Lecture 8: Depth perception

Question 1

Name primary visual cortex akas

Answer 1

Area v1
Striate cortex - stripped pattern when stain and look at

Question 2

Name secondary cortex akas

Answer 2

Area v2
Extrastriate cortex

Question 3

Describe retinotopic mapping

Answer 3

Spatial organization of visual field preserved in brain
Neighbouring areas of retina mapping onto neighbouring areas of primary visual cortex - v1
Point by point manner
Spatial relationships preserved in lgn and v1 = corresponds to specific regions in v1

Question 4

How much cortical space in v1 dedicated to central vision

Answer 4

More cortical space dedicated to central vision than peripheral vision

Question 5

What does fovea have

Answer 5

Higher density of ganglion cells than peripheral retina

Question 6

Descrbe what lgn shows

Answer 6

Reflects fovea’s asymmetry of ganglion cells
= 2x as manny parvocellular layers as magnocellular layers

Question 7

Describe cortical magnification

Answer 7

V1 further amplifies total number of neurons devoted to central vs peripheral vision where the central 10 degrees of visual field (1% of visual field) occupies 50% of v1s surface
Asymmetry further enhanced
More spaced allocated for processing visual info in Center of visual field

Question 8

What are retinal ganglion cells sensitive to

Answer 8

Frequency
Not orientation
Like on center, off surround
Cannot tell is vertical or diagonal
Cells will fire the same - same activity, light and darkness produce same effect regardless of orientation

Question 9

Descrbe response properties of v1 neurons

Answer 9

By combining info from several retinal ganglion cells= possible to detect orientation of lines
Hubel and Wiesel
Pattern diff for reach cell - since there are many = combine activity
Ap firing rate related

Question 10

Describe how v1 neurons can detect orientation

Answer 10

Area v1 neuron connected to lgn neuron connected to retinal ganglion cell
Area v1 neurons have preferred orientation
If light perfectly aligns with center of cells = all fire= repsond vigorously
If receptive field organized differently = will be different and respond less

Question 11

When are v1 neurons most active

Answer 11

Best around 70 degrees = preferred orienttaion

Question 12

Describe tilt after effect

Answer 12

Have diff populations of neurons that specialize in certain frequencies and orientation
V1 neurons = turned to that orientation and d naturally become tired = less and less response

Question 13

Describe tilt after effect- ADAPTATION

Answer 13

Looking at pattern fo stripes for a certain time will tire neurons and shift the balance to opposite direction
Then shift to opp direct = neurons habituate - become tired after fire for a while

Question 14

WHAT is orientation encoded by

Answer 14

orientation encoded by a population of neurons

Question 15

What does perception of objects rely on

Answer 15

Activity across whole pop of neurons in v1

Question 16

Describe illusion effect = titled lines

Answer 16

Neurons tuned to vertical lines = will repsond most to this pattern
Neurons around 45 degrees exhibit decrease firing rate comapred to before habituation occurred
Ones not close to 45 degrees = wont change bc not habituated
= percieve orientation of lines as to the right
Hubel and Wiesel = thought could explain how see objects but actually more complicated

Question 17

What is a hyper column

Answer 17

1 mm block of striate cortex - contains all machinery Jesse ray to look after everything the visual cortex is responsible for - in a certain small part of the visual world
V1 neurons organized into hyper columns

Question 18

Describe hyper columns

Answer 18

Each contains cells corresponding to every possible orientation - 0-180 degrees, with one set preferring info from left eye and one set preferring info from right eye
Associated with specific area in visual field

Question 19

Describe hyper columns = image

Answer 19

Insert electrode perpendicular to cortex and went through and looked at layers
Each column = have same orientation preference
Each neighbouring column = orienttaion close to other but diff angle
Each has 3 hyper columns per eye

Question 20

Describe simple cells

Answer 20

Respond to light with increasing intensity when orientation matches receptive field
Lines with certain orientation
Orientation selectivity represented by tuning curves (firing rate vs line orientation)

Question 21

Describe complex cells

Answer 21

Some detect motion in their receptive fields
Selective for line orienttaion and often for movement direction
Not simple

Question 22

Describe receptive field properties

Answer 22

Of complex cells
Larger and less well defined than simple cells
Some span whole hemifield responding to specific orientation/movements across area

