Video: How do we see colours? | Andrew Stockman

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so this is white light passing through a dispersive prison and this is a visible spectrum from about 420 nanometers in the violet through 500 nanometers and

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the green 580 yellow 610 and orange and 650 red and some of the slides that have this along the bottom axis so how dependent I'll be in color what do you

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think we depend on color a lot a little lots okay so this is a scene without color this is a singlet car so look at

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this scene can you tell me what fruit mrs. this one this one this one so you

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get a point so if I change the color you can see immediately which Springs a witch so kind important because it helps us to discriminate objects from the syrup from their surroundings

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but how important is it if I take this scene and spit it into it's a chromatic or monochromatic components and into its chromatic components down here you can see that most of the details contained

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in the a chromatic image the combative components by itself provides relatively limited information the detail of both space and time is really contained

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within a dramatic information so I I'm setting myself up for failure beginning because I'm telling you color is not that important so how do we see color an

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image of the outside world is rejected service of the iron retina it's inverted it's projected by the lens and cornea this is the rear surface of the retina it's carved in with light-sensitive

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rods and cones this is the central vision where they were just colors elcome showing red and countryman green and s shown in blue there are three

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types of human colors one more thing sensitive to the way that sensitive short make them sensitive and they're responsible for daytime a dramatic and traumatic vision there's one type of

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weather etc responsible for nighttime vision the rods and that was that's automatically the rods are much more sensitive than the cones and they decide to operate at the lower right levels

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from passive rod threshold where you can see just a few photons up to where rods saturation occurs just below indoor lighting because our sensitive over much

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larger range from kind of threshold up to 70 light levels of bright sunlight with wrong vision we see this image here in poor detail we had high sensitivity missingno client and you can experience

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it yourself if you go out at night and dark at 40 minutes you will see things with your rods when you do that you'll see something like this you'll see no card and porting time with the colors

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you see color and detail for sensitivities love and forget responsible for a chromatic and romantic vision the light-sensitive photo pigment

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is contained inside the rod in diamond outer segments here this is a blow-up of light passes by the way through the neural layers to the I've seen his of life at the Kona

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here's a bigger bar and this is the light-sensitive opsin seven-transmembrane our piracies sitting inside is important pieces to cram form and the crane for his

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elevenses retinal it's a molecule it's bent here between the 11th and 12th carbon atom so when as photons absorbed and what happens is the marginal

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strength the untwists but that's the first step of the visual process we change them 11 sister on plans and that triggers the transduction cascade which

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needs to really important thing about this is like a switch is all or nothing but photons absorbed or it isn't but whatever photo type it's already has the same effect so this is a univariate

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process it's colorblind and that means the coverage of a first stage your retinas be rather the symbol but what does universe have been in practice and then use n colors as an example and

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here's an encode here's the photons and crucially the effect any edible photon whatever its wavelength is independent its wavelength so if you look at the outcome of the encode already you can't

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tell which way things have been absorbed so all the end come and her photos it would be unsolved what does very wavelength is the probability

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that a photo would be absorbed so green spos'n is much more likely absorbed that a red photo and that's reflected in what's called the spectral sensitivity function and here is Nemco spectral

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sensitivity wavelength among abscissa and sensitivity among the ordinate and this is in the blood Eunice so most has to be done being you need more photos to

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have an effect high sensitivity up here you need less budgets have effect so you're more sensitive in the brain and you are on the red or in the violent and we tend to use log scales of these

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graphs because with other lenses besides of detail the tail is here so you might be sensitive if these photons in order sensitivity your most sensitive degree

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and these sensitive to the red now you have three lights of equal intensity fed by the height you look at those and they

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only differ in intensity if you increase the intensity of each that conversation that sensitivity lasting and make this one brighter this one brighter and these

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four LED lights look identical so the point is that with a single photo sector you're combining all the lights look the same so if it's a light gets brighter then if

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you get brighter because it's even a more intense or because you change the wavelength to one you're more sensitive to if it's divin it could be because you change the way things to one your lessons to or mutilated dinner you don't

