Topic 7: Colour Perception

Question 1

How is the perception of colours created?

Answer 1

Created by nervous system activity when light that has no colour is reflected into your eyes and activates three types of retinal cone photopigment

Question 2

What are the three main functions colour perception serves?

Answer 2

Can help us identify things
Can help us classify things
Can help inform our actions

Question 3

Brain injury resulting in an inability to name colours

Answer 3

Colour anomia

Question 4

Colours of the visible spectrum are associated with…

Answer 4

different wavelengths of light

Question 5

How are object colours determined?

Answer 5

Determined by the specific wavelengths of light that are reflected from, or transmitted through, that object

Question 6

Colours with hue

Answer 6

Chromatic colours

Question 7

Occurs when some wavelengths are reflected from an object more so than others

Answer 7

Selective reflection

Question 8

Colours without hue

Answer 8

Achromatic colours

Question 9

% of light reflected from an object vs. wavelength

Answer 9

Reflectance curves

Question 10

What do reflectance curves tell us about colour perception?

Answer 10

Reflect a range, but each selectively reflects more light in one part of the spectrum over the others = colour perception of that object

Question 11

Occurs when only some wavelengths pass through transparent objects while others do not.

Answer 11

Selective transmission

Question 12

Creation of colours that occurs when coloured paints/pigments are mixed together

Answer 12

Subtractive colour mixing

Question 13

Explain subtractive colour mixing

Answer 13

Paints absorb the same wavelengths they absorbed when they were alone, so the only wavelengths reflected are those that are reflected by all paints

Question 14

Creation of colours that occurs when lights of different colours are superimposed

Answer 14

Additive colour mixing

Question 15

Explain additive colour mixing

Answer 15

When coloured lights are superimposed all the light that is reflected from the surface by each light alone is also reflected when lights are combined.

Question 16

Colours that appear in the visible spectrum

Answer 16

Spectral colours

Question 17

Colours that do not appear in the visible spectrum

Answer 17

Nonspectral colours

Question 18

What is the major limitation in describing colour?

Answer 18

Language: Difficulties describing differences between colours

Question 19

Three perceptual dimensions of colour which together create and allow us to describe the large number of colours we can perceive…

Answer 19

Hue
Saturation
Value

Question 20

Perception of chromatic colours, or variations of these colours

Answer 20

Hue

Question 21

Amount of “whiteness” added to a colour

Answer 21

Saturation

Question 22

“Light-dark dimension” of a colour

Answer 22

Value

Question 23

Idea that our perception of colour is determined by the activity in three different cone photopigments that have different sensitivities

Answer 23

Trichromacy of colour vision

Question 24

Evidence that it is a function of three distinct pigments comes from…

Answer 24

Colour matching experiments

Question 25

According to the trichromacy of colour vision theory, light of a particular wavelength stimulates...

Answer 25

Each of the 3 photopigments, but to different degrees

Question 26

What are the relative wavelengths of short, medium, and long waves as they relate to photopigments?

Answer 26

(S) - Short-wavelength pigment = ~419 nm (M) - Medium-wavelength pigment = ~ 531 nm (L) - Long-wavelength pigment = ~ 558 nm

Question 27

Rare form of colour blindness – “complete colour blindness”

Answer 27

Monochromacy

Question 28

What produces monochromacy?

Answer 28

bsence of cone receptors results in the perception of only shades of lightness (white, grey, black), with no chromatic colour present

Question 29

Colour vision with two pigments

Answer 29

Dichromacy

Question 30

Considering the difficulties in determining what exactly a dichromat perceives, what do we rely on?

Answer 30

Those with unilateral dichromacy

Question 31

What are the three types of dichromacies?

Answer 31

Protanopia: Missing long-wavelength photopigment Deuteranopia: Missing medium-wavelength photopigment Tritanopia: Missing short-wavelength photopigment

Question 32

What did Hering (1878) claim with regards to colour perception?

Answer 32

Our perception of colour is determined by the activity of two opponent mechanisms: a blue-yellow mechanism and a red-green mechanism

Question 33

What is the modern evidence to support Hering's opponent-process theory of colour vision?

Answer 33

Presence of opponent neurons in the visual cortex Excitatory response to wavelengths in one part of the colour spectrum; inhibitory response to wavelengths in the other part

Question 34

Our perception of an object’s colour remains relatively constant when the amount of illumination is changed

Answer 34

Colour constancy

Question 35

Our perception of an object’s lightness remains relatively constant under different intensities of illumination

Answer 35

Lightness constancy

Question 36

Why is colour constancy helpful?

Answer 36

Helps with object recognition/identification regardless of illumination

Question 37

Why does lightness constancy occur?

Answer 37

Occurs because the relative proportion of light being reflected into the eye stays the same regardless of illumination