L. Itti: CS564 - Brain Theory and Artificial Intelligence University of Southern California

1Laurent Itti: CS564 - Brain Theory and Artificial Intelligence. Saccades 1

L. Itti: CS564 - Brain Theory and Artificial IntelligenceUniversity of Southern California

Lecture 15. Saccades 1

Reading Assignments: TMB 6.2The Modular Design of the Oculomotor System in Monkeys

Peter Dominey, Michael Arbib, and Amanda AlexanderSections: Description, Architecture

Supplementary Reading:Crowley-Arbib Saccade ModelM. Crowley, E. Oztop, and S. Marmol


From Schemas to Neural Networks - A Case Study: Modeling the Control of Saccades

Classical Model of Reflex Saccades

Expanding the Model to Bring in

Cortical Functions

Brainstem Saccade Burst Generator

Eye Plant RETINA Superior

Colliculus

Retinotopic Mapper

Brainstem Saccade Burst Generator

Eye Plant RETINA Superior

Colliculus

Retinotopic Mapper

Target Memory Remapping

PP

SC

vmsm

ms

FOn

FEF

vm

sm

vs

CD

sm

vsSNR

vsmsqv

TH

qv

LGN

VisCx

wta

Brainstem Saccade Generator

eye movement

RetinaVisInput

delay

FEFvsFEFms

FEFvsFEFms

swit

chPPctr

delay

FOn

Filling in the Schemas: Neural Network Models Based on Monkey NeurophysiologyPeter Dominey & Michael Arbib: Cerebral Cortex, 2:153-175

Develop hypotheses on Neural Networks that yield an equivalent functionality: mapping schemas (functions) to the cooperative cooperation of sets of brain regions (structures)

FEF

CAUDATESC

SNr

SG

VisCx

PPMD


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.


Experiment - Double Saccade


Double Saccade -- Neural Array Activity Snapshot


Brain Stem Saccade Burst Generator

LLBN-Long Lead Burst Neurons, MLBN-Medium Lead Burst Neurons, EBN-Excitatory 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.


Bringing in SC and FEF

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.


Simple Saccade Task

time

+


Experimental Setup


Timing Diagram for Simple Saccade 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. Notice that the eyes do not move until the "posteriorParietalCenter", a specific neuron in the model of LIP, goes low.


Memory Saccade Experiment

time

+

+

+


Timing Diagram for Memory Saccade Experiment

"visinM2P2" is the stimulus for the target, "fixation" is the fixation timing, "verticalTheta" is the vertical eye movement response, and "horizontalTheta" is the horizontal eye movement response


Double Saccade Experiment

time

+


Timing Diagram for the Double Saccade Experiment

"visinM3P0" is the stimulus for the first target and "visinM3P3" is the stimulus for the second target. "fixation" is the fixation timing, "verticalTheta" is the vertical eye movement response, and "horizontalTheta" is the horizontal eye movement response.


Timing Diagram for Lesioning of SC Experiment

Output of SC is disabled.

"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.


FEF Stimulation with SC Lesioned

time

+

FEF Stimulation


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.


The Full Dominey Model

DCEP-Damped Change in Eye Position7a/LIP-Oculomotor Region of Posterior Parietal Cortex

Retina,VisCxDelay(d1)

Mechanism A

7a/LIP/PP

FEF

SC

LLBN,MLBN

EBN MNTN

PN RI

Brain Stem – Saccade Burst Generator

trig

DCEP

velocity

dimension




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L. Itti: CS564 - Brain Theory and Artificial Intelligence University of Southern California