Block 2- Depth and size perception

Question 1

What type of features are depth and size, what does this mean?

Answer 1

Depth and size are veridical features

Directly relates to our actions

Eg grabbing cup - eg need to know how far away a cup is and how big it is

Question 2

What is the problem with depth perception?

Answer 2

2D vision in a 3 D world

Retinal image - 2 dimensional, its a flat representation

Referred to as the inverse projection problem

Therefore, we have to rely on depth cues

Question 3

What are the different types of depth cues?

Answer 3

Body related:
-Body-related (oculomotor) cues

Stimulus related:
-Monocular (pictorial, motion-based)

-Binocular (retinal disparity) stimulus-related cues.

Question 4

What does body related depth cues mean and what are the two types?

Answer 4

Body related = Feel whether an object is close or far away from us

So our body helps us decide

There are two main cues for this:

-Accomodation
-Convergance

Question 5

How does accommodation as a body related depth cue work?

Answer 5

Accommodation - Describes the process that our ciliary muscles relax and tighten -depending on whether an object is close to us or far away from us

And our brain, when deciding whether an object is close to us or far away from us, takes the state of the cilliary muscles relaxed or tightened into account

So our brain tells us that an object is close to us or far away from us - because it knows whether the ciliary muscles have relaxed or tightened

Question 6

How does convergence as a body related depth cue work?

Answer 6

Converage describes the fact that when an object is quite far away from us, our eyes are quite parallel

Near- Eyes go inwards - So eye muscles pull your eyes inwards

=Congergance

So again the idea is tha our brain takes into account this information - to decide if object is far away or close based on eye muscles

Question 7

What are the two different types of monocular depth cues?

Answer 7

• Pictorial depth cues
  -Motion- based cues

Question 8

What are all of the different pictorial depth cues, what is the mnemonic to remember this?

Answer 8

• Occlusion
  -Relative height
  -Relative size
  -Perspective convergence
  -Familiarr size
  -Atmosphere perceptive
  -Texture gradient
  -Shaodws

Odd rubber robots play frisbee at taco shops

Question 9

What is the pictorial cue of occlusion?

Answer 9

Occluded objects are further away than occluding objects

Question 10

What is the pictorial cue of relative height?

Answer 10

Objects higher in the visual field are further away than objects lower in the visual field

So from the image we can see that the mountain is the furthest away, then the tree, then the flowers

This is all true as long as we are standing on a flat surface

Unless on a hill, then objects with their base closer to the horizon are further away

Question 11

What is the pictorial cue of relative size?

Answer 11

When two objects are equal in size, the one that is further away takes up less of the visual field

Question 12

What is the pictorial cue of perspective convergence?

Answer 12

Converging parts of objects are further away

eg when they are closer they are more Parallel, and as they tracks get further away they converge

Question 13

What is the pictorial cue of familiar size?

Answer 13

This is about our knowledge of the familiar size of objects

So we know the height of these characters, so we know that actually the dwarf is probably not far away, we know from our familiar knowledge that dwarfs are just smaller

Also - Epstein experiment uses £1 coin and 5p

Question 14

What is the pictorial cue of atmosphere perspective?

Answer 14

Objects further away are less sharp and have a blue tint

Short wave forms are prone to be scattered - as they are shorter

As we perceive them as blue, adds this blue layer

So, this layer is added to objects that are further away from us, as there are more particles in the air between us and the object

So on the moon, there will be no atmosphere perspective as there is no atmosphere on the moon

Question 15

What is the pictorial cue of texture gradient?

Answer 15

Denser textures indicate objects which are further away

Question 16

What is the pictorial cue of shadows?

Answer 16

Eg as we can see, adding the shadow, indicates that this object is closer to us

Question 17

What are the two motion-baed cues?

Answer 17

Motion parralx
Deletion and accretion

Question 18

How does the motion based cue of motion parallax work?

