Higher visual processing

Question 1

What sort of visual information do M and P ganglion cells transmit?

Answer 1

M - motion

P - colour

Question 2

Where do M and P ganglion cells terminate in the primary visual cortex?

Answer 2

M cells - layer 4Ca

P cells - layer 4Cb

Question 3

Which layer of the visual cortex is the input layer for sensory information?

Answer 3

Layer 4

Question 4

How is information from M and P ganglion cells segregated?

Answer 4

Input to different regions of the visual cortex

M - 4Ca

P - 4Cb

Question 5

Where do cells in layer 4Ca of the visual cortex project to?

Answer 5

Layer 4B

Question 6

Describe the characterisitcs of neurons in layer 4B of the visual cortex?

Answer 6

Directionally selective neurons

Only respond to stimuli moving in a certain direction

Allow us to encode motion

Question 7

How much of the brain is involved in vision?

Answer 7

Approximately 40%

V1 + extrastriate cortical areas

Question 8

What are the two parallel visual streams of information that originate from the visual cortex?

Answer 8

Dorsal pathway: takes info from M cells, for ‘where?’

Ventral pathway: takes info from P cells, for ‘what?’

Question 9

What is area MT?

What is its function?

Answer 9

Middle temporal lobe

Area specialised for processing object motion (objects moving beyond a certain speed)

Culmination of dorsal stream

Question 10

Describe the inputs to area MT?

Answer 10

Receives retinotopic input from a number of cortical areas incl V2 and V3

Receives input from cells in Layer 4B of V1

Question 11

Which cortical area is specialised for processing object motion?

Answer 11

Area MT

Question 12

Describe the neurons in area MT?

Answer 12

Large receptive fields

Respond to stimulus movement (respond to different types of motion)

Directionally selective

Question 13

Describe how different colours a perceived?

Answer 13

Mixing of primary colours (blue, red and green)

Determined by how much each of the three colours signlas down to the ganglion cells (combination of all three cones)

Question 14

Describe the receptive field of P ganglion cells?

Answer 14

Colour opponent centre-surround

Question 15

How is comparison achieved in colour vision?

Answer 15

Comparison of what ganglion cells have been told comes from photoreceptors

Depends on centre-surround receptive field of ganglion cells

Comparisons: red and green, blue and yellow

Question 16

Describe what happens when a red/green centre-surround ganglion cell is stimulated with red light in its centre?

Answer 16

PRs hyperpolarised by red light > BCs > ganglion cell is depolarised by light

Question 17

Describe what happens when a red/green centre-surround ganglion cell is stimulated by green light in the periphery?

Answer 17

Green cones stimulated in periphery > hyperpolarised > HCs hyperpolarised by light > singal back to red cone > maximally inhibited

Question 18

Describe what happens when a red/green centre-surround ganglion cell is stimulated by red light in both the centre and periphery?

Answer 18

Get an in between response > brain deletes it

Brain only wants maximal stimulation or maximal inhibition

Question 19

Describe what happens to information from the P ganglion cells?

Answer 19

Inputs into V1, then travels down ventral stream to Area V4/Area IT

Question 20

Describe the properties of the neurons in Area V4/IT?

Answer 20

Large receptive fields

Both colour and orientation selective

Question 21

What is the function of Area V4?

Answer 21

Important for perception of shape and colour

Question 22

What is the function of Area IT?

Answer 22

Important for object recognition, including faces

Neurons respond to wide variety of abstract shapes and colours

Question 23

What is blindsight?

Answer 23

Ability in some blind people for motion detection system to still work

Pathway from LGN to area MT

Question 24

What is the difference between colour vision deficiencies and colour blindness?

Answer 24

Colour vision deficiencies: unable to perceive some colours, confuse certain colours

Colour blindness: inability to perceive any colour

Question 25

How may colour vision deficiencies arise?

Answer 25

Can be acquired or inherited

More commonly inherited

Question 26

Describe the three types of colour vision defects?

Which is most common?

Answer 26

Monochromacy: only have one type of cone

Dichromacy: have only two functional cones

Anomalous trichromacy: have all three cones, but one of them express abnormal pigment and doesn’t work the same as normal cones (most common)

Question 27

How are people that lack:

i) red cones
ii) blue cones
iii) green cones described?

Answer 27

i) Protanope
ii) Deutanope
iii) Tritanope

Question 28

How are people that have abnormal:

i) red cones
ii) green cones
iii) blue cones described?

Answer 28

i) Protanomal
ii) Deutanomal
iii) Tritanomal

Question 29

What is the most common type of colour vision defetc?

Answer 29

Deutanomal: have green cone, but it doesn’t work properly

Question 30

How is colour blindness tested?

Answer 30

Detection test (plates with numbers)

More than 6 wrong > other testing to determine which type