W5 - Colour

Question 1

What is properties of colour

Answer 1

• Interpretation of the brain
• Context-specific

Question 2

What did Issac Newton found in colour

Answer 2

White light is made up up of all visible

Question 3

What did Young and Helmholtz found in colour

Answer 3

3 receptors - Trichromacy RGB

Question 4

What did Edwalrd Hering sugest

Answer 4

Opponency: Red-Green; Blue-Yellow.

First stage: trichromatic

Second stage: Opponent stage

Question 5

Define neural substrate

Answer 5

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

Question 6

Kraukskopf (1982): Aims

Answer 6

Aims: Simple colour detection (Presence or Absense binary)

Question 7

Kraukskopf (1982): Method

Answer 7

• 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)

Question 8

What is a colour space

Answer 8

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

Question 9

What are the 3 cones.

Answer 9

L Cones: Reds

M Cones: Green

S Cones:: Blue

Question 10

What is the cardinal colour space

Answer 10

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

1 Achromatic Axis: Luminance

Question 11

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

Answer 11

Bluish Yellowishness: S - (L+M)

Reddish Greenishness: L-M

Blackish Whitishness: L+ M

Question 12

Kraukskopf (1982): Outcome measure

Answer 12

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

Question 13

Kraukskopf (1982): Results Interpretation

Answer 13

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

Question 14

In psychophysics, who are the subjects

Answer 14

Neurons.

Question 15

What are cardinal neurons. Are there any?

Answer 15

Group of neurons involved in colour vision

No. No single “cardinal neuron”

Question 16

What are properties of cardinal neurons (if any)

Answer 16

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

Question 17

How does the visual system work

Answer 17

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

Question 18

LGN and Cortex connections

Answer 18

More V1 to LGN
Less LGN to V1

Question 19

What are cells in the layers of the LGN

Answer 19

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

Question 20

Derrington (1984): Aim

Answer 20

Are the 3 LGN cells grouped along in cardinal axis?

Question 21

Derrington (1984): Stimuli and Methods

Answer 21

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

Question 22

What is the silent substitution method in Derington (1984)

Answer 22

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)

Question 23

Derrington (1984): Results

Answer 23

Neurons “chromatic signature” fell into 3 subgroups.

Question 24

Derrington (1984): Results from P Cells

Answer 24

1.) Parvo Cellular

Less sensitive to luminance

Senstivity to colour (RG or BY)

Question 25

Derrington (1984): Results from K cells

Answer 25

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

Question 26

Derrington (1984): Results from M Cells

Answer 26

3.) Magno Cellular:

Very sensitive to luminance

NO colour sensitivity.

Question 27

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

Answer 27

Not fully.

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

They only established chromatic signature, not adapatation

Question 28

Krauskopf (1990) Aim

Answer 28

Replicate Derington (1984) in the cortex

Question 29

Krauskopf (1990) Results

Answer 29

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)

Question 30

LGN vs V1 neurons

Answer 30

LGN: Cardinal colour signature but no adaptation

V1: No cardinal colour signature but adapt

Question 31

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

Answer 31

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