Colour Perception

Question 1

Importance of being able to identify colours

Answer 1

Evolution - patterns indicate danger
Detecting predators
Self expression
Identifying objects and people
Culture

Question 2

The visible spectrum

Answer 2

There is an electromagnetic spectrum from short wavelengths to long - small section of visible light (400- to 800 metres)
Some species have infared (warmth) or ultraviolet vision

Question 3

What are humans known as?

Answer 3

Trichromats - having 3 cones, short, long and medium

Question 4

What colour is the long wavelength?

Answer 4

Yellow/red

Question 5

What colour is the medium wavelength?

Answer 5

Green

Question 6

What colour is the short wavelength?

Answer 6

Blue

Question 7

What is the evolution of our cones?

Answer 7

Most of our primates are dichromatic, but now we have 3

Question 8

Why have we evolved to have 3 cones?

Answer 8

Splitting a yellow cone to one that’s medium and long enables us to see red/green differences and can detect blood flow under species skin
Trichromats have the most bare skin on show so need to see changes in blood, indicates health

Question 9

What is the genetic deficiency of cones?

Answer 9

Dichromats - 2 cones
Monochromats - 1 cone
Anomolous

Question 10

Are cone deficiency nature or nuture?

Answer 10

Both
Males are more likely to get it then females
but sometimes acquired, ageing, drugs and hormones

Question 11

Types of dichromats

Answer 11

Protanopia - lacking red, long cone
Deuteranopia - lacking green - medium
Tritanopia - lacking blue, short

Question 12

Types of anomolous

Answer 12

Deuteranomoloy - medium and long wavelength overlap

Protanomoly - long overlaps to medium

Question 13

A cure for genetic deficiency?

Answer 13

Gene therapy on cones on a monkey meant it could see colours it couldn’t see before, brain uses new signal

Question 14

What is human tecrachromacy?

Answer 14

Having 4 cones, 3 normal and shifted red or green
Psychophysical tests - anomaloscope
14 woman, only 1 was behaviourally different
Retina has 4 times but there is lots of machinery in place to use the signal so not everyone will make full use

Question 15

What is cone opponency?

Answer 15

The output of 3 cones is combined to give 3 channels. Colour will fall along an axis:
Red-green - cherry teal LM - parvocellular
Blue-yellow - lime violet, S, konicellular
Black-white - achromatic, magnocellular

Question 16

What is an example of cone opponency?

Answer 16

Colour after effects

Question 17

Where is colour at the cortex?

Answer 17

There are patches of blobs responsible for colour at the cortex (V1) but there are other areas as well V2, V4, V8
Sent to temporal cortex (ventral)
Receives colours in circular ways

Question 18

Why do we prefer some colours?

Answer 18

Biological components theory - we prefer colours that stimulate our visual system
Ecological valence theory - preference is due to colour object associations e.g. we like blue as it associates with the sky

Question 19

Top down effects

Answer 19

Memory of colour influences perception of colour
eg. colour remembered more saturated than they are
If asked to make banana grey, ppts make it blue because blue is opposite to yellow

Question 20

Cerebral achomatopsia

Answer 20

Damage to cortical area, lose colour
Humans with lesions in V4, V8
Functioning cones but things don’t appear coloured, can affect one visual field only - shows importance of cortex