chapter 9 part 1

Question 1

cerebral achromatopsia

Answer 1

a type of colour blindness caused by damage to the cerebral cortex of the brain (ventro medial occipital and temporal lobes)

occurs in the brain compared to most cases, which happen because of the absence of cone receptors

Question 2

colour deficiency or congenital achromatopsia

Answer 2

partial color blindness - people see fewer colors than people with normal color vision and need to mix fewer wavelenghts to match any other wavelength in the spectrum

Question 3

functions of color perception

Answer 3

signaling functions - in both the natural and human made world
- ex is something good to eat? (some people propose that monkey and human color vision evolved for the purpose of picking fruit) should we stop at the intersection or keep going?

also facilitates perceptual organization

recognition and identification

Question 4

newton’s prism experiment

Answer 4

designed to test the hypothesis that white light was a mixture of differently colored lights and that rather than adding color to light, prisms separated white light into its individual components, creating rainbows

experiment:
- light entered through a hole in a window shade and passed through a prism
- colors of the spectrum were separated by passing them through holes in a board
- each color was then passed through a second prism

findings:
- second prism didn’t change the color appearance of any light that passed through it, meaning that individual colors are not mixtures of other colors, unlike white light
- different colors were bent by the second prism to different degrees, suggesting that light in each part of the spectrum is defined by different physical properties and that these physical differences give rise to our perception of different colors

Question 5

chromatic colors

Answer 5

color with hue, such as blue, yellow, red or green

occur when some wavelenthgs are reflected more than others

Question 6

selective reflection

Answer 6

when an object reflects some wavelengths of the spectrum more than others - gives rise to chromatic colors

Question 7

reflectance curves

Answer 7

a plot showing the perceptage of light reflected from an object versus
wavelength

individual objects don’t usually reflect a single wavelength of light

Question 8

selective transmission

Answer 8

only some wavelengths pass through the object or substance
- think juice - cranberry juice selectively transmits long wavelength light and appears red, whereas limeade selectively transmits medium wavelength light and appears green

associated with the perception of chromatic color

Question 9

transmission curve

Answer 9

plots the percentage of light transmitted through a liquid or object at each wavelength

similar to the reflectance curves but with percent transmission plotted on the vertical axis

Question 10

mixing paints

Answer 10

a form of substractive color mixing

when mixed, both paints still absorb the wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common

it is called subtractive color mixing because mixed colors subtract all the wavelengths they absord on their own - FEWER WAVELENGTHS ARE REFLECTED

Question 11

mixing lights

Answer 11

a form of additive color mixing

when mixed, all of the light that is reflected from the surface of each light when alone is also reflected when the lights are superimposed

means that the wavelengths are each light are added to each other - thats why it is called additive color mixture - MORE WAVELENGTHS ARE REFLECTED

Question 12

compare substractive and additive color mixing

Answer 12

substractive: fewer wavelengths are reflected when colors are mixed because each color substracts wavelengths from the mixture

additive: more wavelengths are reflected because mixing lights causes more wavelengths to be reflected

Question 13

compare substractive and additive color mixing

Answer 13

substractive: fewer wavelengths are reflected when colors are mixed because each color substracts wavelengths from the mixture

additive: more wavelengths are reflected because mixing lights causes more wavelengths to be reflected

Question 14

why is indigo excluded from the list of spectral colors

Answer 14

humans have a difficult time distinguishing it from blue and violet

Question 15

spectral vs non spectral colors

Answer 15

spectral: colors that appear in the visible spectrum

non spectral: colors that do not appear in the spectrum because they are mixtures of other colors - there are lots and lots of different mixtures (it is estimated that we can tell the difference between about 2.3 million different colors)

Question 16

what are the three perceptual dimensions of color?

Answer 16

hue - the experience of a chromatic color, such as red, green, yellow, or blue, or combinations of these colors

saturation: the intensity of color

value/lightness: the light to dark dimension of color

Question 17

desaturated colors

Answer 17

colors that take on a faded or washed out appearance

happens from low saturation in chromatic colors as would occur when white is added to a color

Question 18

color solid

Answer 18

a solid in which colors are arranged in an orderly way based on their hue, saturation, and value

meant to illustrate the relationship among hue, saturation, and value

Question 19

munsell color system

Answer 19

a depiction of hue, saturation, and value - different hues are arranged around the circumference of a cylinder with perceptually similar hues placed next to each other

the order of the hues around the cylinder matches the order of the colours in the visible spectrum

saturation is depicted by placing more saturated colors toward the outer edge of the cylinder and more desaturated colors toward the center

value is represented by the cylinder’s height, with lighter colors at the top and darker colors at the bottom

Question 20

trichromacy of color vision

Answer 20

idea that color vision depends on the activity of three different receptor mechanisms

