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Survey of the Senses > Midterm 2 - Topic 8 > Flashcards

Midterm 2 - Topic 8 Flashcards

1
Q

Light as a coloured stimulus

A

Visible light only forms a small part of the electromagnetic spectrum

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2
Q

How can light vary?

A

In its wavelength (hue) and amplitude (brightness)

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3
Q

The physical term of wavelength corresponds with the psychological term of:

A

Hue

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4
Q

The physical term of purity corresponds with the psychological term of:

A

Saturation

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5
Q

The physical term of reflectance corresponds with the psychological term of:

A

Lightness

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6
Q

The physical term of intensity corresponds with the psychological term of:

A

Brightness

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7
Q

Newton’s Prism Experiment

A

Sir Isaac Newton was the first person to study colour in a scientific fashion
His simple experiment demonstrated that white is actually made up of all the colours in the visible light spectrum

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8
Q

What is colour?

A

Only a property of light, not of the objects

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9
Q

Objects may look as if they are coloured, but what is really happening?

A

They are only reflecting light from selected parts of the spectrum

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10
Q

What is the perceived colour partly determined by?

A

The nature of the light falling on the surface (illumination) and the nature of the absorption and reflectance of the surface

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11
Q

Who was the first person to propose a way to define colours? What were they aware of?

A

Newton
Was only aware of the wavelength, and did not attempt to classify colours in terms brightness

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12
Q

What did Newton produce? Explain

A

Only produced a colour wheel
Not sufficient to allow a complete account of the organization of colours

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13
Q

What psychological term is represented in the colour wheel?

A

Only hue

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14
Q

What is the most recent way that was developed to organize colour?

A

The Munsell colour solid has been developed as the best way to represent the quasi-infinite # of combinations of hue, saturation, and brightness producing the colours we know

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15
Q

What is the Munsell colour solid?

A

A series of colour wheels stacked on top of each other

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16
Q

In the Munsell colour solid, what is each individual colour wheel in the stack associated with? How about the top and the bottom?

A

A specific brightness
Top: Lighter colours associated with light grays and white
Bottom: Darker colours associated with dark gray and black

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17
Q

What is the physical purity of a stimulus determined by?

A

The amount of achromatic light

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18
Q

Colours on the edge of the Munsell colour solid are:

A

Pure, highly saturated
As we move inward, more and more achromatic light is added, producing less saturated colours

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19
Q

Why is the Munsell colour solid pointed at both ends? Example?

A

Because some combinations of saturation and brightness are impossible
E.g., Cannot have unsaturated black

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20
Q

It is impossible to talk about the organization of colour without:

A

Discussing colour mixing

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21
Q

2 ways to mix colours

A

Subtractive (paint, filters)
Additive (light)

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22
Q

What does colour mixing involve?

A

Combining different colours together

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23
Q

What is the idea behind colour mixing?
Difference in this between subtractive and additive colour mixing

A

To find a set of base colours that will allow any possible colour when mixed together
Subtractive and additive colour mixing require different primary colours

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24
Q

Subtractive colour mixing

A

Mixing pigments
Only involves one source of light
What is reflected back is what we see

