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Survey of the Senses > 2.8 Colour Perception > Flashcards

2.8 Colour Perception Flashcards

1
Q

Colour Perception is…

A

INDIRECT . we dont see colour, we code it

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2
Q

Light as a coloured stimulus:

A 
we only see a small amount of the electromagnetic spectrum 
wavelength: HUE 
amplitude: BRIGHTNESS 
purity: saturation 
AND 
reflectance: lightness
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3
Q

reflectance

A

amount of light object reflects.

Crucial fo colour perception

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4
Q

newtons prism experiment

A

first to study colour in experiment

demonstrated white is all colours

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5
Q

colour is a property of..

A

light not of an object

object is simply reflecting the light and absorbing selected part of spectrum

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6
Q

perceived colour is a combo of…

A

nature of light falling on the surface (illumination)

nature of absorption and reflectance of surface

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7
Q

color wheel

A

developed by newton through his prism experiments

classifies on wavelength (hue) not brightness or purity/saturation

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8
Q

color solid

A

by munsell (1940s)

included saturation and brightness

series of colour wheels stacked on top of each other

3D stacks is brightness

each stack is a specific hue and middle of wheels is achromatic,

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9
Q

Achromatic light

A

colourless light
determines light purity
more achromatic light = less saturation
(middle of the colour wheels)

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10
Q

Colour mixing

A

subtractive (paint and filters ) and additive (light)

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11
Q

subtractive primaries

A

red yellow blue

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12
Q

additive primaries

A

blue red green

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13
Q

when mixing complementary colours

A

you get achromatic light
additive = opposite of colour wheel

additive = white

subtractive = dark brown

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14
Q

CIE Chromaticity space

A

quantifying amount of each primary (produces specific hue)
y axis: % of green
x axis: % if red
what is left = % of blue

when adding brightness: 
z axis (3d): brightness

computers also include saturation and brightness

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15
Q

Neural Coding

A

Perception of colour relies on a neural code. which is coded in electrical activity in visual system

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16
Q

Benham colour wheel

A

example of sensation not equaling perception

as the disc spins (black and white) you end up seeing colour. opposite direction give you its complementary colour

shows that perception of colour is influenced by:

  • Speed
  • Distance
  • Direction
  • Lighting conditions
17
Q

Univariance

A

photoreceptors response is summarized by one variable that specifies amount of light aborbed.

Each photopigment responds to preferred wavelength
- but the neural response of photoreceptors does not specify wavelength

therefore given proper intensity, all wavelengths can effect a single receptor in some way

therefore we must have more than one type of photoreceptor (which must be solved through the theories)

18
Q

Trichromatic Theory

A 
Young and Helmholtz 
- it was an intuitive theory 
- human eye has 3 photopigments 
- relative activation of each determines the colour percieved 
.... % of cone activation = coding 
Red Green and Blue

Supported by:

  • Rushton: composition of ingoing and returning light found 2 cone types
  • Microspectrophotometry: using dissected retinal tissue determined how much light of each wavelength is absorbed found 3 cone types
19
Q

Absoprtion Curve

A

relative responsiveness of each cone. Blue far off then green then red

20
Q

Opponent process theory

A

Hering (1878)
“Why cant we see blueish-yellow or reddish-green
- There must be an opponent process
= 6 primary colours (3 types of receptors in pairs)
- 3 cones complementing 3 receptors (in pairs equaling 6)

Hue Cancellation
Some colours cancel each other out
because complementary adding = achromatic
—- must be a decrease and increase in activity

21
Q

Achromatic system in Opponent Process

A

White Black
Codes brightness
increase in activity with light

22
Q

Chromatic System in Opponent Process

A

Red/Green
Increase w/ red, decrease w/ green

Yellow/Blue
increase w/ yellow, decrease w/ blue

23
Q

Truth about colour perception

A

@ receptor level: trichromatic theory
@ higher levels: opponent process theory

evidence: responses to coloured light at horizontal cell level (opponent responses to colour)

24
Q

Short wavelength Cones

A

Excitatory: +B , -Y
Inhibitatory: +Y , -B

25
Q

Medium wavelength cones

A

Excitatory: + G, -R , and +Wh - Bl
Inhibitatory: +R -G and -Wh +Bl

26
Q

Long Wavelength Cones

A

Excitatory: +Y -B, and +R -G ,and +Wh -Bl
Inhibitatory: +B -Y, and +G -R, and -Wh +Bl

27
Q

Colour opponency

A

oppoenent cells throughout visual system except receptors
EX: LGN cells generate both on/off responses to send info to higher processing
in cortex its more complex: double opponent process

28
Q

LGN opponency

A

+ in the middle, - in surround / vise versa (on/off)

29
Q

Visual cortex opponency

A

+- in middle and -+ in surround

30
Q

Theory on hue perception

A

relative amount of activity in opponent cells

31
Q

Theory of lightness perception

A

activity rate of black and white cells

32
Q

Theory on saturation perception

A

which cells are more active

33
Q

Trolands theory

A

explaining why benham color wheel doesnt work with theories

this is because single channel may be used to percieve color, with color information coded into neural “morse code”

34
Q

Factors that effect colour vision

A

region of retina stimulated (better in fovea)

exposure duration (too quick: white patch, too long: adaptation)

Deficits (loss of cones)

  • red/green : 8% genetic x linked
  • yellow/blue genetic autosomal
35
Q

achromatopsia

A

selective loss of colour vision associated with damage to temporal and/or occipital areas

36
Q

Red/Green Colour Blind

A

dichromatic colou deficiency. absense of either red or green cones

37
Q

Anamalous Trichomacy

A

one of the 3 cone types has abnormal absoprtion curve

38
Q

constancy of colour

A

perceived colour of object is determined by light reflecting off of it

which depends on the light hitting in (the wavelength)

and sunlight is constantly changing

our brain fixes this through:

  • light adaptation
  • colour contrast

Survey of the Senses (12 decks)

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