Question 23

Describe specialized complex cells

Answer 23

End stopped cells
Respond best to moving bars of specific length that end within their receptive fields - responsive to lengths of lines
Do not fire if bars exceed their receptive field
Involved in detecting angles, corners, and boundaries

Question 24

What forms basis of depth perception

Answer 24

Visual system good at keeping track of left and right fields = forms basis of depth perception

Question 25

Describe depth perception generall

Answer 25

We naturally perceive depth - see 3d But visual info reaching retina = 2d Bc retina flat memrbane

Question 26

Describe depth perception and Kant

Answer 26

Space = a priori form Mind already knows space exists before receiving sensory info Uses a priori knowledge to interpret sensory info Sensory info does not tell us about depth Know depth exists Nervous system pre arranged to extract 3d from 2d

Question 27

How do we infer depth

Answer 27

Use 2 cues = Monocular cues Binocular vision and stereopsis

Question 28

Describe monocular clues

Answer 28

Do not need 2 eyes Implicit inference - mostly logical Ex = Tricked into thinking all stairs go up or down

Question 29

Describe binocular vision and stereopsis

Answer 29

Seeing with 2 eyes Refers to perception of depth we get from binocular vision Much more hard wired

Question 30

What are pictorial clues

Answer 30

Depth cues Inferred from static image Using monocular vision Help brain interpret depth in 2d scenes

Question 31

Name types of pictorial cues

Answer 31

Occlusion Relative size Familiar size Linear perspective Texture gradient Aerial perspective Shading

Question 32

Describe occlusion - pictorial cues

Answer 32

A depth cue wehre one object partially blocks another = indicates that blocked object is father away One of most reliable depth cues

Question 33

Desire accidental viewpoint - pictorial cues

Answer 33

Specific line fo sight that creates an ambitious or misleading depth interpretation Ex = object behind another, could be that that object has cut out but looks whole bc of accidental viewpoint, also like an art structure = look at certain Angle and looks like a face

Question 34

Describe relative size - pictorial cues

Answer 34

Comparison of size between items without knowing absolute size of either one All things being equal = assume smaller objects farther away than large ones

Question 35

Describe familiar size - pictorial cues

Answer 35

Comparison of size when knowing absolute size of one of the items Can infer the absolute distance because we know exact size of one of teh objects Ex=Know approx how big chair is in relation to humans

Question 36

Describe relative height - pictorial cues

Answer 36

For objects touching ground = those higher in visual field, appear further away, looks like occlusion but if look at higher = far For objects floating in air = shadows cna help infer their relative heights

Question 37

Why does relative height infer depth - pictorial cues

Answer 37

Objects further away = seen with a wider angle relative to our body When look at something close = decrease viewing angle When sight parallel to ground - perpendicular to body = experience greatest feeling of distance - horizon

Question 38

Describe texture gradient - pictorial cues

Answer 38

Pattern that repeats Depth cue based on geometric fact that items of teh same size form smaller, closer spaced images father away they get Further = appears smaller, for chairs, where are bird appears larger when further

Question 39

Describe linear perspective - pictorial cues

Answer 39

Lines that are parallel in the 3d world wil appear to converge in a 2d image as they extend into distance Lines project = to vanishing point = apparent point at which parallel lines receded in depth convergence

Question 40

What can linear perspective also result from - pictorial cues

Answer 40

Combo of relative size and relative height = produces strong impression fo depth

Question 41

Describe aerial perspective - pictorial cues

Answer 41

Depth cue based on implicit understanding that light scattered by atmosphere More light scatted when look through more atmosphere More distant objects appear fainter, bluer and less distinct - Bluer bc Rayleigh scattering and whiter bc mie and non selective scattering

Question 42

Describe shading - pictorial cues

Answer 42

Variations in light and shadow on surface provide info about its shape, depth, orientation Objects with gradual shading changes = appear curved Sharp contrasts = suggest edges or discontinuities in depth Brain assumes light comes form above - influencing depth perception

Question 43

What are dynamic cues

Answer 43

Strong Related to movement Movement of images on retina

Question 44

How is depth perceived when observer stationary

Answer 44

Depth perceived through relative movement of objects at diff depths (kinetic depth effect) Effect strong for rotating spheres = where luminance variations father enhance depth perception - sphere videos

