Chapter 4-Temporal Vision Flashcards
what is temporal vision
concerned w/ the ability to perceive temporal modulations of light or changes in luminance over time
w/out temporal changes, we wouldnt be able to detect what
our surroundings
how is it possible to detect a luminance grating that is static/doesnt move?
luminance grating is always moving on our retina.
the retinal img always moves
there is some temporal modulation on sptial luminance gratings due to what
eye movements
what is the troxler effect
small movements do not move the retinal image and this system fails
how can temporal vision be measued
w/ flashes with a time interval btwn them
- usually studied w/ luminance gratings that alternate btwn min adn max luminance over time
- FLICKERING
what is temporal luminance modulation
“flicker”
-has luminance modulating throughout time (not space)
what is one cycle in temporal freq
the time from peak luminance to peak luminance
-or trough to trough luminance
what is the unit for defining spatial freq
1 degree of visual angle
what is the unit for defining temporal frq
1 sec
what is temporal contrast of luminance modulation
differenc ein luminance exprssed as %contrast
-difference btwn the max and min values of a flicker
what is low temporal contrast
waht is high temporal contrast
diff btwn max and min luminace of this flicker is small
-high temp: the diff btwn the max and min luminace of this flicker is greater
what is the spatial resolution limit
the max spatial cycles per degree of visual angle somebody can detect
what is the temporal solution limit
the max temporal cycles per 1 sec someone can detect or the fastest flickering
what is the maximum flickering we can detect called
-what can it determine
critical flicker frequency (CFF) and dtermines the temporal VA
for temporal freq above the CFF the stimulus appears how
steady or fused
who is reponsible for temporal resolution
determined at an early stage at the visual pathway as it can be described by the temporal prop of the photoreceptors and ganglion cells
waht are factors that affect CFF
retinal illuminance
retinal location
stimulus size
retinal adaptation
what does CFF increased w/
retinal eccentricity
CFF is a function of _____ for different retinal eccentricities
retinal illuminance
CFF is higher in fovea or peripheral retina?
peripheral retina
mid or peripheral retina is more sensitive to flicker?
peripheral
bc of diff temporal properties of parvocelluar and magnocellular pathways
-central: mostly midget ganglion cells
what is granit harper law
CFF increases as the stimulus size increases
once rods are dark adapted, what happens to temporal resolution
decreases
what do dark adapted rods suppress
cone flicker sensitivity
bc of the increase at the horizontal cell’s response when the rods were desensitived
what is the minimum contrast that we still see the light flickering?
temporal contrast senstivity
what is the temporal contrast sensitivty function
temporal contrast sensitivity as a function of temporal freq
what is low freq drop off
why?
our sensitivyt to low temporal freq below this point decreases and we can no longer detect them
bc of troxler effect
waht is the troxler effect
when one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear
what can explain the troxler effect
the low sensitivity to low tempoarl frequencies
what does the peak sensitivty show that the neurons respond maximally to
that the majority of the neurons respond maximually at stimuli w/ intermediate temporal freq
what is the high freq cut off
due to the inability of neurons to signal high temporal freq
the point where the fucntion intersects the x axis is the maximum CFF we can perceive at ….
100% luminance modulation
what is the low freq drop off due to
due to a lag btwn the center and the surround of a receptive field
for every luminance modulation there are 2 CFF. what are they for
one for low end and one for the high end of the freq range
ex. for 5% luminance mod we arent able to perceive flicker for freq lower than low CFF 3Hz and higher than high CFF 50Hz
for everyday life, where does the peak sensitivity of temporal contrast sensitivty range
- for everyday life, the max CFF is what
- for low light levels the max CFF can be as low as what
btwn 10 and 20 Hz
60Hz
10Hz
which pathway that is sensitive to low spatial freq and high temporal freq believed to be early affected in glaucoma and IOP w/o vision loss
magnocellular pathway
what does the freq doubling technology test
the sensitvity to low spatial freq gratings that flicker fast
patiends w/ AMD who have a reduced temporal sensitivty btwn _______Hz are at risk for developing neovascular AMD (wet AMD)
5 and 40 Hz
what can discriminate pre-neovascular pts from normal pts
temporal sensitivty to just 2 temporal freq (5 and 10 Hz)
what is the broca-suzler effect
brightness is a perceptual phen and not something that can be measured w/ an instrument
what phenomenon does the broc-suzler effect see
that short duratoin light appear brighter than another steady light w/ the same avg luminance
what happens to the brightness of a flickering light? does it change with temporal freq?
yes, flicker of approx 10Hz appear brigher than flicker of lower or higher temporal freq
what is the brucke-bartley phen
if a light is flickering w/ a temporal freq equal to CFF and we start reducing its temporal freq then there will be a point where the flickering light appears brighter than b4
-point of enchancemnt is around 10Hz
what is the bruke bartley phen a direct consequence of
broca-suzler effect
what is the talbot plateau law
a fused flickering light appears the same in brightness as a steady light w/ luminance equal to the time avged luminance of the fused light
what is masking
the effect a ‘masking’ stimulus has on the detection of a test stimulus that is presented before, during, or after the masking stimulus
masking vs adaptation
adatation: long process, adapting stimulus is presented for a long time and the effect of adaptation lasts long
masking: short. short stimulus and the effect lasts a couple of hundrend millisecs
how can backward masking be explained
latency in the neuronal response to a near threshold test stiumulus
what can simultaneous and forwad masking be explained by
signal detection theory
-masking stim generates lots of neuronal activity while the test stim generates lower
what do metacontrast and paracontrast suggest in masking
there are lateral interactions btwn the neurons and that there is also some overlap of their receptive field
masking occurs not only when flashes are separted in time, but also in…
space
what is paracontrast
what is metacontrast
when it is presented before the masking stimulus (backward masking)
-when it is presendted after the masking stimulus (foward masking)
