Chapter 5 Flashcards
Why is it important that we be able to see in color?
~ tell the difference between ripe/unripe
~ safety reasons
~ COLOR HELPS US DETECT EDGES
What are the three major physical dimensions of light, and what perceptual dimensions do they correspond to?
- WAVELENGTH (Hue/color)- yellow vs. green; red vs. blue, etc. &
- INTENSITY (Brightness) perceived intensity of color
- SPECTRAL PURITY (Saturation) e.g. “pale” vs. “vivid”; wash out a color by adding white light (de-saturate)
Explain Newton’s groundbreaking experiment concerning the spectral purity of sunlight.
~ he passed sunlight through a shutter and then prism light
~ isn’t pure, it’s made up of seven primary colors that can’t be reduced anymore.
~Sunlight is composite light made up of more than one wave length
Discuss the trichromatic nature of human color vision. What anatomical area is this theory associated with?
Theory that the color of any light is defined in our visual system by the relationships between a set of three numbers, the outputs of three receptor cones (green, red, blue). Located in the retina
~ colors we see are the result of ratio of signals.
Discuss the univariance principle.
~ The response of a single photoreceptor tells the brain how much light has been absorbed, rather than which wavelength
~infinite set of different wavelength intensity combinations can elicit the same exact response
~Can’t use a single photoreceptor to tell which color is being absorbed
~ color is entirely a variation of the brain by how much light as been absorbed, can only extract SOME usable info of wavelength
Describe the three cone types.
- S-Cones: sensitive to short wavelengths (blue cones)
- M-Cones: sensitive to middle wavelengths (green cones)
- L-Cones: sensitive to short wavelengths
Why is it important for us to have all three cone types?
It’s important to have all three because color of the same wavelengths can be differentiated.
Compare and contrast photopic vs. scotopic vision
Photopic: day vision, provides color & detail perception; uses CONE cells
Scotopic: monochromatic vision is low-lit conditions (night); uses ROD cells
Describe how metamers can be produced.
~ different mixtures of wavelengths that look identical. more generally, any pair of stimuli that are perceived as ~ identical in spite of physical differences
~green & red stimulate brain as if it was yellow
~physically different but perceptually equal
Compare and contrast additive color mixing vs. subtractive color mixing
subtractive: blue & yellow reflects green. changing of reflectance of a surface
additive: emitted light
What is color constancy? How does the brain achieve it?
no matter what illuminant properties are, color appears to stay same
to maintain color constancy:
1. light adaptation
2. color contrast-colors further apart in wavelength are easier to tell apart than colors that are closer
Describe the opponent-process theory of color vision
Postulated about three independent receptor types which all have opposing pairs: white and black, blue and yellow, and red and green. These three pairs produce combinations of colors for us through the opponent process.
- trichromatic theory is incomplete, cannot explain color after images
- opponent process theory: antagonistic center & surround (CAN explain color after images)
Describe the receptive field properties of double-opponent color cells. At what level of the visual system are such cells first seen?
Double-opponent cells reside in collections called blobs in layer 4 of V1 & have larger receptive fields than simple opponent cells, so they can “see” more of the ambient illumination.
~ circular receptive field in LGN
It is MOST responsive to the difference in wavelength between light in the center & the surround of its receptive field. (slides 33 and 34)
Briefly describe how the three major channels (1 achromatic, 2 chromatic) are formed
achromatic: overall light levels-black & white (M+L cone)
chromatic: red/green (L/M) & blue/yellow (M/L vs S) channel
color after images
Major types of congenital color abnormalities
dichromat
monochromat
anomalous trichromacy
