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Perception > Exam 2 Deck > Flashcards

Exam 2 Deck Flashcards

Exam Feb 27

1
Q

Agnosia is

A

Inability to recognize visual objects with intact visual acuity

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2
Q

Agnosia results from

A

Results from damage to inferior temporal cortex

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3
Q

Contralateral Hemifield Neglect

A

Inability to attend to contralesional space

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4
Q

Contralateral Hemifield Neglect results from

A

posterior parietal lobe damage (usually right

side)

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5
Q

Effect of Lesions in the Monkey: Inferior Temporal Cortex

A

Food hidden under object
• Monkey must select proper object to get reward
– Must have intact object recognition system • Can not do with inferior temporal lesion
• Can do with parietal lesion

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6
Q

Effect of Lesions in the Monkey: Posterior Parietal Cortex

A

• Food hidden in well farthest from peg
• Monkey must choose location farthest from peg to get reward
– Must have intact spatial relationships system • Can not do with posterior parietal lesion
• Can do with inferior temporal lesion

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7
Q

Two Visual Pathways Beyond V1

A
  • -> Dorsal “Where” spatial location stream. located in posterior parietal
  • -> Ventral “What” object feature stream located in inferior temporal
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8
Q

Law of Proximity

A

Things that are close together belong together

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9
Q

Law of Similarity

A

Things that are alike get grouped together

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10
Q

Law of Good Continuation

A

Things that result in straight or smoothly curving lines, rather than abrupt angles, get grouped together
– We see a curved line over a straight, not two lines with abrupt angles

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11
Q

Law of Common Fate

A

Things that move together get grouped together

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12
Q

Closure

A

We group things that close

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13
Q

Common Region

A

Things that are enclosed together belong together

– Can overcome proximity

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14
Q

Connectedness

A

• Things that are connected to each other belong together

– Can also overcome proximity

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15
Q

Illusory Contours

A
  • Gestalt laws of perceptual organization and figure/ground principles are illustrated by seeing illusory figures
  • By altering features of picture elements, illusory occluding objects can be perceived
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16
Q

Grouping Principles and the Kanizsa riangle

A

• Law of Good Continuation
– Straight lines and smooth angles are more likely than sharp
corners
• Law of Simplicity
– The simplest explanation is 3 disks and 2 triangles rather than 3 ‘hats’ and 3 ‘pac-men’
– So that’s what the visual system perceives

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17
Q

What’s the Figure & What’s the Ground?

A

• We can find the edges
– Separates the green from the blue • But is one thing in front of another?
– Probably see green objects on a blue background

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18
Q

Occlusion Determination Heuristics

A

• A “heuristic” is a ‘rule-of-thumb’
– A rough rule that works most of the time • Two occlusion heuristics
– Relatability – Non-accidental features

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19
Q

Relatability

A

• Edges that can be connected with a simple curve (e.g. elbow) are “relatable”
– Likely belong to the same object, even if occluded
– Like Gestalt good continuation
• If we see relatable features, we’re more likely to perceive that
something is occluded

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20
Q

Non-Accidental Features

A

• When 3D objects overlap, they create some specific kinds of junctions that don’t vary by viewpoint
– Y or ‘arrow’ junctions • Corner
• Not an occlusion – T junctions
• Intersecting edges • Occlusion

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21
Q

T/F: The perceptual system tries to find an interpretation that depends on an accident of viewpoint

A

false, it tries to find an interpretation that would be consistent across most viewpoints, so one that does not depend on accident

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22
Q

Resolving Perceptual Ambiguity

A

• Early vision
– Pretty simple
• Dots and bars
• Not much question about whether a dot is there or not
• Middle vision – More complex
• Which edge belongs to what object • Not always clear

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23
Q

How Does the Perceptual System Decide Which is the Best

Interpretation?

