Vision Continued (colour vision) Flashcards
How many colour words do we have
Approx 11
How many colours can we see?
Up to 20 thousand colours and shades
How can we tell different colours/shades apart?
We use light and wavelength
We can perceive in the range of …….in light waves
380-740nm
Higher light wavelengths we see tend to see colours as
Reds etc
Smaller light waves are seen as colours:
Blues and purples
If the wavelength is higher than the highest then we see
Infrared wavelengths
Infrared spectrum wavelengths are
We can’t detect them visually, outside our visual perception.
Photoreceptors in the retina are sensitive to different
Wavelengths
Preferential absorption is
Absorbs only a Particular range of wavelengths
The brighter the light the
More we are able to detect it
Colour is a product of our perception rather than our
Reality
What colours we see is largely based on
The way our individual visual system is set up/designed
Three steps to colour perception: 1st step is:
Detection: light must first be detected by the retina
2nd step to colour detection is:
Discrimination: have to be able to tell wavelengths apart
3rd step to colour perception:
Appearance: different colours go with different objects. Colours remain relatively constant as viewing conditions change I.e in different lighting etc
Two broad light section conditions are:
Photopic
Scotopic
Photopic is
Light is bright enough to saturate cones and rods. Ie sunlight
How many different types of cones are there?
3
Scotopic is
Light that is bright enough to stimulate rods and not cones. Ie moonlight
Phototopic and Scotopic are apart of which step of colour perception?
- Detection
How many kinds of photoreceptors?
4
What are the 4 kinds of photoreceptors?
1 kind are rods
3 are cones
Different kinds of cones are sensitive to different wavelengths of light due to the
Different photopigment they carry
S-cones are sensitive to what kind of wavelengths?
Short (420nm)
M-cones sensitive to……….wavelengths
Medium (535nm)
L-cones are sensitive to
Long wavelengths (565nm)
What is the problem of univariance?
We can’t just rely on the output of one type of photoreceptor to tell us what wavelength we are encountering in terms of light. For any single photoreceptor there is an infinite pairing of wavelengths that produce the sane response rate for that particular type of photoreceptor
To solve the univariance problem we rely
On the combined out put of the three types of cones
The combined pattern activation/output of the three cones is called
Trichromatic theory
450nm and 625nm produces the
Same level in M-cones need to add S-cones and L-cones to really distinguish the colour
Brain looks at the patterns across all cones to
Try and figure out what light frequency it’s actually detecting
The relationship/relative ratio of activation from each type of cone tells us
About different wavelengths
The rod gives us info on the
General illumination conditions.
Most objects produce a
Combination of different wavelengths
We see one colour when we look at items because we are restricted by our
Trichromatic visual system
How do we only see on colour from a particular object?
Using trichomatic visual system
Yellow light with a medium frequency produces the same amount of activation in the
M and L cones
Combo of red and green lights produce same activation in L & M cones as what colour…
Yellow
When you mix green and yellow light together you actually see
Yellow light
Visual system can’t tell apart between a
Single yellow light and a mixture of red and green lights
Metamer is
Any pair of stimuli that are perceived as being identical by our perceptual system even though they are physically different
We only need three primary colours to get all the different colours because
We have only three types of cones
Are the primary colours of paint different to those of light?
Yes
Primary colours of light are:
Green red and blue
Additive colour mixing is
The mixing of light colours
Subtractive colour mixture is
The mixing of pigments/paint
Mixing green and red light =
Yellow
Mixing red and blue light =
Pink (magenta)
Mixing blue and green light =
Light blue (cyan)
Three primary colours mixed and you get
White light
Subtractive light mixing primary colours are :
Yellow magenta and cyan
Secondary subtractive colours are:
Red green blue black in middle
Trichomatic visual scale is used as a basis for
Printing, computers, TV etc because we only need 3 primary colours to give us the effect of lots of different colours
The other way our visual system works that can’t be explained by the trichromatic colour theory…
Afterimages
Afterimages are
After looking at an image you see it looking away at a white space
Afterimages are different from the actual image how?
Colours on the afterimage are inverted (darker bits lighter yellow bits blueish) etc
Visual opponent process theory
Certain colours that can combine together and we can see combinations of those colours.
Combinations of colours we CAN see are:
Greeny-yellow
Bluish-green
Yellowy-red
Combos of colours we should never be able to see:
Greeny-red
Yellowy-blue
Whiteish-black
Cone-opponent cells are cells that
Work similarly to ganglion cells they have centre surround receptor fields. Stimuli activate it’s centre and it produces inhibition.
Cone-opponent cells increase our
Perception to colour contrast.
Cone-opponent cells process colour by
Encoding it in terms of its proportion of red or green and blue or yellow
How do opponent processes explain afterimages?
When staring at a green image for a long time green receptors become temporarily desensitised. Patches of red light can be seen when looking at a white wall. Opponent colours red and green!
Trichromatic theory is what type of Visual processing?
Photoreceptor level
Opponent process theory is what level of visual processing?
Ganglion cell, LGN and V1 level
Does everyone see colour in exactly the same way?
Yes. Similar ways. Use meta metric matching in experiments
How much % of pop are colour blind?
8% male .5% female
Dueteranope
A person who has no M cones. Reduced red/green discrimination. Green looks red.
Protanopia
Person who lacks L cones. Reduced red/green discrimination. Reds look green
Tritanopia
Person who lacks S Cones (rare). Blue is black. Sees world in green, red, yellows.
Sensory systems have different
Receptors, signalling pathways and processing areas in the brain.
Many of our sensory pathways pass through the
Thalamus (except smell)
Benefits of our senses combining…
Gives us survival advantage
Why does our senses combining give us a survival advantage?
We generate coherent internal representation of the world
Increased accuracy and reliability of experience
Taste combines
Taste, smell, trigeminal nerves (tells about touch experiences in our mouth)
Walking combines these:
Propriception, vision
Engaging in conversation combines these:
Audition, vision mcgurk effect
Identifying objects combines these
Audition, vision, touch, smell, taste
Synaesthesia is
Colours may elicit the sensation of sound. Associations made between apparently unrelated phenomena!
Synaesthesia types
Colours elicit sounds
Shapes elicit tastes
Sounds elicit smell
Ordinal personification (numbers have characters)
We all may have some form of synaesthesia for example in the case of
Music and emotion
How is synathesia caused?
Cross modal connections between normally separate brain areas produces brain cross-activation. Genetic link. Psychological reality not physical.
Can be a connection between synaesthesia and
Metaphor
Why connection between synaesthesia and metaphor?
Due to some modalities having the same qualities/pattern. They feel qualitivity similar in ways Ie Kiki and bobar
How do we screen for synaesthesia?
How many no 2s? Can pick out 2s VERY quickly with colour
