lecture 1- colour vision

Question 1

visible lights spectrum extends from..

Answer 1

wavelength ( λ) of 400 nm (blue) to 700 nm (red)

Question 2

what is nm?

Answer 2

nm is a nanometre (10-9 metres)

Question 3

what are the two receptors?

Answer 3

-rods (night vision)
-cones (day vision)

Question 4

what does each photopigment respond to?

Answer 4

each photopigment responds to a preferred wavelength, but the neural response of the photoreceptor does not specify wave length

Question 5

what is univariance principle?

Answer 5

a photoreceptors response is summarised by one variable that specifies the amount of light absorbed

Question 6

state: given the proper intensity, all wavelengths can affect a single-pigment receptor in the same way

Question 7

state: an eye with only one type of photo-pigment cannot see colours

Question 8

two-pigment system enables…

Answer 8

enables an eye to extract some wavelength information

Question 9

why can two-pigment systems confuse colours?

Answer 9

because any one wavelength can be matched by a pair of wavelengths

Question 9

how many photopigments does the human eye have

Answer 9

the human eye has three photopigments sensitive under photopic conditions, so it is trichromatic (three-coloured)

Question 9

what is trichromatic?

Answer 9

three-coloured

Question 9

what will any wavelength produce?

Answer 9

any wavelength will produce three responses, a trio that is less likely to be confused with any other single wavelength

Question 9

what are the three conetypes?

Answer 9

L,M and S

Question 10

M cones

Answer 10

M cones are medium wavelength sensitive (yellows and greens)

Question 10

patterns of cones in the retina

Answer 10

• there are approx twice as many L than M
• many fewer S cones than M & L cones
• central parts of the retina have no S cones
• central parts of the retina have an additional overlying yellow pigment called macular pigment
  -colour vision varies in different parts of the retina

Question 10

s cones

Answer 10

s cones are short wavelength sensitive (blues)

Question 10

L cone

Answer 10

L cones are long-wavelength sensitive (reds, oranges and yellows)

Question 10

human vision is

Question 10

trichromacy and human vision

Answer 10

human vision is trichromatic meaning we have three colour processes (R, G and B)

Question 11

trivariance and human vision, what is subsequent processing?

Answer 11

subsequent processing is trivariant meaning two opponent colour channels and one brightness channel

Question 12

what colour and brightness are opponent channels?

Answer 12

-the opponent colour channels are red/green and yellow/blue
-the opponent brightness channel is light/dark

Question 13

what can physically different combinations of energy produce?

Answer 13

physically different combinations of energy can produce identical colour experiences eg red and green lights when overlapped appear yellow in the right proportions

Question 14

what do metamers suggest?

Answer 14

metamers suggest that the visual system can generate equivalent neural responses to physically different stimuli

Question 15

what do colour mixing experiments show?

Answer 15

colour mixing experiments (using not more than three primary colours in beams of light to match the colour of another beam of light) showed that any colour can be matched by suitable adjustment of intensity