Sensation
The Eye: Vision
Spectrum of light - The electromagnetic spectrum is the
spectrum of all forms of light across the many frequencies it travels
at. The light we see is a small, slim sliver of the electromagnetic spectrum.
It is significant to us, because it is through these few wavelengths of
light all the richness of the world is conveyed to us. Light is Invisible
if the wavelength is too short or too long.
Notes on the structure and function of the eye. 
The Image is reversed in the eye, this is "fixed" by the brain.
Light waves must be focused to be seen. the Cornea focus the light waves into a narrower beam.
The Pupil allows light into the interior of the eye.
The Iris controls the amount of light allowed to enter.
The Lens focus, focus , focus
The Retina - begins transduction
The Eyeball's shape affects vision
Nearsightedness - eyeball to long
Farsightedness - eyeball to short
Retina: a miniature camera-computer has two types of photoreceptors:
Rods to see in dim light
Cones to see color
Transduction (light to nerve impulses) occurs in the retina. The transmission path to the brain is the optic nerve. There is a blind spot where the optic nerve exits the eye but it is not noticed because the eye is constantly moving.
Visual pathways: eye to brain
- The optic nerve connects to the thalamus for initial processing. Next stop the occipital lobe.
- The primary visual cortex in the occipital lobe using specialized cells adds detail.
- The visual association areas in the occipital lobe add meaning and complete the process producing vision.
Color vision - theories
The trichromatic theory of color vision is based on the premise that there are three classes of cone receptors serving color vision. One of the more important empirical aspects of this theory is that it is possible to match all of the colors in the visible spectrum by the appropriate mixing of the three primary additive colors red, green, & blue. When these are mixed
equally white is produced.
 FYI: The three primary subtractive (pigment) colors are red, blue, & yellow. When pigment colors are mixed
equally black is produced.
The opponent-process theory
Afterimages show opponent pairs: red-green & yellow-blue
When excited or inhibited, ganglion & thalamic cells signal
one of the pair colors.
Physiology shows: Trichromatic + Opponent-processes are combined.
Color blindness
Monochromats - no cones = no color
Dichromats - cannot tell red from green
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