Temporal Vision Flashcards
Concerned with changes in luminance across space
Spatial vision
Concerned with changes in luminance over time
Temporal vision
What is the peak of the sinusoid deal wave called
Modulation depth, amplitude, contrast
The stimuli whose luminance caries sinusoidally over time
Temporal sinusoids
A temporal sinusoid manifests sinusoidal changes in luminance over _______
Time
Modulation depth changes with respect to _____
Time
At what modulation depth is it more steady
Low modulation depth
What modulation depth is there more flickering
High modulation depth
A temporally modulated stimulus of a low modulation depth, as in may not be resolved, appearing ______
Steady
As the modulation depth increased, however, it may be resolved and seen as _______
Flickering
Rate of change of frequency with time
Temporal frequency
Low temporal frequency stimulus may be seen as a _____ at a low rate
Snickering at a low rate
A higher temporal frequency stimulus may appear to _____ at a higher rate
Flicker
Temporal frequency is typically given in
Hertz
Modulation depth and temporal frequency in slow flicker
Low for both
For a fast flicker, what is the modulation depth and temporal frequency
High
As the temporal frequency is increased, a frequency is reached at which flicker can no longer be resolved at that frequency, is called the
Critical flicker fusion frequency (CFF)
A frequency is eventually reached that cannot be resolved, and the stimulus appears
Steady
This temporal frequency that appears steady, the CFF, represents the _________ of the visual system for a given modulation depth
The high temporal resolution limit
Temporal acuity
The CFF increases _____ with the log of the retinal illumination
Linearly
CFF is considered _____ under photopic compared to scotopic conditions
Higher
Due to a general speeding up of retinal processes that occurs at increasing levels of light adaptation
If you increase retinal illuminate, what happens to CFFF
Increases linearly
How do you determine temporal MTF
- 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
The modulation depth is slowly increased until the subject reports the screen ________
Flickering
The modulation depth at which the subject first sees flicker is the
Threshold
The reciprocal of the modulation depth at which the subject first sees flicker is the
Relative sensitivity
Stimuli that fall outside of the TMFT are seen as fused or steady; they are not ___________ temporally
Resolved
Those stimuli that fall under the graph are _________ and perceived as flickering
Resolved temporally
TMTF show maximal sensitivity to __________ frequencies
Moderate
For the TMTF, the high frequency cutoff represents the highest temporal frequency that can be
Resolved at 100% modulation
Larger stimulus in CFF
Larger stimulus increases CFF
CFF increases with the log of the ________ area
Stimulus
Receptor field size and eccentricity effecting temporal properties
Temporal properties of the retina are similar across eccentricity
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
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
What is temporal acuity better in the periphery
When enough luminance which means a much larger stimulus size
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
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
Infants ability to resolve temporal stimulus
Decreased
In the TMTF curve, the reduction in low frequency temporal sensitivity tells us ______ changes in illumination are not seen
Very gradual
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
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
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
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
When looking at a target, does the eye move or stay still
Even when fixating a target, small involuntary eye movements occur continuously
Lateral inhibition
The receptive field center and surround have different signs
The center and the surround also respond with different latencies
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
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
What is the low frequency cut off caused by
Phase lag
What is the high frequency cut off due to
Neural constraints
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
Why does the neural response limit the high cut off freqncy
It is neither fast nor transient enough to allow resolution
This provides information regarding both spatial and temporal processing of visual information
Masking
This reduced the visibility of a stimulus referred to as the target
Mask
What kind of testing is masking used in
Psychophysical (subjective) testing
What is forced choice
Patient must respond to certain stimulus to get to the next stimulus
Types of visual masks
Simultaneous masking
Backward masking
Forward masking
Both the mask and target are present at the same time
Simultaneous masking
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
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
What kind of masking is more pronounced in amblyopes
Simultaneous
Which is better to measure VA for an amblyope, standard eye chart or isolated optotypes
Isolated
The reduction in acuity caused by surrounding spatial patterns is sometimes referred to as the
Crowding phenomenon
Examples of crowding examples
Letters inside circles and squires.
Flanking rings/optptypes
The target precedes the mask
Backward masking
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
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
_____ within the retina is though to contribute to metacontrast.
Lateral inhibition
The mask precedes the target. Reduces the visibility of the subsequently presented target
Forward masking
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
A high temporal frequency tumulus may appear flickering at _____ rate
Higher
Temporal frequency is given in hertz, 1 Hz is
1 cyl/s
The CFF for scotopic conditions is ______compared to photopic conditions
Lower
When testing under scotopic conditions, CFF is expected to be closest to
20Hz
The CFF for a given percentage modulation is 50Hz. A stimulus of 55Hz, presented at this given percentage modulation is seen as
Steady
Beyond CFF, the stimuli appears steady because
It cant be resolved
As the area of the stimulus increases, the CFF ______
Increases
The detection of high temporal frequency is limited by
Speed of measure processing
The reduction in sensitivity to low temporal frequencies is caused by
Lateral inhibition (phase lag)
What prevents our visual world from disappearing when we fixate on object?
Small, inhibitory eye movements
When the modulation depth very small, the screen appears
Steady
A maximal TMTF value of a young healthy eye is
10Hz
At which of the following temporal frequencies does the TMTF sho max sensitivity
Moderate
When flickering light falls on the retina, nearby blood vessels
Dilate
The VA of amblyopia patients is poorer when measured using Snellen acuity chart than when measured with isolated optotypes because of
Simultaneous masking
When a mask reduces sensitivity to previously presented spatially adjacent stimulus, the phenomenon is referred to as
Meta contrast
When optotypes are surrounded by spatial patterns, the VA ____
Decreases
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
TMTF and glaucoma
Better to test for glaucoma than VF
-good for ARMD and RP too
