This document discusses various aspects of temporal vision:
1) Temporal vision refers to time-related changes in vision and the analysis of luminance over time, such as detecting flickering lights.
2) Temporal stimuli are often modulated sinusoidally over time, varying in depth of modulation and temporal frequency. Higher modulation causes flickering while lower frequencies appear steady.
3) The critical flicker fusion frequency (CFF) is the highest rate at which a flickering light appears fused rather than flickering and depends on factors like luminance.
4) Temporal modulation transfer functions (TMTF) describe sensitivity to modulation at different frequencies, showing band-pass characteristics with reduced sensitivity at very low and
To know Humphrey visual field analyser
To know about various types of perimetry
To identify field defect
To recognize that field defect is due to glaucoma or neurological lesion
To know that field defect is progressive or not
Interpretation of HVFA
To know Humphrey visual field analyser
To know about various types of perimetry
To identify field defect
To recognize that field defect is due to glaucoma or neurological lesion
To know that field defect is progressive or not
Interpretation of HVFA
Detailed instumentaion and use of manual Lensometer and just a outline of automated lensometer.
I have used the picture of manual lensometer with out the parts describtion because i have explained orally by showing the picture..
Hope u all like it and may help you in learning better. :)
Detailed instumentaion and use of manual Lensometer and just a outline of automated lensometer.
I have used the picture of manual lensometer with out the parts describtion because i have explained orally by showing the picture..
Hope u all like it and may help you in learning better. :)
Aim: This study investigated the eff ect of video games on Critical fl ickering fusion frequency rate
(CFFFR).
Background: CFFFR is the rate of successive light fl ashes from a stationary light source at which the
sensation of fl icker disappears and the light becomes steady. CFFFR with higher values suggested that
greater perceptual accuracy. The eye and brain act together to perceive fl ickering light. The activities
in the retina and brain are synchronized as a part of the visual process. If the modulation i.e. fl icker
frequency is high enough, the visual system will perceive fl ickering light as a continuous steady light.
This CFFFR has been used in the studies on physiology of vision, Stress, drug research.
Results: In the present study CFFFR was measured in two age-matched groups of healthy volunteers
whose ages ranged from 18 – 45 years with 75 subjects in each group. Test group consists of Media
players who were played video games since their childhood. Control group consists of Non-Media
players who did not know how to play the video games. The scope of the present study is to know
the eff ect of video games on CFFFR. The results in our study showed that CFFFR threshold increases
signif cantly in media players when compared to non – media players (p<0.001).This study also
showed that CFFFR signif cantly decreases as the age increases and high CFFFR threshold were
recorded in media players who played puzzle and brain games than the action adventure and sports
games. The gender eff ect on CFFFR was not signif cant but higher CFFR values were recorded for men
than women.
Conclusion: This study proved that playing video games can develop cognitive skills, high level
thinking skills, problem solving complex, concentration, logical thinking, imagination and creativity
but on the other side teenagers who spend an ample amount of time playing games experience eff ects
which are not so benef cial at all.
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[1] Part-1/2 (52 minutes): https://youtu.be/-O_mYoeg-us
[2] Part-2/2 (51 minutes): https://youtu.be/IhHHHZYcY0o
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2. Introduction
Stimulus considerations
Temporal modulation transfer functions
Critical flicker fusion frequency
Other temporal visual effects
Masking
3. Temporal aspect of vision is a time related
vision.
It is concern the analysis of changes in
luminance over time.
Example: task involves detection of flicker
produced by a flashing light.
Temporal vision is closely related to the ability
to perceived motion.
4. Temporal vision is frequently studied with
stimuli with luminance that varies sinusoidally
over time.
A temporal sinusoid manifests a sinusoidal
change in luminance over time.
From the sinusoidal graph we must take in
mind the two stimulus consideration:
Depth of modulation
Temporal frequency
5. Graph stimuli with
luminance that varies
sinusoidally over time
• Luminance profile for a
stimulus with luminance
that is temporally
modulated in a sinusoidal
manner over time.
