Psych*2390: Depth Perception

Front 1

Depth perception

Back 1

• Depth perception involves determining how far something is away from you. It is used all the time – very important in co-ordination such as reaching or catching.

Front 2

Why is depth perception difficult?

Back 2

We live in a three-dimensional world but the retina is flat like a postage stamp. Essentially we have a three dimensional world but the retina is flat like a postage stamp.

Front 3

Constructive Approach

Back 3

The constructive approach believes we must look at a lot of cues and reason about the image and figure out how far things are. Perception is reason.

Front 4

Ecological Approach

Back 4

Perception is like responding to the right information. Problems arise because we don't take into account that organisms move.

Front 5

What are some physiological cues to depth?

Back 5

1. From lens
2. Convergence of eyes

Front 6

From lens

Back 6

Using the ciliary muscle to determine depth. If it's bulging it's close, if it's flattening it's far.

Front 7

Convergence of eyes

Back 7

As something gets closer you end up turning your eyes inwards, whereas if something is farther you straighten your eyes out.

Front 8

What are some pictorial cues?

Back 8

1. Relative and Familiar Size
2. Overlap
3. Height in the field of view
4. Shading
5. Linear perspective
6. Atmospheric perspective
7. Texture gradients

Front 9

Relative and Familiar Size

Back 9

This cue relies on knowledge - if you know the actual size you can use the visual angle directly to figure out the distance because it has taken away the ambiguity.

Front 10

Overlap

Back 10

Something close is going to cover up something that is farther away.

Front 11

Height in the field of view

Back 11

Things to look farther away if they're closer to the horizon line.

Front 12

Shading

Back 12

The assumption that light comes from above.

Front 13

Linear perspective

Back 13

Parallel things seem to come together toward a vanishing point.

Front 14

Atmospheric perspective

Back 14

As things extend away in depth they look blurrier.

Front 15

Texture gradients

Back 15

Textural elements get more crowded together with depth. This cue is a combination of linear perspective and relative size.

Front 16

What are some motion based cues?

Back 16

1. Relative motion/motion parallex
2. Accretion/deletion
3. Motion in depth

Front 17

Relative motion/motion parallex

Back 17

Say a man is on board a train - the things close seem to be moving in the opposite direction as he is whereas the things farther away seem to be moving in the same direction.

Front 18

Accretion/deletion

Back 18

• Demonstration: Professor Trick stands in front of the table. As she walks by the table she deletes part of the table, and as she keeps going the table will accrete.

• Accretion is growing, deletion is shrinking – object that looks farther away appears to be growing and shrinking

Front 19

Motion in depth

Back 19

As something gets closer it looms and grows larger.

Front 20

How is depth information derived from stereopsis?

Back 20

It is derived by random dot stereogram - these are a bunch of dots that are arranged strategically (some are shifted) to create the illusion of a 3D image. There doesn't need to be any contours for this effect.

Front 21

Stereo-correspondence

Back 21

Stereo-correspondence involves determining which side on the left eye image matches which part on the right and comparing the two.

Front 22

Auto-stereograms

Back 22

Illusions caused by solving the stereo-correspondence problem incorrectly.

Front 23

What causes auto-stereograms?

Back 23

They are caused by solving the stereo-correspondence problem incorrectly. When you correctly match up images dot 1 and dot 2 will create images in the back of the eye. If there is an error the visual system matches up the wrong dots. The visual system incorrectly believes there to be a match which results in an illusion position or illusion depth.

Front 24

Retinal disparity

Back 24

Determining how far apart the object is on the left eye compared to the right eye.

Front 25

What are the three possible outcomes?

Back 25

1. Horopter fixation plane
2. Crossed disparities
3. Lunercrossed disparities

Front 26

Horopter fixation plane

Back 26

If the position of the object on the horopter. It’s called zero disparity because the object is falling exactly in the same part of the eye.

Front 27

Objects closer to the horopter (crossed disparities)

Back 27

The position of the object switches from one side to the other depending on which side you look from.

