Reveiw Of Vision

The visual and oculomotor systems Peter H. Schiller, year 2006

Review,

the visual and oculomotor systems

Basic wiring of the visual system

fix

Primates

left hemifield

right hemifield

Horopter (Vieth-Muller circle)

nasal

temporal

PARIETAL LOBE

LGN

NOT p

m

terminal nuclei

MT V

superior colliculi

4

V

3

V

2

V

1

e

TEMPORAL LOBE

er ph is

le ft he m

is ph er

e

m he ht rig

optic chiasm

FRONTAL LOBE

Retina and LGN

pigment epithelium

cones

rods

photoreceptors

OPL cone horizontal

H

ON

OFF

bipolars

ON

IPL AII ON

OFF

amacrine ganglion cells

incoming light

to CN CNS S

Visual cortex

Transforms in V1 Orientation

Direction

Spatial Frequency

Binocularity ON/OFF Convergence Midget/Parasol Convergence

Three models of columnar organisation in V1 Original Hubel-Wiesel "Ice-C

ube" Model

Cortical

Left Eye

Right Eye

Sub-cortical

m

Radical Model

1m

Midget Parasol

Left Eye

Right Eye

Swirl Model

Figure by MIT OCW.

Striate Cortex Output Cell

Intracortical

LEFT EYE INPUT

Midget ON Midget OFF

Midget ON Midget OFF

Parasol ON Parasol OFF

Parasol ON Parasol OFF

luminance color orientation spatial frequency depth motion

RIGHT EYE INPUT

The ON and OFF Channels

The receptive fields of three major classes of retinal ganglion cells

ON

OFF

ON/OFF

inhibition

inhibition

inhibition

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 dark spot

light spot

light stimulation condition time

The midget and parasol channels

MIDGET SYSTEM

PARASOL SYSTEM

neuronal response profile

OFF

ON

time

ON

OFF

Projections of the midget and parasol systems Midget

V1

Mixed

V2

Parasol

w

LGN

P

?

M

MT

V4

Midget Parasol

PARIETAL LOBE

TEMPORAL LOBE

Spatial Frequency H

Processing Capacity

L H

L

Midget System Parasol System

Temporal Frequency H

L L

H

Figure by MIT OCW.

Color vision and adaptation

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 psychological attributes 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 the sum of the luminances of the components. 6. Metamers: stimuli producing different distributions of light energy that yield the same color sensations.

Basic facts about light adaptation 1. Range of illumination is 10 log units. But reflected light yields only a 20 fold change (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 to absorb those quanta . 5. Retinal ganglion cells are sensitive to local contrast differences, not absolute levels of illumination.

The color circle

white

white

Yellow

saturation

Green Red

Blue

black

hue

Response to Different Wavelength Compositions in LGN Blue ON cell Yellow ON cell 90

90

135

135

45

45

Spikes per Second

180

10 20 30 40 50 60

225

0

180

315

20 40 60 80 100

225

270

Red ON cell

90

90

135

135

45

10

225

20

30

315 270

315 270

Green OFF cell

180

0

40

0

180

45

10 20 30 40 50

225

maintained discharge rate

315 270

0

Depth perception

Cues used for coding depth in the brain

Oculomotor cues accommodation vergence

Visual cues Binocular stereopsis

Monocular motion parallax shading interposition size perspective

stereo camera

MOTION PARALLAX, the eye tracks

1

a

2 b

eye movement

a

object motion

1

The eye tracks the circle, which therefore remains stationary on the fovea Objects nearer than the one tracked move at greater velocities on the retinal surface than objects further; the further objects actually move in the opposite direction on the retina.

2

b

Form perception

Three general theories of form perception:

1. Form perception is accomplished by neurons that respond

selectively to line segmens of different orientations..

2. Form perception is accomplished by spatial mapping of

the visual scene onto visual cortex.

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

Eye-movement control

superior colliculus

medial eye fields frontal eye fields parietal cortex

visual cortex MEF p

FEF

LIP

SC ce

sts

V1 ls

BS

V2

medial eye fields

frontal eye fields

parietal cortex

superior colliculus ablated

visual cortex MEF

Anterior system

p

FEF

LIP

SC ce

sts

V2 V1

ls BS

Posterior system

Summary of the effects of electrical stimulation:

FACILITATION

V1 & V2, upper V1 & V2, lower V4 LIP FEF

MEF

INTERFERENCE

FIX INCREASE

NO EFFECT

Summary of the effects of the GABA agonist

muscimol and the GABA antagonist bicuculline

Target selection muscimol

V1

INTERFERENCE

FEF

INTERFERENCE

LIP

SC

Visual discrimination muscimol

bicuculline INTERFERENCE

V1

bicuculline

DEFICIT

DEFICIT

FACILITATION

FEF

MILD DEFICIT

NO EFFECT

NO EFFECT

NO EFFECT

LIP

NO EFFECT

NO EFFECT

INTERFERENCE

FACILITATION

Hikosaka and Wurtz

Saccade to new location

A

1. 2. 3. 4.