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25
Primary colours of subtractive colour mixing
Red, blue, yellow
26
Additive colour mixing
Mixing light Multiple light sources
27
Practical application of colour mixing
Plays and theatres make use of these principles
28
Primary colours of additive colour mixing
Red, blue, green
29
What is a similarity between both types of mixing?
In both types of mixes there are also colours that, when mixed together, will produce complementary colours
30
Where are complementary colours for additive mixtures?
On opposite side of the colour wheel
31
What is the purpose of the CIE chromaticity space?
A way to quantify exactly the amount of each primary colour to produce a given hue
32
CIE abbreviation meaning
Commission Internationale de l'Eclairage
33
What is the CIE chromaticity space based on?
3 imaginary primaries The proportion of each primary defines the hue
34
Explain the CIE chromaticity space graph
y = proportion of green in the mixture x = proportion of red in the mixture Must total to 1.0 Whatever is left is the proportion of blue
35
In CIE chromaticity space, why can't we see 100% on the y or x-axis?
Because it's too saturated
36
How does the CIE space code brightness?
The CIE space/graph can be thought of as a slice through a 3D colour space Third dimension is called z and it specifies the brightness of a stimulus
37
Coordinates of CIE space
Can describe a colour by its x, y, and z coordinates
38
Why should we care about the organization of colour?
We think about this every day when considering what to wear Colours that fit together tend to have common elements in their mixture
39
Code for colour vision
NEURAL CODING vs seeing colour Our perception of colour relies on a neural code Info about the stimulus is encoded as a pattern of electrical activity in the visual system and in the brain
40
What phenomenon of colour vision shows that sensation does not equal perception?
Benham Wheel
41
Benham Wheel
When it spins, we can perceive colour from a given distance When it is stationary, we only perceive black and white
42
What are factors that affect the Benham Wheel?
Distance Speed Direction Lighting conditions
43
What is another factor that can affect our colour perception
Composition of light (i.e., natural sunlight vs artificial light)
44
What does any theory of colour vision have to address?
A basic physiological issue known as the problem of univariance
45
The problem of univariance
Each photopigment responds to a preferred wavelength, but the neural response of the photoreceptor does not specify wavelength Given the proper intensity, all wavelengths can affect a single-pigment receptor in the same way This means that an eye with only one type of photopigment cannot see colours
46
Univariance principle
A photoreceptor's response/how active it is is summarized by one variable that specifies the amount of light absorbed
47
In the univariance problem, what is all coding?
Intensity of light coded in a specific wavelength
48
How do the two leading theories of colour vision handle the problem by univariance? Theorists?
By postulating the existence of more than one type of photoreceptors Helmoltz vs. Hering
49
Trichromatic theory AKA Why?
Young-Helmoltz theory Young proposed it, Helmoltz formalized it
50
Simple basis of trichromatic theory
The human eye has three photopigments, so it is trichromatic (three-coloured)
51
Trichromatic theory
The relative action of each type of pigment determines the colour that is perceived
52
2 broad lines of evidence of support for the trichromatic theory
Rushton Microspectrophotometry
53
Rushton
Composition of ingoing and returning light Two types of cones
54
Microspectrophotometry
Uses dissected retinal tissue Determines how much light of each wavelength is absorbed Three cone types
55
What did Hering claim? Example?
Long before the trichromatic theory was proved right at the receptor level, that it could not explain all the colour phenomena that we can observe Why is that a bluish-yellow or a reddish-green can't exist?
56
Hue cancellation
Some colours cancel each other out: adding the complementary colour (opponent colour) in correct amount results in achromatic (grayish) light
57
What does the opponent process theory state?
That cells show an increase of activity when one colour is presented and a decrease in activity when another colour is presented
58
What does the opponent process theory suggest?
That the visual system has the capability to respond to colour information by decreasing or increasing the response rate
59
What was Hering's formulation of the opponent process theory?
That there are six psychologically primary colours, assigned by pairs to three kinds of receptors
60
opponent process theory 3 kinds of receptors
White-black receptor Red-green receptor Yellow-blue receptor
61
White-black receptor
Increases activity when light is present, decreases activity when light is absent (codes brightness)
62
Red-green receptor
Increase activity with red, decreases activity with green
63
Yellow-blue receptor
Increase activity with yellow, decreases activity with blue
64
What is one problem with Hering's opponent process theory? What do we now know?
Hering thought his theory applied at the receptor level and that the trichromatic theory was wrong That the trichromatic theory holds for the receptor level (Helmotz was correct)
65
Where was the opponent process theory also shown to apply? Explain
At a level beyond the receptors Recording responses to coloured light at the horizontal cells level in goldfish found opponents responses to colour
66
Colour opponency
In fact, opponent cells are found throughout the visual system, except for the receptors For example, LGN cells of the opponent type generate both ON and OFF responses LGN cells send opponent information to higher stages of visual processing
67
Colour opponency in the primary visual cortex
Many cells operate in an opponent process fashion, but not as common as in the LGN Instead, the cortex contains a large number of cells that process colour in a double opponent process
68
Opponency in the visual cortex
Center: Excited red, inhibited green Surround: Excited green, inhibited red Many cells in the visual cortex have a receptive field with a centre that is excited by one colour, and inhibited by the other, while the surround shows the opposite arrangement
69
What is a visual illusion made possible by the opponent process theory
Colour after-effects
70
Hue in opponent process theory
Relative activity among the opponent cells (red/green; blue/yellow)
71
Lightness in opponent process theory
Activity rate of black/white cells
72
Saturation in opponent process theory
Which cells are more active
73
How does the Benham Wheel fit in with the theories of colour vision?
It is not compatible with either the trichromatic or the opponent process theories
74
Summary of theories of colour vision
Three types of photoreceptors - each sensitive to a specific wavelength of light Opponent processes at a level beyond the receptors The time relationship in the neural response
75
Why should we care about theories of colour vision?
They help us understand what is happening in colour vision deficits
76
Explain the region of retina stimulated as a factor affecting colour vision
Colour vision better in the fovea
77
Explain exposure duration as a factor affecting colour vision
Too quick = white patch Too long = adaptation (colour washing off)
78
Colour vision deficiency
Loss of a single cone system Red/green = genetic (X-linked) Blue-yellow = genetic (autosomal)
79
Which type of colour blindness is more common in men? Why?
Red/green Because it is a sex-linked trait
80
Prevalence of red/green colour blindness
8% of men 0.5% of women
81
Achromatopsia
Selective loss of colour vision associated with damage to temporal and occipital areas
82
What is dichromatic colour deficiency caused by? What is it called?
The absence of either red or green cones Red-green colour blindness
83
Anomalous trichromacy
Occurs when one of the three cone types has an abnormal absorption curve
84
Name the three dichromacies
Protanopia Deutereranopia Tritanopia
85
Cause of protanopia
Missing L-type pigment (red)
86
Cause of deuteranopia
Missing M-type pigment (green)
87
Tritanopia cause
Missing S-type pigment (blue)
88
Name the two types of anomalous trichromacies
Protanomaly Deuteranomaly
89
Cause of protanomaly
Abnormal L-type pigment
90
Cause of deuteranomaly
Abnormal M-type pigment
91
Monochromats have
2 missing pigments, therefore they see no colour at all See only luminance level
92
Why should we care about theories of colour vision?
They help us understand what is happening in colour vision deficits
93
What is the perceived colour of an object determined by?
The light reflected from the surface of the object But, the light reflected from an object depends on the wavelengths contained in the light that illuminates the object
94
The wavelength composition of sunlight varies throughout the day. Why do objects not appear to change colour?
Light adaptation and colour contrast allow an object to retain colour constancy

Survey of the Senses (13 decks)

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