Answer 18

Nearby objects glide away quickly

Far away objects glide along slowly

Explanation:

IF you look a the retinal points of the tree - The retinal point moves a long distance

Whereas the image of the house that is in the distance, where the light waves come in more parallel, travel a much shorter distance in the same amount of time

Question 19

How does the motion based cue of deletion and accretion work?

Answer 19

This is about occlusion in motion

Eg as you move throughout the forest, you can see that these stags are getting covered and uncovered by the tree

This seems to suggest that the stags are further away than the trees

Because the trees keep covering up the stags

Question 20

What is a binocular cue, what is the one example of this?

Answer 20

This is a cue that only works, when we look at the world with two eyes

Binocular vision - Stereoscopic Vision, means vision with both eyes

Produces depth cue which is entirely unique

The binocular depth cue is retinal disparity

Question 21

Why does retinal disparity exist?

Answer 21

Retinal disparity exists because our eyes are separated by a few centimetres
So the retinal images in the left and right eyes are slightly shifted
The difference between these two images are the retinal images

Question 22

Why is retinal disparity to important?

Answer 22

Retinal disparity alone is sufficient enough for us alone to perceive 3 dimentionality

It is the most powerful depth cue

Question 23

What is the retinal disparity based on?

Answer 23

The point of fixation is crucial for binocular depth perception

Question 24

What is the horropter?

Answer 24

Imaginary circle that goes through all of the objects that are equally distant

Question 25

How does retinal disparity actually work?

Answer 25

Retinal disparity works through corresponding retinal points The focus point (Freida) will produce corresponding retinal images on BOTH eyes All objects with the same distance as the fixation point, will be represented on corresponding retinal points ( same relative position in both eyes) So Susan and Harry will produce the same retinal image So, objects that are not on the horopter, so not as Farr away as the point of fixation, not equidistant to the point of fixation, but are closer or further away to us, probably don't produce corresponding retinal points So, non corresponding retinal points are produced by objects which are closer or further away to the point of fixation Where the corresponding point would be, and where the actual point is = very different

Question 26

What is stereopsis?

Answer 26

The ability to use retinal disparity as cue to perceive depth Each distance from fixation produces a different amount of retinal disparity The larger is disparity, the further the object is away from fixation

Question 27

What is the neuronal evidence for retinal disparity?

Answer 27

Disparity selective neurons in V1 and along both ventral and dorsal streams We know that there is crosstalk between these two pathways, these disparity selective neurons are some of the crosstalk

Question 28

What is the evidence that retinal disparity is sufficient for 3d vision?

Answer 28

We can see this through the stereoscope This works by: There are two images one one the left side and one on the right side They are the same image Only that one of the images is slightly shifted in space So the right image, is slightly more to the right than the left image If these are presented to a person through the glasses This shift in the image, mimics the shift between the two eyes, and produces retail disparity When we look at the image through the steropscope, we will see one 3 dimensional image, rather than 2 seperate images Our Brian puts them togethe, and perceives retinal disparity, and therefore 3 dimensionality

Question 29

Even with the pictorial depth cues within the stereoscope image, how can we prove retinal dispart is enough on its own to perceive depth?

Answer 29

Random dot stereogram rocess is the same Looking at one image of dots with the left eye, other with the right eye IF they does this through the stereoscope, they will find that there is a circle, square embedded into the images This is because the dots in the image are slightly shifted, as opposed to the other image

Question 30

How does size perception depend on retinal size?

Answer 30

Size of retinal object representations Object representations on the retina are measured In degrees of visual angle The visual angle, depends on the physical object size and the physical distance from the observer Both are important, so its the size and physical distance from the observer This means that two objects, which are very different in size can produce the same visual angle So retinal, optic representations are measured in visual angles ( the angle of an object relative to the observer's eye)

Question 31

What is size distance scaling ( size constancy)

Answer 31

Shows us that size pereception is not only related to the actual size of an object, but takes the distance of the object from us as an observer into account Size constancy is expressed in a scaling equation So this takes into account the size of the retinal image, also the perceived distance of the object

Question 32

What is the size-distance scaling equation?

Answer 32

S= k(RXD) s= perceived size R=size of the retinal image D= Perceived size