1 B

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

A

what?

2

C

What are the objects in the scene? Which object to look at? Which object not to look at? Where are the objects in space?

5. When to initiate the saccade?

B

V1, V2, LIP, FEF, MEF

Br a

A

which?

3

C B

in a

V1, V2, LIP

re a

si nv olv ed

A

which not?

4

C B

V1, V2, FEF, SC

A

where?

5

C B A

LIP when?

C

Midget

V1

Auditory

V2

Mixed

?

?

Parasol

system

w

LGN

Somatosensory

P M

Midget Parasol

system

V4

MT Posterior system PARIETAL LOBE

?

TEMPORAL LOBE

Olfactory

system

w

SC

?

BG

rate code

BS

BS

FRONTAL LOBE FEF MEF

SN vector code

system

vector code place code

Vergence system

Accessory optic system

Smooth pursuit

Anterior system

Vestibular

system

Motion perception

Summary of cell types in V1

s1

s5

D

D L

.1 .2 .3 .4 .5 DEGREES OF VISUAL ANGLE

.1

.3

.2

.4

.5

.7 deg

.6

L D

s2 L

D

s6 .1 .2 .3 .4 .5 .6 .7 DEGREES OF VISUAL ANGLE

.1

s3

D

.8

.2

.3

.2

.3

.4

.5

.6

.7

.4

.5

.6

.7

.8

.9

.9

.1

.2

L

.3

.2

.4

L

s4

.1

1.1 deg

D L

L

1.0

deg

s7

D

.8

D

L

L .1

L

.5

.6

.7

D

.8

.9

1.0 deg

L

D .3

.4

.5

.6

deg

CX

D L

D

.1

.2

.3

.4

.5

.6

.7

.8

.9

1.0 1.1

1.2 deg

Figure by MIT OCW.

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

2

Cortex 1

Cerebellum

Ant

3 climbing fibers Prime axes of retinal direction-selective neurons

NOT

Inferior Olive Semicircular canals

D 1

M 2,3

Vestibular Nucleus

L

rate code

BS

BS

2,3

Terminal Nuclei

vestibulo-ocular reflex

Effects of lesions on vision

Summary of lesion deficit magnitudes PLGN

MLGN

V4

MT

color vision

severe

none

mild

none

texture perception

severe

none

mild

none

BASIC VISUAL FUNCTIONS

VISUAL CAPACITY

pattern perception

fine

severe

none

mild

none

shape perception

fine

severe

none

mild

none

coarse

mild

none

none

none

brightness perception

none

none

none

none

coarse scotopic vision

none

none

none

none

fine

severe

none

mild

mild

coarse

mild

none

none

mild

fine

severe

none

none

none

coarse

pronounced

none

none

none

contrast sensitivity

INTERMEDIATE

stereopsis

motion perception

none

moderate

none

moderate

flicker perception

none

severe

none

pronounced

choice of "lesser" stimuli

severe severe

none

severe

none

visual learning

not tested

not tested

severe

none

object transformation

not tested

not tested

pronounced

not tested

Prosthetics

Figure by MIT OCW.

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

5 4

135

90

5

45

4

135

45 3

3 2

2 1

1

180

0

225

180

0

315

225

315

270 2

3

4

270

270 270

1

3

2

1

2

3

4

270

270

1

315 225

315 225

0 180

0 180

45

90

4

45

135

90

90

135

90

4

3

2

1

The size and location of the regions activated in the monkey V1 by the dots presented in the visual field 90

256 points

5

135

135

45

4

90

55

45

4 3

3 2

2 1

1

180

0

225

180

0

225

315

315

270 2

3

4

270

270 270

1

3

2

1

2

3

4

270

270

1

315 225

315 225

0 180

0 180

45

90

4

45

135

90

90

135

90

4

3

2

1

Illusions

The Hermann grid illusion

The most widely cited theory purported to explain the illusion:

ON

larger response

ON

smaller response

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

Differently oriented vertical and horizontal lines reduce illusion

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

At the eccentricity of 5 degrees the 0.5 by 0.5 degree visual angle area outlined impinges on 365 midget cells and 50 parasol cells. Half of these are ON and half OFF cells. The layout of the ON cells is shown in B and C.

5mm

5 deg of visual angle

Retinal midget cells

0.5 deg of visual angle

Retinal parasol cells