W9: Colour Vision

Question 1

Explain the 3 perceptual dimensions of colour

Answer 1

(200 Steps) Hue: average of distribution of wavelengths entering eye
(20 Steps) Saturation: how washed a colour is; depends on wavelength distribution width
(500 Steps) Brightness: how light a colour is/area under curve

Question 2

Explain colour constancy and the luminance spectrum

Answer 2

Ability to segment reflectance spectrum from illuminated spectrum perceiving reflectance properties despite illumination changes

Luminance spectrum = R spectrum x Illumination spectrum

Question 3

Explain retinex theory of colour constancy and how it is fooled

Answer 3

Visual system compares luminance profile of adjacent areas to determine if colour differences are due to illumination (large areas) or actual colour change (local)

Can be fooled by lights/shadows

Question 4

Explain trichromatic colour theory and its setbacks

Answer 4

Colour perceived from 3 colour receptors producing the primary colour sensations of Red, Blue, Green

Can’t account for colour mixtures/lost pairs/after images

Question 5

Explain Opponent Colour Theory

Answer 5

Colour perceived from 4 primaries in 2 chromatic channels: Red vs Green, Blue vs Yellow) and an achromatic channel: Black vs White

Question 6

Explain Dual Process Colour theory

Answer 6

both trichromatic and opponent-colour theories correct for some different stages of colour processing

Trichromatic stage followed by opponent process stage; based on behavioural data/theory

Question 7

Explain different dichromacy for colour blindness

Answer 7

Protananopia (Missing red cones - R/G confusion)
Deuteranopia (Missing green cones - R/G confusion)
Tritanopia (Missing blue cones - B/Y confusion)

Question 8

Explain 2 ways of diagnosing colour blindness

Answer 8

Ishihara colour plates - patient detects number
Farnsworth 100 Hue Test - patient orders 25 pieces within each of the 4 hues