Block 10 Flashcards
1
Q
What is temporal vision concerned with
A
Changes in luminance over time
2
Q
Low modulation depth appears
A
Steady
We cant resolve it
3
Q
High modulation depth appears
A
Flickering, we can resolve it
4
Q
What is the unit of frequency
A
Hertz, (Hz)
5
Q
A low temporal frequency is seen as
A
Flickering
6
Q
A higher temporal frequency is seen as ____
A
Flickering
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
8
Q
What does CFF represent
A
The high temporal resolution limit of the visual system
Known as temporal acuity
9
Q
CFF increases linearly with what
A
The log of retinal illumination
10
Q
CFF is higher in this condition
A
Photopic
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
12
Q
What is the reciprocal of threshold
A
Relative sensitivity
13
Q
How stimuli that fall outside the TMTF seen
A
As steady, not resolved
14
Q
Stimuli that fall under the graph of TMTF are seen as
A
Flickering, resolved
15
Q
Where is a maximal sensitivity for TMTF seen at
A
Moderate frequencies
16
Q
CFF increases with what?
A
The log of the stimulus area
17
Q
Receptor field size increases linearly with what?
A
Eccentricity
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
19
Q
T/F flickering light may cause dilation of the retinal blood vessels
A
True
20
Q
Do infants have good temporal resolution
A
No, it is poor
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
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
23
Q
Why don’t sharp edges disappear
A
Because we are sensitive to moderate temporal frequencies
24
Q
Look at lecture 1 slide 24 and 25
A
Look at them
25
What is a mask
It reduces the visibility of a stimulus referred to as the target
26
What is a simultaneous masking
The mask and the target are present at the same time
27
What kind of patient is simultaneous masking more pronounced in
Amblyopia
28
What is backward masking
Target precedes mask
29
What is forward masking
Mask precedes target
30
What is metacontrast
The mask and target are spatially adjacent
31
What is paracontrast
Forward masking where the target and mask are spatially adjacent
32
What is motion perception
Changes in spatial distribution of light over time
33
Where is Motion processed
Dorsal processing stream
34
Test of motion perception can be used o diagnose
Neurological disorders
35
What is real motion
An object actually moves
36
What is apparent motion
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
37
What is a good example of stroboscopic motion
Movies, TV, computer monitors
38
What is the first order stimuli for motion
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
39
What is used to study local motion processing
Stroboscopic stimuli
| Sine wave gratings
40
What is the physiological mechanism for first order stimuli
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
41
More complex first order stimul that require integration of motion cues across a wide expanse of visual space can be presented with what??
Random dot kinematograms
42
What is coherence threshold
The smallest percent coherence that results in the perception of motion in a defined direction (up, down, L, R)
43
Humans have a manifesting coherence threshold of about ______
1%
44
What is minimum displacement threshold (Dmin)
The minimum distance dots must move in a givers direction to elicit the perception of motion
45
What is the maximum displace the threshold (Dmax)
The maximum distance the dots can mov and still elicit motion perception
46
What is global motion perception
The visual system must integrate information from many dots over a broad expanse of the retina involving higher cortical motion centers
47
Monkeys can detect correlated motion when what percent of the dots are moving in the same direction
2-3%
48
Humans can detect correlated motion when what percent of the dots are moving in the same direction
1%
49
Global motion cues
Lecture 2
| Slides 21-23
50
What is motion aftereffect (waterfall illusion)
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
What is motion induced blindness
The brain ignores what the eyes tell it
Lecture 2
Slide 26
52
What is the second order stimuli for motion
Motion perception for more complex stimuli
Texture-defined contours
Processed by different pathways than first order
53
What does the fact that almost all humans can perceive 2nd order motion tell us?
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
What is the magno pathway
High velocity processing system
```
Visual area 5, MT, V5
Motion processing
Where?
Dorsal pathway- parietal
Motion perception-global stimuli
```
55
What happens if there is impairment to the magno pathway
Akinetopsia
56
What is the parvo pathway
Low velocity information processing
Visual area V1 V2 V4
Object processing
What?
Ventral pathway- temporal
Object perception (faces...)
57
What happens if there is an impairment of the parvo pathway
Can't recognize an object
58
How is biological motion detected?
Cortical posterior superior temporal sulcus
59
What is isoluminant
Possessing the same luminance
60
T/F under certain isoluminant conditions the perception of motion is impaired,
True
It can be weak or slower than that actual movement of the bars
Lecture 2, slide 49
61
How can you improve the perception of motion at certain isoluminant conditions?
Add luminance contrast
Lecture 2 slide 49
62
Magno pathway -> motion percetion -> rapid motion
Know this
63
Is color a good stimuli for Magno path?
