Docstoc

Vision

Document Sample
Vision Powered By Docstoc
					            Vision

 Eyes, Optic Nerves, Ganglion
Cells, Occipital Lobe… Its got it
               all!
               Anatomy
Key Elements: Pupil, Lens, Retina, Fovea,
 Photoreceptors- Rods and Cones, Optic
 Nerve, Occipital Lobe
           Visual Transduction
• Begins when light waves enter the eye
• Photoreceptors (rods and cones) on the retina
  interpret the waves
  – Rods work in the dark and are found all over the
    retina (nearly 18X more rods than cones)
  – Cones measure color and are found only on the
    fovea (area of most focus on the retina)
• Bipolar cells take info from rods and cones to
  the GANGLION CELLS (sense/afferent
  neurons)
  – GC AXONS ARE the Optic Nerve.
  – So… TRANSDUCTION occurs in the retina.!
         Brightness Explained
• How much light reaches the retina?
  –Controlled by the PUPIL
    • Dilated Pupil=DARK
    • Contracted Pupil=LIGHT
       –Pupil Dilates in the Dark to expose
        more light waves to the
        photoreceptors
         »Many drugs can interfere with this by acting
          as agonists (replicating the
          neurotransmitters) involved in determining
          Pupil dilation and Contraction! (Primarily
          Dopamine and Endorphin)
      How does the Visual System
            Create Color?
• Color does not exist in the world, only in
  the mind---WHOA!
  – color is a sensation created when light waves
    are transduced (I have no idea if this is the
    correct past tense of transduction) and then
    processed in our visual cortex
  –Only CONES (visual receptor cells) can
   detect color. These are only found in
   the FOVEA
            The Nature of Light
• Electromagnetic spectrum- range of
  electromagnetic energy
   – Visible spectrum- part of the electromagnetic
     field that our brain can interpret in color
       • To interpret energy outside of the visible
         spectrum, we employ devices- radio’s,
         TVs, etc
          –Long waves- red
          –Medium waves- yellows/greens
          –Short waves- blues
Electromagnetic Spectrum
      2 Theories for How we Sense
                 Colors
1. Trichomatic Theory: explains the initial stages
   of color vision- 3 types of cones sense the
   visible light- red, green, and blue
2. Opponent-Process Theory: explains vision
   from the bipolar cells on- upon the sensation
   of 1 color, your brain will inhibit its
   compliment- red/green; yellow/blue, etc
  • This explains the negative afterimage on p
      121
           Color Blindness
• Color weakness- shades and pale
  colors are difficult to distinguish
• Color blindness- cannot see specific
  colors
  –Most red/green
  –Rarely blue/yellow
  –Only 500 ever have reported
    complete color blindness

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:10
posted:9/9/2012
language:Latin
pages:9