Question 21

young-helmholtz theory

Answer 21

trichromatic theory

Question 22

young-helmholtz theory

Answer 22

trichromatic theory- color vision depends on three receptor mechanisms, each with different spectral sensitivites
light of a particular wavelength stimulates each receptor mechanism to different degrees, and the pattern of activity in the three mechanisms results in the perception of a color

Question 23

color matching

Answer 23

support for the trichromacy of color vision theory

shows that any reference colour can be matched provided that observers are able to adjust the proportions of three wavelengths in the comparison

suggests that color vision depends on three receptor mechanisms, each with different spectral sensitivities

Question 24

microspectrophotometry

Answer 24

technique that led to the discovery of three types of cones in the retina

a narrow beam of light is directed into a single cone receptor - makes it possible to determine the pigment absorption spectra of single receptors

by presenting light at wavelengths across the spectrum, it was determined that there were three types of cones

Question 25

three types of cones

Answer 25

short wavelength pigment - 419nm
middle wavelength pigment - 531 nm
long wavelength pigment - 558 nm

Question 26

adaptive optical imaging

Answer 26

technique that made it possible to look into a person’s eye and take pictures that showed how the cones are arranged on the surface of the retina

creates a sharp image by first measuring how the optical system of the eye distorts the image reaching the retina, and then taking a picture through a deformable mirror that cancels the distortion created by the eye

Question 27

aberrations

Answer 27

imperfections on the eye’s cornea and lens that distort light on its way to the retina

Question 28

cone mosaic

Answer 28

arrangement of short medium and long wavelength cones in a particular area of the retina

Question 29

metamerism

Answer 29

the situation in which two physically different stimuli are perceptually identical

in vision, this refers to two lights with different wavelength distributions that are perceived as having the same colour

Question 30

metamers

Answer 30

two lights that have different wavelength distributions but are perceptually identical

they look the same because they both result in the same response in the three cone receptors

Question 31

monochromatism

Answer 31

rare (10 people out of 1 million) form of color blindness that is usually hereditary

monochromats have no functioning cones so vision is created only by rods and only see in shades of lightness (color blind)

because monochromats perceive all wavelengths as shades of grey, they can match any wavelength by picking another wavelength and changing its intensity - this means that monochromats need only one wavelength to match any wavelength in the spectrum

Question 32

principle of univariance

Answer 32

once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost

means that the receptor doesn’t know which wavelength of light it has absorbed, only the total amount it has absorbed

means that in monochromates, we can cause a single pigment to result in identical responses by adjusting the intensities of two lights

Question 33

dichromats

Answer 33

people with just two types of cone pigment - can see chromatic colors, but because they only have two cones they confuse some colorus

need only two wavelengths to match any other wavelength in the spectrum

Question 34

ishihara plates

Answer 34

a display of colored dots used to test for the presence of color deficiency

the dots are colored in a way so that people with normal color vision can perceive numbers in the plate, but people with color deficiency either can’t perceive the numbers or perceive different numbers

Question 35

unilateral dichromat

Answer 35

a person with trichromatic vision in one eye and dichromatic vision in the other

both eyes connected to the same brain, so this person can look at a color with their dichromatic eye and then determine which color it corresponds to in their trichromatic eye

Question 36

three forms of dichromatism

Answer 36

protanopia, deuteranopia, and tritanopia

Question 37

why are males more likely than females to inherit protanopia or deuteranopia

Answer 37

because both conditions are inherited through a gene on the X chromosome

males only have one X chromosome, so a defect in the visual pigment gene on the chromosome causes color deficiency

females have two X chromosomes and are therefore less likely to become color deficient because only one normal gene is required for normal color vision

these forms are called sex linked because women can carry the gene for color deficiency without being color deficient themselves

Question 38

protanopia

Answer 38

affects 1 percent of males and 0.02 percent of females

no long wavelength pigment - perceives short wavelength as blue and as waves get longer and longer it turns to gray

Question 39

neutral point (protonopes)

Answer 39

the wavelength at which protanopes perceive gray 492 nm

past the neutral point they perceive yellow, which becomes less intense at the long wavelength end of the spectrum

Question 40

deuteranopia

Answer 40

affects about 1 percent of males and 0.01 percent of females

missing the medium wavelength pigement

deuteranopes perceive turqouise at short wavelenths and yellow at long wavelengths

Question 41

tritanopia

Answer 41

very rare (0.002 percent of males and 0.001) percent of females

no short wavelength pigment
blye at short wavelenghts, red at long, neutral point at 570 nm

Question 42

neutral point for deuteranopes

Answer 42

498nm

Question 43

neutral point for tritanopes

Answer 43

570nm

Question 44

anomalous trichromatism

Answer 44

a type of color deficiency in which a person needs to mix a minimum of three wavelengths to match any other wavelength but mixes them in different proportions than a trichromat

not as good at discriminating between wavelengths that are close together