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Perception > Block 10 > Flashcards

Block 10 Flashcards

1
Q

What is temporal vision concerned with

A

Changes in luminance over time

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2
Q

Low modulation depth appears

A

Steady

We cant resolve it

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3
Q

High modulation depth appears

A

Flickering, we can resolve it

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4
Q

What is the unit of frequency

A

Hertz, (Hz)

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5
Q

A low temporal frequency is seen as

A

Flickering

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6
Q

A higher temporal frequency is seen as ____

A

Flickering

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7
Q

What is the Critical FLicker Fusion Frequency (CFF)

A

As the temporal frequency is increased, a frequency is reached where the flicker can no longer be resolved

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8
Q

What does CFF represent

A

The high temporal resolution limit of the visual system

Known as temporal acuity

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9
Q

CFF increases linearly with what

A

The log of retinal illumination

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10
Q

CFF is higher in this condition

A

Photopic

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11
Q

How do you determine TMTF

A
  • Initially the depth is very small and the screen is steady
  • the modulation depth is slowly increased until the subject sees flickering (threshold)
  • repeated for large amounts of frequencies
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12
Q

What is the reciprocal of threshold

A

Relative sensitivity

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13
Q

How stimuli that fall outside the TMTF seen

A

As steady, not resolved

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14
Q

Stimuli that fall under the graph of TMTF are seen as

A

Flickering, resolved

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15
Q

Where is a maximal sensitivity for TMTF seen at

A

Moderate frequencies

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16
Q

CFF increases with what?

A

The log of the stimulus area

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17
Q

Receptor field size increases linearly with what?

A

Eccentricity

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18
Q

Why does a stimulus that appears steady in the central vision may appear flickering in the periphery

A

Due to higher temporal resolution of the peripheral retina, for higher luminance

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19
Q

T/F flickering light may cause dilation of the retinal blood vessels

A

True

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20
Q

Do infants have good temporal resolution

A

No, it is poor

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21
Q

What is troxler phenomenon?

A

Very gradual changes in ill illumination are not seen
We have a reduced sensitivity to low temporal frequcniesis the inability to perceive stationary or stabilize retinal images

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22
Q

Why do blurry edges disappear?

A

The changes in retinal illumination are very low temporal frequency. We are not sensitive to low temporal frequencies

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23
Q

Why don’t sharp edges disappear

A

Because we are sensitive to moderate temporal frequencies

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24
Q

Look at lecture 1 slide 24 and 25

A

Look at them

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25
Q

What is a mask

A

It reduces the visibility of a stimulus referred to as the target

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26
Q

What is a simultaneous masking

A

The mask and the target are present at the same time

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27
Q

What kind of patient is simultaneous masking more pronounced in

A

Amblyopia

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28
Q

What is backward masking

A

Target precedes mask

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29
Q

What is forward masking

A

Mask precedes target

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30
Q

What is metacontrast

A

The mask and target are spatially adjacent

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31
Q

What is paracontrast

A

Forward masking where the target and mask are spatially adjacent

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32
Q

What is motion perception

A

Changes in spatial distribution of light over time

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33
Q

Where is Motion processed

A

Dorsal processing stream

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34
Q

Test of motion perception can be used o diagnose

A

Neurological disorders

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35
Q

What is real motion

A

An object actually moves

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36
Q

What is apparent motion

A

When spatially separated lights are flashed in an interval that we sense that a motion has occurred

A.k.a. Stobroscopic motion
Or phi phenomenon

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37
Q

What is a good example of stroboscopic motion

A

Movies, TV, computer monitors

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38
Q

What is the first order stimuli for motion

A

A sinusoidal grating s phase shifted over time to produce a grating that appears to move in one direction.
Consist of a linear exchange of light for dark

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39
Q

What is used to study local motion processing

A

Stroboscopic stimuli

Sine wave gratings

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40
Q

What is the physiological mechanism for first order stimuli

A

Bright stimulus moves across VF
As it moves it activates the receptive fields of visual neurons in its path

When the stimuli si moving at the proper speed, the slower neurons(stimulated first) respond at the same point in time as the faster neurons(stimulate later)

These responses are added together, and it encodes for stimulus speed and direction.
Slide 15 for more info

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41
Q

More complex first order stimul that require integration of motion cues across a wide expanse of visual space can be presented with what??

