Reveiw of Vision

8/14/2019 Reveiw of Vision

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Basic wiring of the visual system


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Retina and LGN


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ON OFF ONipolars

ON OFF

ganglion cells

H

amacrine

AIIamacrine

AII

ON OFF bipolars

pigment epitheliumpigment epithelium

receptors

incoming light

photo-

conesrods

to CNS

cone horizontal

IPL

OPL

rods

to CN

receptors

ON

ON OFF

ganglion cells

H

S

cone horizontal

incoming light

photo-

cones


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Visual cortex


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Transforms in V1

OrientationDirection

Spatial FrequencyBinocularityON/OFF Convergence

Midget/Parasol Convergence


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O r ig inal H ubel-W iesel "Ice-C ube" M od el

Lef t Eye R ig ht Ey e

Lef t Ey e R ight Eye

S w ir l M o d e l

Sub-cortical

Cortical

R a d ic a l M o d e l

MidgetParasol

Three models of columnar organisation in V1

1 m m

Figure by MIT OCW.


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Striate Cortex Output Cell

Intracortical

Midget ON Midget ON

LEFT EYE Midget OFF Midget OFF RIGHT EYE

INPUT INPUT

Parasol ONParasol ON Parasol OFFParasol OFF

luminancecolor

orientationspatial frequency

depthmotion


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The ON and OFF Channels


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The receptive fields of three majorclasses of retinal ganglion cells

OFF

inhibition

ON

inhibition

ON/OFF

inhibition


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Action potentials discharged by an ON and an OFF retinal ganglion cell

Stimulation confined to receptive field center

ON cell

OFF cell

Stimulation of the entire receptive field

ON cell

OFF cell

light spot dark spot

light stimulation condition

time


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The midget and parasol channels


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MIDGET SYSTEM PARASOL SYSTEM

ON OFFON OFF

neuronal response profile

time


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P

Midget

1V

MT

Midget

Mixed

Parasol

w

?

Parasol

LGN

M

PARIETAL LOBE TEMPORAL LOBE

2

V4

V2V

Projections of the midget and parasol systems


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H

H

H

H

L

L

LL

P r o c e s s

i n g

C a p a c

i t y

Spatial Frequency

Temporal Frequency

Parasol SystemMidget System

Figure by MIT OCW.


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Color vision and adaptation


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Basic facts and rules of color vision

1. There are three qualities of color: hue, brightness, saturation

2. There is a clear distinction between the physical and psychologicalattributes of color: wavelength vs. color, luminance vs. brightness.

3. Peak sensitivity of human photoreceptors (in nanometers):S = 420, M = 530, L = 560, Rods = 500

4. Grassman's laws:1. Every color has a complimentary which when mixed propery yields gray.2. Mixture of non-complimentary colors yields intermediates.

5. Abney's law:The luminance of a mixture of differently colored lights is equal to thesum of the luminances of the components.

6. Metamers: stimuli producing different distributions of light energy thatyield the same color sensations.


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Basic facts about light adaptation

1. Range of illumination is 10 log units. But reflected light yields only a 20 foldchange (expressed as percent contrast).

2. The amount of light the pupil admits into the eye varies over a range of 16 to 1.Therefore the pupil makes only a limited contribution to adaptation.

3. Most of light adaptation takes place in the photoreceptors.

4. Any increase in the rate at which quanta are delivered to the eye results in a

proportional decrease in the number of pigment molecules available toabsorb those quanta .

5. Retinal ganglion cells are sensitive to local contrast differences, not absolutelevels of illumination.


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The color circle

white white

Yellow

Green

Red

hueBlue

saturation

black

Response to Different Wavelength Compositions in LGN


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Response to Different Wavelength Compositions in LGNBlue ON cell Yellow ON cell

90 90

30 40 0

45135

225 315

270

50 40 60 80

45135

180

225 315

270

Spikes per Second

20 1006010 20

200

10

45

90

135

225 315

90

135

20 30 40

45

180

225 315maintained discharge rate

10

Green OFF cell Red ON cell

5030 40

0180

0180

270 270


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Depth perception


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Cues used for coding depth in the brain

Oculomotor cues Visual cues

accommodationBinocular vergence

stereopsis

Monocular motion parallax

shadinginterposition

sizeperspective


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stereo camera


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Form perception


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Three general theories of form perception:

1. Form perception is accomplished by neurons that respondselectively to line segmens of different orientations..

2. Form perception is accomplished by spatial mapping ofthe visual scene onto visual cortex.

3. Form perception is accomplished by virtue of Fourier analysis.


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superior colliculus

sts

lsce

pSC

visual cortex

FEF

MEF

frontal eye fieldsmedial eye fields

parietal cortex

V1

V2 LIP

BS


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medial eye fields

lsce

pFEF

MEF

frontal eye fields

BS

Anterior system

Posterior system

visual cortex

parietal cortex

V1

V2 LIP

SC

superior colliculus ablated

sts


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Summary of the effects of electrical stimulation:

V1 & V2, upper

V1 & V2, lower

V4

LIP

FEF

MEF

FACILITATION INTERFERENCE NO EFFECTFIX INCREASE


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Summary of the effects of the GABA agonistmuscimoland the GABA antagonist bicuculline

Target selection Visual discrimination

muscimol bicuculline muscimol bicuculline

V1 V1

FEF FEF

LIP LIP

INTERFERENCE INTERFERENCE

INTERFERENCE FACILITATION

NO EFFECT NO EFFECT

DEFICIT DEFICIT

MILD DEFICIT NO EFFECT

NO EFFECT NO EFFECT

SC FACILITATIONINTERFERENCE Hikosaka and Wurtz

Saccade to new location


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Saccade to new location

A

what?

