Temporal Factors and LGN (M2) Flashcards
What is the flicker fusion frequency range for the photopic system? 1. Scotopic? 2
- 50 to 70 Hz
2. 10 to 20 Hz
What pathway do midget RGCs project to? 1. Parasol RGCs? 2
- parvocellular pathway (P pathway)
2. magnocellular pathway (M pathway)
What is the technique to assess relative brightness of different colored light stimuli? 1. What is the procedure? 2
- Heterochromatic flicker technique
2. adjust radiance until flicker perception is gone (two lights equal brightness to patient)
What are the methods to assess the temporal resolution acuity?
- use flashes of light
2. use temporal sine- and square-wave patterns (more common)
Are temporal sinusoids capable of different modulations and frequencies?
yes for both
What happens to the high-frequency cutoff as the background illumination increases?
cutoff increases (brighter light = temporal resolution improves)
What RGCs feed into the koniocellular pathway? 1. Where are these neurons located in the LGN? 2
- small bistratified RGCs
2. in between the 6 principle LGN layers
What percentage of RGCs project to the dorsal lateral geniculate nucleus?
90%
What is the ability to see your retinal blood vessels in your peripheral vision while your eyes are closed and a penlight is shown on them called? 1. What is this an example of? 2
- Purkinje tree
2. the Troxler effect
What is the idea that a flickering light of 10 Hz appears brighter than a constant light of equal luminance called?
Brucke-Bartley effect
Which layers of the LGN have larger cells (magno)? 1. Smaller cells (parvo)? 2
- layers 1 and 2
2. layers 3,4,5,6
Does the CSF get wider or narrower for individual cortical neurons, relative to LGN neurons (which are narrower than RGCs)?
narrower
What percentage of the neurons in the LGN are parvo? 1. What is their color opponency like? 2. Their response duration? 3. Response timing? 4. Receptive field? 5. Better response to high or low spatial frequencies? 6
- 80%
- yes
- more sustained
- slower
- smaller (with center-surround)
- high
What happens to the high-frequency cutoff as area of the flickering stimulus increases?
cutoff increases (linearly)
What is the range of the low-frequency roll-off of the TMTF?
4-25 Hz
What can be thought of as being the sum result of multiple spatial frequency channels?
human contrast sensitivity function
What do involuntary eye movements make a box with distinct borders look like to the RGC receptive field?
seems like “flashing” white and grey light
What is the measure of the temporal resolving capacity of the visual system at 100% modulation?
critical flicker fusion frequency (CFF) or minimum interval of resolution or temporal acuity
What ocular diseases create reductions in the S-cone driven konio pathway? 1. What is used to detect this? 2
- diabetic retinopathy and glaucoma
2. SWAP
What is the idea that at high frequencies that are above CFF, the apparent brightness is equal to the time-averaged brightness called?
Talbot-Plateau Law
Which pathway is good at detecting flicker and movement?
magnocellular
What is the equation for the modulation(or the temporal contrast) of flickering light?
modulation = (amplitude of wave)/(luminance average)
What is the measure of how the visual system responds to different combos of temporal frequencies and modulations?
temporal modulation transfer function ( also calle temporal CSF)
Where is the high frequency cutoff higher: central retina or peripheral retina? 1. Why? 2
- mid-peripheral retina
2. more parasol RGCs
What are the pigments found in the macula? 1. What are the useful for? 2
- lutein and zeaxanthin
2. protective effect against AMD
What percentage of the neurons in the LGN are magno? 1. What is their color opponency like? 2. Their response duration? 3. Response timing? 4. Receptive field? 5. Better response to high or low spatial frequencies? 6
- 10%
- none (weak)
- more transient (good temporal resolution)
- fast
- large (with center-surround)
- low
Which pathway is good for providing info regarding the spatial details of a stimulus?
parvocellular
What is the idea that the brightness of a flash of light depends on its duration called? 1. Does a longer or shorter duration make for a brighter light? 2
- Broca-Sulzer effect
2. shorter duration
Where is the peak sensitivity for the TMTF?
at an intermediate frequency
Which layers of the LGN received input from the contralateral eye?
layers 1, 4, 6
What is the MAR range for the photopic system? 1. Scotopic? 2
- 0.5 to 1’
2. 5 to 10’
When the magno layers are lesioned what happens to: wavelength discrimination? 1. Detection of high-frequency flicker? 2. What type of spatial frequencies have reduced contrast sensitivity? 3
- unaffected
- reduced
- low
What is the idea that different qualitative attributes of the visual image are separated out within the retina into and carried onto the brain (LGN) via different pathways?
Parallel pathways
What does the heterochromatic flicker technique provide measurements of? 1. How does this compare to the direct comparison method? 2
- luminance efficiency curves
2. better than direct comparison
Do rods have a higher or lower CFF? 1. Why? 2
- lower
2. rods have a higher temporal summation so worse resolution
What is the disappearance of stimuli that are relatively stable on the retina called? 1. What must be true of the image stimuli? 2
- the Troxler effect
2. edges must be gradually changing luminance (blurry borders)
Which layers of the LGN received input from the ipsilateral eye?
layers 2, 3, 5
What is the clinical application of the heterochromatic flicker technique?
measure ocular pigment levels (MPOD)
What neurotransmitter do RGCs release onto the cells of the LGN?
glutamate
What is the unit for the frequency (number of cycles per second)?
hertz (Hz)
What is it called when a subject can’t distinguish flickering light from continuous light?
flicker fusion
Why does low-frequency roll-off of the TMTF occur?
the cones are already getting feedback to reduce light response as the light stimulus turns off
What is the difference of center-surround antagonism in the LGN compared to the RGCs?
- more robust
2. diffuse light usually results in minimal responses
What is the physiology of high-frequency cutoff of the TMTF?
due to firing rates of neurons (faster RGC response = more transient response = better temporal resolution)
When the parvo layers are lesioned what happens to: wavelength discrimination? 1. Detection of high-frequency flicker? 2. What type of spatial frequencies have reduced contrast sensitivity? 3
- reduced
- unaffected
- high
What is their color opponency like for the koniocellular pathway? 1. The response duration? 2. Response timing? 3. Receptive field? 4. Better response to high or low spatial frequencies? 5
- limited
- slow
- slow
- large (without center-surround)
- low
