Colour part 2

Question 1

What is another way we perceive colour?

Answer 1

Opponent process theory

Question 2

What is the opponent-process theory based on?

Answer 2

Colour perception is based on 4 primary colours
Color perception is based on 3 opponent mechanisms
Colour perception is a 3-dimensional construct

Question 3

What are the three colour dimensions according to the opponent-process theory

Answer 3

Red/green
Blue/yellow
white/black

Question 4

How were the three colour dimensions determined for the opponent-process theory?

Answer 4

something is never redish and greenish at the same time

Question 5

What are the 3 things that support the opponent process theory?

Answer 5

Complementary after image
Hue cancellation experiments
Opponent cells in monkey LGN

Question 6

How do complementary after images work?

Answer 6

After staring at colours they look like the opposite colour –> brain interprets it as being the opposite

Question 7

How do hue cancellation experiments work?

Answer 7

Figure out how much yellow you need to cancel our blue or vise versa –> they are opponent mechanisms

Question 8

What is the strength of blue/yellow opponent mechanisms? What does the diagram show?

Answer 8

It takes a lot of yellow to cancel out the blue

They don’t overlap–> not blue and yellow at same time –> mutually exclusive

Question 9

What is the strength of red/green opponent mechanism? what does the diagram show

Answer 9

Takes a lot of red to cancel out green
Red is located both at the high and short wavelengths
They don’t overlap

Question 10

What does the graph look like for the strength of blue/yellow and red/green mechanisms?

Answer 10

Combo of both opponent mechanisms.
Where they switch there is neither colour. Draw a line to determine the colour at that wavelength

Question 11

Where are opponent cells found?

Answer 11

in LGN

Question 12

What are opponent cells

Answer 12

cells that are excited by blue and inhibited by yellow

or cells that are excited by red and inhibited by blue

only represent colour along 2 axis

Question 13

If you have a +B and -Y opponent cell and you shine a blue light on it what happens

Answer 13

faster firing

Question 14

If you have a +B and -Y opponent cell and you shine a yellow light on it what happens

Answer 14

inhibited

Question 15

How are receptors wired together to create red/green opponent cells? Both cases

Answer 15

+R -G (+L, - M) = excitatory L cone and a inhibitory M cone

-R +G (+M, -L) = excitatory M cone and inhibitory L cone

Question 16

How are receptors wired together to create blue/yellow opponent cells? Both cases

Answer 16

+S-ML (+B, -L) = Excitatory S cone and combination of inhibitory M and L cone on another cell

-S, +ML (+L, -B) = Inhibitory S and excitatory combination of M and L

Question 17

What is the colour equivalent of +S, -LM and +L -M

Answer 17

+B, -Y
+R, -G

Question 18

How do we reconcile the trichromatic and opponent process theories?

Answer 18

Treat it as 2 different steps of colour perception

Takes output of receptors and combines them in certain ways

light goes in and triggers receptors (trichromatic theory), then the opponent cells combines the actavation of receptors (opponent-process theory) then info goes to the brain

Question 19

What are the limitations of the trichromatic and opponent process theories?

Answer 19

There theories propose a direct link between proximal stimulus and colour percept

Colour is determined by activation of the L, M, and S photoreceptors

Colour should just be based on light hitting eye then –> not true

Question 20

What are the examples of the limitations of trichromatic and opponent process theories?

Answer 20

Squares of colours look different if they are surrounded by different colours
Or line looks like different colours –> doesn’t tell us this

Scintillating grid illusion –> black circles in center

Rubix cube

Question 21

Explain the rubix cube llusion that is a limit of the trichromatic and opponent process theories

Answer 21

The squares are actually grey –> same cone activation for both but we percive it as blue in yellow light and yellow in blue light

colour processing depends on more than just light hitting eye and 3 cone types

Question 22

What does the light that reflects off an object depend on?

Answer 22

Reflectance - how the object reflects light
Illumination - how light falls on the object

Question 23

Explain what happens if we shine 100 units of light vs 10000 units of light on a checker board?

