06-07. circuits & receptive fields Flashcards

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1
Q

What are neural circuits?

A

Connected cells with combinations of excitatory and inhibitory inputs that detect patterns of external stimulation

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2
Q

What is lateral inhibition?

A

when the output of some receptors has the effect of reducing the signals from neighboring receptors

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3
Q

3 perceptual consequences of lat. inhibition?

A
  1. Simultaneous Contrast
  2. Hermann Grid
  3. Mach Bands
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4
Q

Simultaneous contrast example

A

2 squares of medium grey are surrounded by light grey and black

  • square surrounded by light grey looks darker –> light grey is bright stimulus, and produces lots of lateral inhibition
  • square surrounded by the black looks lighter –> black is dark stimulus, no lateral inhibition
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5
Q

Hermann grid - what is it, what happens?

A
  • Grid of black spots with white lines
  • you see a grey spot in the intersections you’re not focusing on
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6
Q

Hermann grid - why does it happen?

A
  • areas in intersection are surrounded by 4 sides of white (bright, intense stimulus)
    –> produces lateral inhibition, and makes the intersection look darker (grey)
  • areas in between boxes only have white on 2 sides. on the other 2 sides they have black (dim, not intense stimulus)
    –> no/little lateral inhibition, you see bright/normal white
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7
Q

Mach bands - what is it, what happens?

A
  • you see a gradient (of color/brightness) in a constant/uniform band
  • “change in perceived brightness is much bigger than change in physical brightness” !!
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8
Q

Mach bands - why does it happen? Why is it good for us perceptually?

A
  • percept. system amplifies __slight__ differences in brightness (due to lat. inhibition)
  • helps with contour of shape & identifying edges relative to background
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9
Q

What does the lat. inhibition neural circuit look like for mach bands?

A

Look at ppt 06 slides 29&30

(compared to slides 27&28 without lat. inhibition)

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10
Q

How to calculate output of a neural circuit? (equation)

A

Output = input X gain

Excitatory: G>0
Inhibitory: G<0

The problem will give you all info you need

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11
Q

receptive field definition?

A

specific region/area on the retina that, when stimulates, changes the activity of the ganglion cell/neuron

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12
Q

Where are receptive fields smaller?

A

Near the fovea

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13
Q

On center cell explanation?

A
  • excitatory when light strikes center
  • inhibitory when light strikes surround
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14
Q

Off center cell explanation?

A
  • opposite of on cell
  • inhibitory when light strikes center
  • excitatory when light strikes surround
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15
Q

Receptive fields of Lateral Geniculate Nucleus cells?

A
  • NOT very picky/SPECIALIZED
  • they respond BEST to small spots of light
  • but they also respond to bars of light and stimuli that move across the field in ANY direction
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16
Q

2 main types of cortical cells (& their receptive fields)

A
  1. simple cells
  2. complex cells

both much more specialized

17
Q

Simple cells? Respond best to…?

A
  • Have on off areas too, but not center surround
  • respond ONLY to BARS of light
  • have a PREFFERED ORIENTATION
  • neural circuit is made up of several LGN cells oriented in a line (bar)
    -^^ see ppt 7a slide 21-22
18
Q

Complex cells – 3 differences from simple cells?

A
  1. C much more numerous
  2. C responds to both light and dark stim (S prefers one or other)
  3. C responds to stimuli regardless of where they are in receptive field
    –> S has on/off areas
19
Q

Complex cells? Respond best to…?

A

4 types
1. motion (orientation, direction and speed)
2. color
3. size
4. length (end stopped)

20
Q

Feature detectors def & examples?

A
  • They are groups of specialized cells
  • they respond only to specific features of visual stimulation
  • Ex.
    –> simple cells
    –> complex cells
21
Q

Do feature detectors play a role in perception? how do we know?

A
  • yes
  • selective adaptation
  • see ppt 7b slide 6