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PSYC2022 - Perception & Cogition > Slides Week 5 > Flashcards

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
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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)
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3
Q

Visible Spectrum of light

A

Between 400-700 nm

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4
Q

Three Steps to Colour Perception

A
  1. Detection
  2. Discrimination
  3. Appearance
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5
Q

Colour Percption - Detection

A

Wavelengths of light must be detected

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6
Q

Colour Perception - Discrimination

A

We must be able to tell the difference between one wavelength and another

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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.

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8
Q

Scotopic Light

A

Light intensity that is bright enough to stimulate Rod Receptors but too dim to stimulate Cone Receptors

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9
Q

Photopic Light

A

Light that is bright enough to stimulate Cone Receptors AND saturate Rod Receptors to their maximum responses

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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
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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
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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
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13
Q

Metamers

A
  • Different mixtures of wavelengths that look identical
  • Generally any pair of stimuli that are perceived as identical despite physical differences
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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
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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
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16
Q

Pigment

A
  • A material that changes the colour of reflected or transmitted light.
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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
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18
Q

Colour Appearance

A

What Colours will be perceived?

  • Colour Space
  • RGB Colour Space
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19
Q

Colour Space

A
  • A three-dimensional space that describes all colours
  • There are several possible colour spaces
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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
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21
Q

HSB Colour Space

A

Defined by Hue, Saturation, and brightness

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22
Q

HSB Colour Space - Hue

A
  • The chromatic aspect of light
  • The perceived colour of light
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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
Q

Trichromatic and Opponent Process

A
  • 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
Q

Opponent Cell Physiology

A
  • Lateral Geniculate Nucleus has cells that are most greatly stimulated by spots of light with centre-surround organisation
27
Q

Cone-opponent cells

A
  • A neuron whose output is based on a difference between sets of cones
  • These cone-opponent cells also have a centre surround organisation
28
Q

Opponent Colour Theory

A
  • 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
Q

Double Opponent Cells

A
  • 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
Q

Hering’s Idea of Opponent Colours

A
  • 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
Q

Forbidden Colours

A
  • 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
Q

Equiluminance

A
  • A more recent replication of Forbidden Colours
  • Billock & Tsu (2010)
  • suggests Forbidden Colours may be created by using Equiluminance
33
Q

Hue Cancellation Experiments

A
  • 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
Q

Unique Hue

A
  • 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
Q

Qualia

A
  • 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
Q

Does everyone see colours the same way?

A
  • Yes - Lindsey & Brown asked Americans to name colour patches and everyone used the 11 Basic Colours
  • Maybe - Various cultures describe colour differently
37
Q

Cultural Relativisim

A
  • In sensation and perception it is the idea that basic perceptual experiences may be determined in part by the cultural environment
38
Q

Colour Anomalous

A
  • 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
Q

Types of Colour Anomalous

A
  • Deutaranope
  • Protanope
  • Tritanope
  • Cone Monochromat
  • Tetrachromat
  • Rod Monochromat
  • Achroatopsia
  • Anomia
40
Q

Deuteranope

A

An absence of L-Cones

41
Q

Protanope

A

Due to an absence of L-Cones

42
Q

Tritanope

A

Due to an absence of S-Cones

43
Q

Cone Monochromat

A

Has only one cone type; truly colour blind

44
Q

Tetrachromat

A

Due to having an extra cone

Concetta Antica - tetrachrome painter

45
Q

Rod Monochromat

A
  • Has no cones of any kind or type
  • Truly colour blind and very visually impaired in bright light
46
Q

Achromatopsia

A

Inability to see due to cortical damage

47
Q

Anomia

A
  • Inability to name objects or colours
  • In spite of the ability to see and recognise them
  • Typically due to brain damage
48
Q

Colour Contrast

A
  • 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
Q

Colour Assimilation

A
  • 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
Q

Afterimages

A

A visual image seen after a stimulus has been removed

51
Q

Negative Afterimage

A
  • 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
Q

Colour Constancy

A
  • 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
Q

Why is colour constancy possible

A
  • 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
Q

Colour Vision and Human Behaviour -

Ellio & Niesta, 2008

A

Males perceived women as more socially desirable and attractive when they were wearing Red clothes (Ellio & Niesta, 2008) or lipstick (Gueguen, 2012).

55
Q

Colour Vision and Human Behaviour -

Hill & Barton 2005

A
  • Analysed outcomes in four sports in the 2004 Olympics and found athletes clad in red were more likely to win.
56
Q

Colour Vision and Human Behaviour -

Sanches-Vives et al., 2013

A

Found that shining a red light on a virtual arm lowered pain tolerance for heat stimuli.

57
Q

Colour Vision and Human Behaviour -

Elliot et al., 2007

A

Participants who were exposed to the colour red performed significantly worse on an IQ test compared to green or grey

PSYC2022 - Perception & Cogition (16 decks)

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