physiology of vision: a swift overview pixels to percepts a. efros, cmu, spring 2011 some figures...
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Physiology of Vision: a swift overview
Pixels to PerceptsA. Efros, CMU, Spring 2011
Some figures from Steve Palmer
ThalamusLGN
Striatecortex(V1)
DorsalStream
Parietalvisualcortex
Temporalvisualcortex
Eye Opticnerve
Extrastriatecortex
VentralStream
© Stephen E. Palmer, 2002
Understanding the BrainUnderstanding the Brain
Anatomy: The biological study of thephysical structure of organisms.
Physiology: The biological study of thefunctional structure of organisms.
Anatomy versus Physiology
© Stephen E. Palmer, 2002
The Brain is tricky business
• Aristotle thought it’s for cooling the blood• Localized or distributed?
Phrenology
How bad Machine Learning got started…
Localized or Distributed?
Evidence from patients with partial brain damage• Lots of useful data from soldiers in the Russo-Japanese war
But also evidence for distributed nature of processing• E.g. [Lashley] showed “graceful degradation” of memory
performance in rats
© Stephen E. Palmer, 2002
The Visual SystemThe Visual System
Both eye and brain are required for functional vision
Two kinds of blindness: Normal blindness (eye dysfunction) Cortical blindness (brain dysfunction)
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
The Visual SystemThe Visual System
Eyes register optical information Pathways to occipital cortex
“What” pathway to temporal cortex “Where” pathway to parietal cortexConvergence on frontal cortex
Two pathways from V1
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Pathways to the BrainPathways to the Brain
Anatomy of Pathway to Visual Cortex
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Pathways to the BrainPathways to the Brain
The Lateral Geniculate Nucleus (LGN)
Waystation in ThalamusProjections from both eyesSix layersProjects to cortical area V1
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Visual CortexVisual Cortex
“Unfolded” view ofvisual areas in the macaque cortex(sizes not to scale).
Map of Visual Areas in Cortex
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Visual CortexVisual Cortex
Evidence from lesionsof monkey cortex
What/Where Pathways
PrimaryVisualCortex
Dorsal Pathway("Where" System)
Ventral Pathway("What" System)
A
TemporalOccipital
Parietal
Frontal
Ventral Lesion
Dorsal Lesion
Object Discrimination Landmark Discrimination
B C
© Stephen E. Palmer, 2002
Visual CortexVisual Cortex
Visual agnosiaVisual agnosia: Inability to identify objects and/or people Caused by damage to inferior (lower) temporal lobe Disruption of the “what” pathway
What/Where PathwaysEvidence from Neuropsychology
Visual neglectVisual neglect: Inability to see objects in the left visual field Caused by damage to right parietal lobe Disruption of the “where” pathway
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Visual CortexVisual Cortex
Visual FeaturesVisual Features Color Shape Depth Motion
Feature-based Pathways Hypothesis
Featural PathwaysFeatural Pathways Separate neural pathwaysin which different features are processed. RETINA
LGN
V1
V2 MT
ColorForm
DepthMotion
ColorForm
DepthMotion
Color Form DepthMotion
Color Form Depth Motion
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
The Gross SummaryThe Gross Summary
The visual system is composed of many interactive functional parts:
Eye (optics of image formation)Retina (light transduction)LGN (waystation?)Area V1 (hypercolumns)Higher cortical areas (features)Cortical pathways (what/where)
© Stephen E. Palmer, 2002
Image Formation
Digital Camera
The Eye
Film
Monocular Visual Field: 160 deg (w) X 135 deg (h)Binocular Visual Field: 200 deg (w) X 135 deg (h)
The Eye is a camera
The human eye is a camera!• Iris - colored annulus with radial muscles
• Pupil - the hole (aperture) whose size is controlled by the iris
• What’s the “film”?– photoreceptor cells (rods and cones) in the retina
The Retina
Cross-section of eye
Ganglion cell layer
Bipolar cell layer
Receptor layer
Pigmentedepithelium
Ganglion axons
Cross section of retina
Retina up-close
Light
© Stephen E. Palmer, 2002
Cones cone-shaped less sensitive operate in high light color vision
Two types of light-sensitive receptors
cone
rod
Rods rod-shaped highly sensitive operate at night gray-scale vision
Rod / Cone sensitivity
The famous sock-matching problem…
© Stephen E. Palmer, 2002
Distribution of Rods and Cones.
0
150,000
100,000
50,000
020 40 60 8020406080
Visual Angle (degrees from fovea)
Rods
Cones Cones
Rods
FoveaBlindSpot
# R
ecep
tors
/mm
2
Night Sky: why are there more stars off-center?
Electromagnetic Spectrum
http://www.yorku.ca/eye/photopik.htm
Human Luminance Sensitivity Function
Why do we see light of these wavelengths?
© Stephen E. Palmer, 2002
.
0 1000 2000 3000
En
erg
y
Wavelength (nm)
400 700
700 C
2000 C
5000 C
10000 C
VisibleRegion
…because that’s where theSun radiates EM energy
Visible Light
The Physics of Light
Any patch of light can be completely describedphysically by its spectrum: the number of photons (per time unit) at each wavelength 400 - 700 nm.
400 500 600 700
Wavelength (nm.)
# Photons(per ms.)
© Stephen E. Palmer, 2002
The Physics of Light
.
# P
ho
ton
s
D. Normal Daylight
Wavelength (nm.)
B. Gallium Phosphide Crystal
400 500 600 700
# P
ho
ton
s
Wavelength (nm.)