A

• A Perceptual System Metaphor – Decision by committee
• Multiple members – Some cooperate – Some compete
• Make decisions
– e.g. this corner goes with this edge – These edges belong together – This is the figure, this is the ground

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24
Q

Pandemonium: A Perceptual Committee Model

A

• Committee members (“demons”) at multiple levels, shouting
– Feature demons
• “shout” louder when they think their feature is present
– Cognitive demons
• “shout” louder when they think their object is present
– Decision demon
• Listens to the noise and determines who is shouting
loudest
• That’s the representation that ‘wins’

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25
Q

T/F: perceptual “committees” honor physics

A

true, they don’t come up with any decisions that violate physical reality and don’t settle on an interpretation that has rocks floating in
the air

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26
Q

T/F: perceptual “committees” do not avoid accidents

A

FALSE, they discount interpretations that rely on rare or unlikely conjunctions of features

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27
Q

How Do We Recognize Objects?

A

• Template matching?
– Have a template for all objects – Extract a set of features
• Edges
• Corners
– Find out what’s in front of what
• Figure & ground
– Try fitting the figure into a bunch of templates until you find
the one that fits
• When the figure fits, like a piece in a puzzle, we’ve
identified the object

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28
Q

What are some problems with templates?

A

• Object variance
– The same object can have a lot of different exemplars • Dining char
• Rocking chair
• Recliner
– Each exemplar can be seen from many perspectives • Front
• Side
• Back
• We’d need way to many templates for each object for this to
ever work

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29
Q

What are Geons?

A

– Components from Biederman’s structural theory
• “Recognition by Component”
– Every object description consists of geons in specific, non-
accidental configurations

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30
Q

What is Prosopagnosia?

A

• A face-specific agnosia
– Inability to recognize faces
• Implies specific neural area for a special kind of object
recognition
– Located in inferior temporal cortex – Part of the ventral ‘what’ pathway
• Some researchers think there is no such thing as prosopagnosia, but that we have a special ‘expertise’ area, and that we’re all facial experts

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31
Q

Basic Principles of Color Perception

A

• Color
– Not a physical property of matter
– Rather a psychophysical property of the perceptual system • However, based on properties of matter
– Most of the light we see is reflected
• Typical light sources: Sun, light bulb; emit a broad
spectrum of wavelengths 400–700 nm
– Different kind of materials absorb and reflect different
wavelengths of light

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32
Q

Are there “basic” colors?

A

Evidence for basic colors – Color sorting studies – Color words across cultures

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33
Q

what are the four primary colors?

A

– Red
– Blue
– Green
– Yellow

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34
Q

What did Newton discover with the prism?

A

• When white light passes through a prism it is decomposed in to component parts (different wavelengths) of different colors

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35
Q

What wavelength of light is perceived as violet?

A

400-450 nm

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36
Q

What wavelength of light is perceived as blue?

A

450-500 nm

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37
Q

What wavelength of light is perceived as green?

A

500-570 nm

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38
Q

What wavelength of light is perceived as yellow?

A

570-590 nm

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39
Q

What wavelength of light is perceived as orange?

A

590- 620 nm

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40
Q

What wavelength of light is perceived as red?

A

620-700 nm

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41
Q

What is the first hypothesis of photoreceptor response?

A

Hypothesis 1:

– A single photoreceptor that responds differently to different wavelengths could index an object’s color

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42
Q

What are some problems with the photoreceptor hypothesis?

A

Univariance. Different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor
– One type of photoreceptor cannot make color discriminations based on wavelength
• We must have multiple color receptors

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43
Q

How many colors can we see?

A

somewhere between 2,000,000 & 10,000,000 different colors we can perceive

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44
Q

We have 10,000,000 different types of color receptors, one for each of the 10,000,000 possible colors.

A

FALSE, we have 3

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45
Q

Hermann von Helmholtz discovered …

A

Discovered that we have three color spectral sensitivity curves
– Blue
– Green
– Red

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46
Q

Young-Helmholtz Trichromatic Theory

A

• We have three color receptors
• These receptors are sensitive to different parts of the EM
spectrum
• Differential relative activity in these receptors is the basis of
color vision

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47
Q

Trichromatic Theory

A

• Color perception is based on differential activity in the three receptors
– Depending on the energy of light in different frequency bands
• Comparing output of the three receptors allows color computation in the brain

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48
Q

What are S-cones?

A

Cones that are preferentially sensitive to short wavelengths (AKA ‘blue’ cones)

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49
Q

What are M-cones?

A

Cones that are preferentially sensitive to middle wavelengths (AKA ‘green’ cones)

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50
Q

What are L-cones?