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know which of those two things that has happened so with any one favorite sector we would become light and examples of that a blue car Monaco Mets and other

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code vodka vets and you can experience yourself at night with nitrogen two rods provide an automatic light signal so people with normal color vision would

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have three cones with different spectral sensitivities s cones and cones and algorithms which peaked at 441 541 or 566 nanometers and these three color

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receptors of the basis of our color vision so the car to see in the screen in this picture huh are they making property of physics of wirelessly what do you think biology

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physics so it's many bubbles so if you see a yellow patch of light could be made up of yellow white or a mixture of two lights green and red and we can't

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tell the difference between those two months their core metal is meta meza pairs of lights that are physically different but look essentially the same there are many different measures brain

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green combined to make yellow and this is not art this is hanging lights together attractive comics if you add together red and blue light you see purple if you

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have together green and blue Lucy as my hair if you add together all three you see a white so we need about this before

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unity identified online biology the 19th century experiment showed us that color vision was truly try to imagine and trichromacy means that the colonies at the input visual system is relatively

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simple it is a three variable system you can define colors and terms as three numbers and it's exploited in color television and this projector if you look very closely the color television you can see individual dots of light but

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a bright or dinner more modern TVs you see rectangles or different structures you can't see the differences because you use spatially mixing because our eye compass of

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individual pixels so 53 progress of our bright you see white if you just see red the green you see yellow which is just the emergency red so all the colors you

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see on the screen I made up of a mixture of three different lights and it's been used in painting his point that point is painting by Georges Seurat and if you look more closely the painting you can

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see it's actually made up of small loads of pink and this was a tentative additive color mixing in painting and this was done of 19th century so why is

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he revision trichromatic the main reason is we have three comb types s and L but also each one produces a unitary attack so each color color if each photo set

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has colored like how do we see cut or how does it parent how's it encoded by the visual system well if a light changes from green to

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red then because the end cuts of our centers were red the eMCON signal goes down but the elfin signal goes up if the light goes from red to green the N can

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see it goes up is getting canceled more sensitive to green and the L can see who goes up so we encode colors by comparing the outputs of the two of the three

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times so each car title is colorblind but the way the sitting changes as a color changes is different that allows us to encode it colors so color is

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encoded by the relative code outputs a blue light produces big signal s cones less in the end as we held a green light most of the temp cones and a red light

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most in the Elkins and various mixtures produce different ratios so purple light will produce the biggest output in the S cones in the L tracks so that's the way color is intended this first stage of

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vision try dramatically and just point out most mammals including dogs of dichromats they're missing the end codes so they see the fruits then there's something like this so Bulls don't see

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read very well or not it just looks like a shade of yellow try currency developed relatively recently in our history in other

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primates it was a gene duplication which duplicated at the end they all time to make an L by the pigment and it's thought to be Risdon because with only two income

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types we see something like this in the forest canopy there were three clan types you can see the fruit of the trees so isn't that vantage but it's relatively recently it occurred before

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Africa split from South America and currently all primates so that's what happens in the first stage of income level what happens after the Kurds

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happens in the rest of this is the process history can resume the signals the whites absorbed by the rods and cones and the signals transmitted of the bipolar cells getting ourselves up the

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optic nerves the cortex but even this stage the transients are reinfected and we can work out what sort of things happen by just doing a thought

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experiment by color phenomenology so if you imagine a single patch of light single color surrounded by adults around just trying to think of which colors can coexist in that patch and if you have a

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tri-chromatic code and any pair of colors should coexist you should be able to see a reddish green or blue yellow so this packs of light here does it look

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ready at the same time yeah so resin yellows can occur in a single patch this is what quite non-conventional it at the

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same time yes but now if we combine red and green we don't see same patch a regular green together make a yellow so we don't see a single patch

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of light already spring and we also don't see a single patch of light as a blueish yellow we see it as white or gray so there are parents of colors of apparently don't coexist and this net of

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theory of 19th century by some people hairy in which he supposed oh no he was such that red is a post agreement so something could be red or green but not both something can be blue or yellow but

