Lecture 2 - The brain Flashcards

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1
Q

Ganglion cells?

A
  • each ganglion cell receives input from 126 photo receptors - input is not simply added but either excites or inhibits a ganglion cell
  • this depends on where in a ganglion cell’s receptive field the stimulus is located
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2
Q

What is the receptive field of a neuron?

A

the part of the visual field in which a stimulus can modify the neurons firing rate

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3
Q

What is the excitatory area (+) of a ganglion cell?

A
  • ‘on’ area
  • increases the firing rate of a neuron when stimulated
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4
Q

What is the inhibitory area (-) of a ganglion cell?

A
  • ‘off’ area
  • decreases the firing rate of a neuron when stimulated
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5
Q

What are the 3 main types of ganglion cells?

A
  1. magnocellular (M) cells
    - mostly input from rods
    - not colour specific
  2. parvocellular (P) cells
    - input from single M or L cones
    - colour specific (green or red on/off)
  3. koniocellular (K) cells
    - excitatory input from s cones
    - inhibitory input from M and L cones (blue on)
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6
Q

Visual cortex?

A
  • primary visual cortex = V1
  • extra striate visual areas = V2, V3, V4, V5
  • as visual information travels through the cortex there is ongoing neural convergence
  • the neurons receptive fields increase
  • visual information gets more complex with ongoing integration
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7
Q

V1?

A
  • striate cortex (stripy appearance)
  • some V1 neurons are orientation selective =
    -> they respond when a stimulus in their receptive field matches their preferred orientation
    -> they have elongated receptive fields to capture edges in a particular orientation
  • the less the stimulus matches the preferred orientation the lower the neurons firing
  • other neurons are motion direction selective = they respond when a stimulus in their receptive field matches their preferred motion direction
  • other V1 neurons are selective for colour and brightness
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8
Q

V2?

A
  • V2 receptive fields are about twice as large as V1 receptive fields
  • V2 neurons respond to basic stimulus features such as orientation, motion direction and brightness
  • they also respond to more complex features such as length, angles, arcs etc.
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9
Q

Evidence for 2 separate streams?

A
  • the parietal (dorsal) stream processes object locations (where)
  • the temporal (ventral) stream processes object identities (what)
  • moneys with parietal (where) lesions could distinguish a cube from a triangle (object discrimination) while monkeys with temporal (what) lesions could not
  • monkeys with temporal (what) lesions could learn the positions of an object (location discrimination) while monkeys with parietal (where) lesions could not
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10
Q

V3?

A
  • is in the parietal/ dorsal (where) stream
  • receptive fields are 5x larger in V3 than V1
  • integrated information over a large area of the retina
  • perfect for motion perception (where is an object)
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11
Q

V4?

A
  • is in the temporal/ ventral (what) stream
  • receptive fields are 5x larger in v4 than in v1
  • V4 neurons respond to object-defining features (what is an object) such as colour, orientation, complex shapes, texture
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