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
What did Edwalrd Hering sugest
Opponency: Red-Green; Blue-Yellow. First stage: trichromatic; Opponent stage
Define neural substrate
Indicate a part of the nervous system underlying a behaviour or physiological state
Kraukskopf (1982): Aims, Method & Stimuli
Aims: Simple colour detection (Presence or Absense binary)
- Small disc whose colour varied in time along an axis of opponent colour space
- Participants indicated whether a test pulse was visible 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
L+M = Bluish Yellowishness (Luminance)
L-M = Reddish Greenishness
S - (L+M) = Blackish Whitishness
Kraukskopf (1982): Results
Distance from centre = Adapted - Unadapted Threshold
Bigger difference from centre = More adaptation effect
Kraukskopf (1982): Results Interpretation
2 Chromatic and 1 Acrhomatic Axis = Opponency
- ) Each axis shows independent adaptability
- Threshold only raised by adapting to a stimulus along the same axis (unaffected by adaptation to other axes)
2.) Orthogonality: 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
Group of neurons involved in colour vision
What are properties of cardinal neurons
- ) Chromatic sensitivity clustered along cardinal axes (RG/BY/BW): To get pattern of independent adaptability
- ) Change in output after prolonged exposure
How does the visual system work
Photoreceptors > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex
LGN and Cortex connections
More V1 to LGN than LGN to V1
What are cells in the layers of the LGN
- ) Parvo Cellulular: Small (Retinal P cells)
- ) Konio Cellulular: Medium
- ) Magno Cellular: Big (Retinal M cells)
Derrington (1984): Aim
Are the 3 LGN cells grouped along in cardinal axis?
Derrington (1984): Stimuli and Methods
Macaque LGN neuron
- Receptive field locations established with coloured spot stimuli (see how output of neuron change as a function of colour and luminance properties as in opponent space)
- Stimuli modulated until a minimum “null response” is found. Silent substitution method.
What is the silent substitution method in Derington (1984)
Two coloured light exchange with no effect on output of neurons (If Red switch to Blue and no effect = neurons inresponsive and orthogona axisl)
Derrington (1984): Results
Neurons “chromatic signature” fell into 3 subgroups.
1.) Parvo Cellular: Less sensitive to luminance; Specific senstivity to either RG or BY
> Hence, only this gives a true sense of colour
- ) Konio Cellulular: Not sure. But they have a large number of S cones (maybe augment)
- ) Magno Cellular: Very sensitive to luminance; Weak colour sensitivity.
Can Derington’s (1984) study explain cardinal properties
Not fully. The neurons did not change output after prolonged exposure (adaptation). Only established chromatic signature.
Krauskopf (1990) Aim
Replicate Derington (1984) in the cortex
Krauskopf (1990) Results
- In none of each cortical group, there is no clustering. Neurons redistributed across colour plane along the cortex.
- Showed strong adaptation effect & selectivity. Reduce output after prolonged exposure.
LGN vs V1
LGN: Cardinal colour signature but no adaptation
V1: No cardinal colour signature but adapt
What does all the findings suggest in colour and cardinal behaviour. What does it imply?
LGN (Chromatic Signature) + V1 (Adaptation) = Detection of presence.
- There is no modulation of colour. There is no “cardinal neurons” doing “cardinal behaviour”.