A

Random dot kinematograms

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42
Q

What is coherence threshold

A

The smallest percent coherence that results in the perception of motion in a defined direction (up, down, L, R)

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43
Q

Humans have a manifesting coherence threshold of about ______

A

1%

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44
Q

What is minimum displacement threshold (Dmin)

A

The minimum distance dots must move in a givers direction to elicit the perception of motion

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45
Q

What is the maximum displace the threshold (Dmax)

A

The maximum distance the dots can mov and still elicit motion perception

46
Q

What is global motion perception

A

The visual system must integrate information from many dots over a broad expanse of the retina involving higher cortical motion centers

47
Q

Monkeys can detect correlated motion when what percent of the dots are moving in the same direction

A

2-3%

48
Q

Humans can detect correlated motion when what percent of the dots are moving in the same direction

A

1%

49
Q

Global motion cues

A

Lecture 2

Slides 21-23

50
Q

What is motion aftereffect (waterfall illusion)

A

When you view a stationary scenes the various neurons responses cancel each other out, (no motion)

When it starts moving the neurons sensitive to a certain dxn with increase their firing rate (leading to perception of movement in that dxn)

After a while the neurons will fatigue
When you stop the motion the neurons will fire in a slower rate compared to neurons in the opposite direction. This causes drifting

51
Q

What is motion induced blindness

A

The brain ignores what the eyes tell it

Lecture 2
Slide 26

52
Q

What is the second order stimuli for motion

A

Motion perception for more complex stimuli

Texture-defined contours

Processed by different pathways than first order

53
Q

What does the fact that almost all humans can perceive 2nd order motion tell us?

A

That the visual system doesn’t just track objects positions over time to calculate movement since there are no objects to track

Lecture 2
Slide 28

54
Q

What is the magno pathway

A

High velocity processing system

Visual area 5, MT, V5
Motion processing
Where?
Dorsal pathway- parietal 
Motion perception-global stimuli
55
Q

What happens if there is impairment to the magno pathway

A

Akinetopsia

56
Q

What is the parvo pathway

A

Low velocity information processing
Visual area V1 V2 V4

Object processing
What?
Ventral pathway- temporal
Object perception (faces…)

57
Q

What happens if there is an impairment of the parvo pathway

A

Can’t recognize an object

58
Q

How is biological motion detected?

A

Cortical posterior superior temporal sulcus

59
Q

What is isoluminant

A

Possessing the same luminance

60
Q

T/F under certain isoluminant conditions the perception of motion is impaired,

A

True
It can be weak or slower than that actual movement of the bars

Lecture 2, slide 49

61
Q

How can you improve the perception of motion at certain isoluminant conditions?

A

Add luminance contrast

Lecture 2 slide 49

62
Q

Magno pathway -> motion percetion -> rapid motion

A

Know this

63
Q

Is color a good stimuli for Magno path?

A

No

Monochromatic

64
Q

Is color a good stimuli for Parvo path?

A

Yes

65
Q

What are P path characteristics

A

Small RF
Better spatial resolution
Selective for color

66
Q

What are the M path characteristics

A

Better temporal resolution
More sensitive to ow light levels
Monochromatic

67
Q

How does scotopic conditions affect motion perception

A

Objects appear to move slower

68
Q

How do Mesopic conditions affect motion perception

A

Motion perception is impaired

There is incomplete integration of rod/cone signals because they are both active

69
Q

What affect does the velocity of a moving stimulus have on VA?

A

As velocity increases
Resolution acuity stays constant intel velocity reaches 60-80 degrees per second.

Once this is reached the ability to resolve a moving stimulus deteriorates

70
Q

What is the reduction in dynamic visual acuity as target velocity increases due to?

A

Inability to accurately follow the stimulus with tracking eye movements (smooth pursuit eye movements)

71
Q

Higher dynamic VA is associated with

A

Improved ability to detect hazardous situations while driving

72
Q

What is saccadic suppression/saccadic omission

A

When vision is suppressed shortly before, during, and shortly saccadic eye movements

73
Q

What does saccadic suppression enable us to do

A

Look from one object to another without smearing our vision

74
Q

What is saccadic suppression due to

A

The magno path is sensitive to high-velocity movement

It is presumably suppressed to avoid smearing vision

75
Q

If saccadic suppression is caused by an extraretinal signal what would you expect to find

A

Neurons in the cortical motion areas are activated when the scene is moved, but suppressed during saccades