Answer 23

90 units of light reflected off white and 10 units reflected off black
9000 units reflected off white
1000 unites reflected off black

we consider the ratio not the total amount of light boucing off

Question 24

What is lightness constancy?

Answer 24

We tend to perceive whites, grays, and blacks the same under varying illuminations

Question 25

What is the principle that describes lightness constancy?

Answer 25

Ratio principle

Question 26

What is the ratio principle?

Answer 26

Under even illumination, the ratio of reflected light guides perception of lightness absolute amount of light doesn't matter it is the relative amount of light reflected

Question 27

What makes lightness constancy more complicated?

Answer 27

shadows

Question 28

Which squares are reflecting the same amount of light (same lightness)?

Answer 28

A and B A is darker so it reflects less light B is in the shadow so it gets less light to reflect

Question 29

What do the soft edges of shadows create?

Answer 29

Illumination edges

Question 30

What do illumination edges do to our perception?

Answer 30

Our perception of colour depends on them

Question 31

What is the difference between an illumination edge and reflectance edges? for lightness constancy

Answer 31

Illumination edges: same surface, different illumination Reflectance edges different surface with same illumination

Question 32

What guides the distinction between illumination edges and surface edges?

Answer 32

cues including penumbra of shadows and orientation of surfaces

Question 33

What does the light that reflects off an object depend on for colour?

Answer 33

Reflectance - how much the object reflects each wavelength Illumination - how much of each wavelength falls on object

Question 34

What does incandescent light show on a wavelength chart?

Answer 34

higher wavelengths

Question 35

What does sunlight show on a wavelength chart?

Answer 35

it is evenly spread out

Question 36

What does led light show on wavelength chart?

Answer 36

mixed wavelength

Question 37

What happens to the reflected light if you shine each type of light on a green shirt?

Answer 37

Incandescent --> higher wavelength sunlight --> middle LED --> lower wavelength

Question 38

What is colour constancy?

Answer 38

We tend to perceive objects with the same reflectance as having the same colour under varying illuminations

Question 39

What is an example of colour constancy?

Answer 39

can tell room is the same colour even if light is different

Question 40

What is chromatic adaptation?

Answer 40

receptors for a colour fatigue/adapt after continuous stimulation

Question 41

What happens if you put a red light on a green paper and on a person looking at it?

Answer 41

paper only looks slightly red (more yellow) because brain adapts to red to interpret the colour

Question 42

What happens if you put a red light on a green paper and but not on a person looking at it?

Answer 42

paper looks more red

Question 43

How does chromatic adaptation work in lush and arid environments?

Answer 43

Greeness decreases after being in a lush environment Greenness increases after being in arid environment

Question 44

Give example of how context influences colour constancy?

Answer 44

Grey spot in rubix cude looks blue in yellow light and yellow in bluelight

Question 45

How does memory effect the colour we perceive? Explain the experiment?

Answer 45

Image of banana, orange, and 2 shapes were presented to people and they were asked to create a colour match to the grey The grey for the orange was more orange The grey for the banana was more yellow It didn't work for the shapes

Question 46

How does context effect colour constancy? (general)

Answer 46

context is used to infer wavelengths of illumination

Question 47

How does memory effect colour constancy?

Answer 47

Prior knowledge/expectations about colour may provide a top-down influence

Question 48

What are the three factors that effect color constancy?

Answer 48

Chromatic adaptation Context Memory

Question 49

In what areas of ventral pathway does colour get processed?

Answer 49

Retina (cone), LGN, blobs in V1, V2, V4 (specialized)

Question 50

What type of cells for processing colour are in LGN?

Answer 50

Single-opponent receptive field cells

Question 51

What are Single-opponent receptive field cells

Answer 51

Cells that have center surround sensitivity to colour. Center is excited by M cones (green) and inhibited by L cones (red) or for other colours too

Question 52

What type of cells are found in V1 blobs?

Answer 52

Double-opponent receptive field cells

Question 53

What are double-opponent receptive field cells?

Answer 53

One side is excited by M (green) and inhibited by L (red) and the other side is inhibited by M and excited by L

Question 54

What does V4 do for colour processing?

Answer 54

higher/more subjective level of colour perception

Question 55

What happens if you lesion V4?

