Lecture 5: Vision II Flashcards
Describe how visual field projection onto the retina is similar to a camera.
Similarities to a camera
• Lens of the eye projects inverted
image and flipped L to R
• Pupil acts like the aperture
What parts of the visual field do the left nasal retina pick up? What about the right nasal retina?
Outside left visual field
Outside right visual field
Describe the breakdown of the visual field
Superior vs Inferior
Left vs Right
Binocular visual field vs monocular peripheral vision
foveal region
What happens at the optic chiasm?
information from the nasal retina of left and right eye cross over to contralateral sides.
What two optic tracts carry information from the right visual field?
right nasal retina
left temporal retina
Where do the retinal ganglion cells project to?
Lateral geniculate nucleus (90%)
superior colliculus
suprachiasmatic nucleus
pretectum
Describe the order that the retinal ganglion cells (RGN) project? What are the layers?
RGN project in an orderly manner
• Each LGN has a retinotopic
representation of contralateral half of
the visual field
• Fovea is more represented that
periphery (about half is fovea)
• Magnocellular (Ventral 2 layers)
• Receive input from m-ganglion cells
• Terminate in upper part of layer 4C in V1
• High temporal resolution and contrast based
• Parvocellular (Superior 4 layers)
• Receive input from P retinal ganglion cells • Terminate in lower part of 4C in V1
• High spatial information and color
• Koniocellular pathway (interlaminar)
• Receive input from K ganglion cells
• Project to layer 2/3 in “patches”
• Plays a role in color vision, carrying input from short wavelength cones
• Magnocellular (Ventral 2 layers) of the LGN
Receive input from m-ganglion cells
• Terminate in upper part of layer 4C in V1
• High temporal resolution and contrast based peripheral vision
Parvocellular (Superior 4 layers) of the LGN
Receive input from P retinal ganglion cells • Terminate in lower part of 4C in V1
• High spatial information and color
Koniocellular pathway (interlaminar) layer of LGN
Receive input from K ganglion cells
• Project to layer 2/3 in “patches”
• Plays a role in color vision, carrying input from short wavelength cones (blue hues)
A portion of the RGN project to the superior colliculus. What does it do?
Retinal ganglion cells project directly to the superficial layers and form a map of the contralateral visual field
- Cells from the superior colliculus project through the pulvinar nucleus (thalamus) to cerebral cortex
- Indirect pathway from retina
- ‘Blindsight’
• Heavily involved in saccadic eye
movements
• Damage to this region results in
slower, smooth pursuit type eye movements
What is blind sight?
When the eyes are damaged but RGN still project to the superior colliculus. It’s a phenomena where they can still detect stimulus (color of light) at a higher-than-chance rate even when they can’t see.
Some of the RGN project to the suprachiasmatic nucleus. WHat does it do?
SCN is involved in entrainment of circadian rhythms
• Located within the hypothalamus, at the base of the diencephalon

Some of the RGN project to the pretectum. What does it do?
Within the midbrain
• Is the initial component of the pupillary light
reflex pathway
• Clinically significant
• Pupils of both eyes should respond identically to a light stimulus
• Help to locate location of lesion • ER test for brainstem function
After RGN project to the LGN, where do the LGN projections go?
LGN projections sweep back to primary visual cortex (V1 in the occipital lobe)
Describe the pathways of the projections of LGN.
Inferior fibers (carrying information about the superior visual field) sweep around the lateral horn of the ventricle within the temporal lobe and is referred to as Meyer’s loop
- Superior fibers (carrying information about the inferior visual field) travel through the parietal lobe
- End up on the inferior and superior banks of the calcarine sulcus
Describe some different visual field deficits.
Describe the striate cortex
Striped
Half of V1 id dedicated to the fovea
Spatiotemporal Tuning in Primary Visual Cortex
Tuning to angular orientations
They also found movement vector preferences in other cells, that fired when movement was in a specific direction
Anatomical organization of V1
- Approximately 2mm thick, laminar in organization
- 6 Layers total- all gray matter
• Layers identified based on density and size of
neurons
- Most input from LGN arrives at 4C (spiny stellate cells)
* 4C communicates with other layers of V1 - Pyramidal cells in superficial layers project to extrastriate cortex
**• Ascending outputs**
• Pyramidal cells in deeper layers project to subcortical regions
**• Descending outputs**
Functional organization of V1
- Organized by columns
- Neurons in the same position along the surface of the cortex, but in different layers, share receptive fields and orientation preference
- As cells are recorded along the surface of the cortex, response properties change
- Receptive field shifts, can still be overlapping
- Orientation preference will shift, but in well organized manner
What is the pinwheel organization of the V1
Orderly mapping of orientation preference
- To ensure that all parts of the visual field have the same capacity to perceive orientations
- Orientation preference has a “pinwheel” arrangement
Describe binocular vision
Stereopsis is the sense of depth that results from viewing the world with two eyes
• Each eye receives a slightly different angle
• Objects in front or behind fixation project onto different non-corresponding points on each retina
- Creates ocular ‘disparity’
- Neurons within V1 (and higher) visual areas that are sensitive to disparity
- Far cells
- Near cells
- Tuned zero cells
• Also uses information about eye vergence
- Only good for about 6m (20ft)
- Certain professions require stereopsis
Show the extrastriate visual areas
Describe the two-stream theory of cortical vision
Two processing streams identified
Dorsal stream: vision for action (where)
Ventral stream: vision-for-perception (what)
Describe some specialized tasks and how they relate to the two-stream visual path theory.
Neuropsychological evidence showing ventral deficits (can’t decipher object orientation) but can place objects into a certain orientation that they know about (dorsal-motor; where)
Specialized tasks: our brain views dots differently (ventral perception) but our dorsal stream has no problem helping our grip size to be the same for the two “different” balls
Achromatopsia (what region does it affect)
V4 (color processing)
therefore black adn white vision
akinetopsia (what region does it affect)
V5/ hMT
Process movement of visual field.
World appears in flashes
What is visual form agnosia
Can’t identify objects (details, but can’t say “it’s a bunny”)
Damage to lateral occipital lobe
Simultanagnosia
Damage to parietal lobe
Can’t attend to two objects at once
(works with dorsal stream, can’t say “where” two separate things are)
What are the two associative agnosias?
prosopagnosia (facial recognition)
word agnosia
Prosopagnosia
damage to the fusiform gyrus
issues with favial recognition
Word agnosia
damage to anterior occipital lobe
can’t tell a string of letters is a word anymore, even if they could read before.
