Week 2 Lecture 5: Colour Vision Flashcards
What does colour depend on?
wavelengths of light
What is a wavelength?
the distance between one wave peak and the next
What is the range of the wavelengths humans can see?
400 to 700 nm
What different wavelengths correspond to?
different colours
Why did evolution give us eyes that see 400-700 nm?
The power in sunlight peaks at these wavelengths and the atmosphere is most transparent to these wavelengths
What are 3 cones that most humans sense colour with?
Red (63%), green (31%) and blue (6%)
What are orgnanisms that sense colour with three types if cones called?
Trichromats
What light (wavelength) does red and green cone pigments prefer?
Yellow and yellow-green light
What light (wavelength) does blue cone pigments prefer?
Blue light
What light (wavelength) does rhodopsin prefer?
Blue-green light
What light (wavelength) does melanopsin prefer?
Blue light
How does the brain infer colour?
By comparing the data from the three types of cone e.g. yellow light affects red and green cones but blue cones so if red and green cone are hyperpolarized, the brain perceives yellow
Can the brain infer the wrong colour?
Yes, e.g. a red and green light can produce the same cone activities a yellow light would so the brain perceives yellow either way
How do we perceive colour?
By mixing the primary colours of light (red, green, blue), we can produce any colour perception which corresponds to a pattern of activity in the 3 types of cones
What are spectral colours?
The colours of the rainbow, colours that can be evoked by the light of a single wavelength
What are extraspectral colours?
Colours like purple and white, colours that are evoked by a mix of wavelengths
What are ganglion cell colour signals?
Combinations of cone signals
What are ganglion cells excited by red and green light called?
Yellow channels (R + G)
What are ganglion cells excited by red light and inhibited by green light (or vice versa) called?
Red-green opponent channels (R - G / G - R)
What are ganglion cell excited by blue light and inhibited by red and green light (or vice versa) called?
Blue-yellow opponent channels
What opponent channels thought to explain?
Afterimages
What is most common variant of colour blindness?
Red-green colour blindness or Daltonism
What is the inheritance pattern of red-green colour blindness
Colourblind fathers have colour-normal daughters who have colour blind sons
What chromosome is gene for red and green visual pigments located?
The X-chromosone
How does mutations at the loci for red and green visual pigments affect women?
If one X-chromosone codes for faulty pigment then the other X-chromosone compensates. If the two X-chromosones code for different functional pigments, the woman may be tetrachromat
What is reflectance?
The intrinsic colour of a surface or the tendency of a surface to reflect certain wavelength and absorb others
Why is reflectance important?
It carries information about an object e.g. reflectance of a banana tells you its ripeness
What does the light sent to our eyes depend on?
Reflectance and illumination
What is colour constancy?
Our ability to infer the reflectance of an object by comparing parts of the image
What can colour constancy affect?
Our perception of brightness, hue and saturation