A

Cones that are preferentially sensitive to long wavelengths (AKA ‘red’ cones)

51
Q

T/F: Each wavelength in the visible spectrum will result in a unique response pattern across the receptors

A

TRUE

52
Q

T/F: Light usually comes to our eyes as pure wavelengths

A

FALSE, all light is a mixture of wavelengths

53
Q

T/F: Reflected light has some wavelengths absorbed but still a mixture of wavelengths reflected

A

TRUE

54
Q

What two colors are mixed together to perceive yellow light?

A

red and green

55
Q

What are metamers?

A

• Different combinations of wavelengths of light that produce the same perceived color
– 550 nm + 650 nm gives same color percept as 590 nm light • Thus they are metamers
– Note that these are not ‘blends’
• Not like mixing chocolate & coffee to make mocha
– The individual wavelengths are still there
• They just activate the receptors in the same way • Results in the same color percept

56
Q

Combing lights is ________

A

additive color mixing

57
Q

Combining pigments is ________

A

subtractive color mixing

58
Q

Additive Color Mixing

A

• Combine short wavelength light
– Appears blue
• With combined middle and long wavelength light
– Appears yellow
• Get short, middle, and long wavelength light
– Appears white

59
Q

Subtractive Color Mixing

A

• Instead of blue and yellow light, take blue and yellow paint
– Top paint patch absorbs (i.e. subtracts) most long wavelengths reflecting mostly short and some middle
• Appears blue
– Bottom patch absorbs mostly short wavelengths reflecting
mostly middle and some long • Appears yellow

60
Q

Color Subtraction

A

• Mix the blue and yellow together
– Subtracts the long and short wavelengths
• What’s left unsubtracted is the middle – Appears green
• This is how painting mixing works

61
Q

What can trichromatic theory not explain?

A
  • Contrast effects

* Afterimages

62
Q

What are contrast effects?

A

– Same wavelengths
– Same activation pattern
– Different color percepts

63
Q

What are afterimages?

A

-No color in the stimulus
– Color in the percept
• Afterimages demonstrate opposition color pairings
– Stare at red, get green afterimage (and visa versa) – Stare at blue, get yellow after image (and visa versa)

64
Q

What was Ewald Hering’s “opponent process” theory?

A

• Knew about after images
• Also noted that color-blindness often was paired
– e.g. red/green color blind, rarely yellow/blue but never yellow/green or red/blue
• Noted that some color combinations were never described – e.g. you can have ‘bluish-green’ or ‘yellowish-red’ colors, but
not ‘reddish-green’ or ‘bluish-yellow”
• Proposed three opponent color mechanisms
– Green-off, Red-on – Blue-off, Yellow-on – Black-off, white-on

65
Q

Receptors are _______

A

trichromatic.

- Three types of cones sensitive to different parts of EM spectrum

66
Q

Retinal ganglion and LGN cells are _________

A

Opponent Process.

– Color center-surround organization

67
Q

Explain what is used for the Mondrian experiment

A 
•  The Mondrian
– A large screen with patches of different colors •  Three pure wavelength light sources
– Long (red light) 
– Medium (green light) 
– Short (blue light)
•  Telephotometer
– Measures the intensity of reflected light 
– Aim at a patch on the Mondrian
68
Q

Explain the Mondrian experiment

A

• Aim photometer at a patch on Mondrian (e.g. a green one)
– Turn on long wave light
• Adjust intensity until photometer reads “60” units reflected
from the patch; turn off – Turn on medium wave light
• Adjust intensity until photometer reads “30 ” unites reflected; turn off
– Turn on short wave light
• Adjust intensity until photometer reads “10 ” units
reflected; turn off
• Turn all three lights on: Ask subject “what color is the patch?”
– Spectral content of light reaching subject’s eyes = 60 long, 30 medium, 10 short
– Subject reports patch color is green

69
Q

Explain the repeat of the Mondrian experiment

A

• Aim the photometer at a blue patch
– Adjust light sources so the SAME wavelength reflectance is measured as before, but now from the blue patch
• Spectral content at eyes reflected from blue patch = 60 long, 30 medium, 10 short
– Ask what color the subject sees
• Subject reports “blue” (even thought the wavelengths
reflected from the patch reaching the eye are EXACTLY
the same as from the green patch)
• Do the same for a red patch, subject reports “red”

70
Q

What did the Mondrian experiment find?

