Colour

Question 1

Colour subtraction

Answer 1

Subtracting (absorbing) parts of the spectrum of light present in ordinary white light, by means of coloured pigments

Question 2

What colour would you see when directing a white light through both the red filter and the green filter?

Answer 2

Black

This is because a pure red filter only allows through red light and a pure green filter only allows through green light. Together this means that they allow no light and appear black

Question 3

What is the 3 receptor basis of colour vision?

Answer 3

possessing of three independent channels for conveying colour information, derived from the three different types of cone cells in the eye:
green, red and blue

Colors perceived are determined by differing proportions of excitation in the three cones types.

Question 4

What is the problem of colour constancy?

Answer 4

A particular wavelength combination reflected from a surface (and the particular combination of excitation in the three cone types) can yield experience of different colours in different situations.

Question 5

True or false?

Receptive fields and the expectation that colour perceived would reflect only the light coming from the patch in question.

Answer 5

True

Question 6

Reflected light is a property of what?

Answer 6

The environment

Question 7

The visual system, via the cones detects what?

Answer 7

Reflected light and interprets the light-energy as colour.

Question 8

Define colour constancy

Answer 8

Our ability to perceive different objects as always having the same colour independently of where we see them, or in what lighting conditions.

Question 9

Why are artificial fluorescent lights are yellowish to white

Answer 9

That is, the wavelengths of light generated by a light bulb is yellow

Question 10

What part of the brain has the parts most important for vision and where is it located?

Answer 10

Occipital lobe and at the back of the brain

Question 11

What part of the occipital lobe is imprortant for vision?

Answer 11

The visual cortex

Question 12

What do cells found in the first part of the visual cortex - area V1 do?

Answer 12

They respond to a certain combination of wavelengths of light

They sum up the different cones’ excitation with a different weight for each cone

Question 13

Where do V1 cells get there input from?

Answer 13

photoreceptors

Question 14

From area V1 the cells project (send fibres - axons) which other visual area? and via what area?

What do cells do in this area?

Answer 14

V4 via V2

Cells respond in more complex fashion, in a way that corresponds more to the perceived colour of an object.

They have activity that parallels our conscious experience

Question 15

What area is constancy apparent in?

Answer 15

Constancy is not apparent in area V1, but it is in area V4

Question 16

In terms of colour constancy, perceived colour of an object depends not only on the relative amount it excites the three kinds of cones but…

Answer 16

but also on the relative amount it excites the objects around it

(relative brightness in each of the three cone channels)

by considering the overall balance of cone excitation across multiple objects, the visual system is able to compensate for the colour of the light.

Question 17

When white light is beamed through a prism what happens?

Answer 17

The prism separates the white light into the different wavelengths of which it is composed, which we perceive as different colours.

Question 18

Longer wavelengths bend more or less than shorter wavelengths?

Answer 18

Less

Big car turning round a corner is harder

Question 19

the wavelengths of visible light range from about?

Answer 19

10-6 to 10-7m

Question 20

What is a nanometer?

Answer 20

a billionth (10-9) of a metre and is usually abbreviated nm (1 m = 1,000,000,000 nm).

Question 21

True or false?

Different wavelengths in the visible range of the electromagnetic spectrum correspond to different colours (hues).

Answer 21

True

ultraviolet, blue, green, orange, infared

Question 22

The colours of surfaces are determined by?

Answer 22

the wavelength composition of the light reflected off the surface.

Question 23

Why does a black surface look black?

Answer 23

Because it absorbs all the visible wavelengths of light falling (or incident) on the surface, so there is no light reflected.

Question 24

Why does a white surface look white?

Answer 24

It reflects all the visible wavelengths in the incident light

Question 25

What does the fovea do?

Answer 25

Fovea is the central portion of the retina that contains only cones (rod free zone). It forms the site which produces the sharpest vision and greatest colour discrimination. It is located in the centre of the macula.

Question 26

What does the retina do?

Answer 26

receives light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.

Question 27

What does the optic disk do?

Answer 27

Because there are no rods or cones overlying the optic disc, it corresponds to a small blind spot in each eye.

Where neurons come into the eye

Question 28

What are the two types of photoreceptors?

Answer 28

rods and cones (three types of cones and one rod)

Question 29

Where are rods distributed?

Answer 29

Across the retina, except on the fovea and the blind spot, they are more sensitive to light than cones

Question 30

When do rods work well?

Answer 30

Low light, not involved in colour, this is why at night we can’t see colour

Question 31

Where are cones concentrated?

Answer 31

In the fovea and are sparse in the periphery of the retina

Question 32

What is the main difference in cone types

Answer 32

Their sensitivity or responses to the different wavelengths, a consequence of their different photopigments.

Question 33

Order of length of wavelength sensitivity of cones

Answer 33

Blue
Green
Red

Question 34

What determines the colour we see?

Answer 34

The pattern of activity among the three cone types that determines the colours we perceive.

Question 35

The perception or the experience of colour is created by what?

Answer 35

Our nervous system

Question 36

True or false?

Light rays are electromagnetic forms of energy and have no colour at all. They have different wavelengths, and our visual cortex transforms that difference into a colour experience.

Answer 36

True

Question 37

What are colour deficiencies associated with?

Answer 37

Missing cone types

Question 38

Why is colour blindness more common in males?

Answer 38

Because the genes for the red and green colour receptors are located on the X chromosome, of which males have only one and females have two.

Question 39

What is the additive colour system?

Answer 39

The colour of light resulting from the mixture or addition of two or more wavelengths of light.

Question 40

What is the receptive field?

Answer 40

Used to describe the part of the sensory surface that an environmental stimulus must impinge upon to make a neuron fire.

Question 41

What is light?

Answer 41

electromagnetic waves

Question 42

What is a tuning characteristic?

Answer 42

the type of stimulus necessary to make the neuron work