lecture 1- colour vision Flashcards
visible lights spectrum extends from..
wavelength ( λ) of 400 nm (blue) to 700 nm (red)
what is nm?
nm is a nanometre (10-9 metres)
what are the two receptors?
-rods (night vision)
-cones (day vision)
what does each photopigment respond to?
each photopigment responds to a preferred wavelength, but the neural response of the photoreceptor does not specify wave length
what is univariance principle?
a photoreceptors response is summarised by one variable that specifies the amount of light absorbed
state: given the proper intensity, all wavelengths can affect a single-pigment receptor in the same way
state: an eye with only one type of photo-pigment cannot see colours
two-pigment system enables…
enables an eye to extract some wavelength information
why can two-pigment systems confuse colours?
because any one wavelength can be matched by a pair of wavelengths
how many photopigments does the human eye have
the human eye has three photopigments sensitive under photopic conditions, so it is trichromatic (three-coloured)
what is trichromatic?
three-coloured
what will any wavelength produce?
any wavelength will produce three responses, a trio that is less likely to be confused with any other single wavelength
what are the three conetypes?
L,M and S
M cones
M cones are medium wavelength sensitive (yellows and greens)
patterns of cones in the retina
- 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
s cones
s cones are short wavelength sensitive (blues)
L cone
L cones are long-wavelength sensitive (reds, oranges and yellows)
human vision is
trichromacy and human vision
human vision is trichromatic meaning we have three colour processes (R, G and B)
trivariance and human vision, what is subsequent processing?
subsequent processing is trivariant meaning two opponent colour channels and one brightness channel
what colour and brightness are opponent channels?
-the opponent colour channels are red/green and yellow/blue
-the opponent brightness channel is light/dark
what can physically different combinations of energy produce?
physically different combinations of energy can produce identical colour experiences eg red and green lights when overlapped appear yellow in the right proportions
what do metamers suggest?
metamers suggest that the visual system can generate equivalent neural responses to physically different stimuli