Answer 55

Lesion can cause cerebral achromatopsia

Question 56

What is achromatopsia?

Answer 56

cortical colorblindness due to brain damage

Question 57

What are other cortical areas involved in colour perception? What did they do for the study?

Answer 57

Green area for colour specifically Yellow area for shape, texture and colour Ask people if colour is same or different to see which areas respond

Question 58

What do researchers use to test colour perception abilities?

Answer 58

Ishihara plates

Question 59

What are the 4 types of colour anomalies?

Answer 59

Monochromatism Dichromatism Anomalous trichromatism Tetrachromatism

Question 60

What is Monochromatism?

Answer 60

Only have rods, no cones (or one cone type) True colour blindness (everything is grey) Only know how much light not frequency info

Question 61

What is Dichromatism?

Answer 61

Missing only one of three cone types

Question 62

What are the three types of dichromatism?

Answer 62

Tritanopia Deuteranopia Protanopia

Question 63

What is Tritanopia?

Answer 63

Missing S-cones

Question 64

What is Deuteranopia?

Answer 64

Missing M-cones

Question 65

What is Protanopia?

Answer 65

Missing L-cones

Question 66

What is anomalous trichromatism?

Answer 66

Have all 3 cone types but one (or more) of the opsins is slightly different than normal (different frequencies)

Question 67

What is tetrachromatism?

Answer 67

Have 4 cone types

Question 68

What is considered congenital colourblindness?

Answer 68

monochromatism

Question 69

What types of dichromatism are most common in males?

Answer 69

Protanopia Deuteranopia

Question 70

What colour blindness is protanopia and deuteranopia? what does it look like?

Answer 70

red-green colour blindness stuff looks blue and yellow

Question 71

What colour blindness is tritanopia? what does it look like?

Answer 71

green/blue colour blindness looks pink (and a bit blue)

Question 72

Why is dichromatism more common in males?

Answer 72

Sex-linked issues because genes related to cones are on the X chromosome Males (XY) only have one chance to get a typical copy

Question 73

Is anomalous trichromatism also more common in males?

Answer 73

Yes

Question 74

What are the three types of anomalous trichromatism?

Answer 74

Protanomaly Deuteranomaly Tritanomaly

Question 75

What is Protanomaly?

Answer 75

Malfunctioning L cones

Question 76

What is Deuteranomaly?

Answer 76

Malfunctioning M cones

Question 77

What is tritanomaly?

Answer 77

Malfunctioning S-cones

Question 78

What does anomalous trichromatism look like?

Answer 78

Some colour diminishment

Question 79

How do you get tetrachromatism?

Answer 79

Women who's father has anomalous trichromatism due to an X-chromosome mutation may have both a typical copy of the gene from her mother and the anomalous copy This results in 4 cone types

Question 80

What are the 4 cone types in tetrachromatism?

Answer 80

3 regular and one mutated L, M. S and L'

Question 81

What are the spectral sensitivities of the 4 cone types?

Answer 81

L> L' > M > S

Question 82

How many colours can tetrachromats see?

Answer 82

Maybe 100 million

Question 84

How many colours would a tetrachromat require inorder to match all stimuli in a colour matching experiment?

Answer 84

4

Question 85

Do tetrahchromats perceive metamers in the same way as trichromats?

Answer 85

No, a metamer for a trichromat may look different for a tetrachromat

Question 86

What would happen if there were two stimuli with the same S, M and L responses but the L' cones have different responses?

Answer 86

A trichromat would perceive them as metamers (identical) but a tetrachromat would perceive them as different

Question 87

What does colour in art teach us about colour on the page?

Answer 87

Colour on page is different from the colour we perceive

Question 88

What is local colour?

Answer 88

colour of paint on page

Question 89

Give examples of painters who mastered local colour

Answer 89

Monet in snow painting Zurburan in orange painting (not typical orange colours) Self portrait by Rembrant

Question 91

What does the painting A Sunday afternoon on the island of la grande jatte show?

Answer 91

Playing with idea that colour on page has complicated relationship to how something is perceived Uses colour for shadows