Perceiving colour

Question 1

What is colour good for?

Answer 1

The detection and segmentation of objects, ripeness of fruit and veg.

Question 2

What is it in the environment that allows us to perceive change in colour?

Answer 2

The dependance on the amount of visible light waves, the more light reflected off an object the colour will change.

Question 3

How do we perceived different wavelengths?

Answer 3

Short-Blue
Medium- Green
Long- Red
Long and medium together- Yellow
Long medium and short together-White.

Question 4

What is the process of transduction?

Answer 4

When a photon strikes a photopigment, it splits it into two molecules (isomerization).
The splitting starts a chemical reaction that causes the photoreceptor to send an electrical signal to the bipolar cell. i.e. transduction took place.
The bipolar cell conveys this electrical signal to the ganglion cell that sends it up the optic nerve towards the brain.

Question 5

Which two element make up a photopigment?

Answer 5

Opsin and retinal.

Question 6

How are different spectral sensitivities created?

Answer 6

Due to the absorption spectra of the individual visual pigments.

Question 7

At what spectra do rod pigments absorb best at?

Answer 7

500nm

Question 8

At what spectra do cone pigment absorb best at?

Answer 8

Short (s)- 420nm
Middle (m)-530nm
Long (L)- 560nm

Question 9

How much light can 480 and 600 wavelengths absorb?

Answer 9

480=10%

600= 5%

Question 10

What is the principle and univariance?

Answer 10

The idea that wavelength and light are interchangeable due to the only and main function always being isomerization in the same type of photoreceptor, i.e. single class of photoreceptors.

Question 11

What does the principle of univariance show about rod cells?

Answer 11

They cannot signal colour as they only have a single type of photo pigment therefore no matter the wavelength of light intensity they are still interchangeable.

Question 12

Why can cone cells produce colour but rods cant?

Answer 12

Because cone cells have 3 different photo pigments and spectral sensitivities, S,M and L.

Question 13

What colours so S M and L sensitivities produce in cone cells?

Answer 13

S- Blue spectrum
M- Green and neutral spectrum
L- Red spectrum

Question 14

How do cone cells produce all of the colour wheel out of the 3 pigments?

Answer 14

Because multiple wavelengths can be transmitted at once causing colours such as yellow to be visible.

Question 15

Why does one specific colour become the most visible?

Answer 15

Because the colour that becomes visible directly correlates to the pigment that is the most active.

Question 16

What is the Trichromatic theory of colour vision?

Answer 16

Thomas Young and Herman von Helmholtz theory in 19th century. Derived from psychophysical experiments of colour matching in human subjects.

Question 17

What is the colour matching experiment?

Answer 17

Participant had dials in which the wavelengths of the photo pigment can be controlled producing, S M and L waves. Participants had to use the waves to match the colour presented by the observer.

Question 18

What were the findings of the colour matching experiment?

Answer 18

Subjects with normal vision could not match all test wavelengths unless they had more than 2 wavelengths (at least 3). Concluded that colour vision is trichromatic, required three colour mechanisms.

Question 19

What did Ewald Hering do in the 1800’s?

Answer 19

Observed that when colours that are perceptually similar are arranged in a circle they can fall into four distinct groups. Red, Green, Blue or Yellow.

Question 20

What are the two perceptual opponent channels suggested by Hering?

Answer 20

Blue- Yellow, Red-Green

Question 21

Why are the Opponent-Process and Trichromatic theory not mutually exclusive?

Answer 21

Because neither psychologist had knowledge of the rod and cone cells, and the three photopigments. Neither theory is wrong they just do not explain the same aspect of colour theory.

Question 22

Which elements of colour vision do the Trichromatic theory and the Opponent-Process theory explain?

Answer 22

Trichromatic theory- explains the responses of the cones in the retina.
Opponent-process theory explains the neural responses of cells connected to the cones further up the visual system.

Question 23

What is additive colour mixing?

Answer 23

When mixing light of different wavelengths superimposing blue and yellow lights lead to white as all three S,M and L wavelengths are interacting.

Question 24

What is subtractive colour mixing?

Answer 24

When mixing paints or different pigments, additional pigments reflect fewer wavelengths therefore mixing blue and yellow leads to green rather than red. Mixing all three colours would lead to dark colours or black.

Question 25

What is saturation?

Answer 25

Intensity of the dominant wavelengths in the colour, adding white to a colour makes it less saturated.

Question 26

What is hue?

Answer 26

The perception of the frequency of light.

Question 27

Are there any physical colour in the world?

Answer 27

No it is only a percept, there is only different distributions of spectral intensity that are capture by three types of cone cells and due to their different spectral sensitivities they perceive colour.

Question 28

Why do different organisms see colour differently?

Answer 28

Because they have different photoreceptors which have different sensitivities to spectra.

Question 29

What is monochromatisms?

Answer 29

Only rods function, ability to perceive in black white and grey tones. Poor visual acuity, very sensitive to bright light.

Question 30

What is protanopia?

Answer 30

Affects about 1% males and 0.02% females, do not have any L cones.

Question 31

What is deuteranopia?

Answer 31

Affects about 1% males and 0.01% females, no M cones.

Question 32

What is tritanopia?

Answer 32

Affects 0.002% males and 0.001% females, no S cones.

Question 33

Why are deficiencies more popular in males than females?

Answer 33

Because the genome for colour deficiencies is on the X chromosome therefore when there is a defect females can overrule it as they have another X whereas males do not, sex linkage condition.

Question 34

What type of deficiency is protanopia, tritanopia and deuteranopia?

Answer 34

Dichromats, only have 2 working cone cell types not three.

Question 35

How is the cells on the retina organised?

Answer 35

Rod or cone cells converge to a bipolar cell which then is followed by a ganglion cell connecting to the optic nerve.