Colour Flashcards
What kinds of animals can see in colour?
Birds Fish Reptiles Insects Primates
(All other mammals, besides primates, don’t see colour)
How many types of cones do primates have in the eye that are used for colour vision?
Three
What is a biological advantage for colour vision (for primates)?
Colour vision adds contrast between objects and their background, which makes it useful in foraging for food
True or false: the cones in primates’ eyes are particularly beneficial for distinguishing red and orange against a green background
False
Distinguishes red and YELLOW
Birds are able to see colours in the UV range that others cannot see at all. What is the biological advantage of this?
Colours of a potential mate’s feathers indicate how healthy the bird is. Since they can see colours that other animals can’t, they can still communicate with other birds about how healthy they are while hiding from predators
How can colour vision in non-mammalian animals be used for foraging?
Bees see ultraviolet hues on flowers that act as nectar maps (invisible to humans)
What are the two different types of colour mixing?
Subtractive
Additive
What is subtractive colour mixing?
When you mix different colours and alter the combinations wavelengths that are absorbed (subtracted)— you’re subtracting wavelengths out
(Results from light that is reflected off of the surface)
If an object looks blue to us, does that means it’s reflecting or absorbing the “blue” wavelength?
Reflecting
It’s absorbing all of the other colours
What are the primary colours in subtractive mixing?
Cyan
Magenta
Yellow
(can make all of the colours in the rainbow)
What is additive colour mixing?
When coloured lights add their dominant colour to the mixture
What are the primary colours in additive mixing?
Red
Green
Blue
What is the complementary colour of red?
Cyan
What is the complementary colour of green?
Magenta
What is the complementary colour of blue?
Yellow
With additive mixing, when you mix a primary colour with its complement, you get _____ or _____
Grey or White
If you hold a magnifying glass to a yellow patch on a TV screen, what will you see?
A bunch of red and green dots (not yellow)
If two colours are close enough together, what will our visual system do?
Fuse them together
True or false: human colour perception is based on subtractive mixing
False
Additive mixing
What are the two theories of colour vision?
Trichromatic
Opponent-Process
What is the trichromatic theory of colour vision based on?
The proposal that the retina contains three diff kinds of receptors, each maximally sensitive/responsive to diff wavelengths of light
What is another name for the trichromatic theory of colour vision?
Young-Helmholtz theory
What does it mean when you say a receptor is ‘maximally responsive’?
Means that a given receptor will respond to other wavelengths less strongly than it would to its peak wavelength
When you perceive yellow, what does this indicate about the cones and their stimulation levels?
Red and green cones are equally stimulated
When you perceive white, what does this indicate about the cones and their stimulation levels?
All three cones (red, green, and blue) are equally stimulated
Which photopigments are the cones maximally responsive to?
The primary colours:
Red
Green
Blue
What is the elegance of the trichromatic theory?
Provides simple explanation for variety of phenomenon
Fits with additive colour mixing
Physiological evidence for three types of cones exist
What were some problems with the trichromatic theory?
Yellow seemed to be a primary colour (when asked to describe the most basic colour, people described yellow)
Couldn’t explain the law of complementarity (that certain pairs of wavelengths produce white)
Couldn’t explain the complementarity of afterimages (i.e. why do you see a yellow afterimage when you stare at a blue stimulus?)
What does the opponent-process theory of colour vision propose?
That each receptor is made up of a pair of opponent processes.
Each is capable of being in one of two opponent states. It can only be in one of those states at a time.
According to the opponent-process theory, what are the three pairs of photoreceptors and what are their abilities?
Blue-yellow (give ability to see yellow and blue)
Red-green (give ability to see greens and reds)
Brightness (give ability to distinguish bright from dim light)
What wavelengths are the brightness photoreceptors excited by?
Excited by lights of ANY wavelength
What is the elegance of the opponent-process theory?
Explains why:
- a mixture of complementary wavelengths appear white
- afterimage is the complementary colour
- we can imagine some colours (reddish yellow, blueish green) and not others (reddish-green, blueish yellow)
Why can we can imagine some colours (reddish yellow, blueish green) and not others (reddish-green, blueish yellow), according to the opponent-process theory?
These colour pairs (reddish-green, blueish yellow) are opposite and occur from differential activation of the same receptor type.
It’s impossible for the red-green receptor to be active in both states at the same time
Explain how the two theories combine to explain colour perception.
The output of the cones in retina (organized in trichromatic fashion) is input for the next layer of colour processing in the ganglion cells and onwards (organized in opponent fashion)
Colour coding continues in opponent arrangement until it reaches the brain
What is the colour of the afterimage?
The complementary colour of the original image
What does it mean if a ganglion cell colour receptor is inhibited?
It is firing lower than baseline
What signals to the brain what colour is being seen? (i.e whether it’s red or green)
The rate of firing
Why do afterimages occur?
