Lecture 4 (Colour Perception)-compressed

Question 1

List four functions of colour perception.

Answer 1

• Find things (like berries)
• Determine if fruit is ripe
• Spot and identify poisonous animals
• Identify a potential mate

Question 2

What is visible light?

Answer 2

Electromagnetic radiation with wavelengths varying from about 400 nm to about 700 nm.

Question 3

What constitutes white light?

Answer 3

A mixture of all wavelengths of visible light.

Question 4

Define an opaque object.

Answer 4

An object that light cannot pass through and is not transparent.

Question 5

How is the colour of an opaque object determined?

Answer 5

By the light that it reflects.

Question 6

What happens when an opaque object absorbs blue light but reflects red light?

Answer 6

It looks red.

Question 7

What determines the colour of a transparent object?

Answer 7

The colour it transmits.

Question 8

What does blue paint absorb and reflect?

Answer 8

Absorbs red light but reflects blue and green light.

Question 9

What is the result of mixing blue and yellow paint?

Answer 9

A mixture that absorbs both red and blue light but reflects green light, appearing green.

Question 10

What is the Munsell colour system used for?

Answer 10

To categorize colours according to value (lightness), hue (colour), and chroma (saturation).

Question 11

What are the three types of cones in the retina?

Answer 11

• S cones – 419 nm (blue)
• M cones – 531 nm (green)
• L cones – 558 nm (red)

Question 12

How do humans distinguish between colours?

Answer 12

By comparing the relative activities of the three types of cones.

Question 13

What is monochromatism?

Answer 13

A condition affecting about 1 in 100,000 people where individuals have no functioning cones and see only in shades of gray.

Question 14

What types of colour deficiency are there?

Answer 14

• Monochromatism
• Dichromatism

Question 15

What are the three types of dichromats?

Answer 15

• Protanopes
• Deuteranopes
• Tritanopes

Question 16

What is the prevalence of Protanopia in males and females?

Answer 16

1% in males and 0.02% in females.

Question 17

What colours can Protanopes not distinguish?

Answer 17

Red and green.

Question 18

What do dichromats typically need to match colours?

Answer 18

Just two lights.

Question 19

What visual experience do unilateral dichromats provide insight into?

Answer 19

The experience of dichromats, as they can compare normal trichromatic vision with dichromatic vision.

Question 20

What are the three cone types in the trichromatic theory of colour vision?

Answer 20

Short (S), Medium (M), Long (L)

These cones respond maximally to different wavelengths of light.

Question 21

What do protanopes lack?

Answer 21

L cones

Protanopes are individuals with a type of colour blindness due to the absence of long-wavelength cones.

Question 22

What do deuteranopes lack?

Answer 22

M cones

Deuteranopes are individuals with a type of colour blindness due to the absence of medium-wavelength cones.

Question 23

What do tritanopes lack?

Answer 23

S cones

Tritanopes are individuals with a type of colour blindness due to the absence of short-wavelength cones.

Question 24

What are four functions of colour perception?

Answer 24

• Find things (like berries)
• Determine if fruit is ripe
• Spot (and identify) poisonous animals
• Identify a potential mate

Question 25

What happens when you mix red and green light?

Answer 25

Yellow light ## Footnote Mixing red and green light results in the perception of yellow.

Question 26

What happens when you mix blue and yellow light?

Answer 26

Light that looks white ## Footnote Mixing blue light with yellow light (which contains both green and red) results in light that appears white.

Question 27

What is Protanopia?

Answer 27

Type of colour deficiency where L cones are absent ## Footnote Protanopia affects approximately 1% of males and 0.02% of females.

Question 28

What is Deuteranopia?

Answer 28

Type of colour deficiency where M cones are absent ## Footnote Deuteranopia affects approximately 1% of males and 0.01% of females.

Question 29

What is Tritanopia?

Answer 29

Type of colour deficiency where S cones are absent ## Footnote Tritanopia is very rare, affecting about 0.002% of males and 0.001% of females.

Question 30

What is the opponent-process theory of colour vision?

Answer 30

The perception of colour is determined by three colour opponent channels: red-green, blue-yellow, and white-black ## Footnote This theory explains how colours are processed in the visual system.

Question 31

What is an afterimage?

Answer 31

A visual illusion that occurs after staring at a stimulus for a prolonged period ## Footnote Afterimages provide evidence for the opponent-process theory.

Question 32

What physiological evidence supports the opponent-process theory?

Answer 32

Existence of colour opponent channels ## Footnote Signals from cones are processed in the cortex into these channels.

Question 33

What causes an afterimage when viewing a red stimulus?

Answer 33

L cones are more stimulated than M cones ## Footnote The red percept is activated while the green percept is suppressed.

Question 34

What happens when a white stimulus is shown after viewing a red stimulus?

Answer 34

Green cones respond more strongly than red cones ## Footnote This results in seeing a green afterimage.

Question 35

What happens when viewing a yellow stimulus?

Answer 35

L and M cones are more stimulated than S cones ## Footnote The yellow percept is activated while the blue percept is suppressed.

Question 36

What is colour constancy?

Answer 36

The ability to perceive the colour of an object consistently under varying lighting conditions ## Footnote This phenomenon explains why a green sweater appears green even under red light.

Question 37

What two factors determine the colour of light reflected by an object?

Answer 37

Reflectance and Illumination ## Footnote The reflected light is the product of these two factors.

Question 38

What is habituation in the context of colour perception?

Answer 38

Becoming less sensitive to a specific colour over time ## Footnote This helps explain why objects may appear a different colour under different lighting.

Question 39

What is discounting the illuminant?

Answer 39

The process by which the visual system adjusts for the colour of the light source ## Footnote This allows for accurate colour perception despite changes in lighting.

Question 40

Why can’t we perceive bluish yellow or reddish green?

Answer 40

These combinations are impossible because blue and yellow, and red and green are opponent colours ## Footnote This is a key aspect of the opponent-process theory.