• A computer screen that
turns on and off with a
sinusoidal time course
would produce a
illimunance profile similar
to that given in this figure.
• “A” refers to amplitude of
modulation.
6. A temporally modulated
stimulus is produced by a light
source for example the computer
monitor that will turn on and off.
To produce temporal sinusoid,
the light source must turn on and
off with a sinusoidal course.
7. The visibility of a temporally
modulated stimulus is related to its
depth of modulation.
May be two of modulation:
Low depth of modulation steady field
High depth of modulation flicker.
8. When depth of
modulation is low,
light source appears
steady. (Figure A)
When depth of
modulation is large,
light source resolve
and seen flickering.
(Figure B)
9. The percentage of depth of modulation of a
temporally modulated stimulus is given by:
Where A= amplitude of modulation
Iave = time-averanged luminance
Percentage modulation = A(100)
Iave
10. Low temporal
frequency flicker at
the slow rate. (Figure
A)
High temporal
frequency flicker at
the faster rate. (Figure
B)
11. CFF represent the high frequency resolution
limit of the visual system for a given depth of
modulation.
Typically given in the Hertz (Hz)
1 Hz = 1 cycle per second.
12. Definition
Frequency of the light stimulation at the which it
becomes perceive as a stable and continuous
sensation.
That frequency depends upon various factors:
Luminance
Color
Contrast
Retinal eccentricity
13.
14. Ind. view a light
source that is
modulated at
given temporal
rate
Initially,
modulation
depth is very
low; screen
appear steady
Slowly
increase—
until subject
report
flickering
Threshold??–
modulation at
which person
first sees flicker
Relative
sensitivity
(1/
Percentag
e
Modulatio
n)
Frequency
(Hz)
Flicker
1 3 10 36 100
15. 1 36103 10
0
No Flicker
Stimuli fall outside
TMTF are seen as
fused/steady; not
temporally resolved
Flicker
Stimuli fall under
TMTF are temporally
resolved, perceived as
flickering
Relative
sensitivity
(1/
Percentage
Modulation)
Frequency
(Hz)
Temporal Modulation Transfer
Function (TMTF)
•Relative sensitivity as function of temporal frequency
•Band pass shape
•Sensitivity for detection of flickers FALLS OFF at both low and high temporal
frequencies
16. • Very slow /gradual
changes are not
seen
Low
temporal
frequency
• High frequency
drop off the TMTF
High
temporal
frequency
17. Very slow /gradual changes are not seen
Ie: sun set
We aware the changing illumination, we don’t actually
perceived the change itself
Ie: minute hand on a watch
Origin of low frequencies TMTF drop offs
Due to time lags inherent lateral inhibition within retina
Low temporal frequency stimuli maximize these
inhibitory interaction with a resultant reduction in
sensitivity
18. High frequency drop off the TMTF
Ie: household incandescent light bulb
Bulb modulated at 60Hz
Because we are sensitive to high-frequency temporal
modulation, bulb appear steady rather than flickering
Origin of low frequencies TMTF drop offs
Due to neural limitation in coding high temporal
frequency information
A frequency is reached can not be response because
of limitation of neural response
19. Highest or lowest temporal frequency that can
be resolved at a given percentage modulation
20. 1.00
0.25
0.01
1 3 4 10 36
100
Frequenc y ( Hz )
CFF CFF
For 4.0 percent modulation, relative sensitivity of ¼, or 0.25, a line
extended from this point intersects the TMTF at two points at 4 and 10 Hz,
represents the low and high frequency. Stimuli < 4 Hz or >10 Hz are seen
as fused, not resolved and appear steady.
RelativeSensitivity(1/percentageOfmodulation)
21. Relative sensitivity
( 1 / percentage
Modulation )
1 3 10 36 100 Frequency ( Hz )
≈ 100 td
≈ 1000 td
≈ 10 td
The increasing background illumination has different effect on relative
sensitivity for low and high temporal frequencies. In low frequency,
increasing the illumination has no effect on relative sensitivity.
