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COGS 101A Exam 1 > Lecture 9 - Convergence and Receptive Fields > Flashcards

Lecture 9 - Convergence and Receptive Fields Flashcards

1
Q

receptive field

A

part of the retina that responds in someway to affect the firing rate of target neurons

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2
Q

receptive field is always on the…

A

RETINA!

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3
Q

Receptive field corresponds to

A

a region in space (ex the visual field)

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4
Q

if activity is changing then we should see this in neurons its converging on later

A

if something is downstream the receptive field is still the receptive field on the retina

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5
Q

If a receptor connects to an inhibitory neuron, can it still be part of the receptive field?

A

YES, it’s still sending a signal (even it’s inhibitory) that can affect the firing rate

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6
Q

it’s not “on” that means activity, instead it’s…

A

any change in state

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7
Q

Primary Visual Cortex - V1

A

signals give us feature detectors

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8
Q

Where do retinal signals go?

A

optic nerve (bundle of axons from the retina) travels to the LGN down the optic track to V1

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9
Q

optic nerve

A

Approximately 1 million
ganglion cells send axons out of
each retina. These axons form
the optic nerve

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10
Q

superior colliculus

A

important for focusing the eyes: multisensory (touch, hearing, sight) and helps you plan out where the eyes will go and your attention

10% of the axons from the retina end up here

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11
Q

LGN (lateral geniculate nucleus)

A

part of the thalamus

90% of the axons from the retina end up here

About 900,000 ganglion axons
go to each LGN

about 360,000 LGN axons (40%) go to visual cortex. So, some processing is taking place.

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12
Q

How are retinal signals organized

A

the different parts of the eye seem to be segregated: visual field can be broken up into the left and right visual fields

everything opticly in the left it’s gunna end up on the right side of BOTH retinas

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13
Q

information to left visual field goes to

A

the right side of both retinas and the right LGN

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14
Q

Spatially organized transmission:

A 
Items in the left visual field go the 
right side of both retinas. 
• Signals from the right side of both retinas go to the right lateral 
geniculate nucleus (LGN).
• Right visual field goes to the left 
side of the retinas and left LGN.
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15
Q

how are retinal signals organized?

A

Each LGN receives signals from both eyes, but the signals from each eye are sent to different layers.

layers are segregating which eye the info came from !!

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16
Q

each (half) eye sends
signals to both LGNs, but the
information from each eye is

A

is kept segregated.

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17
Q

LGN is a relay nucleus

A

taking info from the retina and sends it along to V1 because of its orgnaization

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18
Q

retina and LGN organize activation by…

A

spatial maps of a particular kind, in close register with the retina (retinotopic map)

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19
Q

Retinotopic map

A

each place on the retina corresponds to a place on the LGN

keeps all the cells/activity retinotopically organized

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20
Q

To determine retinotopic maps, perform ….

A

single cell recordings

record from neurons with an electrode that penetrates the LGN obliquely

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21
Q

LGN regulates (processes) ….

signals are received from?

A

…neural information from the retina and cortex before passing it to the primary visual
cortex (V1).

  • Signals are received from the retina, the cortex, the brain stem, and the thalamus.

– Signals from the eyes (bottom-up data) are organized by visual field, receptor type, and type of environmental information (e.g. color, orientation,
motion, etc.).

–

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22
Q

what may be happening in the LGN?

A

when you’re getting top-down information (it’s a dalmnation) - background knowledge biasing certain neurons to fire more and inhibiting others

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23
Q

LGN as perceptual gatekeeper?

A

Perhaps some of the feedback from cortex amplifies signals (or inhibits competing neurons) to enhance certain
features in a noisy environment.

– Background knowledge may help select visual images based on what you expect to see.

– Note: this kind of feedback happens at
many levels in the brain.

24
Q

receptive fields in LGN

A

are center surround (same as in the retina)

25
Q

Visual field information
segregated by….

from retina to LGN

A

…hemisphere

26
Q

Information from each eye
kept separate…

from retina to LGN

A

…. in LGN by layers.

