perception-colour vision anomalies Flashcards
what happens in your brain when an image is represented
-signals go to your eye from your brain, and you will have an amount of signals from blue, green and red receptors going into your brain
-you can represented the total amount of signal from red green and blue going into your brain in the systematic plot(look at slides)
-the nervous system can look at the red and green and look at the difference and minus one from the other
-it can also add them up (therefore its black and white)
what does the the triangle in a cie diagram represent
-the triangle represents all the colours you can produce in that specific device , so any colours that fall outside the triangle
-if triangle covers most of the diagram, that device will represent as true a colour as it is on the device
trichromacy and trivariance
-human vision is trichromatic i.3 we have 3 colour processes (red,green,blue)
- (after getting the signal it is transferred into 3 opponent processes) subsequent processing is trivariant, i.e two opponent colour channels and one brightness channel
-the opponent colour channels are red/green, yellow/blue
-the opponent brightness channel is light/dark (black/white)
how do we measure these colours
-CIE chromaticity diagrams (look at slides)
-every colour you could imagine is on this diagram
-you can calculate the coordinates of a colour and those co ordinates can show on this diagram
abnormalities of colour vision
-congenital
-acquired
congenital- (present from birth) encoded in genetic makeup
acquired - those with normal colour vision develop partial or total loss of colour vision
munsell colour system
hue
value
chroma
hue- is the quality that distinguishes colours
value (brightness) is related to the intensity of light
chroma (saturation) distinguishes pale from vivid
what is it called if someone’s photoreceptors dont work
-we have 3 photoreceptors, they either work well,normal or not well
-if all 3 aren’t working well, we can them anomalous and they all become anomalous trichromat
what happens if somebody is missing a colour photoreceptor
-if someone has 3 (all) photoreceptors they are trichromat, if they have 2 they are dichromat, if they have one they are monochromatic
anopia
if you are blind to something - you dont see it
names for missing certain photoreceptors
-1 (pro)long -red
,2) (du) medium- green
3) (tri) short -blue
-if you cant see the red one, its called protanopia
-if green one is missing - dutanopia
-if blue one is missing tritanopia
terms for anomalous photoreceptors (photoreceptors that dont work properly)
protanomally
deuteranomally
tritanomally
how does anomalous trichromacy occur
-occurs when all three cone types are present but one has an abnormal absorption curve. the severity of the anomaly depends on how abnormal is the absorption.
-thus there are simple anomalous observers and extreme anomalous observers
define dichromatic colour deficiency
-is caused by the absence of either L,M, or S cones leading to protanopia , deuteranopia and Tritanopia
rod or cone monochromacy
-where there is only one photoreceptor type present, so there is no colour perception
graphs of
-normal trichromat
-anomalous trichromat
-protanope, deuteranope and tritanope
look at slides
-anomalous one has all 2 however the green one is shifted
-protanope-red curve was missing
-deuteranope - missing the green curve
-tritanope - missing the blue curve
how do
-protanopes
-deutranopes
-tritanopes
view the world
look at the slides
-protanope - dont really see pinky /red (only see yellows to blues in the colour spectrum)
-deuteranope - same as protanope (minor variations) (blues to yellows)
tritanope - dont see blues (colour spectrum looks green to reds)
cone monochromats
rod monochromats
how do they see the world?
-if have cone(your a cone monochromat) the world is in black and white
-if you are a rod monochromat world is also black and white
-the difference is that cone monochromates (cones have higher density ) their visuals are detailed, so see the world in high definition, but just black and white. rod monochromats however, they don’t have good resolution so everything is blurry. rods saturate in bright conditions, so they would have to wear glasses during the day, to reduce light levels for rods to function or they would be totally blind.
colour deficiencies are more common in ___
men
acquired abnormalities of colour vision
-cerebral achromatopsia/dischromatopsia
- ## a selective loss/deterioration of colour vision associated with the damage to temporal and occipital areas of the ventral pathway (loss of colour vision after an injury)
acquired abnormalities of colour vision
-aging and diseases of the eye
-ilness, ageing or trauma can cause colour vision anomalies and defects.
-typically disorders of the retinal vascular system and ageing result in yellow-blue losses (congenital anomalies and defects affect the red-green system)
-however optic nerve lessions, cone degeneration and poisons can cause red-green losses
cerebral achromatopsia
-temporal cortex in humans
-lingual and fusiform gyrus
-lingual and fusiform gyrus in our cortex is areas in our brain associated with colour processing but also face processing
-processing of face and colour are very close together in the cortex ,so people who have issues with not recognising faces would have issues with colour vision(but since its localised so either left or right of the brain it only applies to one side of the vision left or right)
cerebral achromatopsia
-if its in both sides then the world reduces in colour
-if someone has a bilateral stroke in the corresponding areas of fusiform and lingual gyrus, the world goes black and white for them
testing
pseudoisochromatic plates
-at opticians used to check to see if someone can do a profession
-ishihara plates
-plates have something you need to distinguish (in the photo its a number 6)
testing
anomaloscope
- a pattern, a semi circle one side changes colour and one is yellow, you get someone to adjust the changing side to match the colour
the farnsworth-munsell 100 hue test
-used in hospitals
-have tiny dials and each one has different colours
-shuffle them and ask person to put them in order
-by plotting errors can see if someone has colour deficiency
colour vision through life
children have not great colour vision
teenagers have the best
as you get older colour vision deteriorates
