Colour Vision Theory

Question 1

What is colour vision?

Answer 1

ability to differentiate between wavelengths of light within visible light

Question 2

How can we detect different colours?

What is the Principle of univariance?

Answer 2

Ability to detect difference in colour is due to cone response to light.
Multiple cones mean colour info is known bc they respond to different wavelengths - comparing the response @ RGC level allows us to perceive which colour we are seeing.
e.g. if only L cones are activated, then it’s known that it’s red light even though no wavelength info is present

The wavelength info is lost, but intensity info is kept

Question 3

What are the three opponencies?

Answer 3

Blue/yellow
Green/red
Black/white

Question 4

What is the set up of a blue on cell?

Answer 4

Not centre surround

Question 5

What is the set up of a red on cell?

Answer 5

Centre surround

Question 6

Where is the receptive field of a yellow on cell?

Answer 6

In the LGN

Question 7

What is trichromatic theory and how was it proven?

Answer 7

Colour vision relies on 3 receptors
Proven using colour matching experiments which found that any test colour could be matched by combining 3 other wavelengths (sometimes 2)

Question 8

Why can’t colour be seen when there’s only one cone?

Answer 8

Principle of univariance - more than one cone needed in order to compare signals as wavelength info is lost.

Question 9

How does a monochromat perceive different wavelengths?

Answer 9

Higher wavelength receives more intense reaction as sensitivity to higher wavelengths is increased

Question 10

How can a monochromat tell if a light is just brighter or a different wavelength?

Answer 10

They can’t - the PR will respond the same if the brightness of a lower wavelength is increased as it would to a stimulus of a higher wavelength

Question 11

What did Hering’s colour experiments conclude?

Answer 11

Four colours are perceived and are opponent to each other (i.e. have shared pathways which respond to the stronger colour)

Question 12

What can happen if you view a colour for an extended period of time?

Answer 12

Colour aftereffects
Adaptation time causes pathway to ‘get used’ to viewing that colour. When the colour is removed, the opponent colour is seen bc there is reduced sensitivity of the colour which was just being viewed, so it’s perceived that you are viewing the opposite.

Question 13

At what level is trichromacy theory correct?

Answer 13

Photoreceptors

Question 14

At what level is opponency theory correct?

Answer 14

RGC

Question 15

Where do M & L cone responses combine to create R-G opponency?

Answer 15

RGC receptive fields

Question 16

How is B-Y opponency created?

Answer 16

Responses from S cone and yellow input from M & L cones feeds into RGC receptive fields

Question 17

What is a R+G- RGC receptive field?

Answer 17

Red-on cell
Excitatory response to red
Inhibitory response to green
Red perceived when cell is excited

Question 18

What is a B+Y- RGC receptive field?

Answer 18

Blue-on cell
Excitatory response to blue
Inhibitory response to yellow
Blue perceived when cell is excited

Question 19

What is a Y+B- LGN receptive field?

Answer 19

Yellow-on cell
Excitatory response to yellow
Inhibitory response to blue
Yellow perceived when cell is excited

Question 20

Is the R-G chromatic channel parvo- or magnocellular?

Answer 20

Parvocellular

Question 21

Is the B-Y chromatic channel parvo- or koniocellular?

Answer 21

Koniocellular

Question 22

Is the achromatic luminance channel parvo- or magnocellular?

Answer 22

Parvocellular

Question 23

Which area of the brain processes colour?

Answer 23

V4

Question 24

Do blobs or interblobs perceive colour?

Answer 24

Blobs

Question 25

What do interblobs perceive?

Answer 25

Object form

Question 26

How do blobs and interblobs work together to form an image?

Answer 26

Parallel processing

Question 27

What could occur to an image if there is damage to interblobs?

Answer 27

Colour perceived, but unable to perceive the shape of the object

Question 28

Which layer do koniocellular neurones synapse in V1?

Answer 28

Layer 3

Question 29

Which layer do parvocellular neurones synapse in V1?

Answer 29

Layer 4C(beta)

Question 30

Where does chromatic and achromatic information separate in V1?

Answer 30

Post-synaptic projections from layer 4C(beta) to layer 3

Question 31

What is colour constancy?

Answer 31

Ensuring perceived colour stays the same in different illumination conditions

Question 32

What do double opponent cells do in V4?

Answer 32

Removes common colours to maintain colour constancy

Question 33

Which cells achieve colour constancy?

Answer 33

Double opponent cells