Depth, Size And Illusions

Question 1

We perceive…

Answer 1

A 3D world but the image on our retina is 2D

Question 2

Cues

Answer 2

Use cues to extract depth info
Cues are info in the retinal image that’s correlated with depth
Across our lives we learn to associate cues with depth
Associations become automatic through repeated exposure

Question 3

What happens to the image on the retina

Answer 3

The image on the retina is upside down. Perception flips it

Question 4

3 broad cues

Answer 4

Bits of info that are:

1: oculomotor = minds get from muscles around eye (sensing position of eyes)
2: monocluar= extracted from images by either eye independently
3: binocular = extracted from images by both eyes working together

Question 5

Ocular convergence

Answer 5

Oculomotor Cue

Inward movement of eyes and the corresponding muscle tension when focusing on near objects

Question 6

Lens accomodation

Answer 6

Oculomotor cue where tension is detected in the ciliary muscles
Accomodation is the change in lens shape when focusing on near or far objects
Far = relaxes
Close = contacts

Question 7

Monocular cues are mostly

Answer 7

Pictorial cues - information extracted from 2D images

Also non-pictorial cues - info cannot be extracted from static 2D image

Question 8

Occlusion

Answer 8

When an object partially covers another

Object that is occluded is usually deeper in the visual field

Question 9

Relative height

Answer 9

Looking below horizon = objects higher are more distant

Looking above horizon = objects lower are more distant

Question 10

Relative size

Answer 10

When objects are equal size, the closer ones will take up more of your visual field

Question 11

Perspective convergence

Answer 11

Parallel lines appear to approach each other at greater distances

Question 12

Perspective convergence in art

Answer 12

European art- effect loss in middle ages and reemerged in Renaissance

Question 13

Familiar size

Answer 13

Knowledge of familiar objects can help us infer which objects are closer

Question 14

Atmospheric perspective

Answer 14

Distant objects are blurrier and can have blue/grey tint

Question 15

Texture gradient

Answer 15

Equally spaced elements are more closely packed as distance increases

Question 16

Shadow

Answer 16

Position of objects shadow can be helpful to perceive depth

Question 17

Cues combined

Answer 17

Cues are more useful when they give consistent info

Question 18

Motion parallax

Answer 18

Non-pictorial monocular cue

Near objects glide rapidly past and far objects move slowly

Question 19

Occlusion via movement

Answer 19

Non-pictorial cue
Objects are covered and uncovered as we move relative to them
Covering = deletion
Uncovering = accretion

Question 20

Binocular cues involve

Answer 20

Comparing the slightly different views presented in each eye

Question 21

Binocular disparity

Answer 21

Disparity between different images created by objects falling in different locations on the retina

Question 22

Corresponding points

Answer 22

The forea is always the corresponding point as whatever is focused on falls on the same spot on both retinas

Question 23

Horopter

Answer 23

Unfocused things fall on the corresponding point if they are on the an arc called the horopter
Images not on the horopter fall on non-corresponding points

Question 24

Crossed disparity

Answer 24

Crossed: object inside horopter = appears closer
Uncrossed: object outside horopter= appears further

Question 25

Stereoscopes

Answer 25

Take advantages of binocular disparity to create depth in a pair of 2d images

Question 26

Chromostereopsis

Answer 26

See red circle in front of blue
Some see no differences and minority reverse
Effect reverses on white background
From slightly different refractions of light from colours = non-corresponding points on eye

Question 27

Corresponding problem

Answer 27

How does our visual system combine images

Potentially from specific features of objects but this doesn’t explain objects like random-dot stereograms

Question 28

Depth perception other species

Answer 28

Animals use same eves as humans
But binocular disparity requires front facing eyes for overlapping fields of view
Predators tend to have front facing
Prey tend to have side facing (lateral)

Question 29

Environmental cues to size

Answer 29

Size and depth perception are interrelated

Size is a cue for depth and depth is a cue for size

Question 30

Retinal image size

Answer 30

Visual angle is the amount of the retina that an image occupies
Far away = smaller image = less angle
Close = big image = greater angle

Your thumb at arms length covers 2 degrees of visual angle

When depth cues are absent, perceived size determined by retinal image size eg- moon and sun have almost same visual angle but moons bigger so it covers sun during eclipse

Question 31

Removing depth cues

Answer 31

With depth cues provided judgements were based on physical size
With depth cues removed judgements were based on the size of the retinal image eg the visual angle

Question 32

Size constancy

Answer 32

Perception that objects size is relatively constant even if the size of retinal image changes
Expressed in the size-distance scaling equation
Brains have no control over visual angle but try to keep perceived size of object the same
Eg visual angle goes up distance from object must go down

Question 33

Emmert’s law

Answer 33

Retinal size of an after image stays constant
Perceived size changes with distance
Closer afterimage = smaller it seems (follows size- distance scale)

Question 34

Nonveridical perception

Answer 34

Occurs during visual illusions

Stimulus dimensions that are only subjectively perceived to be there

Question 35

Muller-lyer illusion

Answer 35

Arrows with different faces fins - shorter arrows have inward fins
Explanation: size constancy misapplied to 2D
Perceive fins as belonging to objects pointing
If an objects coming towards us its closer = smaller

Question 36

Miller-lyer problems with size constancy

Answer 36

Dumbbell version (no fins but circles) = same perception
Also occurs in 3D images that don't implicate depth (things at the same distance but spread apart)

Question 37

Conflicting cues muller-lyer

Answer 37

Perception depends on:

1: actual length of lines
2: overall length of figure

Conflicting cues are integrated into a compromised perception of length

Question 38

Ponzo illusion

Answer 38

Horizontal objects placed over train tracks
Upper object seems longer but same size
Misapplied Size constancy

Question 39

Ames room

Answer 39

Room constructed to look normal with one eye view
Left corner is actual further away
Explanations:
1 - size-distance scaling: person on left has smaller retinal image + perceived distance is the same = perceived size must be smaller

2- relative size: size perception is relative to other objects (filling whole room)

Question 40

Moon illusion

Answer 40

Moon appears larger on the horizon
Explanations:
1 - apparent depth theory: horizon is surrounded by other depth cues
2- hastened heavens theory: horizon is perceived as further away than sky = small retinal image size larger on horizon

Question 41

Forced perspective

Answer 41

When photos remove depth cues to change the size of people

Leaning tower of Pisa where people look like they’re holding it