Colour Perception

Question 1

Primate Colour Perception

Answer 1

especially well-suited for distinguishing red and yellow against a green background

• helpful for foraging
• detecting predators or prey, determining ripeness of fruit, richness of soil, sunset to predict weather

Question 2

Colour Perception in Other Animals

Answer 2

can see other colours that we can’t (UV spectrum)

• birds: signals of health in colour of feathers
• bees: responds to specific patterns that we are unaware of for foraging (nectar maps)

Question 3

Colour Mixing

Answer 3

few receptor types whose activity can be combined in various proportions to make every conceivable colour

Question 4

Primary Colours

Answer 4

the three colours that can be combined in various proportions to make every colour in the spectrum
-base colour - cannot be reduced

Question 5

Subtractive Colour Mixing

Answer 5

when coloured pigments selectively absorb some wavelengths and reflect others

• kindergarten paint mixing
• primary colours are red, yellow and blue

Question 6

Complementary Colours

Answer 6

opposite respective primary colour, always makes brown when mixed

Question 7

Additive Colour Mixing

Answer 7

when coloured lights add dominant colour to the mixture

• used in our nervous system
• primary colours are red, green, and blue - used together in different proportions to make all the different colours that we see
• complementary colour mixing gets grey or white

Question 8

Trichromatic Theory

Answer 8

proposes that the retina contains 3 different kinds of cones

Question 9

Empirical Observations of Colour Mixing

Answer 9

you can match all of the colours of the visible spectrum by the appropriate mixing of 3 primary colours, therefore you only need three types of receptors
-human eye has three types of cones, spectrally selective photopigments maximally respond to primary colours

Question 10

Elegance of Trichromatic Theory

Answer 10

fits with additive colour mixing

physiological evidence for 3 types of cones

Question 11

Problems with Trichromatic Theory

Answer 11

yellow seems to be a primary colour
complementarity
after image - why is yellow the afterimage of blue?

Question 12

Opponent Process Theory

Answer 12

each colour receptor is made up of pairs of opponent colour processes

• each receptor is capable of being in one of 2 opponent states, but can only be in one state at a time
• green/red and blue/yellow
• bright/dim receptors are excited by every wavelength

Question 13

Elegance of Opponent Process Theory

Answer 13

can explain why after image is the complementary colour

• why mixtures of wavelengths appear white
• fits with why we can imagine some colours and not others

Question 14

In the Retina

Answer 14

Trichromatic Theory

• 3 component receptors or cones that are maximally responsive to a certain wavelength
• red, green, blue
• response of receptors differentially affect what happens further down the line

Question 15

Ganglion Cells and Onward

Answer 15

Opponent Process Theory

-red/green, blue/yellow, light/dark

Question 16

Red Light (Example)

Answer 16

Stimulates red cone, excite red/green ganglion cells, signal that stimulus is red

Question 17

Yellow Light (Example)

Answer 17

equally stimulates red and green cones, red cones excites red/green ganglion cells while green cone inhibits red/green ganglion cells and excites blue/yellow ganglion cell

• red/green signals cancel out
• blue/yellow is excited and signals that stimulus is yellow

Question 18

Afterimage

Answer 18

is the complementary colour of the thing you just stared at

Question 19

Rate of Fire

Answer 19

signals to the brain what colour is being seen

-faster(excites) or slower(inhibits) than baseline means different colours

Question 20

Rebound Effect

Answer 20

when a receptor is excited/inhibited for a prolonged period of time, the same colour will go into the opposite state when you stare at a neutral colour

Question 21

High Resolution Channels

Answer 21

one cone to one ganglion cell

-small receptive field that, when stimulated, will cause the ganglion cell to increase or decrease its firing rate

Question 22

Low Resolution Channels

Answer 22

(away from fovea) many cones to one ganglion cell

-large receptive field that causes ganglion cell to increase or decrease firing rate

Question 23

Receptive Fields

Answer 23

Donut shaped

• respond to colour in the centre-surround fashion
• increases rate of firing if strikes in the middle portion (red)
• decreases rate of firing if strikes outer ring (green)
• response is strongest if both of the above is true, weakest if the opposite is true

Question 24

Higher Level Colour Processing

Answer 24

sent to the LGN after ganglion cells

has 6 layers

Question 25

Magnocellular

Answer 25

first two layers of LGN

-processing form, movement and depth

Question 26

Parrocellular

Answer 26

next 4 layers of LGN

-colour processing from red/green cone and finer detail

Question 27

Koniocellular

Answer 27

sublayers of LGN

-info from blue cones to primary visual cortex

Question 28

Cytochrome Oxidase (CO) Blobs

Answer 28

regions of cytochrome oxidase containing neurons that are distributed at roughly equal intervals over the primary visual cortex

• neurons respond exclusively to colour information, show little/no response to shape, orientation or movement
• oval in shape
• arranged into columns that project down into layers 2 and 3 (and less so in layers 5 and 6) of the primary visual cortex
• respond in opponent fashion
• passed into visual association areas (analyzed further in ventral stream)

Question 29

Total Colour Blindness

Answer 29

everything is in shades of grey

-vary rare

Question 30

Protanopia

Answer 30

red/green colour blindness

• cones filled with photopigments for green
• no way of responding differently to green and red
• lacking photopigments, not cones
• can tell the difference if there is a slight difference in the way each colour absorbs light

Question 31

Deuteranopia

Answer 31

Red/green colourblindness
-cones filled with photopigments for red
no way of responding differently to green and red
-lacking photopigments, not cones
-can tell the difference if there is a slight difference in the way each colour absorbs light

Question 32

Tritanopia

Answer 32

Yellow/blue colour blindness

• extremely rare
• equally present in both males and females
• blue cones are either lacking or defective
• see reds/greens/greys