B

C

A

1 1. What are the objects in the scene?

2A

B

Cwhich?

2. Which object to look at?

A

B

C

5

when?

5. When to initiate the saccade?4. Where are the objects in space?

where?

A

B

C

4

3. Which object not to look at?

which not?

3

A

B

C

B r a i n a r e a s i n v o l v e d

V1, V2, V4,IT, LIP, etc.

V1, V2, LIP,FEF, MEF

LIP

V1, V2,FEF, SC

V1, V2, LIP


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BS

ras

?

BS

rate code

SC

SN

BG

vector code

P

Midget

1V

w

w

Parasol

LGNM

PARIETAL LOBE TEMPORAL LOBE

2

V4

V2

Midget

?

??

Mixed

Posterior system

Pa ol

MT

FRONTAL LOBEFEF MEF

vector code

place code Anterior system

V Auditory system

Somatosensory

system

Olfactory system

Smooth pursuit system

Vergence Accessory Vestibular

system optic system system


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Motion perception

Summary of cell types in V1


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CXDL

L

LL

L

L

L

L

L

L

L

D

D

D

D

D

D

D

D

D

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.1 1.2 deg

.1 .2 .3 .4 .5

.1 .2 .3 .4 .5 .6 .7 .8

.1 .2 .3 .4 .5 .6 .7 .8 . 9

.4.1 .2 .3 .5 .6

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 deg

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 deg

deg

deg

1.1

.1 .2 .3 .4 .5 .6 .7 deg

L

D

D

s6

s7

s5s1

s2

s3

s4

DEGREES OF VISUAL ANGLE

DEGREES OF VISUAL ANGLE

Figure by MIT OCW.

Major Pathways of the Accessory Optic System (AOS)


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BS

Major Pathways of the Accessory Optic System (AOS)Velocity response of AOS neurons = 0.1-1.0 deg/sec

Number of AOS RGCs in rabbit = 7K out of 350K

BS

rate code

D

M

L

TerminalNuclei

Inferior Olive

Cerebellum

climbing fibers

Ant

NOT

VestibularNucleus

Semicircularcanals

12

3

1

2,3

2,3

Cortex

Prime axes of retinaldirection-selective neurons

vestibulo-ocularreflex


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Effects of lesions on vision

Summary of lesion deficit magnitudes


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severe

VISUAL CAPACITY PLGN MLGN V 4 MT color vision

coarse scotopic vision

brightness perception

contrast sensitivity

motion perception

flicker perception

fine

coarse

stereopsis fine

coarse

pattern perception

shape perception

texture perception

fine

coarse

severe

severe

severe

severe

severe

severe

severe

mild

mild

mild

mild

mild

mild

mild

mildnone

none

none none none

none none

none none none

none none

none none

none none

none none

none none

none none none

none none none

none

none

none

none

none

none

moderate moderate

pronounced

mild

pronounced

fine

choice of "lesser" stimuli

not tested visual learning

not tested

not tested

not tested

none none

none

not tested

severe

severe

severe

pronouncedobject transformation I N T E

R M E D I A T E

B A S I C V I S U A L F U N C T I O N S


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Prosthetics


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Figure by MIT OCW.

The size and location of the regions activated in the monkey V1 by the dotted circle presented in the visual field90 90

5 5


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3

2

1

4

5

3

2

1

4

5

12 3

4

123

4

0

45

315

270

90 90

180

225

135

270

270

0180

135 45

315225

12 3

4

123

4

0

45

315

270

90 90

180

225

135

270

270

0180

135 45

315225

The size and location of the regions activated in the monkey V1 by the dots presented in the visual field

590 256 points

5590


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5 55

135 4 45 135 4 45

3 3

2 2

1 1

180 0 180 0

225 315 225 315

270 270

2 34 270 270 4 3 2 2 3

4 270 270 4 3 21 1 1 1

315 225 315 225

0 180 0 180

45 135 45 135

90 90 90 90


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Illusions


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The Hermann grid illusion

The most widely cited theorypurported to explain the illusion:

ON ON

larger response smaller response

Due to antagonistic center/surround organization, the activity ofON-center retinal ganglion cells whose receptive fields fall into theintersections of the grid produces a smaller response than thoseneurons whose receptive fields fall elsewhere.

Differently oriented vertical and horizontal lines reduce illusion


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Differently oriented vertical and horizontal lines reduce illusion

Retinal ganglion cell receptive field layout at an eccentricity of 5 degrees


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At the eccentricity of 5 degrees the0.5 by 0.5 degree visual angle areaoutlined impinges on 365 midgetcells and 50 parasol cells. Half ofthese are ON and half OFF cells.

The layout of the ON cells is shownin B and C.

5mm

5 deg of visual angle

Retinal midget cells Retinal parasol cells

0.5 deg of visual angle

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Reveiw of Vision