colour perception

Question 1

why is colour important?

Answer 1

helps to identify objects, interpret environment, communicate information and make aesthetic and social judgments

Question 2

what do we use colour for?

Answer 2

use colour for object recognition, foraging, detecting ripeness or health, social and sexual signalling, aesthetic preference and visual communication

Question 3

where does colour perception come from?

Answer 3

the responses of cone photoreceptors in the retina and the brain’s interpretation of their signals

Question 4

what are cone photoreceptors?

Answer 4

retinal cells responsible for colour vision, functioning best in bright light

Question 5

what is human trichromacy?

Answer 5

presence of 3 cone types, maximally sensitive to short (S), middle (M) and long (L) wavelengths

Question 6

how did trichromacy evolve?

Answer 6

to help primates forage for ripe fruit and berries by distinguishing red-green colour differences (Regan et al. 2001)

Question 7

how is colour linked to socio-sexual signalling?

Answer 7

bare skin colour provides socio-sexual signals related to blood oxygenation, which trichromatic primates can detect (Changizi et al 2006)

Question 8

what is genetic colour vision deficiency?

Answer 8

occurs when one or more cone types are missing or altered, affecting colour perception

Question 9

what is monochromacy?

Answer 9

having only one cone type or none, relying mainly on rods

Question 10

what is dichromacy?

Answer 10

having only 2 functioning cone types

Question 11

what is protanopia?

Answer 11

absence of L (long-wavelength) cones

Question 12

what is deuteranopia?

Answer 12

absence of M (medium-wavelength) cones

Question 13

what is tritanopia?

Answer 13

absence of S (short-wavelength) cones

Question 14

what are anomalous trichomats?

Answer 14

have three cone types, but one cone’s sensitivity is shifted

Question 15

what is deuteranomaly?

Answer 15

when the M cone is shifted towards L wavelengths

Question 16

what is protanomaly?

Answer 16

when the L cone is shifted towards M wavelengths

Question 17

how common is colour vision deficiency?

Answer 17

about 8% of men and less than 1% of women have a genetic colour vision deficiency; can also be acquired through ageing, drugs or hormones

Question 18

can colour vision deficiency be cured?

Answer 18

gene therapy has successfully turned dichromatic squirrel monkeys into trichromats by introducing a red opsin gene (Mancuso et al 2009)

Question 19

what did gene therapy studies show about the brain?

Answer 19

brain can use new colour signals even if the circuitry was not active early in life

Question 20

what is human tetrachromacy?

Answer 20

occurs when some women have 4 cone types instead of 3

Question 21

does having 4 cones guarantee better colour vision?

Answer 21

no, extra cones do not guarantee tetrachromacy; additional cortical processing is required

Question 22

how common is behavioural tetrachromacy?

Answer 22

only one woman has been conclusively shown to be behaviourally tetrachromatic (Jordan et al 2010)

Question 23

what is cone opponency?

Answer 23

how cone signals are combined and contrasted to form opponent colour channels

Question 24

what are the three cone-opponent channels?

Answer 24

L/(L+M): cherry-teal
S/(L+M): violet-lime
L+M: achromatic (luminance)

Question 25

where are colour-opponent cells found in the LGN (Lateral Geniculate Nucleus)?

Answer 25

Parvocellular: L/(L+M) Koniocellular: S/(L+M) Magnocellular: luminance (black-white)

Question 26

what are colour after-effects?

Answer 26

changes in colour perception following prolonged exposure to a colour

Question 27

what is memory colour?

Answer 27

typical colour we associate with familiar objects (e.g. bananas are yellow)

Question 28

how does memory colour affect perception?

Answer 28

to make banana appear grey, extra blue must be added to counteract the expected yellow, an effect not seen with simple shapes (Hansen et al 2006)

Question 29

why do we prefer some colours over others?

Answer 29

colour preference may be influenced by biological factors and learned associations

Question 30

what is the Biological Components Theory?

Answer 30

suggests colour preferences are partly rooted in biological differences (Hulbert & Ling, 2007)

Question 31

what is the Ecological Valence Theory?

Answer 31

colour preference depends on how positively or negatively we feel about objects associated with that colour (Palmer & Schloss, 2010)

Question 32

what is WAVE in Ecological Valence Theory?

Answer 32

WAVE measures how good or bad the objects associated with a colour are

Question 33

what colour patterns do people prefer aesthetically?

Answer 33

people tend to prefer blue-yellow variations, which dominate natural scenes

Question 34

is preference for natural colours universal?

Answer 34

not necessarily, preferences may be culturally mediated

Question 35

what is colour constancy?

Answer 35

brain's ability to subtract the effects of illumination and recover true surface colour (Purves & Lotto, 2002)

Question 36

how does illumination affect perceived colour?

Answer 36

same physical colour can appear different under different lighting conditions

Question 37

why do the cube tiles appear different colours but are the same?

Answer 37

brain compensates for illumination, making physically identical grey tiles appear blue or yellow

Question 38

what does 'The Dress' illusion demonstrate?

Answer 38

shows individual differences in colour constancy and assumptions about illumination (Witzel et al, 2017)