Topic 8 Colour Flashcards
(42 cards)
What are the three parameters used to define the colour of an object and what do they mean?
1) Hue: the actual colour
2) Saturation: vividness of the colour (amount of colour relative to white)
3) Brightness: light intensity
In order to process colour, the human visual system uses 3 broadband detectors rather than many narrowband ones, what is the advantage of such an approach?
Number of cells.
A narrowband system requires too many cells to process all colours at all locations in the retina and hence the ability to see fine detail would be impaired.
What are the two types of colour mixing, what is the major difference between them, and give examples of each type?
1) Additive mixing (more light in the mixture than in the components)
2) Subtractive mixing (less light in the mixture than in the components)
Example:
Adding all the spectral colours together:
Perceive white by additive mixing
Perceive black by subtractive mixing
If you added all the spectral colours together in an additive-colour mix, what colour what you get, what if you did the same in subtractive colour mix? Why are the two resultant colours different?
1) Get white in additive mix:
white is the sum of the components
2) Get black in subtractive mix:
light is removed by adding colour, so black which is common to all components remains
What are metamers?
Physically different stimuli that are perceived as identical.
Can a monochromatic system provide the basis for perceiving colour? Why?
No.
It cannot discriminate colour.
It only has one type of receptor and can only see differences in intensity.
Can a dichromatic system provide the basis for perceiving colour? Why?
Yes, but having deficit in colour perception. The system may compare relative amount of firing (ratio of activity).
In a dichromatic system, what is the neutral point and what is the consequence of it?
Neural point is at a crossover point of the two response curves, where two kinds of cones are equally excited, giving the same kind of response as white light, therefore light of a single wavelength is perceived as white.
What is the trichromatic theory of colour perception?
Colour perception based on the relative activity of three receptor types.
3 primaries are needed to match all colours.
What is the opponency model of colour perception?
Colour vision is mediated by three opponent mechanisms
Explain how both models are correct?
Opponent pairing states how the three cone types are combined.
What is meant by the concept of a colour-blind processing system?
A processing mediated only by the M(magnocellular) system which is only luminance sensitive and cannot use colour info.
How could you test whether a system, e.g. motion or stereo processing, are colour blind and what are the disadvantages of the various experimental techniques?
1) Isoluminance approach: remove all luminance info from the stimulus, leaving only colour info.
1. impossible to totally remove luminance info
2. this luminance cue may signal depth or motion, and it may differ to that signalled by colour.
2) Alternative approach: have the stimuli contain both colour and luminance info, but define the luminance info.
Describe the three main colour spaces used to define colour.
1) CIE space: based upon colour matching studies and hence the trichromatic theory.
2) Perceptual colour space: based upon colour appearance studies.
3) Cone space: based upon the response of the cones.
What is one of the main uses of the CIE colour space, i.e. what can it predict?
Predicting colour mixtures. The mixture of any 2 colours will lie along the straight line connecting the two compon.
Describe the various types of retinal-based colour blindness and discuss whether it is accurate to call them colour blind.
Monochromats are the only colour blindness that can’t perceive colours.
Dichromats actually are colour deficit, not really colour blindness because they see colours. One of the cone photopigments is missing.
What are the two main colour tests?
Farnsworth-Munsell 100 Hue test
Ishihara test
What is amnesia and what are the two different types of it?
A loss of memory (forgetfulness).
Retrograde: loss of memories prior to an event;
Anterograde: inability to form new memories.
Who is HM?
The most famous research subject in the history of brain study.
Why did he need surgery and what was removed?
HM had seizures.
Amygdala, most of hippocampus, and some surrounding cortex from both temporal lobes.
What impact did that have on his memory, what memories were impaired and what were not?
He had anterograde amnesia but not retrograde amnesia.
He lost ability to form new declarative memory, but could retrieve old memories and form nondeclarative memory.
What studies implicate the hippocampus in encoding declarative long-term memories?
London taxi drivers have larger hippocampus.
H.M. having anterograde amnesia about declarative memory.
What findings indicate that the hippocampus is not involved in the storage of most memories?
H.M. could retrieve memories consolidated before his surgery.
What information do place and grid cells in hippocampus process?
1) Place cells: Encoding selective spatial locations.
2) Grid cells: Encoding latitude and longitude info, active at intersection point.
