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SFS - Higher Visual Processing


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Visual system requires roughly how much of the brain for visual capacity?
What is the problem of processing visual information?
The forward problem of optics and the inverse problem of vision.
Injury to back of the head (occipital lobe) might induce what?
Visual disturbance or loss
Pathway of visual tract.
retina > optic nerve > optic chiasm > optic tract > lateral geniculate nucleus of thalamus > optic radiation to primary visual cortex
How do human visual abilities differ from a camera?
We record AND perceive
Major targets of retinal ganglion cells.
Retinal recipient nuclei
90% of retinal ganglion cells terminate here.
Four locations other than LGN that retinal ganglion cells terminate.
superior colliculus (5-7%), suprachiasmatic nucleus (circadian), pretectum (pupillary light reflex), and accessory optic system (stabilize one's gaze)
Rapid, pointing eye movements moderated by tehh superior colliculus.
a. Pupillary light reflex circuit pathway.
b. Out of nearly a million ganglion cells, how many take this route on each side for the reflex?
a. Photons reach retina > optic nerve > optic chiasm > pretectal olivary nucleus sends fibers to BOTH Edinger-Westphal nuclei > CN III > Ciliary ganglion > ciliary nerves > iris constrictor muscles
b. only a few thousand
Result of a lesion in the LGN > cortex. Can someone with a cortical lesion act on visual information?
Complete blindness, but some reflexes can remain. Yes, they can act on visual information, but have no conscious awareness of it.
Caused by lesions in retina to LGN to primary visual cortex system?

What about lesions in other parts of the cortex?
Specific visual field defects.

Lesions in other parts of the cortex will cause more subtle visual defects.
Involves a very limited ability to perform visually guided tasks when there is destruction along the visual tract; in the apparent absence of conscious perception. Will respond to certain visual stimuli, but they claim to see nothing.
Lesions here will cause more subtle defects in person's ability to comprehend what they are looking at. Normal visual fields and acuity.
Extrastriate cortex
What is:
a. OS
b. OD
a. oculus sinistra (left eye)
b. oculus dextra (right eye)
Injury to right optic nerve results in what?
OD blindness
Lesion at optic chiasm leads to what?
bitemporal hemianopia. Lateral half of vision in each eye is knocked out.
Lesion to right optic tract will result in what?
left homonymous hemianopia (left half of visual field knocked out in both eyes)
Lesion to right Meyer's loop will result in what?
Left superior quadrantanopia (superior lateral quadrant is knocked out equally in both eyes)
Lesion to visual cortex will result in what?
Left or right homonymous hemianopia with macular sparing.
Three other names for primary visual cortex.
Striate cortex, Area 17, Area V1
Possible cause of lesions to visual system?
pituitary tumors
Mapping in visual cortex.
Retinotopic map. Most of primary visual cortex is in the calcarine sulus, while the fovea is near the surface. Periphery is deeper.
Attributed to the nose getting in the way of vision. Allows right eye to see further right than left eye can, and the inverse, etc.
Right and left monocular crescents
Most expensive effort in vision.
analyzing and computing the image
Part of the retina with a lot more detail than the periphery. Lot more information to analyze. Has a larger, strecthed out retinotopic map in cortex.
Term describing larger representation of fovea than rest of eye on the visual cortex.
Cortical magnification factor. Greatest amount of visual work occurs at 0 degrees.
Names for LARGE and SMALL ganglion cells leaving the retina in a parallel pathway.
MAGNO (large) and PARVO (small) ganglion cells.
Ganglion cells not sensitive to color contrast, but have higher sensitivity to low contrast stimuli and temporal frequency, and lower sensitivity to spatial frequency (don't see fine detail.
M cells
Ganglion cells that respond to quickly moving objects (high temporal) and only see broad detail (low spatial).
M cells
Ganglion cells that have higher sensitivity to spatial frequency, and see color.
P cells
Ganglion cells that do not respond to quickly-moving stimuli, but process fine detail.
P cells
Ganglion cells that cross.
1, 4, 6
Ganglion cells that do not cross.
2, 3, 5
The two most ventral layers are what type of cell layers? The 4 most dorsal layers are what type of cell layers?
M-cell layers; P-cell layers
Is there binoculular computation between M & P cell layers bilaterally?
Are most of the synapses on relay cells in the LGN from the retina?

What cells make local connections?

LGN receives inputs from where else?


Brainstem, visual cortex (feedback), and peri-geniculate nucleus
Are there more interneurons than relay neurons?
Layer 4 of the six visual cortex layers.
Stria of Gennari. Visual cortex has expanded 4th layer.
LGN to Area V1 pathway.
Thalamocortical or geniculostriate pathway.
Deals with orientation of image, unlike ganglion cells of retina and LGN, which only differentiate between on/off center and surround.
Area V1
V1 cells that have discrete excitatory and inhibitory subregions like retinal ganglion cells, but RF subregions are not radially symmetric. Cell doesn't respond to uniform strip of light
V1 simple cells
V1 cells that do not have discrete excitatory or inhibitory regions. Selective for orientation. Gerneralize and can be more abstract.
V1 complex cells
If you had an ellipse and reversed the pink middle and gray sides, which V1 cells would recognize the difference?
Simple cells
While retina > LGN > V1 are obligatory for vision, what allows us to see well?
Rest of the regions (V2)
Dorsal stream pathway.

What type of cells does it involve and what do they tell us?
V1 > V2 > MT > Post. parietal cortex

Magno/M cells. Tells us "where" an object is in space.
Ventral stream pathway.

What type of cells does it involve and what do they tell us?
V1 > V4 > Inf. temporal cortex

Involves mostly parvo/P cells and tells us "what" we are seeing.
A lesion where will result in trouble with landmark discrimination in relation to other objects?
posterior parietal lobe
A lesion where will result in trouble telling different shapes apart?
Inferior temporal cortex
Cortical area closely associated to V1, higher level of abstraction as it fill in the details from contextual information.
V2 (has both M and P cells) and is neither ventral nor dorsal.
Cortical area that is more ventral stream and deals with complex color and form/shape (spirals) properties
Cortical area (ventral stream), with high specificity in distinguishing between two faces. Can have large RF, but still high specificity.
IT - inferior temporal cortex
Loss of the ability to recognize faces with no corresponding loss of acuity or visual field defects.
Cortical area inovlved in motion and perception of motion. Small component of the dorsal stream.
MT (V5) Middle temporal cortex

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