Topic 4: Colour

Question 1

why do we perceive colour?

Answer 1

it provides info about the world
-signaling info, perceptual organization, object recognition, cultural transmission (colours mean different things in different societies), aesthetics

Question 2

wavelengths

Answer 2

we can detect light form 400-700 nm

Question 3

pure wavelengths

Answer 3

monochromatic light

• single wavelength where you dtect the actual wavelength
• laser pointer

Question 4

reflectance curves

Answer 4

we usually see light from all visible wavelengths

-something looks red because theres more red compared to other wavelengths

Question 5

white/grey/black

Answer 5

reflect all wavelengths equally

vary on percentage of reflectance

Question 6

reflective and subtractive colour mixing

Answer 6

Cyan magenta yellow process colour
ex. blue paint absorbs more lights than blue so its reflected
yellow + blue = green as combo of absorbed wavelengths

Question 7

transmission and additive colour mixing

Answer 7

RGB colour model

LCD computer monitors

Question 8

colour space

Answer 8

humans can discriminate at least 2 million colours

use 3d colour space

Question 9

Hue
saturation
Value

Answer 9

• chromatic or rainbow colour (circular)
• amount of white added (horizontal_
• how light/dark the colour is (vertical)

Question 10

other versions of colour space

Answer 10

hue saturation lightness

red green blue

Question 11

inverted spectrum argument

Answer 11

is my perception of red the same as yours

subjective quality of colour - how would we even figure this out

Question 12

thrichromatic theory

Answer 12

-colour is based on 3 principle colours
colour perception is based on 3 receptor types (SML)
colour perception is a 3d construct
adding more colours wont make a difference and two doesnt work

Question 13

colour matching experiments

Answer 13

P attempts to match test field by adjusting the brightness of lights shining on comparison field
-exactly 3 lights of different wavelengths are necessary to match all test field colours

Question 14

metamerism

Answer 14

two different stimuli are perceptually identical
580 and (530+620) can be perceived as the same colour
how computer monitors work

Question 15

opponent process theory

Answer 15

colour perception is based on 4 primary colours

• colour perception is based on 3 opponent mechanisms
• colour perception is 3d construct

Question 16

opposites of opponent process theory

Answer 16

red and green
blue and yellow
black and white

Question 17

complementary afterimages

Answer 17

shows connection between colours as opposite colour shows up after on blank square

Question 18

hue cancellation experiments

Answer 18

need to understand wiring of receptors opponent cells in LGN

-certain cell will fire the most for blue and not yellow - specific to colour detector

Question 19

limitations of trichromatic and opponent process theories

Answer 19

propose a direct link between proximal stim and colour percept
-colour is determined by activation’s of SML photoreceptors
surrounding context has large influence on our perception of colour

Question 20

illumination

reflectance

Answer 20

how light falls on the object
-how the object reflects light
brain attempts to separate these two even though they arrive together

Question 21

lightness constancy

ratio principle

Answer 21

we tend to perceive whites/grey/balck the same under varying illumination
-under even illumination, the ratio of reflected light guides perception of lightness

Question 22

shadow and lightness constancy

Answer 22

areas in shadow have soft edges
solid edges make it look darker
soft edges (shadow make it look lighter)

Question 23

chromatic adaptation

Answer 23

P’s will perceive the paper as being redder when the light source is red and your light is white
both you and paper in red light - you can see it as green since youre adapted
can change levels of certain colour in attempt to notice differences

Question 24

v4 lesion

Answer 24

can cause cerebral achromotopsia

cortical colourblindness

Question 25

monocrhomatism

dichromatism

Answer 25

only have rods and no cones, true colour blindness

missing one of the 3 cone types

Question 26

protanopia
deuteranopia
tritanopia

Answer 26

missing L cone
missing M cone
missing S cone

Question 27

anamalous trichromatism

tetrachromatism

Answer 27

have all 3 cone types but one of the opsins is slightly different than normal
have 4 cone types