W5 - Colour Flashcards
What is properties of colour
- Interpretation of the brain
- Context-specific
What did Issac Newton found in colour
White light is made up up of all visible
What did Young and Helmholtz found in colour
3 receptors - Trichromacy RGB
What did Edwalrd Hering sugest
Opponency: Red-Green; Blue-Yellow.
First stage: trichromatic
Second stage: Opponent stage
Define neural substrate
Indicate a part of the nervous system underlying a behaviour or physiological state
Kraukskopf (1982): Aims
Aims: Simple colour detection (Presence or Absense binary)
Kraukskopf (1982): Method
- Small disc whose colour varied in time along an axis of opponent colour space
- Participants indicated test pulse visiblity before/after prolonged exposure to a stimulus modulated along given axis
- Contrast/visibility of pulse varied until “threshold” reached (75% correct)
What is a colour space
Method by which a light and colour may be represented such that its definition is unique and replicable
What are the 3 cones.
L Cones: Reds
M Cones: Green
S Cones:: Blue
What is the cardinal colour space
2 Chromatic Axes (Colour): R-G; B-Y
1 Achromatic Axis: Luminance
What is the cone’s relationship to the cardinal colour space (What does S,M,L correspond to). Which one is luminance
Bluish Yellowishness: S - (L+M)
Reddish Greenishness: L-M
Blackish Whitishness: L+ M
Kraukskopf (1982): Outcome measure
Distance from centre = Adapted - Unadapted Threshold
(Bigger difference from centre = More adaptation effect)
- If adapted someone on R-G and tested on B-Y
- Distance from centre = 0
- If adapted someone on R-G with greater effects on tulse pulse on R-G, distance from centre
- Distance from centre + big
Kraukskopf (1982): Results Interpretation
2 Chromatic and 1 Acrhomatic Axis = Opponency
1.) Each axis shows independent adaptability/orthogonality
- Threshold only raised by adapting to a stimulus along the same axis (unaffected by adaptation to other axes)
- 3 independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex
In psychophysics, who are the subjects
Neurons.
What are cardinal neurons. Are there any?
Group of neurons involved in colour vision
No. No single “cardinal neuron”
What are properties of cardinal neurons (if any)
- ) Chromatic sensitivity clustered along cardinal axes (RG/BY): To get pattern of independent adaptability
- ) Adapatation/ Change in output after prolonged exposure
How does the visual system work
Photoreceptors > Horizontal > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex
LGN and Cortex connections
More V1 to LGN
Less LGN to V1
What are cells in the layers of the LGN
- ) Parvo Cellulular (P Cells) : Small
- ) Konio Cellulular: Medium
- ) Magno Cellular (M Cells): Big
Derrington (1984): Aim
Are the 3 LGN cells grouped along in cardinal axis?
Derrington (1984): Stimuli and Methods
Macaque LGN neuron
- Coloured spot stimuli to establish receptive field
- Examine neuronal output changes as a function of colour and luminance properties
- Modulated across 3 orthognal planes until “null response” is found
- Silent substitution method
- Preferred stimulus of neuron = Orthogonal to null plane in 3D space
What is the silent substitution method in Derington (1984)
Two coloured light exchange with no effect on output of neurons
This indicates that the neurons are inresponsive and the preferred stimulus is orthogonal (right-angle)
Derrington (1984): Results
Neurons “chromatic signature” fell into 3 subgroups.
Derrington (1984): Results from P Cells
1.) Parvo Cellular
Less sensitive to luminance
Senstivity to colour (RG or BY)