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not both and the trichromatic theory of the hellmouth's and the opponent d repairing when competitors but if you

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look at the responses of these cells you find color potency and you find current planet red green cells where the L and M cones are opposed to plus L minus M you

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see these various four types of cells where elevating tentacles reposed in the resident and you also find cells in which the S phones propose develop the same so the common phenomenology has its

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foundation actually in the neural circuitry and those is a simplification you find it actually in this next stage of vision of the retina so the first page of region that cones is

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trichromatic in the second stage becomes power opponent where the different signals so what about I think about division well again I've already said

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most of the detail is encoded in the and there is an important pathway the visual system which is effectively helped our Center which encodes detail

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and space motion and also fine spatial detail Lewis encoded by packing together the other mankind signals so if you add

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together two universe signals if you end up the univariate combined information system so color is in many ways separate for movements so here is a common scene

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again I want you to adapt to this color pattern or you to stare at that cross please and then I'm going to do something staying across I know you tell

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me what I've done so I can build up it after which and after which is going to be the complementary colors to what you're looking at so when you see a purple you'll see a green yourself

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so what did I do so I just changed me just to put up a black and white a correct image and they color fill in a detailed image so this

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fuzzy colored image very much fills in the detailed English so the a graphic image this was leading edge just to show

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you is not very covers if you look at this image look at the cross you're going to see some very unappetizing fruit okay so this is also an example of how

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color fills in these borders are simply preventing borders in doctor directions but this whole central area of peripheral energy fills with color this is slightly blue this is slightly yellow

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soylent green side yellow and large and these things the colors tend to fill in borders and here too this is the way like television this

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european system filling in the side is finding the ways it's not actually there and here's an even spread of it when you see this whole circle here as slightly

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tinted so color very much fills in the aromatic signal the a chromatic image so that's what happens in single patches of light but what we see in color is much more complex and it depends not only on

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trying to read the code and components in people's home and to what occurred before you see it and also on which color surrounding color so I'm going to start off with a color effect if you

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look at this cross here again and a little bit so you can see the complementary colors by these cuts were and if you blink the colors should come back

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the colors are very strongly here's another example which I think we do fine if you look at this lady's nose taking

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90 P and the complementary of that slightly blue black is actually a flashing time so this is apparently a

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famous Indian actors get if you blink and come back so if you look across what you see you see bring light is it really there

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if you followed your eyes of disappears so what you're seeing as an afterimage moving around okay contrast effects these top of bottom squares are identical if you

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surround them as color they check their appearance so this green produces a great color this rather green card is blue yellow color and this yellow a blue time to give contrast effects whether

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we're the surrounding color induces office apparently Center and again you see that in this example these rings are so identical but because those are anybody the colors look very different

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you see that so they really look like it's a contrast effects and that was used in art by many artists the regular you contrast here blue yellow and the

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red green here which enhances the appearance of the colors the simulation is where on small scale little dots actually combined add together so to surround these the different colors they

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change in appearance so here if you're surrounded with red and it's like a red up which is surrounded green it looks like arena and similarly here in here these kind of changes and a struggle reflective is a monk religion when these

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Reds changing the color depending on which bar a batsman okay now I'm going to find a computer

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brain and show you a list of words and the combat and what I want you do this to say to yourself of language as you like it

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he ain't come not of the word says are you ready okay okay that's not so fast okay so it's

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fairly easy because the two I'll say okay ready for next one here we go three two one so this is known as a screw plate and

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beginning an experiment supremely the colored and the ink color because at some central location the information about cholera is arriving before the information about the conflict okay I'm

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troubling you seen this so heads up who sees it as blue and gold and who sees it has blackened something else why should God

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so this course might comedians there at the time so we said leaders and it depends on the assumptions you make about the color of the illuminant what kind of a light

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source or about shadows it's very it's very confusing and you can see they talked about he know I can't begin to work but this is great here is actually identical to this square here this black

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water this one is illuminated by blue lights have you seen it must be yellow and this continent is my red wedding soon it must be great this sort of idea about

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illuminate and shadows changes our session a good deal