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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