Slides Week 5 Flashcards
1
Q
Basic Principles of Colour Vision
A
- We see objects when we detect the light reflected from them
- Depending on Atomic Structure objects absorb some wave lengths and reflect others
- It is reflected light that is perceived as colour
- Colour is not a physical property but a psychophysical property
2
Q
Atomic Structure
A
- Atoms consist of three basic particles: protons, electrons, and neutrons
- The nucleus (center) of the atom contains the protons (positively charged) and the neutrons (no charge)
- The outermost regions of the atom are called electron shells and contain the electrons (negatively charged)
3
Q
Visible Spectrum of light
A
Between 400-700 nm
4
Q
Three Steps to Colour Perception
A
- Detection
- Discrimination
- Appearance
5
Q
Colour Percption - Detection
A
Wavelengths of light must be detected
6
Q
Colour Perception - Discrimination
A
We must be able to tell the difference between one wavelength and another
7
Q
Colour Perception - Appearance
A
We want to assign perceived colours to lights and surfaces in the world and have those perceived colours be stable over time regardless of different lighting conditions.
8
Q
Scotopic Light
A
Light intensity that is bright enough to stimulate Rod Receptors but too dim to stimulate Cone Receptors
9
Q
Photopic Light
A
Light that is bright enough to stimulate Cone Receptors AND saturate Rod Receptors to their maximum responses
10
Q
Preferential Absorption
A
- Retina contains three types of cone receptors that differ in sensitivity to light
- They are each most sensitive at
- short wavelenghts
- medium wavelenghts
- long wavelentghs
- There is one type of Rod and it’s peak sensitivity sits between short and medium wavelenghts
11
Q
Principle of Univariance
A
- There is an infinite set of wavelength intensity combinations
- They can elicit exactly the same response from a single type of photoreceptor
- A single type of photoreceptor cannot make colour discrimination based on wavelength
- A single photorecptor has different responses to lights of different wavelenths but the same intensity
12
Q
Trichromatic Theory
A
- Also known as the Young-Helmholtz theory
- The theory that the colour of any light is defined by:
- Our visual system
- The relationships of numbers
- Outputs of three receptor types now know to be the three cones
13
Q
Metamers
A
- Different mixtures of wavelengths that look identical
- Generally any pair of stimuli that are perceived as identical despite physical differences
14
Q
Additive Colour Mixing
A
- Physical Definition: A mixture of lights reflected from a surface to the eye
- Psychological Definition: perceiving colour in the effects of those lights added together
- Shining two lights that look one colour each and perceiving a different colour producing and additive colour mixture
15
Q
Subtractive Colour Mixing
A
- A mixture of pigments where some of the light from pigment A is subtracted from pigment B
- Only the remaining pigment contributes to the perception of colour
- This is denoted when we use colour filters
16
Q
Pigment
A
- A material that changes the colour of reflected or transmitted light.
17
Q
The limits of a rainbow
A
- If you combine lights that look red and blue you get purple, But there is no purple on the spectrum
- Purples are non-spectral colours that join the ends of the spectrum into a colour circle
18
Q
Colour Appearance
A
What Colours will be perceived?
- Colour Space
- RGB Colour Space
19
Q
Colour Space
A
- A three-dimensional space that describes all colours
- There are several possible colour spaces
20
Q
RGB Colour Space
A
Defined by the outputs of long, medium and short wavelengths
- Long Wavelength = Red
- Medium Wavelength = Green
- Short Wavelength = Blue
21
Q
HSB Colour Space
A
Defined by Hue, Saturation, and brightness
22
Q
HSB Colour Space - Hue
A
- The chromatic aspect of light
- The perceived colour of light
23
Q
HSB Colour Space - Saturation
A
The Chromatic Strength of a hue
24
Q
HSB Colour Space - Brightness
A
The distance from black in colour space
25
Trichromatic and Opponent Process
* Information about the difference between pairs of cone receptor signals is sent to the brain
* Create afterimages and simultaneous contrast
* Sending separate S, M, L signals to the brain is not particularly useful as M and L have similar sensitivities
* Computing differences between Cone responses is more useful to transmit information
26
Opponent Cell Physiology
* Lateral Geniculate Nucleus has cells that are most greatly stimulated by spots of light with centre-surround organisation
27
Cone-opponent cells
* A neuron whose output is based on a difference between sets of cones
* These cone-opponent cells also have a centre surround organisation
28
Opponent Colour Theory
* The theory that perception of colour depends on the output of three mechanisms
* Each is based on an opponency between two colours:
* Red-Green
* Blue-Yellow
* Black-White
* Some LGN cells excited by L-Cone activation in the centre but inhibited by M-Cone Activation in their surround and vice versa
