W5 - Colour Flashcards

1
Q

What is properties of colour

A
  • Interpretation of the brain
  • Context-specific
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2
Q

What did Issac Newton found in colour

A

White light is made up up of all visible

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3
Q

What did Young and Helmholtz found in colour

A

3 receptors - Trichromacy RGB

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4
Q

What did Edwalrd Hering sugest

A

Opponency: Red-Green; Blue-Yellow.

First stage: trichromatic

Second stage: Opponent stage

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5
Q

Define neural substrate

A

Indicate a part of the nervous system underlying a behaviour or physiological state

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6
Q

Kraukskopf (1982): Aims

A

Aims: Simple colour detection (Presence or Absense binary)

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7
Q

Kraukskopf (1982): Method

A
  • 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)
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8
Q

What is a colour space

A

Method by which a light and colour may be represented such that its definition is unique and replicable

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9
Q

What are the 3 cones.

A

L Cones: Reds

M Cones: Green

S Cones:: Blue

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10
Q

What is the cardinal colour space

A

2 Chromatic Axes (Colour): R-G; B-Y

1 Achromatic Axis: Luminance

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11
Q

What is the cone’s relationship to the cardinal colour space (What does S,M,L correspond to). Which one is luminance

A

Bluish Yellowishness: S - (L+M)

Reddish Greenishness: L-M

Blackish Whitishness: L+ M

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12
Q

Kraukskopf (1982): Outcome measure

A

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
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13
Q

Kraukskopf (1982): Results Interpretation

A

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
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14
Q

In psychophysics, who are the subjects

A

Neurons.

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15
Q

What are cardinal neurons. Are there any?

A

Group of neurons involved in colour vision

No. No single “cardinal neuron”

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16
Q

What are properties of cardinal neurons (if any)

A
  1. ) Chromatic sensitivity clustered along cardinal axes (RG/BY): To get pattern of independent adaptability
  2. ) Adapatation/ Change in output after prolonged exposure
17
Q

How does the visual system work

A

Photoreceptors > Horizontal > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex

18
Q

LGN and Cortex connections

A

More V1 to LGN
Less LGN to V1

19
Q

What are cells in the layers of the LGN

A
  1. ) Parvo Cellulular (P Cells) : Small
  2. ) Konio Cellulular: Medium
  3. ) Magno Cellular (M Cells): Big
20
Q

Derrington (1984): Aim

A

Are the 3 LGN cells grouped along in cardinal axis?

21
Q

Derrington (1984): Stimuli and Methods

A

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
22
Q

What is the silent substitution method in Derington (1984)

A

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)

23
Q

Derrington (1984): Results

A

Neurons “chromatic signature” fell into 3 subgroups.

24
Q

Derrington (1984): Results from P Cells

A

1.) Parvo Cellular

Less sensitive to luminance

Senstivity to colour (RG or BY)

25
Q

Derrington (1984): Results from K cells

A

2.) Konio Cellulular: Not sure. But they have a large number of S cones (maybe augment)

26
Q

Derrington (1984): Results from M Cells

A

3.) Magno Cellular:

Very sensitive to luminance

NO colour sensitivity.

27
Q

Can Derington’s (1984) study conclude cardinal properties of neurons?

A

Not fully.

Remember they need to fulfil 2 properties: (1) Chromatic Senstiivity (2) Adaptation

They only established chromatic signature, not adapatation

28
Q

Krauskopf (1990) Aim

A

Replicate Derington (1984) in the cortex

29
Q

Krauskopf (1990) Results

A

V1

  • In each cortical group, lack of clustering (i.e. neurons redistributed across colour plane) suggest no cardinal signature
  • Showed strong adaptation effect (Reduce output after prolonged exposure)
30
Q

LGN vs V1 neurons

A

LGN: Cardinal colour signature but no adaptation

V1: No cardinal colour signature but adapt

31
Q

What does all the findings suggest in about cardinal behaviour? Which neurons?

A

LGN (Chromatic Signature) + V1 (Adaptation) = Detection of presence.

Cardinal Behaviour

There is no modulation of colour. There is no “cardinal neurons” doing “cardinal behaviour”. Can only be explained on the basis of a combination of LGN and cortical properties