Question 45

Describe motion parallax - dynamic cues

Answer 45

Images closer to observer move faster across visual field than images further away Brain uses info to calculate distances of objects in environment = infer disatcne of object when moving in parallel fashion to scene

Question 46

Describe motion parallax - dynamic cues - in real situations

Answer 46

Observer can move eyes to track object - which will give observer impression that objects beyond their fixation = moving in same direction as them Objects located beyond fixation point look like following you/going in opposite direction Seems like object beyond fixation point moves in same direction as you, not true tho bc moving eyes at same time you are moving

Question 47

Describe optic flow - dynamic cues

Answer 47

Apparent motion of objects in visual scene produced by relative motion between observer and scene Objects closer to observer will move more rapidly Objects in focus of expansion wont move (closer to focus of expansion = wehre we headed to = move slower)

Question 48

Describe binocular cues - oculomotor depth cues = vergence

Answer 48

Eye convergence for near objects - move eyes inwards Divergence for distant ones - move eyes outwards

Question 49

Describe binocular cues - oculomotor depth cues = Accomdoation

Answer 49

Ciliary msucles contract and adjust lends shape for focu Nervous system keeps track of degree of accommodation and uses it to infer depth Accommodation = not binocular cue

Question 50

Describe binocular cues - oculomotor depth cues = Absolute depth perception

Answer 50

Unlike pictorial cues Both fo these allows use to tell wehre object located better = accommodation and vergence

Question 51

Describe binocular cues - oculomotor depth cues = Vergence limit

Answer 51

Reliable up to 2m Perceive degree of divergence and use as depth cue

Question 52

Describe binocular cues - oculomotor depth cues = Accommodation limit

Answer 52

Active up to ~6m (beyond = optical infinity) Cannot tell difference in distance of objects beyond 6m

Question 53

Describe stereopsis - binocular cues

Answer 53

Rich impression fo depth we get from seeing with both eyes Relies on binocular disparity

Question 54

Describe binocular disparity

Answer 54

Slight difference in images perceived by each eye due to their horizontal separation Which brain uses to calculate depth and percieve a 3d view of environment 2 eyes do not receive same image = helps infer depth

Question 55

Describe Vieth muller circle - gen

Answer 55

Imaginary geometric circle in visual space Passes through point of fixation and optical centres of both eyes Represents theoretical locations fo objects that produce corresponding retinal points in both eyes = result in no binocular disparity = appear at same depth as fixation point Concept used to explain basis of binocular vision and depth perception

Question 56

Describe Vieth muller circle - explain

Answer 56

Q = on circle established by fixation point So Q = projected on corresponding points Inversely = red point lands on disparate points on left and right eyes retina = green point is perceived as a single image, but red = double Corresponding/non corresponding retinal points = helps infer depth of object = distance

Question 57

Describe Vieth muller circle - image

Answer 57

R = not projected to corresponding retinal points bc not on circle Fovea = same point Q = always to left of fovea = same location on both eyes But r is not

Question 58

What is horopter

Answer 58

Spatial region in visual space wehre objects project images onto corresponding retinal points in both eyes Objects on horopter appear to be at same depth as point of fixation and are perceived without binocular disparity Horopter cna take diff shapes depending on viewing conditions - like distance of fixation Includes vieth muller circle under idealized conditions

Question 59

What is panums fusional area

Answer 59

Region in visual space around horopter where slight binocular disparities can still be fused by brain to produce single unified perception of depth Objects within area = seen as single despite differences in images projected onto retinas of each eye Objects outside panums fusional area = may appear double - diplopia Area critical for maintaining binocular vision and depth perception Fused into one unitary percept - provides rich depth perception

Question 60

Describe image of steropsis - horpter and fusional area

Answer 60

Panum fusional area = area where vision capable fo integrating input from left and right visual fields despite binocular disparity Horopter = space wehre objects fall on corresponding retinal points - Oval shape, bc eyes not fully sphere

