Lecture Week 5

Question 1

From Spots to Stripes

Answer 1

• The retinal ganglion cells are interested in detecting spots of light • The brain is interested in perceiving stripes

Question 2

Principles of Colour Vision

Answer 2

• Colour is not a physical property • There is no such things as colour • Colour is a psychophysical property of vision • The way we perceive reflected light is interpreted as colour by the brain

Question 3

Three steps to colour detection

Answer 3

1. Detection
2. Discrimination
3. Appearance.

Question 4

Colour Detection: Step 1 - Detection

Answer 4

Wavelengths of light must be able to be detected by receptors

Question 5

Colour Detection: Step 2 - Discrimination

Answer 5

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

Question 6

Colour Detection: Step 3 - Appearance

Answer 6

• We decide how to categorise perceived colours of lights and surfaces
• We want these categories to be stable over time

Question 7

Scotopic light

Answer 7

• Relates to Rods
• Dim light, moonlight, no colours
• Does not stimulate Cone Receptors
• When Rods are saturated they don’t respond

Question 8

Photopic Light

Answer 8

• Bright enough to stimulate Cones and Saturate Rods
• Stimulates photoreceptors to maximum responses

Question 9

Preferential Absorbtion

Answer 9

• Cones exitatory activity changes depending on the wavelength of light
• Three cone types prefer their maximally sensitive light of short, medium or long

Question 10

Principle of Univariance

Answer 10

• A single Photorecptor can give the same response to an infinite set of wavelength variations
• Thus one photoreceptor alone cannot discriminate colours based on wavelength
• We need 2-3 cones to discriminate colours from light wavelengths
• We can detect light with one cone but not discrmininate colour with only one cone

Question 11

Trichromatic Theory

Answer 11

• Also known as Young-Helmholz theory
• We have three types of cones
• We need to know the variance in Nanometers between S-cones, M-cones and L-cones to pinpoint the exact Nanometers of a particular wavelength and perceive a colour

Question 12

Metamers

Answer 12

Sometimes different mixtures of wavelengths may look identical but but have different levels of Nms; they may thus be perceived as identical

Question 13

Additive Colour Mixing

Answer 13

• What happens when we mix different wavelengths of light
• The wavelengths add together and this will change the perception
• The lights do not actually combine physically, but the mind will add them together to change the perception

Question 14

Non Spectral Colours

Answer 14

• There is no such thing as purple light wavelengths
• We perceive Spectral colours when the edges of two wavelengths blend together.

Question 15

Opponent Cell Physiology

Answer 15

• Lateral Geniculate Nucleus has cells that have centre surround organisation
• They are maximally stimulated by spots of light

Question 16

Cone-opponent Cells

Answer 16

• A neuron that receives energy from two or more sets of cones
• Its output is based on the difference between these cones
• Also have centre-surround organisation

Question 17

Opponent Colour Theory

Answer 17

• Colour Perception depends on the output of three mechanisms -
• Each mechanism is based on two colours
  
  • Red-Green
  • Blue-Yellow
  • Black-White