because it is more reliable
What will the brain do when there are 2 cues conflicting?
The brain will try to average them
Final percept of shape will be biased towards…?
The most reliable cue
Define dominance
When two cues define very different shapes or depths, the brain may choose to ignore one in preference for the other
When two cues define very different shapes or depths, the brain may choose to ignore one in preference for the other
This is known as…?
Dominance
What tends to arise when one cue’s assumptions are invalid?
Large cue conflicts
Large cue-conflicts tend
to arise when …?
One cue’s assumptions are invalid
Large cue-conflicts tend
to arise when one cue’s
assumptions are invalid
Which cue will usually dominate?
Usually the cue with valid assumptions will dominate
An image shows multiple hot hair balloons of different sizes up in the air
Here, the depth is defined by elevation and relative size cues that are very different
Relative size cue dominates
Which cue is invalid in this image and why?
Elevation cue is invalid in this situation because the objects are not on ground plane
So we assume balloons that are small are further away from us and balloons that are big are closer to us
When an invalid cue dominates, it creates an illusion
Give an example of an illusion that is caused by the dominance of invalid cues
Ames room illusion
Ames room illusion is an example of the dominance of an invalid cue
Which invalid cue dominates in this illusion?
Perspective cue = assumes lines in the world are parallel and perpendicular to each other
Ames room illusion is an example of the dominance of an invalid cue
Which cue is ignored in this illusion?
Relative size cue = The larger the object, the closer it is to us
Relative size in conflict
with perspective. Perspective wins.
What illusion does this apply to?
Ames room illusion
Define interaction
Some cues are ambiguous, but other cues can disambiguate them
Some cues are ambiguous, but other cues can
disambiguate them
This is known as…?
Interaction
A cylinder with an ambiguous texture cue can be perceived as convex or concave
What are we likely to perceive this as?
Convex because we have a bias for convex objects
A cylinder with an ambiguous texture cue can be perceived as convex or concave
How do we disambiguate ambiguous texture cues?
By using binocular disparity
Describe the model of cue integration by Landy et al. (1995)
List 2 points
- Interaction stage
- Cues interact and disambiguate each other
- Compromise stage
- Cues are averaged together
Ambiguous cues such as texture and shading can be disambiguated by …?
Other less ambiguous cues
Ambiguous cues such as texture and shading can be disambiguated by other less ambiguous cues
Evidence suggests this stage occurs …?
Prior to cue compromise
What 4 problems can cue integration help overcome?
- Unifying our percept of the world
- Differences in cue reliability (compromise)
- Conflicting information (compromise & dominance)
- Cue ambiguities (interaction)
What cue(s) integration can help to overcome differences in cue reliability?
a. Interaction
b. Compromise
c. Dominance
b. Compromise
What cue(s) integration can help to overcome conflicting information?
a. Interaction
b. Compromise
c. Dominance
b. Compromise
c. Dominance
What cue(s) integration can help to overcome cue ambiguities?
a. Interaction
b. Compromise
c. Dominance
a. Interaction
Recovering depth from 2D retinal images is a difficult problem
This is known as…?
Inverse problem
Define inverse problem
Recovering depth from 2D retinal images is a difficult problem
