colour perception

Question 1

Human trichromacy

Answer 1

3 cone types, maximally sensitive at:
short (blue)
middle (green)
long (red) wavelengths

more long and middle than short

Question 2

we have 3 cones to allow us

Answer 2

to distinguish between different colours

evolution:
ripe vs unripe
oxygenated vs deoxygenated blood

Question 3

monochromatic primates

Answer 3

• nocturnal
• do not need colour

Question 4

monochromats

Answer 4

one cone

Question 5

dichromats

Answer 5

Protanopia - lack L cone

Deuteranopia - lack M cone

Tritanopia - Lack S cone

Question 6

shifted

Answer 6

not as able to use the different signals between the two cones - to identify colour changes

Question 7

colour vision deficiency stats

Answer 7

8% men - linked to sex chromosomes
less than 1% women

ageing, drugs, hormones = higher likelihood

Question 8

Gene therapy cure

Answer 8

• inject viral DNA - injects genetic information to code for 3rd cone into the eye
• did this on squirrel monkeys - men di and women tri so potential that mechanism is present

Question 9

Human techchronomy

Answer 9

• some women have 4 cone types
• usual 3 plus a shifted red or green cone
• tested to see if this means they can see more colours - only one women showed behavioural signs

Question 10

cone opponency

Answer 10

the output from the three cones is combined and contrasted to give 3 cone-opponent channels

Question 11

3 cone-opponent channels

Answer 11

L/L+M cherry teal
S/L+M violet lime
L+M achromatic or luminance axis (bright vs dark)

Question 12

3 cone opponent channel connected to LGN

Answer 12

Parvocellular - L/L+M
Koniocellular - S/L+M
Magnocellular - luminance

Question 13

colour after-effects

Answer 13

stare at a photo for a while and then a blank page - will see the photos opponent colours

Question 14

adaption

Answer 14

prolonged exposure to a stimulus reduces sensitivity

Question 15

colour at the cortex

Answer 15

v1 has blobs/patches of cells that are sensitive to colour

Colour and motion are SEPERATE
Colour info is sent along ventral processing stream along the ‘what’ pathway
Used to help identify what objects are

Question 16

cerebral achromatopsia

Answer 16

damage to small cortical region can cause loss of colour perception

this is evidence for the cortex generating colour

if you only have damage to one then may only lose it in one half visual field

Question 17

memory colour

Answer 17

objects have a typical colour

banana = yellow

if we edit banana to look grey - ps overshoot by adding blue because the brain expects the banana to be yellow so when we get to grey the brain adds a bit

blue = yellow opponent colour so it balances it

Question 18

aesthetic response to colour

Answer 18

ecological valence theory

Question 19

ecological valence theory

Answer 19

colour preference is due to colour-object association

e.g. if we like water we like blue more

Question 20

preference for colour combinations
natural scenes

Answer 20

people prefer yellow-blue and orange-blue

may be due to the fact these are the colours found in natural scenes which we are often exposed to

Question 21

colour constancy

Answer 21

brain is able to keep the colour of objects the same
e.g. if you brought a banana from a bright room to outside - still yellow

if a surface is grey under yellow light - surface must actually be blue - opponent colours

Question 22

Anomalous trichromats

Answer 22

Deuteranomaly (M shifted toward L)

Protanomaly ( L shifted to M)

Question 23

biological combinations theory

Answer 23

you can account for colour preference by weighting how much you care about the different cone opponent processes