Lecture 8 Flashcards
RGC Pathway
RGC axons → optic nerve → optiv chiasm → brain many regions
*60% cross hemispheres - nasal *
temporal stay
Conscious vs unconscious vision
Conscious: LGN → VI (striate cortex)
Subconscious: most other pathways
Where is:
circadian rhythm
head & eye movement
pupillary light reflex
(hypothalamus)
Circadian rhythm: suprachiasmatic nucleus
RGCs express melanopsin, photosensitive
Head & eye movement: superior colliculus
Pupillary light reflex: RGCs → protectum → EWN → oculomotor nerve → ciliary ganglion → constrictor muscles of iris → pupil diameter increases!
(monocular stimuli → biocular response)
Optokinetic reflex (what, pathway, blocking)
What:
stabilizing moving scenes
both saccade (fast) & smooth pursuit (slow)
Path:
dsRGCs → nucleus of optic tract → cranial nerves for eye muscles
Blocking: blocking directional selectivity REMOVES reflex
Primary visual pathway (inc. flipping & Meyer’s loop)
Info flipped horizontally & vertically
Meyer’s loop: superior/inferior VF
take opposite paths
(see 8.5)
Magnocellular layers
Ventrals LGN layers
Project to 4Cα, 4 layers
From parasol GCs
Transient & motion sensitive responses
Parvocellular layers
Dorsal LGN layers
Project to 4Cβ, 2 layers
From midget GCs
Sustained responses & color info
Koniocellular layers
Interdigitale
Project to patches in layer 2/3 of V1
Not parasol or midget cells
Retinotopic map
Foveal region overrepresented
Neighboring parts together
Deficits & striabisneus
(see 8.10)
Striabismus: eyes don’t properly align
esotropia, exotropia, amblyopia: →←, ←→, untreated
Properties:
What do cells care about?
What excites V1?
Care about: shape, orientation, direction, size, temporal ƒ
V1: small circles don’t excite, but lines do
(Hubel & Weisel)
PVC Architechture
6 layers: 2/3 are grouped, 4 divided 4A-C
Projections:
- LGN axons → 4C & a bit of 4A
- superficial pyramidal cells → elsewhere
- deeper PCs → sub-cortically (includes LGN & superior colliculo)
Orientation:
↕️ columns - same location represented
↔️ different feature selective responses
Orientation pinwheels
In a given receptive field area, all orientatios are present (every 1 mm)
Binocular vision
Starts in PVC
Input in separate LGN layers (layer 4)
Stereopsis (depth) starts in V1
far, near & tuned zero to compare
Aperture problem
V1 receptive fields are small → direction of motion difficult
MT integrates for overall direction