A

• In all cases the spectral content of light at the retina reflected from the patch was the same
– Long: 60; Medium: 30; Short: 10
• Yet the perceived color was different
– Red, green, or blue
• Thus, while perceived color is related to light wavelength, it is
not determined by wavelength – Something else contributes

71
Q

Explain the “void” experiment

A

• Set light reflected from green patch equal (e.g. L:30; M:30; S: 30
• Restrict the field of view so that only that one patch is visible – Subject reports color is grey
• Allow to see all patches, keeping light constant – Subject reports patch color, e.g. “green”
• Spectral content from patch is same
– Percept ‘pops’ back and forth from gray to green

72
Q

What did the “void” experiment find?

A

If only one reflectance surface is in the field of vision, color perception is entirely determined by wavelengths of light reflected from the surface
• If more than one surface if available, perceived color is dependent on both the reflected wavelengths from the surface and the reflected wavelengths from the surrounding surfaces

73
Q

T/F: The percentage of a given wavelength of light reflected by something is always the same

A

TRUE

74
Q

Define: Biological Color Separation

A

• Any scene will have a different light/dark brightness pattern for each of the three cone types
– The light/dark pattern is different for each receptor • it’s a color separation
– These light-dark patterns are the same, independent of the illuminant, only the relative intensity changes
• Thus the color system can ‘correct for the illuminant’

75
Q

What is Land’s Retinex Theory?

A

• The visual system compares the reflectance (brightness) records across all the surfaces (colored patches) for each cone
– How much ‘blue’, ‘green’, and ‘red’ brightness there is
– Gives an estimate of the spectral content of the illuminant
• The visual system then compares the light/dark patterns at a
given patch for each cone
• The results of the two comparisons are combined to obtain a
color perception, corrected for illumination
• This is a computation (and a kind of complicated one), not a
simple reflection of the world

76
Q

Where does the color process happen in the brain?

A

Color is part of the photopic system

- cones –> Parvo but then a slightly different pathway

77
Q

V1 Color Areas

A

• In V1, color information is processed in “pegs” or “blobs” in the hypercolumns
– The initial brightness records are probably assembled here

78
Q

Higher cortical color processing

A

• The final comparison of brightness records probably occurs in cortical area V4 in prestriate cortex
– In the monkey V4 neurons are the first ones to respond to perceived color rather than wavelength of light
– Lesions to human V4 leads to achromotopsia, the inability to see color

79
Q

Define: Euclidian geometry

A

– Parallel lines remain parallel as they are extended in space – Objects maintain the same size and shape as they move
around in space
– Internal angles of a triangle always add to 180 degrees – etc.

80
Q

T/F: Brain must reconstruct Euclidean geometry from two flat, distorted projections from the retinas to create a 3D image.

A

TRUE, the brain has to answer the question “what is in front of what?” from a flat picture.

81
Q

What are some depth cues in a 2D image?

A

• Monocular cues – Pictorial cues
• Static cues in 2D representations – Movement cues
• Dynamic cues in 2D representations • Oculomotor cues
– Physiological feedback from the eyes
• Binocular cues – Binocular disparity cues
• Derived from the differences in images on the two retinas

82
Q

Monocular (Pictorial) Depth Cues

A

• Occlusion (things in front block things behind)
• Relative size (how big compared to scene)
• Texture gradient (equally spaced elements get packed in the
distance)
• Relative height (proximity to horizon)
• Familiar size (how big compared to knowledge)
• Atmospheric (aerial) perspective (haze)
• Linear perspective (convergence)

83
Q

Define: Occlusion

A

A cue to relative depth order when one object obstructs the view of part of another object

84
Q

How do we know that there is depth?

A

• The Retinal Image is Ambiguous
– First do object recognition
– Then figure out what’s in front of what
• Could be top object arrangement – Violates Gestalt principles
• Bottom more likely
– Circle in front of square in front of triangle – Conforms to Gestalt principles

85
Q

What do nonmetrical depth cues do?

A

Provides only qualitative information about the depth order
(which thing is in front of what) but not depth magnitude
(how far in front the thing is)

86
Q

What do metrical depth cues do?

