physiology of colour Flashcards
what is subtractive colour mixing
mix two wavelengths together and what you have left when each has subtracted its wavelengths are some remaining medium wavelengths
what is additive colour mixing
mix two light together and what you get is the addition of light being reflected off the surface
what is the principle of univariance
respinse of a photoreceptor is a function of just one variable (number of photons absorbed)
describe weak light and principle of univariance
at wavelength of peak sensitivty (few incidents photons, a large fraction of the of them absorbed)
describe strong and the principle of univariance
of lower sensitivuty (many incididence photons a small fraction are absorbed)
what does the spectrum graph of absorbed wavelengths show
medium cone gets same activation from blue and orange light
short wavelenght cone activated most for blue lightand not at all for orange light
what does the spectrum graph of absorbed wavelengths suggest
to see a different colour you need to compare differences in L M and S cones
what were hermann ludwig von helmholts 3 key concepts
you match any visible light with a combo of three spectral lights due to three classes of light detectors
there are infinately many spectra that give rise to same colours= metamers
there seem to be four unique hues
what is opponent processinf
there are three cone types
three cones can code three pieces of info about stimulus = coordinated in cone space
what is adaptation
neurons adjust firing to adap to average stimulus
describe colour adaption in retina
different cones adapt to colour theyre sensing
when neutral background is shown opponent channels are balanced and respond around 0
describe humans dimensions
3 dimensions = 3 axes = 6 end points
describe relationship between L and M cones
very close so process very similar information and this is inefficient
what are L and M cones being similar inefficient
bandwidth out of is expensive- fatter optic disk, thicker nerve fibre layer
how do we code L M and S cones differently
use cone responses
what are the 3 cdimensions of colour vision
L-M
L+M
S-(l+M)
describe L-M dimension of colour vision
also called opponent red/green axis and signals differences in quantal catches of L and M cones
describe L+M colour vision
the luminance axis signals the sum of L an M cone catches
describe s-(l+m) colour vision
an opponent blue-yellow axis
what range is colour visible over
spatial temporal frequencies
describe changing luminance and colour vision
edges more visible even for high frequencies
what is the general cause of colour blindness
missing or abnormal opsin genes- usually L and M
why are L and M cones more involved in colour blindeness
they are on x chromosome and so men are more affectede
what is the most common colour deficit
anomalous trichromacy
what is anomolous trichromacy
discrimination is poorer along red/green axis but still present
what is the rarest colour deficiency
tritanopia where individuals lack functioning s cones
what cause colour deficits
faulty opsin genes
what does loss of L or M opsins lead to
loss of red/green leaving blue/ yellow
what does loss of s opsin lead to
leaves only red/green
what is protanopic
lost l opsin
what is deuteranopic
lost m opsin
what is tritanopic
lost s opsin
what is a key component of the ecology of colour vision
many animals only have L and S cones
