Temporal Vision Flashcards
1
Q
Concerned with changes in luminance across space
A
Spatial vision
2
Q
Concerned with changes in luminance over time
A
Temporal vision
3
Q
What is the peak of the sinusoid deal wave called
A
Modulation depth, amplitude, contrast
4
Q
The stimuli whose luminance caries sinusoidally over time
A
Temporal sinusoids
5
Q
A temporal sinusoid manifests sinusoidal changes in luminance over _______
A
Time
6
Q
Modulation depth changes with respect to _____
A
Time
7
Q
At what modulation depth is it more steady
A
Low modulation depth
8
Q
What modulation depth is there more flickering
A
High modulation depth
9
Q
A temporally modulated stimulus of a low modulation depth, as in may not be resolved, appearing ______
A
Steady
10
Q
As the modulation depth increased, however, it may be resolved and seen as _______
A
Flickering
11
Q
Rate of change of frequency with time
A
Temporal frequency
12
Q
Low temporal frequency stimulus may be seen as a _____ at a low rate
A
Snickering at a low rate
13
Q
A higher temporal frequency stimulus may appear to _____ at a higher rate
A
Flicker
14
Q
Temporal frequency is typically given in
A
Hertz
15
Q
Modulation depth and temporal frequency in slow flicker
A
Low for both
16
Q
For a fast flicker, what is the modulation depth and temporal frequency
A
High
17
Q
As the temporal frequency is increased, a frequency is reached at which flicker can no longer be resolved at that frequency, is called the
A
Critical flicker fusion frequency (CFF)
18
Q
A frequency is eventually reached that cannot be resolved, and the stimulus appears
A
Steady
19
Q
This temporal frequency that appears steady, the CFF, represents the _________ of the visual system for a given modulation depth
A
The high temporal resolution limit
Temporal acuity
20
Q
The CFF increases _____ with the log of the retinal illumination
A
Linearly
21
Q
CFF is considered _____ under photopic compared to scotopic conditions
A
Higher
Due to a general speeding up of retinal processes that occurs at increasing levels of light adaptation
22
Q
If you increase retinal illuminate, what happens to CFFF
A
Increases linearly
23
Q
How do you determine temporal MTF
A
- views stimulus at given temporal rate
- modulation depth small first and the screen appears steady
- the modulation depth is slowly increased until the subject reports screen is flickering
- the modulation depth at which the subject first sees flicker is threshold
- its reciprocal is relative sensitivity for flicker resolution
- repeated for a large number of temporal frequency
24
Q
The modulation depth is slowly increased until the subject reports the screen ________
A
Flickering
25
The modulation depth at which the subject first sees flicker is the
Threshold
26
The reciprocal of the modulation depth at which the subject first sees flicker is the
Relative sensitivity
27
Stimuli that fall outside of the TMFT are seen as fused or steady; they are not ___________ temporally
Resolved
28
Those stimuli that fall under the graph are _________ and perceived as flickering
Resolved temporally
29
TMTF show maximal sensitivity to __________ frequencies
Moderate
30
For the TMTF, the high frequency cutoff represents the highest temporal frequency that can be
Resolved at 100% modulation
31
Larger stimulus in CFF
Larger stimulus increases CFF
32
CFF increases with the log of the ________ area
Stimulus
33
Receptor field size and eccentricity effecting temporal properties
Temporal properties of the retina are similar across eccentricity
34
What are the things that have to happen for the temporal properties to be similar across eccentricity
The stimulus size needs to increase to match the size of the ganglion receptive field size, the field increases for ganglion in the periphery
35
Stimulus which appears steady in the central vision may appear flickering in the periphery due to the ________ of the peripheral retina, for higher luminance
Higher temporal resolution
36
What is temporal acuity better in the periphery
When enough luminance which means a much larger stimulus size
37
What about the peripheral retina is important for increased temporal acuity?