When a colour receptor is excited/inhibited for a long period of time, there is a rebound effect when you stare at a neutral colour (white). The same colour receptor will go into the opposite state, causing you to perceive the complementary colour
When there is a rebound effect, and the receptor switches to the opposite state, does the receptor then fire at:
a) less than baseline
b) baseline
c) more than baseline
Why?
a) less than baseline
Pigments are bleached out bc of prolonged exposure to one pigment
In high res channels (i.e. the fovea), ____ cone(s) is transmitting info to _____ ganglion cell(s)
a) one, several
b) several, one
c) one, one
d) several, several
c) one, one
In low res channels (i.e. away from fovea), ____ cone(s) is transmitting info to _____ ganglion cell(s)
a) one, several
b) several, one
c) one, one
d) several, several
b) several, one
Ganglion cells have receptive fields. What are these and what do they do?
They are regions on the retina. When stimulated, they cause the ganglion cell to increase or decrease its firing rate
What are the size of the receptive fields in high-res cells?
Small
What are the size of the receptive fields in low-res cells?
Large
What are the shape of the receptive fields of the ganglion cells?
Donut shaped
Ganglion cells respond to colour in a centre-surround fashion. What does this mean? Give an example with red-green.
Excited by red and inhibited by green.
The receptive fields are donut shaped. The inner circle has red cones in the inner circle and green cones in the outer circle.
Maximally excited if red light hits inner circle and maximally inhibited with green light hits outer circle.
If green light strikes the center (or vice versa), the effect isn’t that great.
Ganglion cells respond to colour in a centre-surround fashion. What happens when yellow light strikes?
Yellow = red + green
So both areas are stimulated. The excitation and inhibition cancel each other out and there is no overall change.
How many layers does the LGN have?
Six
Which layers in the LGN process info about movement and depth?
Magnocellular layers
How many magnocellular layers (in LGN) are there?
2
Which layers in the LGN process info about colour from the red-green ganglion cells and info about form and fine detail?
Parvocellular layers
How many parvocellular layers (in LGN) are there?
4
How many sublayers in the LGN are there?
Six (one for each layer)
What are the sublayers in the LGN called?
Koniocellular sublayers
What do the koniocellular sublayers in the LGN do?
Transmit info from yellow-blue ganglion cells to primary visual cortex
How do the cells in the LGN respond (to colour) compared to the retinal ganglion cells?
In the same opponent, center surround fashion
i.e. if yellow hits center –> fires more rapidly. If blue hits outer —> fires less than baseline
Where do the parvocellular layers and the koniocellular sublayers send info?
To primary visual cortex in occipital lobe
What are cytochrome oxidase blobs (CO blobs)?
Regions of cytochrome oxidase containing neurons that are distributed at roughly equal intervals over the primary visual cortex
The neurons in the CO blobs respond to:
a) Colour
b) Shape
c) Orientation
d) Movement
e) All of the above
f) Everything, except for a)
a) Colour
Describe the shape and organization of the CO blobs
Oval (if looking at from surface of primary visual cortex)
Depth wise, they are arranged in columns that project down into layers 2 and 3 (and less so in layers 5 and 6) of the primary visual cortex
How do the CO blobs respond (to colour) compared to the retinal ganglion cells and the LGN?
Also in an opponent, center surround fashion
What is the shape of the receptive fields in CO blobs and how does each part affect the firing rate?
Donut- shaped
Center increases firing
Outer decreases
Where is information from colour integrated with other info (i.e. shape, orientation, movement)?
Extrastriate cortex (ventral stream)
What is monocular colour blindness?
Colour blind in only one eye
What are the three types of common colour-blindness?
Protanopia
Deuteranopia
Tritanopia
How do people with protanopia and deuteranopia perceive the world and what are they lacking (in terms of colour)?
They see the world in shades of yellow, blue and grey
red/green colourblind
Why do people with protanopia and deuteranopia lack the ability to see red and green?
They are lacking the colour photo pigment in the cones
What are the colour photo pigments like in the cones of people with protanopia?
Red cones that are filled in with the photo pigments for green
(two green cones, one blue)
What are the colour photo pigments like in the cones of people with deuteranopia?
Green cones that are filled in with the photo pigments for red
(two red cones, one blue)
If there was a slight difference in the way each cone perceived light, how would that effect people with protanopia and deuteranopia?
A slight diff is all they need to tell the diff between green and red (even if they don’t see it as brightly as people with normal vision)
How do people with tritanopia perceive the world and what are they lacking (in terms of colour)?
See the world in shades of red, green, and grey
blue/yellow colour blind
Are protanopia and deuteranopia more prevalent in males or females? Why?
a) males
b) females
c) both
a) males
The gene is carried on the x chromosome
Is tritanopia more prevalent in males or females? Why?
a) males
b) females
c) both
c) both
The gene is NOT carrie on the x chromosome
Why does tritanopia occur (what’s up with their cones)?
Blue cones are either lacking or defective
True or false: blue, red, and green cones are present in the same amount in the retina
False
Blue cones are less frequent
