Download PPT Lecture Slides: January 22, 2002

The Brain
from retina to extrastriate cortex
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
1
Neural processing responsible for
vision
• photoreceptors
• retina
– bipolar and horizontal cells
– ganglion cells (optic nerve)
•
•
•
•
•
optic nerves
optic chiasma (X)
lateral geniculate body
striate cortex
extrastriate cortex
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
2
Lateral inhibition
• Edge detection and contrast enhancement
• Bipolar, Horizontal and Ganglion cells
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
3
Lateral inhibition
• If no activity in neighboring photoreceptors,
output = output of photoreceptor
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
4
Lateral inhibition
• if activity in neighboring photoreceptors,
– output is decreased, possibly absent
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
5
Lateral inhibition via addition and
negative weights
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
6
Another example
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
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Different kinds of ganglion cells ==
different sets of weights
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
8
Optic nerve
• axons of the ganglion cells
– 1 million optic nerves
– 120 million photoreceptors
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
9
From light to vision
Lateral Geniculate Nucleus (LGN)
Geniculo-Striate Pathway
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
Striate
Cortex
11
Striate cortex
(primary visual centre)
• Neurons are edge detectors
fires when an edge of a particular orientation is present
2002/01/21
(LGN)
Striate
Cortex
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
12
Striate cortex
(primary visual centre)
• Neurons are edge detectors
fires when an edge of a particular orientation is present
(LGN)
frequent output
Striate
Cortex
vertical bar
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
13
Striate cortex
(primary visual centre)
• Neurons are edge detectors
fires when an edge of a particular orientation is present
(LGN)
infrequent output
Striate
Cortex
diagonal bar
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
14
Edge detection
• each cell “tuned” to particular orientation
– vertical
– horizontal
– diagonal
• cats: only horizontal and vertical
• humans: 10 degree steps
• edges at particular orientations and positions
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
15
Extrastriate cortex
(beyond the striate cortex)
2002/01/21
V1
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
16
Extrastriate cortex
• Each area handles separate aspect of visual
analysis
– “V1-V2 complex”: Map for edges
– V3: Map for form and local movement
– V4: Map for colour
– V5: Map for global motion
• Each is a visual module
– connects to other areas
– operates largely independently
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
17
Finally
• What was the purpose of this presentation?
• Which question remains unanswered?
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
18
Slides after this point review neuron function and
vocabulary. We did not cover them in lecture,
but you may find them useful.
Gregory covers this pp 68-74
Coren, Ward, Enns in an appendix
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
19
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Neural cell (neuron)
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Input s from ot her neurons
D e nd r it e s
Cell body
A xo n
Out put
Out put ( t o ot her neurons)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
20
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Out put
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
21
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Out put
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
22
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Neural cell (neuron)
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Input s from ot her neurons
D e nd r it e s
Out put
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
23
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Neural cell (neuron)
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Input s from ot her neurons
D e nd r it e s
Cell body
Out put
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
24
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Neural cell (neuron)
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Input s from ot her neurons
D e nd r it e s
Cell body
A xo n
Out put
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
25
The brain - processor of information
Eyes are actually a part of the brain
Ganglion cells are a special type of neuron:
Neural cell (neuron)
Ganglion cell
2002/01/21
Input s
from
phot orecept ors
Input s from ot her neurons
D e nd r it e s
Cell body
A xo n
Out put
Out put ( t o ot her neurons)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
26
Input signals on dendrites affect voltage on cell body
2002/01/21
-when voltage change is sufficiently high,
cell begins to fire
axon
axon
terminals
-action potentials (spikes) sent along axon,
towards terminals
-speed ≈1 m/sec (narrow) to 100 m/sec (wide)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
27
Input signals on dendrites affect voltage on cell body
2002/01/21
-when voltage change is sufficiently high,
begins to fire
cell
-action potentials (spikes) sent along axon,
towards terminals
-speed ≈1 m/sec (narrow) to 100 m/sec (wide)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
28
Input signals on dendrites affect voltage on cell body
2002/01/21
-when voltage change is sufficiently high,
begins to fire
cell
-action potentials (spikes) sent along axon,
towards terminals
-speed ≈1 m/sec (narrow) to 100 m/sec (wide)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
29
Input signals on dendrites affect voltage on cell body
2002/01/21
-when voltage change is sufficiently high,
begins to fire
cell
axon
axon
terminals
-action potentials (spikes) sent along axon,
towards terminals
-speed ≈1 m/sec (narrow) to 100 m/sec (wide)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
30
Output strength represented by rate of firing along
axon of neuron
2002/01/21
Typical rates: 200-1000 spikes per second
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
31
Output strength represented by rate of firing along
axon of neuron
2002/01/21
Typical rates: 200-1000 spikes per second
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
32
Output strength represented by rate of firing along
axon of neuron
2002/01/21
Typical rates: 200-1000 spikes per second
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
33
Output strength represented by rate of firing along
axon of neuron
2002/01/21
spikes travel down axon
axon
axon
terminals
low output strength = low frequency of spikes
Typical rates: 200-1000 spikes per second
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
34
Output strength represented by rate of firing along
axon of neuron
2002/01/21
spikes travel down axon
axon
axon
terminals
low output strength = low frequency of spikes
Typical rates: 200-1000 spikes per second
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
35
Information processed by neurons activating each
other in sequence
2002/01/21
-output of one neuron = input of next
-connection = synapse
conne ct ions
( sy n a p se s)
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
36
But excitation is not the only way that neurons
interact…
2002/01/21
PSCY202-005, Term 2, Copyright Jason Harrison, 2002
37