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Lecture 5 notes

by: Jennifer Gittleman

Lecture 5 notes Psyc4106W

Jennifer Gittleman
Sensation and Perception
Dr. Philbeck

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Sensation and Perception
Dr. Philbeck
Class Notes
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This 9 page Class Notes was uploaded by Jennifer Gittleman on Wednesday October 28, 2015. The Class Notes belongs to Psyc4106W at George Washington University taught by Dr. Philbeck in Fall 2015. Since its upload, it has received 15 views. For similar materials see Sensation and Perception in Psychlogy at George Washington University.


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Date Created: 10/28/15
400 500 600 700 Visible Light Ultr Ii 39 frared Radar FM TV AM AC Gamma ra s Xra s y y V39OI Rays circuits raw I u Color perceptual quality not physical quality 0 Blue short green middle red long 0 Three perceptual dimensions 0 Hue the color name we give to our subjective experience when we re looking at an object wavelength is physically measureable can change if something is next to another color why hue isn t completely determined by wavelength 0 Saturation perceptual experience of colorfulness of color how saturated a color ishow deep of a color it is inverse of how much white light as you increase the white light in the color the saturation goes down 0 Lightness how light or dark something seems intensity of light coming off of an object Visible light electromagnetic radiation that we can see 400700 wavelengths Saturation increases outwards and gets less saturated as it goes in lightness is up and down hue dimension goes around in a circle left pic Lightness goes up and down hue goes around outside and saturation increases outwards right pic Reflectance percenlagel 7 7 lypmg band 7 am a l l U j Elli at g l r is t in ree li39l H 5E I Lie f H piggrnenl pigment i 1H If 5 lquot 39i 39 aquot 3 r a ll Cl f Hquot i a if it i 1 ii i k quota ti Hill 5 carrLlM Fr 7 r r 1 r V li39c ED jmmquotquot Eliquot a l 1 a39a 1 i quot1 n l 39 EEEEE ill with IEiEIiCI i p p r Fm l 7 W wigI P if 39l l Hquotquot5ff vifill Sill EDD Till lll tl l EllEl lQNl filing How much of each of these wavelengths gets re ected off the object re ectance Objet looks green because object re ects green part of spectrum White has a high re ectance and there s no strong re ectance on which wavelengths get re ected more Gray has no predominant wavelength Black only re ects a small proportion of light Re ects wavelengths when it peaks and absorbs when it is the slope Reflectance igereentagei l l i 7 till Eli P El range Lairritiiin Tomam a x Cabbage Waval hglli rir riji Some fruits and veggies that have a characteristic color that goes along with these objects re ect in the spectrum Lemons have short wavelengths Tomatoes have a long wavelength Color Mixing We can discriminate about 200 different wavelengths We can see 500 steps in brightness We can see 20 different steps in saturation In total we can discriminate about 2 million colors We can describe all colors we discriminate using four names red yellow green and blue Two types of color mixing Additive color mixing we are mixing together lights 0 Blue lter appears blue because the light comes out of lter primary has short wavelength 0 Yellow lter appears yellow because the light comes out of lter primary has middle wavelength Superimpose two beams of light you re getting a mixture of all the wavelengths that the blue wavelengths and yellow wavelengths the light re ects so you get something close to being white light Subtractive color mixing we are mixing together pigments If you have blue paint we see it as blue because it re ects short wavelengths but it absorbs long wavelengths If you you have yellow paint we see it as yellow because it re ects medium and long but absorbs short wavelengths o If you mix blue and yellow pigments together the only part where they re ect is in the medium part of spectrum mixture is still going to absorb what blue and yellow absorb o Exceptions Take blue lter and put it over yellow lter you ll see green and not white because the light that comes through yellow lter is letting through medium and long wavelengths but that light is then going through blue lter which lets through short wavelengths the only light that passes through both lers is which lter lets the wavelength through Using pigments but have them combined in an additive fashion If you look at comics there s a lot of dots of different colors or a TV there are dots of colors 0 Trichromatic color theory Young Helmholtz what are the primary pieces of evidence and what does it not account for or does account for has it been disproved 0 Based on the results of color matching experiment 00000 O 0 First piece of evidence for trichromatic color theory color matching