Task 3 true colours

Question 1

Colours we can see

Answer 1

blue, green, yellow, red and combinations of these

Question 2

Visible spectrum

Answer 2

from short wavelength (400nm) to long wavelength (700nm)
o	400-450 violet
o	450-490 blue
o	500-575 green
o	575-590 yellow
o	590-620 orange 
o	620-700 red

Question 3

Selective reflection

Answer 3

when some wavelength are more reflected than others

Question 4

Selective transmission

Answer 4

only some wavelength pass through the object or substance (water, cranberry juice)

Question 5

Trichromatic Theory of colour vision: (Thomas Young + Hermann Helmholtz)

Answer 5

o Depends on three different receptor mechanisms
o Colour matching experiment: observers adjust the amount of three different wavelength of light mixed together in a comparison field until the clour of this mixture matched the colour in a single wavelength field
o Young-Helmholtz theory of colour vision:
 Depends on three receptor mechanisms each with different spectral sensitivities
 Light of a particular wavelength stimulates each receptor different, and the pattern of activity results in colour perception

Question 6

Cones

Answer 6

o S-cone: max absorption: at 419-nm
o M-cones: max absorption at 531-nm
o L-cones: max absorption at 558-nm
 Differences are created by different structure of the long opsin part

Question 7

Metamerism

Answer 7

the situation in which two physical different stimuli are perceptually identical

Question 8

Principle of univariance

Answer 8

once a photon of light is absorbed by a visual pigment molecule, the identity of the photons wavelength is lost.
o Univariance: the molecule doesn’t know the wavelength of the photon it only knows how much it absorbs
o So we can cause a single pigment so recognize a colour by adjusting the intensity of light

Question 9

Opponent-process theory of colour vision

Answer 9

colour vision is caused by opposing responses generated by blue and yellow and by red and green (later in visual system)
o Seeing a green field creates a red afterimage and seeing a yellow field creates a blue afterimage (and vice versa)

Question 10

Opponent neurons

Answer 10

located in the retina and lateral geniculate nucleus that respond excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
 B+ Y− neuron because the wavelengths that cause an increase in firing are in the blue part of the spectrum, and the wavelengths that cause a decrease are in the yellow part of the spectrum
• B + Y cells receives excitatory input from S cone and inhibitory from cell A which sums the inputs from the M and L cones
 R+ G− neuron, which increases firing to light in the red part of the spectrum and decreases fi ring to light in the green part of the spectrum. There are also B− Y+ and G+ R− neurons
• L-cone send excitatory input to bipolar cell, whereas the M-cones send inhibitory input to the cell

Question 11

Hue cancellation

Answer 11

Aims at seeing how much of the opponent colour needs to be added in order to cancel all perception of other colours

Question 12

Cone-opponent cell

Answer 12

Cell type in retina and lateral geniculate nucleus that respond with excitatory response to light from one part of spectrum and with inhibitory response to light from another part.
 LGN – Structure in thalamus that receives input from retinal ganglion cells and has input and output connections to visual cortex.
 Example – Most exciting place is in pure red or pure green area. In this case, the cell is excited by red and not green.

Question 13

Colour centre in the brain

Answer 13

o Fusiform face area (FFA), extrastriata body area (ESB) and prarahippocampal place area (PPA)
o What pathway: normally used for shapes and sizes but is apart of the colour perception mechanism
o Colour perception results from activity in many different visual areas that respond not only to colour but to other qualities

Question 14

Types of opponent neurons in the cortex

Answer 14

have receptive fields with side by side regions (important for perceiving colour within regions)
o Double opponent neurons: responds best to a medium-wavelength vertical bar presented to the left side of the receptive field and to a long-wavelength vertical bar presented to the right side of the receptive field (perceiving boundaries between different colour)

Question 15

Chromatic colours

Answer 15

blue, green, and red

Question 16

Achromatic colours

Answer 16

white, grey or black, occur when light is reflected equally across spectrum

Question 17

Additive colour mixture

Answer 17

adding up wavelength of each light in the mixture.

Question 18

Mixing paint

Answer 18

both pains still absorb the same wavelength they absorbed when alone, so the only wavelength reflected by both paints in common (subtractive colour mixture)

Question 19

Colour deficiency

Answer 19

Only partial loss of colour perception, associated with problems with the receptors in the retina that are present since birth

Question 20

Monochromat

Answer 20

can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. So, they need only one wavelength to match any colour, and sees only in shades of grey
o No functioning of cones (has characteristics of rod vision in dim and bright light)
o Poor visual acuity and are sensitive to bright lights

Question 21

Dichromat

Answer 21

needs only two wavelengths to match all other wavelength (males are more prone to this because of X chromosome , 50-100 times more likely)
o Protanopia: perceives short-wavelength as blues, increasing until a point where it gets grey (neutral point) above this he perceives yellow (misses long wavelength pigment) (1% males 0,02 females 50 times more)
o Deuteranopia: A deuteranope perceives blue at short wavelengths, sees yellow at long wavelengths, and has a neutral point at about 498 nm (misses medium wavelength pigment)
o Tritanopia: blue at short wavelengths, red at long wavelengths, and a neutral point at 570 nm (missing short wavelength pigment) (different spectrum)

Question 22

Anomalous trichromat

Answer 22

needs three wavelengths just as normal. But he mixes these wavelengths in different proportions. Not as good as distinguish wavelengths that are close together

Question 23

Unilateral dichromat

Answer 23

a person with trichromat vision on the one eye and dichromat vison on the other

Question 24

Colour constancy

Answer 24

we perceive colour of objects being relatively constant even under changing illumination
o Based on prior information which the brain uses to make sense of the world