Front 28

Why do we experience a jump in images when we switch eyes?

Back 28

Because of crossed disparities.

Front 29

Items behind the horopter (lunercrossed disparities)

Back 29

Object is further away than where you are fixating.

Front 30

Panem's fusion area

Back 30

Area around the horopter. You can fuse the left and right image together to get a single image viewed in three dimensions.

Front 31

Tilt after effect

Back 31

This occurs when a person has adapted to one line orientation. They spend time looking at one line orientation and then switch to look at an image of vertical lines. Afterwards they will see lines in the opposite orientation. What they saw before will influence how they see the vertical lines.

Front 32

What did researchers observe about the tilt after effect?

Back 32

You can adapt the left eye and have the right eye closed. Even though you have adapted the left eye, you will see the after effect in the right eye.

Front 33

What does this observation imply?

Back 33

• The fact that the tilt-after effect transfers across eyes must mean that some cells in the brain take information from both the left and right eye.

• These are cells that take information from both eyes, and in particular some binocular cells responsible for line orientation.

• Those cells are still fatigued when they look with the other eye because it’s the same cell!

Front 34

What are binocular cells in the striate complex responsible for?

Back 34

These cells take information from both the left and right eye.

80% of cells respond to information from either the left or right eye.

Front 35

Striate cortex hypercolumns

Back 35

Little chunks of tissue that are looking for activity in a particular part of visual space.

Front 36

Orientation columns

Back 36

Seek line orientation

Front 37

Ocular dominance columns

Back 37

Columns for the left eye and columns for the right eye.

Front 38

Disparity sensitive columns

Back 38

These look for a specific difference

Front 39

Critical periods

Back 39

Periods of time in which we must have certain experiences or abilities do not develop.

Front 40

What happened when researchers deprived kittens of eye sight during critical periods?

Back 40

Kittens are born blind and begin to see around four months. Scientists put an eye patch on the left eye the first day and then the right eye for the 2nd day and so on switching back and fourth. Because the kitten never gets information from both eyes binocular cells don’t develop properly. The cat will not develop normal depth perception. This will only occur if done during the critical period of four weeks to four months.

Front 41

Strabismus

Back 41

This is an imbalance of the eye muscles. The brain suppresses one eye because it’s getting so much information it can’t handle it. This means people could end up cross-eyed or wall-eyed.

Front 42

Why do images get suppressed?

Back 42

Binocular rivalry

Front 43

Cheshire Cat Illusion

Back 43

How the visual system deals when there are two completely different visual images.

Front 44

What is an example of the Cheshire Cat Illusion?

Back 44

Take a person and balance a mirror in such a way that on one side there’s a blank wall and on the other a mirror. The right eye has a blank wall the left has a picture of your friend. Very quickly your eye will suppress the blank wall. The image with the most contours and the most complicated will be the one that you see. If you move your fingers on the side of your eye you will see that your fingers become superimposed on the image of your friend.

Front 45

Amyglopia

Back 45

When one eye has a much lower quality image than the other the brain starts to ignore it and thus won’t develop depth perception properly.

Front 46

Converse problem

Back 46

The same actual size will produce a variety of retinal image sizes.

Front 47

Size constancy

Back 47

We see things as the same even if we are moving farther away and the image is shrinking.

Front 48

How is size constancy achieved?

Back 48

People use depth information. The retinal image plus depth information.

Front 49

Ponzo illusion

Back 49

The depth cues makes things that are the same size look very different. Linear perceptive cues fool us into believing that they’re different sizes.

Front 50

Armes room

Back 50

We look through one eye which messes up linear perception cues. This causes people to look like they are changing size. By limiting a person to monocular vision, they have to rely on monocular cues which are misleading due to the shape of the room.

Front 51

The Horopter

Back 51

An imaginary arc that goes through point of fixation and indicated location of objects that fall on corresponding points of two retinas.

Front 52

Corresponding retinal points

Back 52

Places on the retina that overlap in each.