Week 10 - color vision Flashcards
Wavelength
Light has a wavelength, it is the distance from one peak to the next, different wavelengths correspond to different colours.
Wavelength range in which we can normally see
400 nm to 700nm
But we can also see very powerful infrared lights and some people who have had their cataracts removed can see ultraviolet light
Why did evolution give us eyes that see 400–700 nm?
The power in sunlight peaks there. Also, Earth’s atmosphere is
most transparent to these wavelengths.
And sea water, where eyes first evolved, is most transparent < 500
nm.
3 types of cones
red (63%), green (31%) and blue (6%)
What light do blue cones prefer
blue light
What are we called because we sense three types of colour
trichromats
What light do red and green cone pigments prefer
yellow and yellow-green light
How does the brain infer colour
comparing data from 3 types of cones
What light does rhodopsin prefer
blue-green light
What light does melanopsin prefer
blue
How do we produce ANY colour perception
by mixing three wavelengths
what happens when red and green cones are hyperpolarizes but blue cones arent
percieve yellow light
how can the brain be fooled when it comes to percieving colour?
A red and green light can produce the cone activities as a yellow light would and so we would still see yellow
Spectral colours
Those that can be evoked by light of a single wavelength. They are the rainbow colors, from violet through blue,
green, yellow and orange to red.
Extraspectral colours
colors such as purple or white are evoked only by a
mix of wavelengths, e.g. we see purple when 2 or more wavelengths
affect red and blue cones more than green cones.
R + G cells
yellow channel
ganglion cells that are excited by red and green light
R - G cells
red-green opponent channel
ganglion cells that are excited by red light but inhibited by green light
G - R cells
ganglion cells that are excited by green light but inhibited by red light.
B - R - G cells
ganglion cells that are excited by blue light but inhibited by red and green light
B-(R+G)
what explains after images
opponent channels
two types of blue - yellow opponents channel
B-(R+G)
(R+G)-B
Daltonism
Red green color blindness
How can a woman be a tetrachromat
If her 2 X-chromosomes code, say, 2 different functional “red” cone
pigments or any color
inheritance pattern for red green color blindness
color blind fathers
have color-normal daughters who have color blind sons.
The genes for the red and green cones lie on the X chromosome. problems at these loci underlie 95%of all variations in color vision.
reflectance
its tendency to reflect certain wave-
lengths of light and absorb others.
the reflectance of an object carries information about it
color constancy
our brains can usually infer the reflectance, so we
see the ripe banana as yellow even in green light.
how does the brain infer reflectance
comparing it to different part of the imge
