Vision

Question 1

What does the retina contain?

Answer 1

Photoreceptors

Question 2

What do photoreceptors do?

Answer 2

Convert light to changes in membrane potential

Question 3

What is the output of the retina via?

Answer 3

Ganglion cells

Axons in the optic nerve

Question 4

What do bipolar cells do?

Answer 4

Link photoreceptors to ganglion cells

Question 5

What do horizontal cells do?

Answer 5

Mediate lateral interactions

Question 6

What are the two types of photoreceptors in the retina?

Answer 6

Rods

Cones

Question 7

What are cones?

Answer 7

Less sensitive than rods

Operate optimally in daylight

Question 8

What are rods?

Answer 8

More sensitive than cones (x1000)
Operate optimally in low light levels (twilight)
Saturated in daylight

Question 9

Where are cones?

Answer 9

Concentrated at the fovea

Question 10

Where are rods?

Answer 10

More numerous in the peripheral retina

Question 11

What do rods and cones differ in?

Answer 11

Connectivity
Sensitivity
Distribution

Question 12

What do cones connect?

Answer 12

1 to 1 with bipolar and ganglion cells

Question 13

What do rods converge on?

Answer 13

Ganglion cells

Question 14

How many types of cones does the retina contain?

Answer 14

3 types

Question 15

What are these types of cones?

Answer 15

Maximally sensitive to a different wave length of light
Blue cones
Green cones
Red cones

Question 16

What is the trichromacy theory?

Answer 16

The colour we perceive is largely determined by the relative activation of blue, green and red cones

Question 17

What can be used to test for red-green colour-blindness?

Answer 17

Ishihara’s cards

Confusion of shades of red and green

Question 18

How many people have red-green colour-blindness?

Answer 18

2% of the male population

Question 19

What is missing in individuals with red-green colour-blindness?

Answer 19

Cones sensitive to red light are missing

Question 20

What is a receptor field?

Answer 20

Area of retina it receives input

Question 21

What is on centre retinal ganglion?

Answer 21

Light is stimulus that excites them

Question 22

What is the off centre retinal ganglion?

Answer 22

Stimulated by shadow

Question 23

How are ganglion cells organised?

Answer 23

Concentric centre surround (excitatory-inhibitory) receptive field organisation

Question 24

What is the illumination responses to stimulation in the centre cancelled by?

Answer 24

The response to stimulation in the surround

Question 25

What are maximum response to in luminance contrast?

Answer 25

Light-dark boundaries

Question 26

How many M type cells are involved in luminance contrast?

Answer 26

10%

Question 27

How many P type cells are there?

Answer 27

90%

Question 28

What are P type cells sensitive to?

Answer 28

Different wavelengths

Question 29

What do colour-opponent centre surround receptive fields respond to?

Answer 29

Light of one wavelength in the centre is cancelled by light of another wavelength in the suround

Question 30

What colour pairs cancel?

Answer 30

Red-green | Blue-yellow

Question 31

Where do the optic nerves of each eye join?

Answer 31

Optic chiasm

Question 32

Where do fibres from the nasal retina meet?

Answer 32

Both eyes cross (partial decussation) | Cross at the optic chiasm

Question 33

What do optic tracts carry information about?

Answer 33

Info relating to visual hemisfield

Question 34

Where do optic tracts project on to?

Answer 34

Lateral genicualte nucleus (LGN) of the thalamus

Question 35

What does the LGN consist of?

Answer 35

6 layers

Question 36

What types of cells are in the LGN?

Answer 36

M-type and P-type

Question 37

Where do M and P cells project?

Answer 37

M- magnocellular layers (1 and 2) | P- parvocellular layers (3-6)

Question 38

What are the receptive field properties of the LGN neurones similar to?

Answer 38

Ganglion cells

Question 39

What are LGN neurones primarily?

Answer 39

A relay to the cortex- information from different ganglion cells and different eyes is carried by segregated parallel lines

Question 40

Where do thalamic relay neurones from the LGN terminate?

Answer 40

Layer IV of primary visual cortex

Question 41

Where does information from 2 eyes project?

Answer 41

Alternating bands called ocular dominance columns

Question 42

What do simple cells show?

Answer 42

Orientation selectivity

Question 43

What are the different cortical areas that are specialised for different visual processing tasks?

Answer 43

V1 V5 V4

Question 44

What does the V1 do?

Answer 44

Parcels out information to other specialised areas of cortex

Question 45

Where do thalamic neurones terminate in V1?

Answer 45

Layer IV

Question 46

What are cortical neurones like in V1?

Answer 46

More elaborate receptive fields- several relay neurones feed into them

Question 47

What does V1 also extract?

Answer 47

Additional information | E.g. orientation, selectivity, direction selectivity

Question 48

What does V1 parcel out?

Answer 48

Visual information to other specialised ares of the cortex

Question 49

What is V5 specialised for?

Answer 49

Motion analysis- stimulated by viewing a moving pattern of black and white squares

Question 50

What do lesions of V5 lead to?

Answer 50

Akinetopsia | Can't see objects if they move

Question 51

What is V4 specialised for?

Answer 51

Colour vision- stimulated by viewing an abstract pattern of colours

Question 52

What do lesions of V4 lead to?

Answer 52

Achromotopsia | See only in shades of grey