Question 61

Name 2 kinds of disparities

Answer 61

Crossed disparity Uncrossed disparity

Question 62

Crossed disparity - definition

Answer 62

Occurs when object closer to you than point of fixation In front of horopter

Question 63

Crossed disparity - Explanation

Answer 63

Image of object falls on outer (temporal) side of retina in both eyes From left eyes view = located to right of fixation point From rigth eyes view = located to left of fixation point

Question 64

Crossed disparity - Result in perception

Answer 64

Indicates object in front of fixation point and closer to you in 3d space

Question 65

Uncrossed disparity - defintion

Answer 65

When object father away from you than point of fixation = past horopter

Question 66

Uncrossed disparity - Explanation

Answer 66

Image of object falls on nasal side of retina in both eyes From left eye view = located to left of fixation point From right eye view = located to right of fixation point

Question 67

Uncrossed disparity - Result in perception

Answer 67

Brain interprets as indicating object behind fixation point = father away in 3d space

Question 68

Describe v1 binocular neurons

Answer 68

Different binocular neurons in v1 encode all categories of retinal disparity (zero, crossed - near, uncrossed - far) Neurons allow perceiving depth within panums fusional area Neurons tuned to diff degrees of disparity Other columns that receive input form both eyes = allow stereopsis

Question 69

Describe v1 binocular neurons = graph

Answer 69

Zero disparity = tuned zero , no differences, fire if no disparity, more neurons tuned to 0 disparity = when on horopter Tuned near = bit of crossed disparity Number of neurons decrease with increasing disparity = point where so much disparity that image cannot be resolved- gradual= perception of depth decreases as get away from horopter

Question 70

What is stereoscope

Answer 70

Device for presenting one image to one eye and another image to other eye Popular in 1900s Many children in modern days have view master = also a stereoscope Get sense of depth that comes from binocular rivalry

Question 71

How do movies look 3d

Answer 71

Each eye must receive a slightly different view of teh scene - just like in real life Early method = anaglyphic glasses = red lens and blue lends = colour filters Current methods= use polarized light and polarizing glasss to ensure that each eye sees a slightly different image= use polarity/ orienttaion of light wave

Question 72

Describe correspondence problem

Answer 72

Visual system has to match images from left and rigth eyes In binocular vision - problem of figuring our which bit of image in left eye should be matched with which bit in right eye Like for objects not in panums= projected to non corresponding retinal points so how does system know to connect points or that it is same object

Question 73

Do we need to recognize objects to have stereopsis? Explain 2 hypotheses

Answer 73

1 = r and l eye —> each do object recognition then —> binocular integration —> stereopsis 2 = right and a left eye —> both do binocular integration - automatically before object recognition —> BOTH stereopsis —> both object recognition

Question 74

Describe what stereogram proves

Answer 74

Object embedded in random dot stereogram = can only see object with both eyes. = Proves hypothesis 2 Both eyes need to recognize object together

Question 75

What is random Dot stereogram

Answer 75

Visual pattern consisting of 2 images made up of random dots When viewed with both eyes - using stereoscopic vision - the 2 images create illusion of 3d shape or object floating in space

Question 76

Describe generation of random dot stereogram

Answer 76

2 similar random dot patterns created Section of one pattern shifted slightly horizontal - left or right - relative to corresponding section in other pattern

Question 77

Describe disparity of random dot stereogram

Answer 77

Horizontal shift creates binocular disparity when the 2 images viewed together Disparity mimics differences in the images seen by the left and right eyes in real world 3d viewing

Question 78

Describe perception of random dot stereogram

Answer 78

When each eye views one image - using a stereoscope or by crossing/uncrossing eyes = brain fuses 2 patterns Shifted section appears as a 3d object or surface due to the brains interpretation of disparity

Question 79

Describe crossed disparity stereogram

Answer 79

Start with random grey shoes - subset dots that are different = shift positions for right eye = moves left Can play with this = object will be perceived as closer

Question 80

Describe uncrossed disparity stereogram

Answer 80

Subset dots move to rigth for right eyes view Can play with this = object will be perceived as farther

Question 81

What is binocular rivalry

Answer 81

Competition between the 2 eyes for control of visual perception Evident when complete diff stimuli presented to 2 eyes

Question 82

Why do we not experience diploid for objects outside panum fusion area

Answer 82

Bc visual system represses image coming from one eye - prevents you from seeing double Randomly switches every few seconds