22. Log Retinal Illumination
CFF(Hz)
Scotopic
vision
Photopic Vision
70 Hz
20 Hz
For high-frequency, relative sensitivity increases with CFF increasing
approximately with the log of retinal illumination. Probably related to a
general speeding up of retinal processes that occurs at increasing level of
light adaptation.
Graphical presentation of Ferry Porter Law
23. Granit – Harper Law
CFF increases with the log of the stimulus area.
For a given percentage modulation, flicker is more likely
to be perceived if the stimulus is large.
The extrafoveal retina ;
better in detecting the flicker and movement than the
foveal retina contribute the “where” system
which alert us to the presence of visual stimuli that
require immediate attention.
Retinal parasol ganglion cells display high sensitivity to
high temporal frequencies and may contribute to the
peripheral retina’s superior sensitivity to the stimuli.
24. Once a stimulus is detected by the where
system, it is examined with foveal
vision.(display highly developed visual acuity)
Involving the midget (parvo) ganglion cells,
Most concentrated in the fovea.
Midget cells Parvo layers
Striate cortex
Higher cortical areas (forming
the cortical what system )
25. The Broca-Sulzer effect, which describes the
apparent transient increase in brightness of a
flash of short duration. Subjective flash
brightness occurs with flash durations of 50 to
100 milliseconds.
This phenomenon is associated with temporal
summation and explains the leveling off of
brightness to a plateau.
26. When the light is turned on, time is required
for temporal summation to reach threshold for
light of low luminance. Light of high
luminance reach this threshold very quickly.
As flash duration increases, brightness levels
off to a plateau as temporal summation begins
to breakdown according to Bloch’s law after
the critical duration.
The apparent transient peak in brightness is
probably due to an underlying neural
mechanism.
27.
28. The Brücke-Bartley effect is the phenomenon in
which a flickering stimulus appears brighter than
the same stimulus presented unflickering.
The Brücke-Bartley (brightness enhancement) effect
is a phenomenon related to the Broca-Sulzer effect.
When the frequency is gradually lowered below the
CFF, the effective brightness of the test field begins
to rise.
Not only does the brightness reach a value equal to
that of the uninterrupted light, but the brightness
even transcends it, reaching a maximum when the
flash rate is about 8 to 10 Hz.
29. The Talbot-Plateau Law describes the brightness of
an intermittent light source which has a frequency
above the CFF.
This law states that above CFF, subjectively fused
intermittent light and objectively steady light (of
equal colour and brightness) will have exactly the
same luminance. In another words, brightness
sensation from the intermittent light source is the
same as if the light perceived during the various
periods of stimulation had been uniformly
distributed over the whole time.
The Talbot-Plateau Law applies only above the CFF.
30.
31. Involves the use of stimulus
(Mask)reduce the visibility of another
stimulus(target)
Various types of masking:
- simultaneous masking
- backward masking
- forward masking
32. Mask and target present at the same time
Both frequencies share the same spatial
frequency channels causes reduction in the
visibility of the target gratings
More pronounced in patients with amblyopia
Crowding phenomenon- low acuity viewing
row of letters rather than viewing isolated
letters
33. • Target precedes the mask
• Even though the mask occurs after the target,it
reduces the visibility of the target
• Typically occurs when mask is brighter than
target
• Mask transmitted along the neural pathways at
a relatively rapid rate
• This enables it to surpass the preceding target
and interfere with its detection
34. Mask precedes the target
Mask reduces the visibility of the subsequently
presented target
Characterized temporal vision
How to determine TMTF??
Ind. view a light source that is modulated at given temporal rate
Initially, modulation depth is very low; screen appear steady
Slowly increase—until subject report flickering
Threshold??– modulation at which person first sees flicker
Procedure repeated for a large number of temporal frequencies to obtain TMTF
This figures displays TMTFs under various levels of retinal illumination. The increasing background illumination has different effect on relative
In comparison,
Enables us to examine a visual stimulus in detail such that it can be identified