Week 7 Colour Spaces & Pathology Flashcards
What is the CIE International Commission on Illumination Colour Space and what model of colour processing does it align with?
- CIE maps onto trichromatic theory
The primaries that the CIE chose are easier to represent/graph
The three primaries can produce any colour
Looking at relative activation of 3 primaries = the sum of their colour activities must equal 1
2D graph - We can infer the activity of the 3rd primary by adding together the first two
What are 4 advantages of using the CIE colour space map?
- Shows location of fully saturated colours
- Predicting colour mixtures (what colour are perceived when colours are mixed)
- Gives location of white and complementary colours that make white
- Colour mixing can be seen by drawing a line between 2 colours of equal intensity, the combined colour is the midpoint
Q. Why are only 2 primaries needed from 550 nm - 700 nm?
We can make any two primaries from 550 nm - 700 nm, because the blue cone is no longer sensitive after 550 nm, so our trichromatic colour vision is actually dichromatic after 550 nm. After 550 nm, the activation of red and green cones can make any colour
Q. Which colour area should you chose TV range of colours, broad or narrow?
The narrow area would not have particularly saturated colours because the area between the 3 coordinates only includes desaturated colours, making the appearance of the screen look washed out
What qualities do rod-monochromats have and what do they need?
They have no cones, often photophobic & poor spatial acuity
Need to wear super dark sunglasses to attenuate the amount of light coming in, as they only have rods that saturate in brighter conditions
while Cone monochromats - one type of photo pigment and poor spatial acuity (around 20/60 vision)
What is the main quality of a dichromat?
- Loss an axis of colours due to one of the cone pigments is missing, L, M or S cone pigment
How could you tell the difference between the red and green wire in bomb disposal if you were colour blind?
- If you didn’t have the red cone missing , you could tell distance of red and green from differences in luminance of green vs. red
Green appears a lot lighter in luminance hue because it’s a higher sensitivity peak, and would be perceived as looking lighter
- If you were missing the green cone and needed to distinguish a green at 525 nm and a red at 625 nm, they would both appear the same colour because they would have the same luminance!
Why do some trichromats fail the Ishihara test? - at a retinal and cortical level
- At a retinal level: some trichromats still have 3 distinct photopigments but one or more of the peak sensitivities of photopigments is slightly different/lower to a neurotypical.
For these people with lowered chromatic contrasts, some shades of red and green can be so low they can’t tell it apart. But they can tell the Farnsworth-Munsell test because the colour contrasts are much more saturated!
- At a cortical damage level, some people can’t do one or another because of cortical damage or impairment on either the colour pathway that impacts colour form processing or colour discrimination
Why do we have a better ability to discriminate red and green from one another?
We have better ability to discriminate red and green hues due to higher density of red and green cones in the retina and in the fovea
The fovea = only green and red cones
Red - green - blue ratio = 31 - 16 - 1
How does the illusion of colour constancy work?
With distance and eye squinting, the brain gets rid of high spatial frequencies of colour discrimination, and cannot resolve variation in colour, so it is averaged out giving the illusion of colour constancy / similar to neon spreading
What is the limbic system involved in?
The limbic system is a network of structures responsible for learning, memory, motivation and olfaction, including the hippocampus, amygdala and fornix
What is the difference between retrograde and anterograde amnesia?
Retrograde [old memories] amnesia = loss of stored memories/prior to event
Anterograde [new memories] amnesia = inability to encode and consolidate new memories after the event
What do the different types of amnesia indicate about memory?
The double dissociation of amnesia implies that the areas involved in memory encoding are not stored in the same area as where memories are stored
What are the 3 ways that non-declarative memory is formed?
- Skill learning: ie. playing an instrument, driving, dancing
- Priming/repetition priming = changes in behaviour due to prior exposure to a stimulus
- Conditioning = learning simple associations between stimuli, is first declarative associations but then become more procedural over time
What neuroimaging technique should be used to test whether a brain region is implicated in memory?
TMS, fMRI and microstimulation - shoudl’ve done for HM
To check impairment of cognition on neural regions, and then an fMRI to detect important regions, during surgery you can do microstimulation while the patient does a task to see whether the region is impaired or the task ability is impaired!
