Transcript No Slide Title - University of Southern California

Michael Arbib: CS564 - Brain Theory and Artificial
Intelligence
University of Southern California, Fall 2001
Lecture 22. Saccades 2
Reading Assignments:
Reprint
Dominey, P. F., and Arbib, M. A., 1992, A Cortico-Subcortical
Model for Generation of Spatially Accurate Sequential
Saccades, Cerebral Cortex, 2:153-175.
The NSL Book
The Modular Design of the Oculomotor System in Monkeys
Peter Dominey, Michael Arbib, and Amanda Alexander
Supplementary Reading in the NSL Book:
Crowley-Arbib Saccade Model
M. Crowley, E. Oztop, and S. Marmol
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Experimental Setup
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Three Types of Saccade
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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delay
FEF
FEF
PP
FOn
PPct r
MD
CAUDATE
ms
Vis Cx
SC
switch
PP
qv
sm
vm
SNr
SG
Filling in the Schemas: Neural
Network Models Based on
Monkey Neurophysiology
vs
VisCx
sm
Peter Dominey & Michael Arbib:
Cerebral Cortex, 2:153-175
CD
TH
LGN
vm
SNR
2D arrays of neurons
 topographic
correspondence from layer
to layer
 external world: 27x27 array
 model retina: 9x9 layer
 each model neuron
represents a small
population of biological
vs

sm
delay
FEFvs
FEFms
SC
vs
ms
qv
FOn
wta
eye movement
FEFvs
FEFms
Brainstem
Saccade
Generator
Retina
VisInput
Experimental Protocols and Simulation Interfaces
An experimental protocol defines
a class of experiments based on:
Preparation used
 External stimuli
 Experimental manipulations : electrical stimulation, drug application, etc.
 Measurements and observations

The protocol can be translated into a simulation interface
for “stimulating” a simulation and displaying the results.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Experiment - Double Saccade
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Double Saccade -- Neural Array Activity Snapshot
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Brain Stem Saccade Burst Generator
trig
C
PN
RI
dimension
EF
velocity
EBN
LLBN,
MLBN
TN
MN
Brain Stem – Saccade Burst Generator
LLBN-Long Lead Burst Neurons, MLBN-Medium Lead Burst Neurons, EBNExcitatory Burst Neurons, PN-Omni-Pause Neurons, RI-Resettable
Integrator, TN-Tonic Neurons, MN-Oculomotor Neurons.
In the present Chapter/Lecture, this is treated as an unanalyzed module
(available from the NSL Library) so that attention may focus on the other
brain regions, which are described next.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Another View of the Dominey Model
DCEP
trig
SC
PN
RI
dimension
Retina,
VisCx
Delay
(d1)
Mechanism A
FEF
velocity
EBN
LLBN,
MLBN
TN
MN
7a/LIP/PP
Brain Stem – Saccade Burst Generator
SC - Superior Colliculus: The midbrain’s path from vision (and other senses) to eye
movement.
FEF - Frontal Eye Field: The cortex’s path from vision to eye movement.
Data point: A cat or monkey can still make saccades if one of SC or FEF is lesioned.
DCEP-Damped Change in Eye Position
7a/LIP-Oculomotor
Region
of Posterior
Parietal
Michael
Arbib CS564 - Brain Theory
and Artificial
Intelligence,
USC, FallCortex
2001. Lecture 22. Saccades 2
9
Visual Input
At every iteration,
eye position determines position
of 9x9 retinal window within
27x27 outside world
if eye velocity over 200deg/sec,
retinal input is reduced
(saccadic suppression)
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Direct connection retinaSC
To superficial layer of SC (vs)
responsible for reflex saccades = short-latency saccades
to target which has not been recently fixated
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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visual pre-processing
LGN, V1, V2, V4 and MT areas
abstracted by a single layer
possible only because we have a
very coarse (9x9) retinal input
with no image noise!
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Dynamic Remapping
Initially, targets A and B are represented on PPv; then
as a saccade is made to A, the representation of B is
shifted via B’ to B’’ which is related to the foveal point
as B was related to A.
B
B’
B”
A
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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quasi-visual cells in PP
Andersen et al. (1988) found
in PP cells that code for future
eye movements.
Quasi-visual because in
double-saccade task
found cells which fire at location
of second target respective
to first target, while there never
was a retinal stimulus there!
right movement field but wrong receptive field
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Remapping
Hypothesis: occurs primarily in PP
(in reality, may occur in many regions at once,
with connections between regions serving for fine-tuning).
problem: eye velocity signals have not been found in PP.
but eye position signals have 
Dominey and Arbib’s computational hypothesis: remapping is
done such as to compensate for difference between current eye
position, and a damped/delayed eye position signal
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Basic structure for
Dynamic Remapping
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frontal eye fields
Bruce & Goldberg (1984): FEF contains:
- visual cells (vm)
(receive input from PP)
- movement cells (ms)
(fire just before saccade)
- visuomovement cells (sm)
(memory: fire during delay
in memory saccade task)
- postsaccadic cells
PPctr: active as long
as fixation cross present
(inhibits eye movements)
FOn = fixation is on
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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superior colliculus
-Input from retina (reflex saccades)
-Input from PPqv  SC qv layer
(yield saccades when FEF
lesioned)
-Inputs from FEF
How can we choose?
WTA array: saccade to
currently strongest target
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Basal Ganglia
SNr provides tonic inhibition
of SC and thalamus, unless
prevented to do so by FEF
(directly or via CD)
Goals:
- prevent saccades while
a target is being fixated
- memorise location of
future target in memory
saccade task
FEF can selectively control the targets for saccades, overriding
collicular attempts to initiate saccades to distracting peripheral targets
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Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Memory Saccade
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Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 22. Saccades 2
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Timing Diagram for Lesioning of SC Experiment
"visinP3M3" is the stimulus for the first target , "fixation" is the fixation timing,
"verticalTheta" is the vertical eye movement response, and "horizontalTheta" is
the horizontal eye movement response.
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Compensatory Saccade:
Stimulation of FEF with Lesioning of SC
A visual target is briefly presented and removed before a saccade can begin.
Before the visual saccade can begin, an electrical stimulus is applied to the
FEF. The monkey will first saccade to the stimulated location and then to the
real target even though timewise the real target appeared first. This is due to
the fact that the the visual signal takes time to get from the retina to the FEF.
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