A

– Provides quantitative (how far) information about distances between objects

87
Q

T/F: Image size can provide a depth cue regardless if we know how big it actually is.

A

FALSE.
The farther away something is, the smaller its retinal image is, thus image size can provide a depth cue but only if we know how big something is

88
Q

Relative Size

A

• A comparison of size between items
– Smaller items appear more distant
– If the things look the same, we can assume they’re about
the same size
– Therefore, smaller ones are more distant
– Don’t have to know the absolute size of any of them

89
Q

T/F: If the different sizes are randomly scattered, rather than along a gradient, relative size is a stronger cue.

A

FALSE.

If the different sizes are organized along a gradient, rather than randomly scattered, relative size is a stronger cue

90
Q

What is Atmospheric Light Scattering?

A

Haze
• Air scatters light
– Results in haze
• The perceptual system ‘knows’ this
– Uses haze as depth cue
• Distant items dimmer and fuzzier than close items
– Also bluer since short wavelength light scatters more • That’s also why the sky is blue

91
Q

Atmospheric Perspective

A
  • Relative height without a texture gradient gives only a weak (or no) depth perspective
  • Relative height plus haze gives a stronger depth perspective
92
Q

Linear Perspective

A

• Parallel lines appear to converge in the distance
– Ultimately converging at the vanishing point
• The visual system uses this as a depth cue

93
Q

Define: Motion Parallax

A

– Near objects appear to move farther than far objects as we go by them
– The retinal projection of a near object travels farther across the retina than a far object for the same movement

94
Q

Define: Deletion and accretion

A

– Changes in occlusion due to movement

95
Q

Define: Optic flow

A

– The distance on object is from us alters its apparent

direction and speed of movement

96
Q

Oculomotor cues

A

• Feedback from eye muscles
– Convergence
• The movement of the eyes towards “crossed” to foveate
near objects – Accommodation
• The change in lens thickness (fattening, mediated by ciliary muscles) to focus on near objects
• These cues are only effective out to ~10 feet

97
Q

Binocular Depth Cues

A

• Binocular disparity cues

– Derived from the differences in images on the two retinas

98
Q

T/F: Animals with eyes on side have overlapping visual fields

A

FALSE. Only animals with forward facing eyes have overlapping visual fields

99
Q

The Vieth-Müller circle

A

Images on the retinas of items on that circle are the same distance from the fovea on both eyes
– They fall on corresponding retinal points

100
Q

The Horopter

A

• Extend that circle so it’s a dome in front of the eyes equidistant as fixation and you have the horopter
– A 3D surface of corresponding retinal points

101
Q

The Horopter and Corresponding Retinal Points

A

• The circle (or 3D dome) with its center halfway between the eyes and the fixation point is the horopter
• Items on the horopter project to corresponding retinal points on the two eyes
– Equal distances between the objects retinal projection and the fovea

102
Q

Binocular Disparity

A

• Objects on the horopter (including the fixation) have zero binocular disparity
– Images fall on corresponding retinal points
• Objects off the horopter have binocular disparity
– Images fall on non-corresponding retinal points – Unequal distances between the fovea and the object’s
projection on the retina
• The farther off the horopter the object is, the larger the
disparity
• Binocular disparity is the binocular depth cue
– Lets the perceptual system know, from two flat projections, how close or far away from fixation distance the object is
• The greater the disparity, the farther from fixation

103
Q

Crossed & Uncrossed Disparity

A

• Retinal image projections with the same amount of disparity can have either crossed or uncrossed disparity
– Crossed disparity
• Retinal projections are outside of fovea • You’d have to ‘cross’ your eyes to focus on it • Closer to you than fixation
– Uncrossed disparity
• Retinal projections are inside of fovea
• You’d have to ‘uncross’ your eyes to focus on it • Farther from you than fixation

104
Q

What is Stereopsis?

