Colour Perception and Vision

Question 1

Colour is important because of:

Answer 1

Indicate danger in nature - signalling 
Additional associative tool - information 
Objects will glow different colours - telling us about properties of objects or things 
Discriminating objects 
Marketing
Aesthetics 
Food
Internal state

Question 2

The Visible Spectrum

Answer 2

The Electromagnetic Spectrum

Snakes can see infrared

Question 3

Cone photoreceptors

Answer 3

• Human Trichromacy - three cone types, maximally sensitive at short (S), middle (M) and long (L) wavelengths
• Combining signals from these three cones can allow us to see all the wavelengths
• Trichromacy evolution related to foraging for ripe fruit/berries
• Dichromatic - two cone types: blue and yellow
• Trichromatic - three cone types: blue, yellow split into red and green
• Bare skin: socio-sexual signals from blood oxygenation
• Monochromatic primates - more hair on their face
• Dichromatic - two cone types so less hair
• Trichromatic - humans and other primates - a lot less hair.

Question 4

Genetic colour vision deficiency

Answer 4

• Some people can be a Monochromat. You only have one cone type so you can only see one colour (very rare)
• Dichromat - could lack the red long wave length (Protanopia), lack green medium wave length (Deuteranopia) or lack blue short WL (Tritanopia)
• Anomolous Trichromats - Deuteranomoly (green cone shifted to red)Protonomoly (red cone shifted to green)
• Overall 8% of men and less than 1% of women have these genetic deficiencies, also acquired colour vision deficiency (ageing, drugs and hormones)
• Sometimes the eye lens yellows because of the sun, harder to distinguish colours

Question 5

Cure for colour vision deficiency?

Answer 5

looked into gene therapy and tested on squirrel monkeys - males are mostly dichromatic. Tried to turn him into a trichromat. Took a gene 9red opsin gene) into the green cone middle WL with a virus to make it hold. He looks at a computer screen and and if you can see it you only see it on the basis of colour and the monkey has to indicate where it is (has to headbut it)

Question 6

Human Tetrachromacy

Answer 6

Some woman have four cone types

The mothers of the men who have this have the shifted cone and the normal cones which means they have 4

Question 7

Cone Opponency

Answer 7

Signal from the LW and the MW are compared with each other to give us a red green scale and then that is compared to give us blue yellow.
Early stages of colour it is channeled along these two subsystems
Then you have black-white

Question 8

Top Down Effects

Answer 8

Memory of the typical colour of objects influences actual perception of colour
Colours of objects remembered as more saturated than they really are (banana is remembered as more yellow)