1. Colour Vision Theory Flashcards
Rods give what type of vision?
Scotopic Vision- NOT used in colour vision (this is vision of the eye in low- light conditions).
Rods or Cones, Which one is found more in the retina?
Rods
What are the 3 types of cones?
- S-blue
- M-green
- L-red
Different types of cones are sensitive to different parts of the..?
Visual Spectrum
Number of colours you can discriminate is defined by the ?
Number of cones
Human visual range?
390-700nm
Describe the sensitivity of cones?
Each cone has an individual sensitivity.
What was the colour matching experiment+ Young’s theory?
Any test wavelength can be matched by mixing 3 other wavelengths.
CONCLUSION: Colour vision depends on a 3 receptor mechanism.
Why can’t we see colour with only 1 cone?
Electric potential difference between inside and outside the cell.
What is the principle of univariance?
All wavelength information is lost.
You can not see colour with only 1 cone is related to which concept?
Principle of univariance
What is meant by monochromat?
Only 1 type of photoreceptor
What is the minimum amount of cones required to perceive colour?
2
Why can’t you see in the dark?
You only have 1 type of rod, so you have nothing to compare against
What is the opponency theory?
Colour is processed by bipolar channels. Referred to as red-green, blue-yellow and black-white.
Are trichromatic and opponency theories related?
Trichromacy: occurs at receptor level.
Opponency: First occurs at the ganglion cell and LNG level. Then the colour opponency channel input from different cones.
Optic radiations connect?
LGN to higher cortical areas (temporal lobe).
Pathways from retina to LGN
Parvocellular pathway: R-G Chromatic channel. Achromatic luminance channel.
Koniocellular pathway: B-Y Chromatic channel.
Where does visual processing in the cortex start?
V1
How are cells in V1 arranged? And what does the arrangement correspond to?
In hypercolumns- each correspond to a retinal point.
Neurones from koniocellular layers synapse in?
Layer 3- known as “blobs”
Neurones from parvocellular layers synapse in?
Layer 4Cβ then post-synaptic projections to layer 3.
Role of blobs
Analysis of object colour
Role of interblobs
Analysis of object form
Describe how the processing of achromatic and chromatic information occurs?
Processed in parallel
V4 receives input from?
Blobs and interblobs
Role of V4
Colour constancy
Role of colour constancy?
Ensures colour perceived remains same under different illuminations. Assesses colour of overall visual field. Processed in V4.
Describe why S-cones are sensitive to blue light?
Within the photoreceptive cells, the photopigment is sensitive to blue light
Thomas Young’s theory was demonstrated by?
A series of experiments with colour matching.
Monochromats can not discriminate between different wavelength of colours, but can still identify the difference, how?
Certain colours will dark, others light.
How many cones do you need atleast to perceive colour?
2
What is a monochromat?
They only have 1 type of photoreceptor
Photoreceptors are what type of cells?
Light sensitive cells
Are cones specific to a particular wavelength?
Cones have a range of wavelengths to which they are sensitive but have the highest sensitivity to a particular wavelength.
Can monochromats make colour discriminations ?
No, certain colours will appear darker.
What response is perceptive with RED- ON Cells?
- Red is perceived when cell is excited.
- No perception when the cell is inhibited.
Is it true that opponent cells have receptive fields?
YES- both in the retina & LGN
Describe the B-Y opponent cell
The receptive field is NOT centre-surround.
1. You perceive blue when cell is excited.
2. No perception when cell is inhibited.
Y+B cells receptive field is identified at?
LGN
What is required to tell 2 colours apart?
Receptive field that contributes to a type of cone and another region next to the cone that contributes to other types of cones.
