Lecture 5: Vision II

Question 1

Describe how visual field projection onto the retina is similar to a camera.

Answer 1

Similarities to a camera
• Lens of the eye projects inverted
image and flipped L to R
• Pupil acts like the aperture

Question 2

What parts of the visual field do the left nasal retina pick up? What about the right nasal retina?

Answer 2

Outside left visual field

Outside right visual field

Question 3

Describe the breakdown of the visual field

Answer 3

Superior vs Inferior

Left vs Right

Binocular visual field vs monocular peripheral vision

foveal region

Question 4

What happens at the optic chiasm?

Answer 4

information from the nasal retina of left and right eye cross over to contralateral sides.

Question 5

What two optic tracts carry information from the right visual field?

Answer 5

right nasal retina

left temporal retina

Question 6

Where do the retinal ganglion cells project to?

Answer 6

Lateral geniculate nucleus (90%)

superior colliculus

suprachiasmatic nucleus

pretectum

Question 7

Describe the order that the retinal ganglion cells (RGN) project? What are the layers?

Answer 7

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

Question 8

• Magnocellular (Ventral 2 layers) of the LGN

Answer 8

Receive input from m-ganglion cells
• Terminate in upper part of layer 4C in V1
• High temporal resolution and contrast based peripheral vision

Question 9

Parvocellular (Superior 4 layers) of the LGN

Answer 9

Receive input from P retinal ganglion cells • Terminate in lower part of 4C in V1
• High spatial information and color

Question 10

Koniocellular pathway (interlaminar) layer of LGN

Answer 10

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)

Question 11

A portion of the RGN project to the superior colliculus. What does it do?

Answer 11

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

Question 12

What is blind sight?

Answer 12

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.

Question 13

Some of the RGN project to the suprachiasmatic nucleus. WHat does it do?

Answer 13

SCN is involved in entrainment of circadian rhythms

• Located within the hypothalamus, at the base of the diencephalon


Question 14

Some of the RGN project to the pretectum. What does it do?

Answer 14

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

Question 15

After RGN project to the LGN, where do the LGN projections go?

Answer 15

LGN projections sweep back to primary visual cortex (V1 in the occipital lobe)

Question 16

Describe the pathways of the projections of LGN.

Answer 16

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

Question 17

Describe some different visual field deficits.

Answer 17

Question 18

Describe the striate cortex

Answer 18

Striped

Half of V1 id dedicated to the fovea

Question 19

Spatiotemporal Tuning in Primary Visual Cortex

Answer 19

Tuning to angular orientations

They also found movement vector preferences in other cells, that fired when movement was in a specific direction

Question 20

Anatomical organization of V1

Answer 20

• 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**

Question 21

Functional organization of V1

Answer 21

• 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

Question 22

What is the pinwheel organization of the V1

Answer 22

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

Question 23

Describe binocular vision

Answer 23

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

Question 24

Show the extrastriate visual areas

Answer 24

Question 25

Describe the two-stream theory of cortical vision

Answer 25

Two processing streams identified

Dorsal stream: vision for action (where)

Ventral stream: vision-for-perception (what)

Question 26

Describe some specialized tasks and how they relate to the two-stream visual path theory.

Answer 26

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

Question 27

Achromatopsia (what region does it affect)

Answer 27

V4 (color processing)

therefore black adn white vision

Question 28

akinetopsia (what region does it affect)

Answer 28

V5/ hMT

Process movement of visual field.

World appears in flashes

Question 29

What is visual form agnosia

Answer 29

Can’t identify objects (details, but can’t say “it’s a bunny”)

Damage to lateral occipital lobe

Question 30

Simultanagnosia

Answer 30

Damage to parietal lobe

Can’t attend to two objects at once

(works with dorsal stream, can’t say “where” two separate things are)

Question 31

What are the two associative agnosias?

Answer 31

prosopagnosia (facial recognition)

word agnosia

Question 32

Prosopagnosia

Answer 32

damage to the fusiform gyrus

issues with favial recognition

Question 33

Word agnosia

Answer 33

damage to anterior occipital lobe

can’t tell a string of letters is a word anymore, even if they could read before.