A

• The perceptual phenomenon of depth – Things appear to ‘pop-out’
• As opposed to flat appearing
– e.g. 3D movies or static images with stereoscopes/colored
glasses/polarizing glasses • Or the real world

105
Q

Angle of Disparity

A

• Angle between P & F and P’ & F’
– Disparity angle = 0 for points on horopter
– The farther off the horoper an object is, the greater the angle
of disparity

106
Q

Disparity-Sensitive Neurons

A
  • There are neurons sensitive to different degrees of binocular disparity
  • These neurons give rise to stereopsis
107
Q

Binocular V1 Neurons

A

• Some visual cortex neurons have binocular input (instead of being monocular dominant)
– These binocular neurons respond best at specific angles of disparity (this one likes 30’)

108
Q

Disparity Tuning in V1

A

• Most neurons respond best to zero (or near zero) disparity
– In the fusion area
• However, some respond best to disparity between retinal
images

109
Q

Bayesian Theory

A
  • P = Probability
  • Sx = Scene X
  • I = Perceptual system input
110
Q

Limited Capacity & Selection

A

• The brain is a limited capacity information processing system
– It cannot process all of the available perceptual information – Must somehow select a subset of available percepts for
additional processing
– This selection is called “attention”

111
Q

Intuition vs. Definition

A

• We may know what attention is intuitively, but it’s hard to define objectively
• Not one thing but a collection of selection processes – selection by novelty
– selection by relevance
– selection by location
– selection by feature

112
Q

T/F: Participants are fastest on valid trials because of facilitation

A

true, they are slowest on invalid trials because of inhibition

113
Q

T/F: How much time there is between the cue and the target changes the reaction time effect

A

TRUE

114
Q

Objects Play a Role in Attention

A

• You get an advantage by paying attention to the object in which the target appears
• You pay a cost by paying attention to the other object
• Even though the distance between the cues and the targets is
the same – Same distance

115
Q

Cues Aren’t Required for Attention

A

• Selection by Relevance

– We attend to things relevant to our current tasks – Even if they’re not changing

116
Q

Treisman’s Feature Integration Model of Visual Search

A
  • The visual system has primitive feature maps – Maps of the locations of primitive features in space
  • These are perceptual maps created and maintained in parallel – i.e. you create a color map and a separate orientation map at the same time and they are independent of each other
117
Q

Search in the Treisman Model

A

• Preattentive stage
– If target is based on a single feature, we can simply poll the
correct map and ask “is the feature present”
• e.g. is there anything in the ‘vertical’ orientation map or
the’red’ color map
• Don’t need to know where it is • It just “pops out”
• Efficient search
• Attentive stage
– If the target is defined by a conjunction of features, the
attention ‘spotlight’ must scan the objects in the scene to see if the target defining features exist in the same place on the relevant feature maps
• e.g. are ‘red’ and ‘vertical’ in the same location • If so, then the target is present
• Inefficient search

118
Q

What are these Primitive Features?

A
  • Orientation
  • Length/Width • Size
  • Curvature
  • Closure
  • Density
  • Color
  • Intensity
  • Intersection
  • Flicker
  • Motion direction
119
Q

The Binding Problem

A
  • Even if features are in the same location, they must be ‘bound together’ to create the proper percept for target identification
  • We still don’t understand binding, but we can confuse the system
120
Q

The Speed of Attention

A

• Attending to spatial locations has a temporal course – Rising for ~150 ms
– Falling back to zero until ~300 ms
– Inhibition until ~700 ms
• What about object attention?

121
Q

Testing Attention Speed

A

• Rapid Serial Visual Presentation (RSVP)
– Present stream of items, one at a time, at fixation, very
quickly (e.g. one every 100 ms)
– Make items distinct from one another (e.g. letters and
numbers)
– Have participants respond to one category of the items (e.g.
the numbers) while ignoring the others • Modified RSVP
– Have two targets instead of one
• e.g. respond to the digits 3 and 7 and ignore all the other
letters and numbers
– Vary the amount of time between successive targets

122
Q

The Attentional Blink

A
  • If the targets occur between about 200 and 300 ms of each other, the participant will miss the second target after getting the first
  • It’s as if their attention selection system ‘blinked’ for a moment following correct identification of the first target
123
Q

The ‘Fishing’ Metaphor of the Attentional Blink

A

• Percepts are like things flowing by in a (dirty) river – Branches
– Old boots
– Tires
– Fish
• We’re fishermen
• Attention is our net
• We can monitor all the things going by until we ‘catch a fish’ – Respond to a target
• Responding to a target takes some time
– During that time our ‘net is out of the water’, and we’ll miss
any other fish (targets) that come along

Perception (6 decks)

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