experiment you set people up with a split eld on one side you have one color light and the other side you have three separate lights that are superimposed called P1 P2 P3 primary lights we chose these lights carefully and have to be primaryindependent lights you can t create any of these by mixing together the other two give knobs so they can adjust intensity not wavelengths of these three lights goal is to make the two sides look exactly the same three lights can be adjusted to make 2 million different lights if you keep these independent lights wavelengths xed you can t match every color on left side 0 The colors that we see come about because we have three types of cone photoreceptors that absorb light in deferent parts of the spectrum and overlap experiment shows we need three knobs to match the light on the left side 0 Metamers two lights that look exactly the same but have different wavelength compositions If the ratio of cone types are active on both sides then they re going to look exactly the same l iglh l a rllgl All Iiiquot Vli39l ll h y with p71 ran iiquot J 3 legal Ln i l 9 ng l l 0 Second piece of evidence for trichromatic color theory microspectrophotometry experiment Have tiny glass tube and you take an individual cone photoreceptor into tube and you pass diff wavelengths of light through the outer segment of the cone and you have detector on other side that tells you how much of the wavelength comes out on other side if most of the wavelength comes out on other side the light was not caught and not sensitive to that wavelength cones break down into three separate types and have diff wavelength sensitivities and they overlap to some extent 1051 longmediumshort what was thought years ago regarding wavelengthsensitive cones Still true we have less short but there is individual variation regarding ratio Adaptive Optics Roorda and Williams 1999 o Took a look in people s eyes and counted proportion of cones without using microspectrophotometry didn t work because optics of eye blur the image too much RampW used adaptive optics and shined a light in eye to estimate the particular pattern of blurring the person s optics produced once they estimated person s optical factors they used tiny mirrors to undue optical blur that person s eye generated used in astronomy now to create high resolution images of stars even if they re looking from the ground Shine a strong light that was mainly in either 5 m or wavelength and bleached cones in that part of retina to see which wavelength was sensitive to light had a way of picking out whether the cones were sensitive to s m or I found people had different ratios to s m or wavelengths left pic shows people have a lot of medium wavelengths right pic shows people have a lot of long wavelengths how the wavelengths are wired together is important for both of these people the number of short wavelength sensitive cones are less than long and medium wavelengths long red mediumgreen shortblue 0 Third piece of evidence for trichromatic color theory color vison de ciencycolor blindness 0 John Dalton had color vision de ciency he was a very famous chemist kept careful notes on which colors seemed to match to him which wavelengths he confused his eyes were preserved and there has been DNA testing on which type of color de ciency he had a lot of people who have a color vision de ciency do not know it can discriminate colors by brightness differences sex linked gene that s critical is on X chromosome males have one X and one Y more common in males people are not missing a whole cone type but the gene that determines the properties in the cones so they don t have photo pigments that allows them to catch the light the way they should so they don t catch the wavelengths they should 0 Lightness is same between red and grey dots Monochromatism 0 People who are rod monochromats cannot discriminate color see everything in shades of gray light is uncomfortable very poor visual acuity can t see ne details if you look directly at something you cannot see it 0 People who are cone monochromats don t have ability to discriminate colors can see light comfortably depending on the type of cone that s available to them they can see ne details if you have only functioning shortwavelength sensitive cones you wouldn t have good acuity but if you have medium or long you can see acuity o Dichromatism o More common than monochromatism part of spectrum that looks gray to them neutral point is a gray line o Protanopia reds and greens may look like different shades of yellow at 492 o Deuteranopia reds and greens may look like different shades of yellow at 498 o Tritanopia Anomalous trichromacy Opponent Process Theory what are the primary pieces of evidence and what does it not account for or does account for has it been disproved o


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