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

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


1
L. Itti CS564 - Brain Theory and Artificial
IntelligenceUniversity of Southern California
  • Lecture 16. Saccades 2
  • Reading Assignments
  • The NSL Book
  • The Modular Design of the Oculomotor System in
    Monkeys
  • Peter Dominey, Michael Arbib, and Amanda
    Alexander
  • Supplementary Reading
  • Crowley-Arbib Saccade Model
  • M. Crowley, E. Oztop, and S. Marmol

2
Filling in the Schemas Neural Network Models
Based on Monkey NeurophysiologyPeter Dominey
Michael Arbib Cerebral Cortex, 2153-175
Develop hypotheses on Neural
Networks that yield an equivalent functionality
mapping schemas (functions) to the cooperative
cooperation of sets of brain regions (structures)
3
Last time, we saw that
  • Double-saccade experiments suggest
    direction/amplitude coding rather than absolute
    target location
  • Lesion/stimulation studies suggest that the
    overall system still works when either SC or FEF
    is missing (but not both!)
  • FEF stimulation just after presentation of a
    visual target (SC lesioned) elicits a saccade
    towards the fake FEF target first

4
Experimental Findings
  • connection FEF ?? PP
  • FEF, PPC ? SC
  • SC ? saccade generator (SG)
  • FEF ? BG (CD and SNr) ? SC (role in
    disinhibition of SC for saccades)
  • Simple saccade study topographic relations
    between sensory and motor areas
  • Memory saccade study cortical and subcortical
    activity that sustains spatial memory
  • Double saccade study dynamic remapping of target
    location with intervening eye movements

5
Basic Model Element Layer
2D array of neurons topographic
correspon- dence from layer to layer external
world 27x27 array model retina 9x9 layer so,
each model neuron represents a small population
of biological neurons
6
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)

7
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

8
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!

9
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

10
Double Saccade Experiment
time
11
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 Arbibs computational hypothesis
    remapping is done such as to compensate for
    difference between current eye position, and a
    damped/delayed eye position signal

12
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

13
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

14
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

15
The Full Dominey Model
  • DCEP-Damped Change in Eye Position
  • 7a/LIP-Oculomotor Region of Posterior Parietal
    Cortex

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