Higher Visual Processing

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What are the 3 parts of the visual system? What is the biggest part?: 1.optical system
2.phottransduction (rods and cones)
3.computation (*biggest part)
How much of the brain is required for visual capacity?: 1/3
Injury to what part of the brain causes visual disturbance/loss?: back of th head (occipital lobe)
What is the visual pathway?: photons reach retina -> optic nerve -> optic chiasm -> optic tract ->lateral geniculate nucleus of thalamus (LGN) -> optic radiation to primary visual cortex
How do humans visual abilities differ from a camera?: we can record and perceive
What are the major targets of retinal ganglion cells?: retinal recipient nuclei (i.e. LGN)
What are retinal recipient nuclei?: groups of neurons that get direct input from retina
Where do 90% of retinal ganglion cells terminate? What is this system responsible for?: in LGN;
conscious vision
Where do the remaining retinal ganglion cells terminate?: Superior colliculus (5-7%)
Suprachiasmatic Nucleus
Pretectum
Accessory optic system
What is the suprachiasmatic nucleus mainly responsible for?: circadian rhythm regulation
What is the pretectum mainly responsible for?: pupillary light reflex
What is the accessory optic system mainly responsible for?: stablilizing one's gaze
What are saccades? What are they moderated by?: rapid pointing eye movements;
the superior collicululs
*Explain the pupillary light reflex circuit.: photons reach retina ->
optic nerve -> optic chiasm ->
pretectal olivary nucleus sends fibers to BOTH Edinger-whestphal nuclei ->
CN III ->
Ciliary ganglion ->
Ciliary nerves ->
iris constrictor muscles
Out of the nearly one million ganglion cells how many take the route on each side for the pupillary light reflex?: a few thousand
What will lesions to the following areas result in: 1. LGN -> cortex pathway 2. cortical lesion 3. retina -> LGN -> primary visual cortex 4. lesions in cortex other than primary visual cortex: 1. comeplete blindness (loss of conscious vision, can still have some reflexes, eg. pupillary)
2. can act on visual info but don't have conscious awareness of it
3. specific visual field defects
4. subtle visual defects
What is blindsight?: involves a very limited ability to perform visually guided tasks when there is destruction along the visual tract; the apparent absence of conscious perception
What do lesions to the extrastiate visual cortex cause?: more subtle defects in a person's ability to comprehend what they are looking at, but with normal visual fields and acuity
What is the LGN a part of?: thalamus
What is oculus sinistra and oculus dextra?: O.S. = left eye
O.D. = right eye
T/F: Fibers from each eye terminate on occiptial cortex bilaterally.: true
Which fibers coming from the retina cross at the optic chiasm?: medial fibers
What does injury to the right optic nerve reuslt in?: right eye blindess
What does a lesion at the optic chiasm lead to? What is this?: bitemporal hemianopia;
lateral (peripheral) half of vision in each eye is knocked out
What does a lesion to the right optic tract cause? What is this?: Left homonymous hemianopia;
left half of visual field is knocked out in both eyes
What does a lesion to the right Meyer's loop (in cortex) result in? What is this?: Left Superior Quadrantanopia;
superior lateral quadrant is knocked out equally in both eyes
What are some synonymous names for the primary visual cortex?: striate cortex, area 17, area V1
What might cause lesions in the visual pathway?: pituitary tumors
What are the right and left monocular crescents attributed to? Which eye can see a little further?: the nose getting in the way of vision;
the right eye
Most of our visual field is (binocular/monocular).: binocular
Where does the initial inversion in the visual field happen? Where is it made right-side-up?: retina;
cortex
What is the most expensive effort in vision?: analyzing and computing the image in the brain
We have a lot more detail in the ______ than we do in the ______.: fovea;
periphery
Which area requires a lot more cicuitry than other areas to interpret its input?: the fovea
T/F: Points that are near each other on the retina will not necessarily be near each other in the cortex.: F, they will be near each other in the cortex too
What is the cortical magnification factor?: the area of the fovea is larger than the rest (relative sizes and orders have been distorted)
where does the greatest amount of visual work occur?: 0 degrees
1.What are M cells? P cells? 2.Sensitive to color contrast? 3.Sensitive to low contrast stimuli? 4.Sensitive to temporal frequency? 5.Sensitive to spatial frequency? 6.Respond to quickly moving stimuli? 7.See (broad/fine) de: 1.Magno (large) and Parvo (small) ganglion cells that leave retina in a parallel pathway
2.M=no, P=yes
3.M=yes, P=no
4.M=yes, P=no
5.M=no, P=yes
6.M=yes, P=no
