Michael Arbib: CS564 - Brain Theory and Artificial Intelligence
Download
1 / 30

Michael Arbib: CS564 - Brain Theory and Artificial Intelligence University of Southern California, Fall 2001 - PowerPoint PPT Presentation


  • 181 Views
  • Uploaded on

Michael Arbib: CS564 - Brain Theory and Artificial Intelligence University of Southern California, Fall 2001. Lecture 22. Saccades 2 Reading Assignments: Reprint

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Michael Arbib: CS564 - Brain Theory and Artificial Intelligence University of Southern California, Fall 2001' - wayde


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Slide1 l.jpg
Michael Arbib: CS564 - Brain Theory and Artificial IntelligenceUniversity 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


Experimental setup l.jpg
Experimental Setup Intelligence



Slide4 l.jpg

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

    • 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 neurons


Experimental protocols and simulation interfaces l.jpg
Experimental Protocols and Simulation Interfaces Monkey Neurophysiology

  • 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.

a

a

a

a

a

a


Experiment double saccade l.jpg
Experiment - Double Saccade Monkey Neurophysiology



Brain stem saccade burst generator l.jpg
Brain Stem Saccade Burst Generator Monkey Neurophysiology

  • 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.


Another view of the dominey model l.jpg
Another View of the Dominey Model Monkey Neurophysiology

  • 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 oneof SC or FEF is lesioned.

  • DCEP-Damped Change in Eye Position

  • 7a/LIP-Oculomotor Region of Posterior Parietal Cortex


Visual input l.jpg
Visual Input Monkey Neurophysiology

  • 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)


Direct connection retina sc l.jpg
Direct connection retina Monkey NeurophysiologySC

  • To superficial layer of SC (vs)

  • responsible for reflex saccades = short-latency saccades

  • to target which has not been recently fixated


Visual pre processing l.jpg
visual pre-processing Monkey Neurophysiology

  • 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!


Dynamic remapping l.jpg
Dynamic Remapping Monkey Neurophysiology

B’

B”

B

A

  • 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.


Quasi visual cells in pp l.jpg
quasi-visual cells in PP Monkey Neurophysiology

  • 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


Remapping l.jpg
Remapping Monkey Neurophysiology

  • 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


Slide16 l.jpg

Basic structure for Monkey Neurophysiology

Dynamic Remapping


Frontal eye fields l.jpg
frontal eye fields Monkey Neurophysiology

  • 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


Superior colliculus l.jpg
superior colliculus Monkey Neurophysiology

  • 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


Basal ganglia l.jpg
Basal Ganglia Monkey Neurophysiology

  • 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


Memory saccade l.jpg
Memory Saccade Monkey Neurophysiology


Timing diagram for lesioning of sc experiment l.jpg
Timing Diagram for Lesioning of SC Experiment Monkey Neurophysiology

  • "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.


Compensatory saccade stimulation of fef with lesioning of sc l.jpg
Compensatory Saccade: Monkey NeurophysiologyStimulation 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.


ad