Chapter 9 Flashcards
three functions of color vision
classify and identify colors (ex. red = stop or anger)
facilitates perceptual organization (ex. seeing one object from another)
allows us to survive (ex. recognizing colors of food)
what did Isaac Newton propose regarding white light?
white light has a mixture of many colors
prism
object that could separate different colors from the white light
visual spectrum
colors that humans can perceive (400 - 700 nm)
match the wavelengths to the color
blue = short
green = medium
yellow = medium/long
red = long
how do wavelengths get processed?
colors of objects are determined by wavelengths that are reflected by light into the eyes
chromatic colors
light is able to reflect different wavelengths (e.g., red, green, blue)
selective reflection
in chromatic colors, some colors reflect more than others
achromatic colors
light reflects equal wavelengths (e.g., white, black, gray)
selective transmission
transparent objects (eg., liquids, plastics, glass) allow wavelengths to pass through
reflectance and transmission curves
used to plot the percentage of light reflected or transmitted to perceive specific wavelengths
two ways to mix color to describe different wavelengths
mixing paints (paint absorbs or takes away colors; short, medium, and long mixed together creates BLACK; SUBTRACTIVE – blue + yellow = green, blue and yellow no longer present)
mixing light (short, medium, and long superimposed or placed over each other creates WHITE; ADDITIVE – green, medium + red, long = yellow, medium-long)
three perceptual dimensions of color
hue (color being assessed)
saturation (perceived intensity and pureness of color; how strong it is)
value/lightness (perceived brightness of the color)
desaturation
fading of a color due to more white in it
trichromatic theory of color vision
three different color mechanisms (for three different wavelengths: short, medium, long) are responsible for color vision
color matching experiment
behavioral evidence for trichromatic theory
adjust 3 wavelengths to match the test field of one wavelength
findings:
adjusting 3 wavelengths = possible to match any colors in the test field
adjusting two wavelengths only = cannot match all colors
normal color vision = requires 3 receptors
test field
the color light the experimenter wants the observer to match
comparison field
observer must manipulate the lighting to match the test field color
3 cone pigments in terms of wavelengths
short wavelength, medium, long
visual pigment molecule
refers to cones because rods only have short wavelengths
retinal bends from opsin to produce light
opsin
protein structure differs representing the three different pigments
metamerism
situation in which colors of different wavelengths create an identical color
metamers
different wavelengths that come together to make a similar color
1 receptor = 1 visual pigment only
wavelengths cannot be identified
color from light looks the same (shades of gray)
principle of univariance
when only 1 receptor exists
receptors can’t detect differences in wavelengths, only the intensity of light
2 receptors = 2 visual pigments
ability to identify 2 wavelengths and not just intensity of light
3 receptors = 3 visual pigments
ability to identify 3 wavelengths, creating perception of many colors
who proposed the two theories of color vision
trichromatic theory of color vision - Helmholtz, Young, and Maxwell
opponent-process theory - Hering
phenomenological method
describing an observation
Hering’s color circle experiment
pure colors that cannot be mixed with other colors: red, yellow, green, blue (primary colors or unique hues)
opponent colors: blue/yellow, green/red, black/white
opponent neurons
located in retina and LGN
respond in excitatory manner to one end of the visible spectrum and an inhibitory manner to the other for color pairings
trichromatic + opponent-process theory
each theory describes physiological mechanisms in the visual system
trichromatic - explains cones in retina
opponent-process - explains neural response from cones to the brain
Ishihara plates
color vision test to diagnose people w/ color deficiency
try to identify number inside dotted circle image
unilateral dichromats
very rare condition where people have normal color vision in one eye but deficient in the other
monochromat (definition + effect on daily life)
has one wavelength to see color; see shades of gray
only rods, no functioning cones
poor visual acuity (unable to see details) and sensitive to bright light
color blindness
dichromat
has 2 wavelengths to see color
perceived some color but not all
males tend to have it more because of lack of extra X chromosome
color deficiency
3 types of dichromats
protanopia (primary - red/long)
deuteranopia (secondary - green/medium)
tritanopia (third - blue/short)
protanopia
lacking red cones
sees short wavelengths (blue)
fades to gray (neutral point) at 492 nm –difficulty seeing green
long wavelengths = yellow above neutral point – difficulty seeing red
deuteranopia
lacking green cones
sees short wavelengths (blue)
fades to gray (neutral point) at 498 nm – difficulty seeing green (lacks medium wavelength pigment)
long wavelengths = yellow above neutral point (cannot see red as much)
tritanopia
lacking blue cones
very rare dichromat
difficulty seeing blue
fades to gray at 570 nm
long wavelengths = red above neutral point (cannot see yellow)
color constancy
we perceive colors of objects as not changing even under different lighting
lightness constancy
we perceived achromatic colors as remaining relatively constant
we may see different shades of gray due to amount of light reflected but color itself doesn’t change
