Temporal Vision Ch. 7 Flashcards
definition of temporal (resolution) acuity
the smallest time interval that can be resolved as flickering
critical flicker (fusion) frequency, or CFF is:
how temporal (resolution) acuity is defined, the highest f you can still perceive flickering
definition of period
the length of time for one complete cycle of light/ dark
definition of flicker rate (frequency)
the number of cycles per second
the talbot-plateau law is when the brightness of a light (strobe) is:
above the CFF
so it is steady, fused
in the talbot-plateau law, if you were to ‘match’ a steady light, you would find the luminance to be:
strobe light’s average luminance
talbot brightness
the brucke-bartley phenomenon is for flicker rates are:
below the CFF (between 5-20 Hz)
in the brucke-bartly phenomenon, how can a flickering light can appear compared to mean luminance
it can appear brighter than steady light with equal mean luminance (may even be greater than Lmax)
how can the temporal resolution limit (CFF) be reached?
due to neurons lagging in their responses
when can the CFF be exceeded?
when the neural response doesn’t have time to stop between flashes
what is the neural basis of the talbot-plateau law
above the CFF, flash duration is very short and the light is never on long enough to stimulate the neurons fully
Ferry-Porter law states:
CFF is proportional to the log of stimulus luminance
Ferry-Porter law means better temporal acuity will occur with ____ light levels
higher
equation for Ferry-Porter law
CFF = k log L + b
k=10 for regular foveal vision
for what range and conditions does Ferry-Porter law hold?
over about 4 log units (limit is at CFF- 50 Hz) foveal
how does Ferry-Porter law change for periphery?
it has a greater slope in the periphery (k>10)
FPF has a ____ effect in the periphery
stronger/greater
FPF (at high luminance levels) has the highest CFF where?
mid-peripheral retina (about 35 degrees)
where is the CFF on the FPF (at low luminance levels)?
CFF is nearly constant across the retina
granit-harper law states
CFF is proportional to the log of stimulus area (size)
grant-harper law states you have better temporal acuity with ____ stimuli
larger
photopic CFF (foveal) is best at ___ Hz
50
scotopic CFF is best at ___ Hz
20
peak CS for temporal CSF
5-20 Hz
depends on light levels
cutoff high flicker rate for temporal CSF
50-70 Hz
varies depending on curve
how does the temporal CSF change with increase luminance?
peak and high cutoff shift right
studies show glaucoma has a loss of what types of flicker rates?
loss of high flicker rate sensitivity
the neurons involved may be in Magnocellular pathway
FDT has a ___ cpd grating and flickers at ___ Hz
20cpd grating at 25 Hz
temporal summation (Bloch’s law) is a trade off between what 2 factors?
time an luminance
in Bloch’s law, the time over which the law applies, the critical duration, can vary between
30 and 100 ms depending on luminance levels
Bloch’s law: as the background luminance increases, the critical duration gets ____ and summation ___
critical duration gets shorter, less summation, more resolution
in Bloch’s law, critical duration is shorter for higher luminance levels (about ___ ms)
30ms
in Bloch’s law, critical duration is longer for lower luminance levels (about ___ ms)
100ms
definition of Broca-Sulker effect
for supra threshold flashes, brightness depends on duration
in the Broca-Sulker effect, we perceive what kinds of flashes differently?
50-100ms flashes brighter than flashes of other durations
how does masking change threshold?
masking increases threshold for a task due to another stimulus being presented before, during, or after target
forward masking is when:
mask presented BEFORE target
backwards masking is when:
mask presented AFTER target
where does masking have the biggest effect?
backward masking
what is metacontrast?
type of backward masking when the target and mask do not overlap spatially
what is paracontrast?
type of forward masking when mask and target do not overlap spatially
how do we know masking is neural and NOT a retinal phenomenon
dichoptic masking tests- still get masking effects even when one target at each eye
units of motion detection
degrees of visual angle/second
temporal frequency=
velocity x spatial frequency
you need at least two retinal points to distinguish between:
motion and static flicker rate
motion detection is limited by:
temporal resolution
independent of velocity itself
how can increasing velocity change the temporal CSF?
shifts the CSF left
