colour vision

Question 1

what is colour vision good for?

Answer 1

detecting objects in the world e.g. predators.
segmentation and perceptual organisation of objects in our environment, segmenting objects from backgrounds in order to see them more clearly.
judging state of objects.

Question 2

why colour?

Answer 2

colour vision allows us to distinguish between objects e.g. seeing the difference between a grapefruit, an orange and a lemon.
also allows use to see that the seasons are changing form the colours of the leaves.
we can distinguish between skin tones, e.g. can see if someone is sick if they look really pale.
allows us to see if meat is cooked through.

Question 3

what are the physical attributes of light?

Answer 3

most of the time we measure reflectance, the light source omits light which reflects off the objects to give it the colour we see.
the size of the wavelength determines what colour we see the object as.
black paper absorbs most of the light whereas the white paper reflects most of the light.

Question 4

how many colours are there in the world?

Answer 4

there are no colours int he world, the colours you see depends entirely on your visual system.
colour is a construct, it is constructed by our visual system and depends on the eye of the beholder.

Question 5

what is trichromacy?

Answer 5

there are three types of cone.

Question 6

what are the three types of cones?

Answer 6

short (blue)
middle (green)
long (red)
on average there are twice as many L cones to M cones.

Question 7

who realised there are three cones?

Answer 7

an scottish physicist called Maxwell, was the first to properly come tot the conclusion that there are three cones by using colour matching.

Question 8

what is the principle of invariance?

Answer 8

the absorption of light by an photoreceptor causes only one effect (ismoerisation) no matter what the wavelength.

Question 9

why do we need at least two types of cones to perceive colour?

Answer 9

because colour vision depends on the comparison of input between two receptors.

Question 10

what are the two variations of colour blindness?

Answer 10

dichromats and anomalous trichromatic.

Question 11

what does dichromat mean?

Answer 11

an individual who only has two cones, they always have S cones so either have L or M cones.

Question 12

what are the three types of dichromat?

Answer 12

deuteranopia, tritanopia and protanopia.

Question 13

what does deuteranopia mean and % does it effect?

Answer 13

individuals have no M cones, affects about 1% of males and 0.01% if females.

Question 14

what does titranopia mean and % does it effect?

Answer 14

no S cones, affects about 0.002% of males and 0.001% of females.

Question 15

what does protanopia mean and % does it effect?

Answer 15

no L cones, affects about 1% of males and about 0.02% o females.

Question 16

why are more males dichromats than females?

Answer 16

colour blindness is an x-linked genetic condition therefore for females to have it they have to have the faulty gene on both X chromosomes whereas aes just need in their ie X chromosome.

Question 17

what does anomalous trichromatic mean?

Answer 17

individuals who have all three cones but in different proportions.

Question 18

why is colour vision dependent on the individual?

Answer 18

the reflectance properties of the objects don’t change, that is physics, but the perception of the object does change meaning that colour vision depends on the individual.

Question 19

what are the two types of anomalous trichromat?

Answer 19

protanomaly and deuteranomaly.

Question 20

what does protanomaly mean and what % does it affect?

Answer 20

the L cones are closer to the M cones, 1% of males.

Question 21

what does deuteranomaly mean and what % does it affect?

Answer 21

the M cones are closer to the L cones, 5% of males.

Question 22

what does an anomalous trichromat mean for an individual?

Answer 22

the spectual difference is much less than a normal person, the colour difference is very different, this is the most common type of visual deficiency. the bigger the difference between L and M cones, the better the vision.

Question 23

what did Ewald Hering observe?

Answer 23

colours fall into four categories based on how much red, green, blue or yellow they contain.
no colours appear as greenish-red or yellowish-blue.

Question 24

why were Hering’s observations phenomenological?

Answer 24

he didn’t do any measurements, he just asked people what they could see, he found that due to being not he opposite of the colour wheel you cannot see greenish-red or yellowish-blue.

Question 25

what did Hering propose about perception of colours?

Answer 25

our perception of colours is based on four primary colours that are process by two perceptually opponent colour channels, blue-yellow and red-green.

Question 26

what does the trichromacy theory rely on?

Answer 26

colour matching.

Question 27

what does the opponent-process theory rely on?

Answer 27

afterimages, simultaneous contrast.