7.M=broad, P=fine
Explain M cells.: Magno ganglion that leave the retina in parallel pathways
not sensitive to color contrast
sensitive to low contrast stimuli & temporal frequency
low sensitivity to spatial frequency (don't see fine detail)
respond to quickly moving objects
Explain P cells.: Parvo (midget) ganglion cells that leave retina in a parallel pathway
high sensitivity to spatial frequency (see fine detail)
see color
not sensitive to temporal frequency (don't respond to quickly moving stimuli)
How do magno and parvo ganglion cells leave the retina?: in a parallel pathway
T/F: Multiple systems and regions of the brain are needed to analyze an image.: True
Where does the division of labor in vision occur?: the retinal ganglion cells
Do M and P cells cross in the chiasm?: no
Which fibers from the 6 layers of the LGN cross?: 1,4,6
What is the mnemonic to remember which fibers cross in the LGN?: 1,4,6 cross the river Styx
2,3,5 stay on the same side
Which layers of the LGN are M-cell layers? Which are P cell layers?: 2 most ventral (1,2) are M cell
4 most dorsal (3-6) are P cell
Is there binocular computation between M and P cell layers bilaterally?: no
What are R cells? What synapses on R cells?: Relay cells in the LGN that relay info from the retina to the visual cortex;
interneurons (most are not directly from retina)
What does LGN receive inputs from?: brainstem, visual cortex, retina, and perigeniculate nucleus (PGN)
Are there more interneurons or relay neurons in the LGN?: interneurons
Where is most of the primary visual cortex in humans? where is the fovea? where is the periphery?: in the calacrine sulcus;
near the surface;
deeper
What is the striate cortex?: heavy band of myelinated axons in layer 4, the stria of Gennari, about the only landmark you can see in the cortex without special stains
(synonym for the primary visual cortex)
What is the pathway from LGN to Area V1 called?: Thalamocortical or Geniculostriate pathway
What layer is the basic input area in the LGN?: layer 4
T/F: Retinal ganglion cells and LGN cells have radically symmetric fields.: True
T/F: You see no changes from LGN -> Area V1.: False, because V1 is very different from retina and LGN
What does V1 deal with with respect to images?: the orientation of the image
What do the ganglion cells of retina and LGN differentiate between?: on vs. off-center and on-surround vs. off-surround (not concerned with orientation of images)
What are the 2 basic types of cells in V1?: V1 simple cells & V1 complex cells
Describe V1 simple cells: What are they like? What is their optimal stimulus? What are they selective for: -like on-surround/off-surround cells in retina; have discrete excitatory and inhibitory subregions
-a vertical/angled strip of light flanked by darkness
-orientation
Describe V1 complex cells: Inhibitory/excitatory regions? What are they selective for? What are they concerned about?: -don't have inhib & excite regions
-orientation regardless of small shifts in position or changes in contrast
-only orientation
How would complex V1 cells note a change in an image?: only if there is a change in orientation
Which type of V1 cells are more precise in their detection of location of stimuli?: simple cells
What regions are obligatory for vision? What do the other regions do?: retina, LGN, V1;
allow us to see well (V2)
Is the striate or extrastriate visual cortex larger?: extrastriate
What is the Dorsal Stream? What cells does it involve and what do they tell us?: V1 -> V2 -> Posterior Parietal Cortex;
Magno cells;
where an object is in space
What is the Ventral Stream? What cells does it mainly involve and what do they tell us?: V1 -> V4 -> Inferior Temporal Cortex;
Parvo cells;
"what" we are seeing
What happens if you lesion the posterior parietal lobe in a primate?: it will have trouble with landmark discrimination in relation to other objects
What will happen if you lesion the inferior temporal cortex in a primate?: it will have trouble telling the different shapes apart
What kind of cells in V2? What is V2 closely associated with? Is it ventral or dorsal? What are its neurons similar to? Size of recpetive fields?: M and P cells
V1
neither ventral nor dorsal
V1 neurons
small receptive fields
What is V4? What does it deal with?: more ventral stream;
complex color and form/shape (spirals) properties
Describe IT (Inferior Temporal Cortex): Where? What is it important for? Size of receptive fields? type of cells?: ventral (last heirarchy of ventral stream)
distinguishing b/w 2 faces
large (~30 degrees)
What is prsopagnosia?: loss of the ability to recognize faces with no corresponding loss of acuity or visual field deficits
What is the Middle temporal cortex(MT)/V5 involved in? What is it a part of?: motion and perception of motion;
a small but significant part of dorsal stream

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