27
Q

Cell receptive fields (center surround) are similar in the…

from retina to LGN

A

… retina and LGN

28
Q

Spatial retinotopic maps are preserved in….

from retina to LGN

A

….LGN

29
Q

Some selective processing occurs - LGN is not simply a…

from retina to LGN

A

…. relay nucleus

30
Q

Occipital Lobe

A

The optic radiation goes
from the LGN to V1, primary
visual cortex.

• V1 has cells with the
smallest receptive fields in
the visual cortex.

• Receptive fields get more
complex from here.

• Information across visual
fields and eyes is now
integrated for the first time
in V1.

31
Q

Hubel and Wiesel

A

demonstrated the firing properties of cells in the striate cortex (V1).

• Using the single-cell recording
method, they recorded cortical cells of anesthetized cats while
presenting different stimuli.

• Received the Nobel prize for
physiology and medicine in 1982.

32
Q

Electrodes that recorded
activation from a cat’s visual
cortex show:

A

• Receptive fields on the retina that are near one another are also near each other in the
cortex!!!!

• This pattern is seen using an
oblique penetration of the
cortex, as was done in LGN.

!!!!Retinotopic maps retained in
the visual cortex.!!!

33
Q

cells in the cortex (V1) respond…

A

….differently than cells in the retina and LGN

34
Q

simple cortical cells

A

come from center surround

  • Side-by-sidereceptive fields
  • Respond to spots of light

• Respond best to bars of light
oriented along the length of the
receptive field

35
Q

Orientation tuning curves

A

• Shows response of simple cortical cell for orientations of stimuli.

• Cells respond best to particular
orientations, and less well to others.

helps to start characterizing the types of receptive fields in V1

36
Q

How do you end up with bar cells?

A

– Simple cells are created by the convergence of LGN axons.

– Points of light will activate the simple cell; however, it is best activated by the correctly oriented bar.

– This is hierarchical processing –

37
Q

hierarchical processing

A

representations are built from simple receptive field and become more complex as you go ‘higher’ in cortex.

38
Q

complex cells

A

even more specific in their responses

like bars of light in a particular location, but also like movement in a particular direction

are made by the convergence of simple cells

39
Q

End-Stopped Cells

A

more specific!!! bar, moving, AND A SPECIFIC LENGTH

come from complex cells

40
Q

hierarchy of cells

A

center surround -> simple cells -> complex cells -> end stopped cells

41
Q

V1 Cells as feature detectors

A

• These neurons fire to specific features of a stimulus. [Think of these as object edge
detectors.]

• Neurons farther along in the visual pathway fire to more complex stimuli in a
hierarchical manner.

• Good to know for the exam.

42
Q

Cells that are feature detectors:

A

– Simple cortical cell
– Complex cortical cell
– End-stopped cortical cell

43
Q

fovea has greater representation in the…..

A

…striate cortex (V1) than

proportionally anticipated.

44
Q

cortical

magnification factor

A

expanding the amount of cortex you’re gunna use when it’s functionally important to the organism

– Fovea accounts for .01% of retina

– Signals from fovea account for 8% to 10% of the visual cortex

– This provides additional
processing for high-acuity tasks.

45
Q

LGN and top down processing

A

More signal comes from the cortex

than the eyes.

46
Q

How are signlas in V1 organized?

retinotopic maps?

A

Retinotopic maps retained in

the visual cortex.

47
Q

simple cells are created by

A

the convergence of LGN axons

48
Q

unlike simple cells, complex cells respond to _____ of bars of light in a specific direction

A

movement

49
Q

How are complex cells activated?

A

– Simple cells were made by the convergence of LGN cells.
– Complex cells are made by converging simple cells
(probably).

50
Q

End-stopped cells respond to

A

moving lines of specific lenghth

moving corners or angles

51
Q

end-stopped cells have no response to

A

stimuli that are too long

stimuli moving in the wrong direction

52
Q

how are end stopped cells formed?

A

made by converging signals from complex cells with striate cortex (V1)

53
Q

cells that are feature detectors

A

– Simple cortical cell
– Complex cortical cell
– End-stopped cortical cell

54
Q

feature detector neurons fire to…

A

…. specific features of a stimulus

55
Q

neurons farther along in the visual pathway fire to more…

A

….complex stimuli in a hierarchical manner

COGS 101A Exam 1 (31 decks)

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