Neuro Ch 5

  1. vision
    constructive process, take in light and infer what must be present in the world

    • we see what we expect
    • unaware to things we aren't conscious to 
    • we see what we need to know
    • hard to see without expectations
  2. light to vision
    sensory transduction: process by which a signal from the world is transformed into electrochemical signals in the nervous system

    photoreceptors in the retina transduce a narrow band of the electromagnetic spectrum (“visible light”)
  3. Anatomy of the Eye
    light passes through cornea, iris controls amount of light that enters, goes through pupil and lense and focuses on retina
  4. retina 
    rods and cons capture light in electrochemical activity through phototransduction
  5. retina 
    • light strikes pigment molecule in the
    • photoreceptor, causing the pigment molecule to break into pieces, which then act on proteins in the cell to change its resting membrane potential
  6. Retina information flow
    photoreceptors --> bipolar cells ---> ganglion --> optic nerve

    amacrine and horizontal cells communicate with other parts of the retina
  7. rods
    • LIGHT
    • sensitive to light but do not respondselectively to any particular wavelength
    • detects degrees of light, good for dim areas

    concentrated in periphery
  8. cones
    • COLOUR
    • less sensitive to light, but the 3 cone types are maximally responsive to different wavelengths
    • bright environments

    concentrated in fovea (central vision)
  9. cones vs rods spatial resolution
    • cones > rods b/c
    • 1. more light can access photoreceptors directly, smaller ganglion
    • 2. each cone connects to its own bipolar cell and then its own ganglion
  10. ganglion cells
    • each retinal ganglion cell only responds to a specific location of the visual scene (receptive field)
    • info of where light originated maintained 
    • optimised to detect edges via differences in light levels from one to the next
  11. centre-surround structure
    • on center vs off center
    • think circle with circle inside
  12. off centre
    • work best when centre on and surround off
    • weak when all on
  13. on centre
    • best when centre off and surround on
    • weak when all on
  14. eyes to brain
    L and R visual fields, temporal semiretina signals stay ipsilateral, nasal semiretina move contralaterally, go to visual cortex
  15. retinal ganglion cell types
    • parvocellular: input from cones. Fine details, form, colour
    • magnocellular: input from rods. Depth, brightness, movement
  16. eyes to thalmus
    • retinal ganglion cells are sent to the lateral
    • geniculate nucleus (LGN) in the thalamus
  17. thalamus to visual cortex
    axons travel from the LGN to V1 via the optic radiation
  18. visual cortex 
    • V1 contains a retinotopic map: each neuron responds to a particular part of the visual field
    • v1 has new neurons
  19. primary visual cortex
    • simple cells: preferred orientation at particular place
    • complex cells: preferred orientaiton at any place
  20. binocular disparity
    • each eye gets slightly different view of the world, how we see in 3D
    • stereopsis: using difference to infer depth
  21. V2
    • direct connections from V1, also retinotopically (topographically) organized but with larger receptive fields
    • illusiory contours
  22. V3, V4, V5
    • cells respond to more abstract stimuli in their receptive fields (e.g., shapes, textures, movement)
    • V5: specialized for motion detection, sends signals to the parietal lobe
  23. inferotemporal cortex
    • representation of abstract and complex stimuli (e.g., faces, scenes, objects)
    • no longer organized retinotopically
  24. processing streams
    ventral and dorsal
  25. ventral stream
    • WHAT pathway
    • from parvocellular cells in LGN, through V1, V2, V4 and inferotemporal cortex
    • tools, animals faces
    • position and size invariance
  26. dorsal stream
    • WHERE pathway
    • from magnocellular cells in LGN, through V1, V2, and V5
  27. fusiform face area
    recognises everything as faces

    • prosopagnosia: inability to recognize face
    • visual agnosia: an impairment in the ability to recognize objects by sight
  28. sparse coding
    small number of clustered neurons that become active in response to a specific visual stimulus

    for stimuli that we are expert at
  29. population coding
    • many neurons distributed over cortical regions are involved, showing varying levels of activity
    • the pattern is important
  30. motion after effect
    • perception of an opposite direction of motion after prolonged viewing of a moving stimulus
    • adaptation to reduce response over time

    neurons will be firing below baseline in favour of the opposite direction of motion
  31. motion blindness
    • happens after damage to motion detecting areas in the dorsal stream (e.g., V5)
    • can't detect motions, just looks like a bunch of still photos getting closer
  32. spatial attention
    • directing attention to particular locations in space
    • dorsal stream is critical for guiding and adjusting the “spotlight” of attention
  33. disorders of attention
    • hemineglect: ignores half of the world; caused by damage to the right parietal lobe
    • balints syndrome: cannot comprehend the big picture of a visual scene though they can see objects individually
    • simultanagnosia: inability to recognize multiple elements in a scene
  34. binocular rivalry
    if different images are presented to each eye, perception shifts back and forth between them
  35. unconscious inference:
    • the brain infers what is likely
    • to be out there given incoming signals
Card Set
Neuro Ch 5
Cognitive Neuroscience Chapter 5