A. Ruby Laser
400 500 600 700
400 500 600 700
# P
ho
ton
s
C. Tungsten Lightbulb
400 500 600 700
# P
ho
ton
s
Some examples of the spectra of light sources
© Stephen E. Palmer, 2002
The Physics of Light
Some examples of the reflectance spectra of surfaces
Wavelength (nm)
% P
hoto
ns R
efle
cted
Red
400 700
Yellow
400 700
Blue
400 700
Purple
400 700
© Stephen E. Palmer, 2002
The Psychophysical Correspondence
There is no simple functional description for the perceivedcolor of all lights under all viewing conditions, but …...
A helpful constraint: Consider only physical spectra with normal distributions
area
Wavelength (nm.)
# Photons
400 700500 600
mean
variance
© Stephen E. Palmer, 2002
The Psychophysical Correspondence
Mean Hue
yellowgreenblue
# P
hoto
ns
Wavelength
© Stephen E. Palmer, 2002
The Psychophysical Correspondence
Variance Saturation
Wavelength
high
medium
low
hi.
med.
low# P
hoto
ns
© Stephen E. Palmer, 2002
The Psychophysical Correspondence
Area Brightness#
Pho
tons
Wavelength
B. Area Lightness
bright
dark
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
.
400 450 500 550 600 650
RE
LAT
IVE
AB
SO
RB
AN
CE
(%
)
WAVELENGTH (nm.)
100
50
440
S
530 560 nm.
M L
Three kinds of cones:
Physiology of Color Vision
• Why are M and L cones so close?
Retinal Processing
© Stephen E. Palmer, 2002
Single Cell Recording
Microelectrode
Amplifier
Time
Electrical response(action potentials)
mV
© Stephen E. Palmer, 2002
Single Cell Recording
© Stephen E. Palmer, 2002
Retinal Receptive Fields
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
© Stephen E. Palmer, 2002
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Receptive field structure in ganglion cells:On-center Off-surround
Stimulus condition Electrical response
Time
Response
Retinal Receptive Fields
© Stephen E. Palmer, 2002
RF of On-center Off-surround cells
Receptive FieldNeural Response
Center
Surround
On Off
Response Profile
on-center
off-surround
Horizontal Position
FiringRate
Retinal Receptive Fields
© Stephen E. Palmer, 2002
RF of Off-center On-surround cells
Receptive Field
Horizontal Position
on-surround
off-center
Response Profile
FiringRate
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Center
Surround
On Off
Neural Response
Surround
Center
Retinal Receptive Fields
Receptive field structure in bipolar cells
Light
Retinal Receptive Fields
© Stephen E. Palmer, 2002
Receptive field structure in bipolar cells
Receptors
Bipolar Cell
A. WIRING DIAGRAM
HorizontalCells
Direct excitatory component (D)
B. RECEPTIVE FIELD PROFILES
LIGHT
Direct Path
Indirect Path
Indirectinhibitory
component (I)
D + I
Retinal Receptive Fields
© Stephen E. Palmer, 2002
© Stephen E. Palmer, 2002
Visual CortexVisual Cortex
aka:Primary visual cortexStriate cortexBrodman’s area 17
Cortical Area V1
ThalamusLGN
Striatecortex(V1)
DorsalStream
Parietalvisualcortex
Temporalvisualcortex
Eye Opticnerve
Extrastriatecortex
VentralStream
Cortical Receptive Fields
Single-cell recording from visual cortex
David Hubel & Thorston Wiesel© Stephen E. Palmer, 2002
Cortical Receptive Fields
Single-cell recording from visual cortex
TimeTime
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Three classes of cells in V1
Simple cells
Complex cells
Hypercomplex cells
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Simple Cells: “Line Detectors”
A. Light Line Detector
Horizontal Position
FiringRate
B. Dark Line Detector
Horizontal Position
FiringRate
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Simple Cells: “Edge Detectors”
C. Dark-to-light Edge Detector
Horizontal Position
FiringRate
D. Light-to-dark Edge Detector
Horizontal Position
FiringRate
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Constructing a line detector
Receptive Fields
Retina LGN
Center-Surround Cells
Simple Cell
CorticalArea V1
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Complex Cells
STIMULUS NEURAL RESPONSE
Time
00o
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Complex Cells
STIMULUS NEURAL RESPONSE
Time
060o
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Complex Cells
STIMULUS NEURAL RESPONSE
Time
090o
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Complex Cells
STIMULUS NEURAL RESPONSE
Time
0120o
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Constructing a Complex Cell
Simple Cells
Cortical Area V1
Complex CellReceptive Fields
Retina
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Hypercomplex Cells
Time
STIMULUS NEURAL RESPONSE
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Hypercomplex Cells
Time
STIMULUS NEURAL RESPONSE
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Hypercomplex Cells
Time
STIMULUS NEURAL RESPONSE
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Hypercomplex Cells
Time
STIMULUS NEURAL RESPONSE
“End-stopped” Cells© Stephen E. Palmer, 2002
Cortical Receptive Fields
Time
STIMULUS NEURAL RESPONSE
“End-stopped” Simple Cells
© Stephen E. Palmer, 2002
Cortical Receptive Fields
Constructing a Hypercomplex Cell
Receptive Fields
RETINA CORTICAL AREA V1
Complex Cell End-stopped Cell
© Stephen E. Palmer, 2002
Mapping from Retina to V1Mapping from Retina to V1
Why edges?
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