chapter 9: perceiving color Flashcards
differentiate between cerebral achromatopsia and color deficiency
cerebral achromatopsia: occurs after cortical injury
color deficiency: occurs at birth because of genetic absence of one or more cone receptors
name the functions of color perception
- facilitates perceptual organization (grouping and segregation of objects)
- signaling functions (ripped fruits, traffic light)
- recognize and identify things
- recognize natural scenes
- perceive gist of scenes
- cue to emotions
explain Newton’s prism experiment
- shine light through prism 1 and colors separate
- block certain light beams with board
- shine beam through prism 2
what are the two important things Newton notices about the light that passed trough the second prism
- second prism did not change the color appearance of any light that passed through it
- degree to which each beams were “bent” by second prism was different
how are the color of objects determined?
determined by wavelengths of light that are reflected from the object into our eyes
distinguish between chromatic and achromatic colors
chromatic: blue, green, red, etc
achromatic: white, gray, black
define selective reflection
when some wavelengths are reflected more than others
(results in chromatic colors)
how does an object appear black or white
- object appears white when all wavelengths of light are reflected
- object appears black when all wavelengths are absorbed
what is a reflectance curve
curve that shows the percentage of light reflected at each wavelength in the visible spectrum for an object
define selective transmission
when only some wavelengths pass through the object or substance, making it seem transparent
what is the difference between subtractive color mixture and additive color mixture
subtractive: paint
↓ wavelengths so B+Y=G
additive: light
↑ wavelengths so B+Y=white
name the seven colors on the visible spectrum
red
orange
yellow
green
blue
indigo
violet
why do modern scientist often exclude indigo from the list of spectral colors
because humans have difficulty distinguishing between blue and violet
what are nonspectral colors
colors that do not appear in the spectrum like magenta
name and differentiate the three perceptual dimensions of color
hue: chromatic colors
saturation: intensity of color
value (lightness): light-to-dark dimension of color
visualize the munsell color system
- hue arranged in a circle around the vertical axis
- vertical axis is value
- saturation increases with distance away from axis
what is Young-Helmholtz theory, the trichomatic theory?
- color vision based on 3 principal colors
- 3 different receptor mechanism
explain the color-matching procedure and the conclusion drawn from it
Ps have to match reference color by mixing different wavelengths of light
- any color could be matched by adjusting proportions of 3 only wavelengths
true or false? only one receptor mechanism needs to be stimulated to perceive light of a particular wavelength
false, each receptors are stimulated at different degrees and the pattern of activity results in perception of a color
explain the microspectrophotometry technique
direct narrow beam of light into a single cone receptor
what were the advances made by the measurements of cones
- exact spectra of the three cone mechanisms
- large overlap between L and M cones
how does adaptive optical imaging works
- creates sharp image by measuring how optical system of the eye distorts the image reaching the retina
- takes picture through deformable mirror that cancels distortion
- results in clear pic of cone mosaic
what are the responses in S, L and M receptors for blue, yellow and white
blue: ↑S, ↓M, ↓↓L
yellow: ↓S, ↑M and ↓L
white: equal
define metamerism
two physically different stimuli are perceptually identical (metamers)
- ex. color matching task
monochromatism is caused by …
having no functioning cones
- only see in shades of light (white, gray, black)
how do monochromats match one wavelength to another
adjust intensity
what is the principle of univariance
once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost
differentiate between monochromat, dichromat and trichromat
monochromat: one type of pigment
- see shades of grey
dichromat: 2 types
- see chromatic colors, but can’t distinguish among all colors
trichromat: 3 types
- can discriminate among more wl across spectrum
what test can be used to diagnose color deficiency
Ishihara plates
what is a unilateral dichromat person
person with trichomatic vision in one eye and dichromatic in the other
why are men more likely to get dichromatism compared to women
gene located on X chromosome
- only one normal gene necessary for normal color vision
- since women have 2, they can carry gene for color deficiency without being color deficient
explain the protanopia condition
- missing L wavelength pigment
- above neutral point: yellow (becomes less intense at end of spectrum)
- below NP: blue
explain the deuteranopia condition
- missing M wavelength
- perceives blue at S wavelengths, yellow at L
- NP: 498 nm
explain the tritanopia condition
- missing S wavelength
- perceives blue at S wavelength, red at L
- NP: 570 nm
define anomalous trichromatism
- mixes wl in different proportions
- not as good as trichromat at discriminating between wl that are close together
what is Hering’s theory, the opponent-process theory
color vision is caused by opposing responses generated by blue-yellow and green-red
what are some evidence of the opponent-process theory
opponent neurons
describe the hue scaling procedure
indicate proportion of red, yellow, blue and green perceived in each color
name 3 reasons why Hering’s theory wasn’t widely accepted
- trichromatic theory
- could not compete with Maxwell’s quantitative color mixing data
- no neural mechanism known at that time that could respond to opposite ways
explain hue cancellation experiments
determine the amount of yellow/green necessary to cancel all perception of blue/red
what are opponent neurons
neurons that respond with an excitatory response to light from part of the spectrum and with an inhibitory response to light from another part
what were the 3 receptive field layouts of opponent neurons
- circular single opponent
- circular double opponent
- side-by-side double-opponent cortical neuron
where are opponent neurons located
- retina
- LGN