* Other cells excited by S-Cone activation in centre but inhibited by (L+M)-Cone activation in there surround
29
Double Opponent Cells
* First found in the Primary Visual Cortex
* Are more complicated, combining the properties of two colour opponent cells from LGN
* Opponent cell information is processed further to allow for opponent colours
30
Hering's Idea of Opponent Colours
* All the colours on the Colour Circle" could be represented by two pairs of opposing colours
* We can have bluish green (cyan)
* We can have reddish yellso (orange)
* We can have bluish read (Purple)
* We cannot have reddish green or bluish yellow
31
Forbidden Colours
* Crane & Piantanida (1983) used eye tracking to force blue and yellow to maintain a stable position on the retina
* This forced two colours to merge causing an impossible colour to appear between blue and yellow
* Subsequent efforts to replicate the findings failed
32
Equiluminance
* A more recent replication of Forbidden Colours
* Billock & Tsu (2010)
* suggests Forbidden Colours may be created by using Equiluminance
33
Hue Cancellation Experiments
* Developed by Hurvich & Jameson (1957) as a way to quantify opponency
* Measured how much of the opposing colour (red) is needed to be added to cancel out the green
34
Unique Hue
* Any of the four colours that can be described with only a single colour term:
* Red
* Yellow
* Green
* Blue
* We can use the hue cancellation paradigm to determine the wavelengths of unique hues
35
Qualia
* Private conscious experiences of sensation and perception
* The question 'is my perceptin of blue the same as your perception of blue?' is a question of qualia
36
Does everyone see colours the same way?
* Yes - Lindsey & Brown asked Americans to name colour patches and everyone used the 11 Basic Colours
* Maybe - Various cultures describe colour differently
37
Cultural Relativisim
* In sensation and perception it is the idea that basic perceptual experiences may be determined in part by the cultural environment
38
Colour Anomalous
* About 8% of the male and 0.5% of the female population has some form of colour deficiency (colour blindness)
* Most colour blind individuals can still make discriminations based on wavelenght
*
39
Types of Colour Anomalous
* Deutaranope
* Protanope
* Tritanope
* Cone Monochromat
* Tetrachromat
* Rod Monochromat
* Achroatopsia
* Anomia
40
Deuteranope
An absence of L-Cones
41
Protanope
Due to an absence of L-Cones
42
Tritanope
Due to an absence of S-Cones
43
Cone Monochromat
Has only one cone type; truly colour blind
44
Tetrachromat
Due to having an extra cone
Concetta Antica - tetrachrome painter
45
Rod Monochromat
* Has no cones of any kind or type
* Truly colour blind and very visually impaired in bright light
46
Achromatopsia
Inability to see due to cortical damage
47
Anomia
* Inability to name objects or colours
* In spite of the ability to see and recognise them
* Typically due to brain damage
48
Colour Contrast
* A colour perception effect in which the colour of one region induces the opponent colour in a neighboring region
* When many colours are present, they can influence each other
49
Colour Assimilation
* A colour perception effect in which two colours bleed into each other, each taking on some of the chromatic quality of the other.
* Colours very rarely appear in isolation. Usually, many colours are present in a scene.
50
Afterimages
A visual image seen after a stimulus has been removed
51
Negative Afterimage
* An afterimage whoes polarity is the opposite of the original stimulus
* Light stimuli produce dark negative afterimages
* Colours are complementary
* This is a way to see opponent colours in action
52
Colour Constancy
* The tendency of a surface to appear the same colour under a fairly wide rangeof illuminants
* To achieve colour constancy we discount the illuminant and determine what the true colour of a surface is regardless of how it appears
53
Why is colour constancy possible
* We assume light sources and surfaces are constant in colour
* Bananas always look yellow in the dark and bright light
* One study showed ppl perceived a yellow banana even when the picture was grey.
* Produced a blue banana to remove the visual illusion
* Example of Opponenet colours
54
Colour Vision and Human Behaviour -
Ellio & Niesta, 2008
Males perceived women as more socially desirable and attractive when they were wearing Red clothes (Ellio & Niesta, 2008) or lipstick (Gueguen, 2012).
55
Colour Vision and Human Behaviour -
Hill & Barton 2005
* Analysed outcomes in four sports in the 2004 Olympics and found athletes clad in red were more likely to win.
56
Colour Vision and Human Behaviour -
Sanches-Vives et al., 2013
Found that shining a red light on a virtual arm lowered pain tolerance for heat stimuli.
57
Colour Vision and Human Behaviour -
Elliot et al., 2007
Participants who were exposed to the colour red performed significantly worse on an IQ test compared to green or grey
