https://vimeo.com/117815404

• Exam 3 next Tuesday, 11/17

• Wrap-up on action
• Vision
• Exam 3 review

• What’s out there?
  • Shape, form, color
• Where is it?
  • Position, orientation, motion

• Wavelength or frequency
• Intensity
• Location/position of source
• Reflects off some materials
• Refracted (bent) moving through other materials

• Eyes categorize wavelength into relative intensities within wavelength bands
• RGB ~ Red, Green, Blue
  • Long, medium, short wavelengths
• Color is a neural/psychological construct

• Cornea - refraction (2/3 of total)
• Pupil - light intensity; diameter regulated by the Iris.
• Lens - refraction (remaining 1/3; variable focus)

• Retina - light detection
  • ~ skin or organ of Corti
• Pigment epithelium - regenerate photopigment
• Muscles - move eye, reshape lens, change pupil diameter

• Image inverted (up/down)
• Image reverseed (left/right)
• Point-to-point map (retinotopic)
• Binocular and monocular zones

• Central 1-2 deg of visual field
  • ~ thumbnail @ arm’s length
• Aligned with visual axis; center of gaze
• Retinal ganglion cells pushed aside
• Highest acuity vision == best for details

• Rods
  • ~120 M/eye
  • Mostly in periphery
  • Active in low light conditions
  • One wavelength range

• Cones
  • ~5 M/eye
  • Mostly in center
  • 3 wavelength ranges

• Outer segment
  • Membrane disks
  • Photopigments
    • Sense light, trigger chemical cascade
• Inner segment
  • Synaptic terminal
• Light hyperpolarizes photoreceptor!
  • The dark current

• Physiologically backwards
  • How?
• Anatomically inside-out
  • How?

• Physiologically backwards
  • Dark current (more NT released in dark)
• Anatomically inside-out
  • Photoreceptors at back of eye

• Bipolar cells
  • Horizontal cells
• Retinal ganglion cells
  • Amacrine cells

• Center region
  • Excites (or inhibits)
• Surround region
  • Does the opposite
• Bipolar cells & Retinal Ganglion cells ->
• Most activated by “donuts” of light/dark
  • Local contrast (light/dark differences)

• Black vs. white (achromatic)
• Long ( red) vs. Medium ( green) wavelength cones
• (Long + Medium) vs. Short ( blue) cones
• Can’t really see reddish-green or bluish-yellow

• Retinal ganglion cells
• 2nd/II cranial (optic) nerve
  • Optic chiasm

• Hypothalamus
  • Suprachiasmatic nucleus
    • Regulates circadian (day/night) rhythm via pineal gland

• Superior colliculus & brainstem

• ~90% of axons from retina

• 6 layers + intralaminar zone
  • Parvocellular (small cells): chromatic
  • Magnocellular (big cells): achromatic
  • Koniocellular (chromatic - short wavelength?)
• Retinotopic map of opposite visual field

• Via optic radiations
• Primary visual cortex (V1) in occipital lobe

• Fovea overrepresented
  • Analogous to somatosensation
  • High acuity in fovea vs. lower outside it
• Upper visual field/lower (ventral) V1 and vice versa

• 6 laminae (layers)
  • Input: Layer 4
  • Output: Layers 2-3 (to cortex), 5 (to brainstem), 6 (to LGN)

• Columns
  • Orientation/angle
  • Spatial frequency

• Columns
  • Color/wavelength
  • Eye of origin, ocular dominance

• Larger, more complex receptive fields
• Dorsal stream (where/how)
  • Toward parietal lobe
• Ventral stream (what)

• What is it? (form perception)
• Where is it? (space perception)
• How do I get from here to there (action control)
• What time (or time of year) is it?