Color Vision (Actual) Exam Graded A+
3 signals of primate visual system - ANS-1. luminance signal
2. red-green color signal
3. blue-yellow signal
Anomalous trichromats - ANS-have all 3 cones with visual pigment molecules, but
spectral sensitivities are abnormal
1. Protoanomoly- long (red) cone abnormal
2. Deutanomoly- medium (green) cone abnormal
(5% men, 4% women) * most common color blindness
3. Tritanomoly- short (blue) cone abnormal
blue yellow signal - ANS-ratio of luminance signal (red + green) : blue cone output
P pathway (color)
chromatic aberration - ANS-different wavelengths of light have different refractive
properties. long wavelengths bend least (red light); short wavelengths bend more (blue
light). blue light refractive rays converge before fovea (therefore no blue cones in fovea,
only red and green).
Color Constantcy - ANS-Ability to determine the color of an object despite changing
illumination conditions
Perception of the color of an object is not based solely on the light reflected from it but
also the light reflected from surrounding objects.
V4 cells
(Mondrian pattern, vary illumination, compare to V1 cell)
The visual system discounts the green illumination somehow by looking at lots of
objects at once (V4 cell has larger RF). Perceives a square appears "green" because it
is "greener" than the things around it. V1 cells can't do this.
Color Opponency Theory and Color After-Effect - ANS-all colors can be broken down
into proportions of 4 primary colors (red, green, blue, yellow). you don't ever perceive
blue-yellow colors or red-green colors. So they must be processed in separate
channels. We also perceive light/dark dimension.
start at the 4 primary opponent colors. adapts out each cone, so when you look at white
squares you get a sensation of the opponent color for the cone you adapted out.
example, stare at red, adapt out red cone, get an after-effect of green. This is analogous
to opponent energy waterfall effect
long wavelength cone excited by red light (650nm), inhibited by green light (550nm),
and only little bit responsive to blue light (450nm).