The number of ganglion are decreased in the periphery, but they have a large reception even field. Stimulus size has to match the receptive field
38
Flicker light and retinal blood vessels
May cause dilation of the them, which is localized to the stimulated area due to the response to local metabolic demand
39
Infants ability to resolve temporal stimulus
Decreased
40
In the TMTF curve, the reduction in low frequency temporal sensitivity tells us ______ changes in illumination are not seen
Very gradual
41
Example of troxler phenomenon
Observe the minute hand on a watch, although we know the minute hand moves, we do not actually see it move
42
The manifestation of the visual systems reduced sensitivity to low temporal frequencies is the inability to perceive stationary or stabilized retinal images, called the
Troxler phenomenon
43
When we look at a picture that has the X in the middle and a fuzzy gray border, what happens and what is that an example of
When looking at the X, the borders disappear
The changes in retinal illuminated are of a very low temporal frequency. Because we are not sensitive to low temporal frequencies, the border disappears
44
When looking at the gray box with the X in the middle and the borders are very distinct, what is happening and why
Eye movements across sharply focused borders result in the introduction of moderate temporal frequencies. Because we are sensitive to these frequencies, the border does not disappear
45
When looking at a target, does the eye move or stay still
Even when fixating a target, small involuntary eye movements occur continuously
46
Lateral inhibition
The receptive field center and surround have different signs
The center and the surround also respond with different latencies
47
Latenices of the center and the surround of a receptive field
They are different. There is a phase lag between the center and the surround
48
For low temporal frequencies, their ______ can cause the center and surround signals to cancel each other, thereby reducing sensitivity
Phase lag
Response of stimulus in each center and surround happen at differnt times. This is called the phase lag. For low frequencies they cancel each other out after a second
49
What is the low frequency cut off caused by
Phase lag
50
What is the high frequency cut off due to
Neural constraints
51
Neural constraints in the high frequency TMTF cut off
The faster a neural system respond, and the more transient its response, the greater its temporal resolution
52
Why does the neural response limit the high cut off freqncy
It is neither fast nor transient enough to allow resolution
53
This provides information regarding both spatial and temporal processing of visual information
Masking
54
This reduced the visibility of a stimulus referred to as the target
Mask
55
What kind of testing is masking used in
Psychophysical (subjective) testing
56
What is forced choice
Patient must respond to certain stimulus to get to the next stimulus
57
Types of visual masks
Simultaneous masking
Backward masking
Forward masking
58
Both the mask and target are present at the same time
Simultaneous masking
59
What is this an example of: a spatial grating (the mask) may interfere with the detection of a stimulus composed of a similar frequency (the target)
Simultaneous masking
60
In simultaneous masking, since both the mask and target may share the same spatial frequency channels, there is a
Reduction in the visibility of the target gratings
61
What kind of masking is more pronounced in amblyopes
Simultaneous
62
Which is better to measure VA for an amblyope, standard eye chart or isolated optotypes
Isolated
63
The reduction in acuity caused by surrounding spatial patterns is sometimes referred to as the
Crowding phenomenon
64
Examples of crowding examples
Letters inside circles and squires.
| Flanking rings/optptypes
65
The target precedes the mask
Backward masking
66
When does backwards masking occur
When the mask is substantiallt brighter than the target, presumably enabling the masks neural response to reach central visual areas first, thereby interfering with detection of the target
67
A form of backward masking where the mask and target are spatially adjacent. The visibility of a briefly presented target is reduced by the subsequent presentation of a spatially adjacent mask
Metacontrast
Target first, then mask placed side by side
Lateral inhibition plays
68
_____ within the retina is though to contribute to metacontrast.
Lateral inhibition
69
The mask precedes the target. Reduces the visibility of the subsequently presented target
Forward masking
70
Type of forward masking where the target and mask are spatially adjacent is referred to as _______. The mask reduced the visibility of a subsequently presented, spatially adjacent target
Paracontrast
71
A high temporal frequency tumulus may appear flickering at _____ rate
Higher
72
Temporal frequency is given in hertz, 1 Hz is
1 cyl/s
73
The CFF for scotopic conditions is ______compared to photopic conditions
Lower
74
When testing under scotopic conditions, CFF is expected to be closest to
20Hz
75
The CFF for a given percentage modulation is 50Hz. A stimulus of 55Hz, presented at this given percentage modulation is seen as
Steady
76
Beyond CFF, the stimuli appears steady because
It cant be resolved
77
As the area of the stimulus increases, the CFF ______
Increases
78
The detection of high temporal frequency is limited by
Speed of measure processing
79
The reduction in sensitivity to low temporal frequencies is caused by
Lateral inhibition (phase lag)
80
What prevents our visual world from disappearing when we fixate on object?
Small, inhibitory eye movements
81
When the modulation depth very small, the screen appears
Steady
82
A maximal TMTF value of a young healthy eye is
10Hz
83
At which of the following temporal frequencies does the TMTF sho max sensitivity
Moderate
84
When flickering light falls on the retina, nearby blood vessels
Dilate
85
The VA of amblyopia patients is poorer when measured using Snellen acuity chart than when measured with isolated optotypes because of
Simultaneous masking
86
When a mask reduces sensitivity to previously presented spatially adjacent stimulus, the phenomenon is referred to as
Meta contrast
87
When optotypes are surrounded by spatial patterns, the VA ____
Decreases
88
Schizophrenia and masking
Large amounts of deficits with masking
- used MRI to test how long the signal took to get from eyes to occipital love
- backwards masking was used
- neural problems for masking deficits
89
TMTF and glaucoma
Better to test for glaucoma than VF
| -good for ARMD and RP too
