Lesson 9 Flashcards
cerebral achromatopsia
sudden color blindness
what does our perception of color depend on?
the wavelength of light that enters our eye
what does our perception of colored objects depend on?
the wavelength of light that is reflected from the object into our eyes.
chromatic colors
blue, green, and red - some wavelengths are reflected more than others
achromatic colors
white, grey, and black - when light is reflected equally across the spectrum
selective transmission
only some wavelengths pass-through the substance or object
transmission curves
plots of the percentage of light transmitted at each wavelength
wavelength transmitted or reflected and perceived color:
short-?
medium?
medium and long?
long?
long, medium, and short?
blue
green
yellow
red
white
subtractive color mixture
subtract all the wavelengths except the color seen- done in mixing paints
the black paper reflects…?
less than 10% of the light that hits it
the white paper reflects…?
more than 80% of the light that hits it
how do we know which wavelength/ color will result from mixing paints?
both paints still absorb the same wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common
AKA: the color that results from the mix is the wavelength that is reflected from both colors.
additive color mixture
mixing lights involves adding up the wavelengths of each light in the mixture, thus mixing lights is called an additive color mixture
what is the connection between wavelength and color for light?
colors of LIGHT are associated with wavelengths in the visible spectrum
what is the connection between wavelength and color for opaque objects?
colors of OBJECTS are associated with wavelengths that are reflected
what is the connection between wavelength and color for transparent objects?
colors of transparent objects are associated with wavelength that are transmitted
mixing paints causes more/fewer wavelengths to be reflected?
fewer (each paint substracts wavelengths from the mixture)
mixing lights causes more/fewer wavelengths to be reflected?
more (each light adds wavelengths to the mixture)
nonspectral colors
colors that do not appear in the spectrum because they are mixtures of other colors (ex:magenta)
what are the 3 perceptual dimensions of color?
- hues
- saturation
- value
what is saturation?
determined by the amount of white that has been added to a particular hue.
what is value?
refers to the light-to-dark dimension of color
HSV color solid
a cylindrical color solid- has the 3 dimensions: hue, value, and saturation
what is the trichromatic theory of vision (Young-Helmholtz theory)?
color vision depends on the activity of 3 different receptor mechanisms
what is the opponent-process theory?
color vision is caused by opposing physiological responses generated by blue and yellow, red and green, and black and white.
how was the Trichromatic theory tested?
color matching - experimenter shines a single wavelength on a test field. then subject matches the reference color by mixing different wavelengths of light in a “comparison field”. Finding = any color could be matched if they adjust proportions of 3 wavelengths.
metamerism
2 physically different stimuli are perceptually identical
metamers
2 identical fields in a color-matching in a color-matching experiment
principle of univariance
once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost.
how does a person with 1 receptor match any wavelength in the spectrum?
adjusting the intensity
people with just one type of pigment who see in shades of gray
monochromats
people with 2 types of cone pigments who see chromatic colors, but confuse some colors together
dichromats
having 3 visual pigments
trichromats
hering’s primary colors
red, yellow, green or blue
what is the afterimage demonstration?
looks at the center of a square with the top two squares being red and green and the bottom being yellow and blue. After 30 seconds when looking at a white surface, the red and green will switch sides and same for blue and yellow.
what are the after images called?
complementary afterimages- because the afterimages is the color of the opposite side of the color circle
hue cancellation
determined by how much of the opposing color is necessary to cancel the sample color.
opponent neurons
the retina and lateral geniculate nucleus that responded with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
which neurons correspond to short, medium, and long wavelengths?
+B = short
-Y = medium and long
where in the brain does the trichromatic theory manifest itself?
the receptors in the retina
where does opponent-process theory manifest itself in the brain?
opponent neurons within the lateral geniculate nucleus
What is important to know about the circuits in opponent-process theory?
their responses are determined by both the wavelength to which the receptors respond best and by the arrangement of inhibitory and excitatory synapses.
prosopagnosia
inability to recognize faces
unilateral dichromat
a person with trichromatic vision in one eye and dichromatic vision in the other
what are the 3 major forms of dichromatism?
protanopia (missing long wavelength pigment)
deuteranopia (missing medium wavelength)
tritanopia (missing short wavelength)
anomalous trichromatism
needs 3 wavelength to match any wavelength like a normal person
reflectance edge
edge where the reflectance of 2 surfaces changes.
illumination edge
edge where the lighting changes
penumbra
fuzzy border at the edge of the shadow