76
Q

Midget RGC sued axons to LGN to form what path

A

P

77
Q

Parasol RGCs send axons to LGN to form what path

A

M

78
Q

What are the major classes of monocular depth cues

A

Pictorial
Angular declination below horizon
Motion parallax
Accommodation

79
Q

T/F monocular depth cues are perceives just as strongly when viewed with one eye as when viewed with both

A

True

80
Q

What are pictorial depth cues

A 
Relative size
Familiar size
Linear perspective
Texture
Interposition 
Clarity
Lighting
Shadow
81
Q

T/F monocular individuals manifest surprisingly ROBUST depth perception due to these cues

A

True

82
Q

What is relative size

A

A depth cue when viewing a scene that includes objects whose sizes can be compared to each other

83
Q

With relative size we perceive large objects as _____

A

Being closer to us

84
Q

What does the relative size cue tell us

A

How far away different objects are relative to each other, but it cant tell us exactly how far away they are

85
Q

Are we able to tell how far an object really is?

A

Yes, our brains use distance-equals-object-size-divided by relative size relationship to enter mine absolute distances

Familiar sizing

86
Q

What is familiar sizing cue

A

Cue is used when viewing objects of known size

87
Q

What is an example of linear perspective

A

Railroad tracks
We assume the tracks is of equal width throughout

The appearance of distance width being narrower gives a sense of depth

88
Q

How does texture gradient work

A

The distance to any object sitting on the texture can be accurately judged by comparing it to the part of the texture the object is sitting on

89
Q

When is interposition used

A

When the view of a scene is partially obstructed

90
Q

What is clarity

A

A form of interposition
Acts as a depth cue because un-obscured objects in a picture or actual scene may be perceived as closer than those that are obscured by haze

91
Q

What are some things that can obscure clarity

A 
Fog
Smoke
Rain
Smog
Makes things look more distant
92
Q

How do shadow and lighting play into depth perception

A

When light falls on an object the object casts a shadow

Shadow is interpreted as falling behind the object, creating a sense of depth

93
Q

What does angular declination below the horization allow us to do

A

Determine object distance
BECAUSE

The object makes an angle with the horizon (ADBTH), the visual system uses this angle to determine distance

94
Q

What is motion parllax

A

Kinetic monocular depth cue

Results when a moving observer fixated on an object which noticing the relative motion of surrounding objects

95
Q

What visual area plats a role in motion parallax and binocular disparity and motion in monkeys

A

MT

V5

96
Q

How does accommodation act as a depth cue

A

During accommodation the dioptric power of the lens increases, allowing near objects to be focused on retina

Can be used to determine the distance of viewed objects

97
Q

What binocular depth cues

A

Retinal disparity

Convergence

98
Q

What does retinal disparity allow

A

It is a binocular depth cue
Allows the visual system to determine distance

Look at slide 22 for ball example

99
Q

What is stereopsis

A

Perception of depth produced by retinal disparity

Most important contributor to depth perception at near

(Not at far because the threshold fro retinal disparity requires objects to separated by great distances)

100
Q

What is physiologic diplopia

A

If retinal disparity is too large, the images fall on retinal positions that signal grossly different directions

101
Q

What is the size illusion

A

Changes in retinal image size does not cause a change in apparent object size at any distance

102
Q

How does our visual system compensate for differences in retinal image size

A

It takes into account the relative distance of an object, size constancy

103
Q

What happens when judgement of distance is erroneous

A

Size Constancy may fail, resulting in size illusion

104
Q

How does size constancy occur?

What is an example

A

Monocular depth cues provide incorrect information regarding relative distance

Moon illusion
Slide 26-27)

105
Q

What is Muller-Lyer illusion

A

Vertical lines with arrows facing different ways

The line is the same size, but the arrow directions make it appear shorter or longer

106
Q

What does measuring a patients stereopsis tell us

A

Important information about the status of the visual system

The minimum amount of disparity required to perceive depth is determined

107
Q

What is the threshold disparity of stereopsis

A

Stereoacuity

Can be as small as 3 seconds of arc

108
Q

What are some things that can reduce stereoacuity

A

Disorders of binocular vision (anisometropia, strabismus) can alter an infants visual experience and retard development of binocular cortical neurons

109
Q

What is monovision

A

When a patients have one eye corrected for near and the other for distance

110
Q

Why doesn’t diplopia occur in monovision

A

Because the unused eye is largely suppressed

111
Q

Does a person with monovision have depth perception

A

Yes, because most cues for depth are monocular

Perception (6 decks)

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