Lecture 10 - introduction to visual pathways and circuits

Question 1

What stream is concerned with the recognition of an object?

Answer 1

ventral (what) stream

Question 2

What stream is concerned with spatial location?

Answer 2

dorsal (where) stream

Question 3

What visible light range is our visual system sensitive to?

Answer 3

380nm (red) to 740nm (purple)

Question 4

Describe the journey of light/information from entering the eye to the brain.

Answer 4

1. information goes to the cornea
2. anterior chamber
3. pupil
4. lens
5. vitreous humour
6. retina and fovea
7. optic nerve
8. brain

Question 5

How is the retina organised?

Answer 5

• seven cell types
• three nuclear layers
• 2 synaptic layers

Question 6

What are the three nuclear layers of the retina?

Answer 6

• outer nuclear layer
• inner nuclear layer
• ganglion cell layer

Question 7

What type of cells does the ONL contain?

Answer 7

photoreceptors - rods and cones

Question 8

What type of cells does the INL contain?

Answer 8

horizontal cells
bipolar cells
amacrine cells

Question 9

What type of cell does the GCL contain?

Answer 9

ganglion cells

Question 10

What are the 2 synaptic layers of the retina?

Answer 10

• outer plexiform layer
• inner plexiform layer

Question 11

What does the OPL make connections between?

Answer 11

synaptic connections between photoreceptors, horizontal and bipolar cells

Question 12

What does the IPL make connections between?

Answer 12

synaptic connections between bipolar, amacrine and ganglion cells.

Question 13

What photoreceptors are responsible for peripheral vision?

Answer 13

rods (120 million) distributed through the retina

Question 14

Describe rod cells.

Answer 14

1. responsible for our ability to see in dim light (scotopic vision)
2. high sensitivity
3. monochromatic
4. low resolution images
5. good motion detection

Question 15

What photoreceptors are responsible for central vision?

Answer 15

cones (6 million) concentrated around the fovea

Question 16

Describe cone cells.

Answer 16

1. work only in daylight (photopic vision)
2. low sensitivity
3. chromatic
4. high spatial acuity
5. narrow angle of coverage

Question 17

How many types of cone cells are there?

Answer 17

3 - S, M and L

Question 18

What are ganglion receptive fields?

Answer 18

each part of a scene is detected by many photoreceptors.
the receptive field is the part of the retinal ganglion cell that can gather information from the visual field

Question 19

What do ganglion cells respond best to and why is this important?

Answer 19

they respond best to contrast not light.
this means they have antagonistic centre-surround receptive fields (the centre must be mainly light while the surround mainly dark vice versa)

Question 20

Do ganglion cells on the fovea have a small or large receptive field?

Answer 20

small - can see more details

Question 21

Do ganglion cells in the periphery have a small or large receptive field?

Answer 21

large - can see less details

Question 22

Projections from the retina to central targets are organised in what fashion?

Answer 22

topographic

Question 23

What does LGN stand for?

Answer 23

lateral geniculate nucleus

Question 24

What is the role of the LGN?

Answer 24

1. brings retinotopic maps from both eyes into register to make it easier for the cortex to combine inputs from the two eyes.
2. other functions - not as well understood.

Question 25

Describe the primary visual cortex V1.

Answer 25

Stria of Gennari (band of myelinated axon (from LGN cells)) running parallel to the surface of the cortex along the calcimine fissure of the occipital lobe.

Question 26

How many layers does V1 have?

Answer 26

-6 - main input from LGN to layer IV

Question 27

How is the striate cortex organised?

Answer 27

in ocular dominance columns, alternating between left and right eyes

Question 28

What are the 3 main cell types in V1?

Answer 28

1. simple cells 2. complex cells 3. hypercomplex cells

Question 29

Describe simple cells.

Answer 29

- sum inputs from LGN with neighbouring RFs to build an elongated RF - orientation selective - monocular or binocular - have separate on and off subregions - perform length summation

Question 30

Describe complex cells.

Answer 30

- receive input from simple cells - orientation selective - spatially homogenous RFs so no on/off subregions - nearly all binoculars - perform length summation

Question 31

Describe hypercomplex cells.

Answer 31

- inhibitory flanks in the ends of RF - response increases with increasing bar length up to some limit - as the bar becomes longer, the response is inhibited.

Question 32

Describe the pathway of the ventral (what) stream.

Answer 32

V1 > ventral peristriate cortex > inferotemporal cortex

Question 33

Describe the pathway of the dorsal (where) stream.

Answer 33

V1 > dorsal peristriate cortex > posterior parietal cortex