II. Perception: the selection, organization, & interpretation of sensory input
   1. this occurs when the sensory signal reach the CNS
   2. temporal coding: timing of action potentials
   3. spatial coding: location of firing neurons
      A. law of specific nerve energies
 

III. light travels in waves
  1. amplitude of the wave determines brightness
  2. wave length of light conveys colors
 
 

II. why might a person need eye glasses
  1. presbyopia: lens can not accommodate

  2. an elongated eye: the image falls in front of the retina (myopia)

  3. a flattened eye: the image falls behind the retina (hyeropia)

  4. spherical aberrations of the cornea: e.g., astigmatism
 

III. cells of the retina
  1. two types of sensory neurons (photoreceptors)
         a. cones:
         b. rods:

  2. bipolar cells: these receive information from rods & cones

  3. ganglion cells: these receive information from bipolar cells
     A. optic disc (blind spot)

  4. Wiring of the eye
      A. convergence: bipolar cells receiving input from many photoreceptors

      B. interneurons make lateral connection between bipolar cells
         a. lateral inhibition:

  5. receptive fields of ganglion cells
      A. receptive field: the part of the retina & the corresponding part of the visual
           world to which the ganglion cells responds
      B. most have a center surround receptive field (helps us see contrast)
 

IV. where does the signal go after leaving the retina

  1. main visual pathway
      A. optic nerve exits retina at the optic disc
      B. some optic nerves axons cross to form the optic chiasm
      C. information travels to the lateral geniculate nucleus of the thalamus
         a. magnocellular layers:
         b. parvocellular layers:
      D. primary visual cortex (striate cortex)
      E. extrastriate cortex: receptive fields get more complex

  2. subpathways for vision (smaller groups of axons leaving the retina

V. perceiving color
      A. trichromatic theory: three types of cones
 a. What causes color blindness?
      B. opponent processing theory: certain colors oppose or inhibit one another

VI. cortical areas for vision:
  1. the visual (striate) cortex
     A. receptive fields have center-surround characteristics
     B. consists of 6 layers that are arranged in parallel bands
     C. there is a columnar organization
     D. there is a map of the contralateral visual field (large % devoted to the fovea)
     E. most neurons are sensitive to the orientation of lines (simple cells)
        a. feature detectors
     F. some neurons respond to moving lines of a particular orientation (complex cells)
     G. some cells respond best when each eye sees a stimulus in a slightly different location
 

 2. the visual association cortex (extrastriate cortex)

   A. color constancy is controlled by the temporal lobe
      a. lesions here can result in achromatopsia (vision without color)

   B. recognition of patterns occur in the inferior (ventral) temporal cortex.
        Damage here results in a visual agnosia
      a. apperceptive agnosia: can not recognize objects by their shape
         -prosopagnosia: can not recognize faces

      b. associative agnosia: person can not name what they see

   C. middle temporal cortex respond best to moving stimuli
      b. bilateral damage can cause a movement agnosia

   D. the parietal lobe is involved in perceiving & remembering the location of objects
      a. Balint’s syndrome occurs with damage to the parietal-occipital region
         -optic ataxia:
         -ocular apraxia:
         -simultanagnosia:

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