No
| Monochromatic
64
Is color a good stimuli for Parvo path?
Yes
65
What are P path characteristics
Small RF
Better spatial resolution
Selective for color
66
What are the M path characteristics
Better temporal resolution
More sensitive to ow light levels
Monochromatic
67
How does scotopic conditions affect motion perception
Objects appear to move slower
68
How do Mesopic conditions affect motion perception
Motion perception is impaired
| There is incomplete integration of rod/cone signals because they are both active
69
What affect does the velocity of a moving stimulus have on VA?
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
What is the reduction in dynamic visual acuity as target velocity increases due to?
Inability to accurately follow the stimulus with tracking eye movements (smooth pursuit eye movements)
71
Higher dynamic VA is associated with
Improved ability to detect hazardous situations while driving
72
What is saccadic suppression/saccadic omission
When vision is suppressed shortly before, during, and shortly saccadic eye movements
73
What does saccadic suppression enable us to do
Look from one object to another without smearing our vision
74
What is saccadic suppression due to
The magno path is sensitive to high-velocity movement
It is presumably suppressed to avoid smearing vision
75
If saccadic suppression is caused by an extraretinal signal what would you expect to find
Neurons in the cortical motion areas are activated when the scene is moved, but suppressed during saccades
76
Midget RGC sued axons to LGN to form what path
P
77
Parasol RGCs send axons to LGN to form what path
M
78
What are the major classes of monocular depth cues
Pictorial
Angular declination below horizon
Motion parallax
Accommodation
79
T/F monocular depth cues are perceives just as strongly when viewed with one eye as when viewed with both
True
80
What are pictorial depth cues
```
Relative size
Familiar size
Linear perspective
Texture
Interposition
Clarity
Lighting
Shadow
```
81
T/F monocular individuals manifest surprisingly ROBUST depth perception due to these cues
True
82
What is relative size
A depth cue when viewing a scene that includes objects whose sizes can be compared to each other
83
With relative size we perceive large objects as _____
Being closer to us
84
What does the relative size cue tell us
How far away different objects are relative to each other, but it cant tell us exactly how far away they are
85
Are we able to tell how far an object really is?
Yes, our brains use distance-equals-object-size-divided by relative size relationship to enter mine absolute distances
Familiar sizing
86
What is familiar sizing cue
Cue is used when viewing objects of known size
87
What is an example of linear perspective
Railroad tracks
We assume the tracks is of equal width throughout
The appearance of distance width being narrower gives a sense of depth
88
How does texture gradient work
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
When is interposition used
When the view of a scene is partially obstructed
90
What is clarity
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
What are some things that can obscure clarity
```
Fog
Smoke
Rain
Smog
Makes things look more distant
```
92
How do shadow and lighting play into depth perception
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
What does angular declination below the horization allow us to do
Determine object distance
BECAUSE
The object makes an angle with the horizon (ADBTH), the visual system uses this angle to determine distance
94
What is motion parllax
Kinetic monocular depth cue
Results when a moving observer fixated on an object which noticing the relative motion of surrounding objects
95
What visual area plats a role in motion parallax and binocular disparity and motion in monkeys
MT
| V5
96
How does accommodation act as a depth cue
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
What binocular depth cues
Retinal disparity
| Convergence
98
What does retinal disparity allow
It is a binocular depth cue
Allows the visual system to determine distance
Look at slide 22 for ball example
99
What is stereopsis
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
What is physiologic diplopia
If retinal disparity is too large, the images fall on retinal positions that signal grossly different directions
101
What is the size illusion
Changes in retinal image size does not cause a change in apparent object size at any distance
102
How does our visual system compensate for differences in retinal image size
It takes into account the relative distance of an object, size constancy
103
What happens when judgement of distance is erroneous
Size Constancy may fail, resulting in size illusion
104
How does size constancy occur?
What is an example
Monocular depth cues provide incorrect information regarding relative distance
Moon illusion
Slide 26-27)
105
What is Muller-Lyer illusion
Vertical lines with arrows facing different ways
The line is the same size, but the arrow directions make it appear shorter or longer
106
What does measuring a patients stereopsis tell us
Important information about the status of the visual system
The minimum amount of disparity required to perceive depth is determined
107
What is the threshold disparity of stereopsis
Stereoacuity
Can be as small as 3 seconds of arc
108
What are some things that can reduce stereoacuity
Disorders of binocular vision (anisometropia, strabismus) can alter an infants visual experience and retard development of binocular cortical neurons
109
What is monovision
When a patients have one eye corrected for near and the other for distance
110
Why doesn't diplopia occur in monovision
Because the unused eye is largely suppressed
111
Does a person with monovision have depth perception
Yes, because most cues for depth are monocular
