Sensation & Perception

Visual System
Normal vision is chromatic in the fovea and achromatic
in the periphery.
Photopigments in the cones allow for color vision. Three
types of cones (red/green, blue/yellow, black/white) allow
for trichromatic vision.
When one type of cone is dysfunctional color blindness
results, this is called dichromatic vision. If two types of
cones are dysfunctional the result is monochromatic
vision. If all three cones are dysfunctional the individual
has achromatic vision.
The trichromatic theory suggests that the relative
activation of these three cone types accounts for the
perception of colors that we see. It does not account for
negative after-images. The Opponent-Process Theory
does account for the negative after-image. Looking at a
single color and then away from that color “turns on” the
opponent color.