Lecture 9 - Convergence and Receptive Fields

Question 1

receptive field

Answer 1

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

Question 2

receptive field is always on the…

Answer 2

RETINA!

Question 3

Receptive field corresponds to

Answer 3

a region in space (ex the visual field)

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

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

Answer 6

any change in state

Question 7

Primary Visual Cortex - V1

Answer 7

signals give us feature detectors

Question 8

Where do retinal signals go?

Answer 8

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

Question 9

optic nerve

Answer 9

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

Question 10

superior colliculus

Answer 10

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

Question 11

LGN (lateral geniculate nucleus)

Answer 11

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.

Question 12

How are retinal signals organized

Answer 12

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

Question 13

information to left visual field goes to

Answer 13

the right side of both retinas and the right LGN

Question 14

Spatially organized transmission:

Answer 14

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.

Question 15

how are retinal signals organized?

Answer 15

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 !!

Question 16

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

Answer 16

is kept segregated.

Question 17

LGN is a relay nucleus

Answer 17

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

Question 18

retina and LGN organize activation by…

Answer 18

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

Question 19

Retinotopic map

Answer 19

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

keeps all the cells/activity retinotopically organized

Question 20

To determine retinotopic maps, perform ….

Answer 20

single cell recordings

record from neurons with an electrode that penetrates the LGN obliquely

Question 21

LGN regulates (processes) ….

signals are received from?

Answer 21

…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.).

–

Question 22

what may be happening in the LGN?

Answer 22

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

Question 23

LGN as perceptual gatekeeper?

Answer 23

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.

Question 24

receptive fields in LGN

Answer 24

are center surround (same as in the retina)

Question 25

Visual field information segregated by.... from retina to LGN

Answer 25

...hemisphere

Question 26

Information from each eye kept separate... from retina to LGN

Answer 26

.... in LGN by layers.

Question 27

Cell receptive fields (center surround) are similar in the... from retina to LGN

Answer 27

... retina and LGN

Question 28

Spatial retinotopic maps are preserved in.... from retina to LGN

Answer 28

....LGN

Question 29

Some selective processing occurs - LGN is not simply a... from retina to LGN

Answer 29

.... relay nucleus

Question 30

Occipital Lobe

Answer 30

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.

Question 31

Hubel and Wiesel

Answer 31

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.

Question 32

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

Answer 32

• 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.!!!

Question 33

cells in the cortex (V1) respond...

Answer 33

....differently than cells in the retina and LGN

Question 34

simple cortical cells

Answer 34

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

Question 35

Orientation tuning curves

Answer 35

• 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

Question 36

How do you end up with bar cells?

Answer 36

– 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 –

Question 37

hierarchical processing

Answer 37

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

Question 38

complex cells

Answer 38

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

Question 39

End-Stopped Cells

Answer 39

more specific!!! bar, moving, AND A SPECIFIC LENGTH come from complex cells

Question 40

hierarchy of cells

Answer 40

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

Question 41

V1 Cells as feature detectors

Answer 41

• 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.

Question 42

Cells that are feature detectors:

Answer 42

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

Question 43

fovea has greater representation in the.....

Answer 43

...striate cortex (V1) than | proportionally anticipated.

Question 44

cortical | magnification factor

Answer 44

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.

Question 45

LGN and top down processing

Answer 45

More signal comes from the cortex | than the eyes.

Question 46

How are signlas in V1 organized? retinotopic maps?

Answer 46

Retinotopic maps retained in | the visual cortex.

Question 47

simple cells are created by

Answer 47

the convergence of LGN axons

Question 48

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

Answer 48

movement

Question 49

How are complex cells activated?

Answer 49

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

Question 50

End-stopped cells respond to

Answer 50

moving lines of specific lenghth moving corners or angles

Question 51

end-stopped cells have no response to

Answer 51

stimuli that are too long stimuli moving in the wrong direction

Question 52

how are end stopped cells formed?

Answer 52

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

Question 53

cells that are feature detectors

Answer 53

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

Question 54

feature detector neurons fire to...

Answer 54

.... specific features of a stimulus

Question 55

neurons farther along in the visual pathway fire to more...

Answer 55

....complex stimuli in a hierarchical manner