Lecture 7 - Colour Vision

1
Lecture 7 - Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

2
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

3
Physical Basis for Colour Perception

• Newtons prism experiments
• white light composed of all frequencies
• spectral reflectance function
• refraction, absorption reflection
• colour mixing
• subtractive (pigments filters)
• additive (projection)

4
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

5
Individual Differences in Colour Perception

• complementary colours
• Hering's hue circle
• 4 unitary hues
• 2 achromatic colours
• colour measurement standards
• CIE chromaticity diagram

6
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

7
Physiological Basis for Colour Perception

• spectral reflectance function
• colour constancy
• retinal distribution of cones
• resolution limit
• additive colour mixing
• e.g. pointillist paintings (Suerat), colour TV

8
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

9
Trichromatic Theory

• spectral sensitivity curve
• 3 types of cones
• metameric match and the principle of univariance
• the problems with one- and two-pigment systems
• colour experience determined by relative activity
  of 3 cone types

10
Key Point

• variation in wavelength will not, by itself, lead
  to a perception of change in colour
• i.e. 1-pigment system will only see differences
  in brightness
• need at least 2 systems to signal change in ratio
  of responses
• (remember everything is signaled by neural
  responses)

11
Key Point

• colour is simply the name we give to the
  subjective experience that corresponds to our
  ability to distinguish between different
  wavelengths of light
• it depends entirely on the eye that is looking

12
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

13
Opponent Process Theory

• pairs of colours, opposing each other
• 3 fundamental colour processes
• one achromatic B W
• two chromatic R-G, B-Y
• evidence for opponent processes
• perceptual impossibilities
• colour contrast
• afterimages
• LGN cell responses

14
Colour Vision

• Physical Basis for Colour Perception
• Individual Differences in Colour Perception
• Physiological Basis for Colour Perception
• Trichromatic Theory
• Opponent Process Theory
• Colour Deficiencies

15
Colour Deficiencies

• dichromacies
• protonopia - missing L type
• deuteranopia - missing M type
• tritanopia - missing S type
• equiluminant chromatic stimuli
• Ishihara plates