Title: L. Itti: CS564 Brain Theory and Artificial Intelligence University of Southern California
1L. 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
2Filling 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)
3Last 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
4Experimental 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
5Basic 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
6Visual 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)
7Direct connection retina?SC
- To superficial layer of SC (vs)
- responsible for reflex saccades short-latency
saccades - to target which has not been recently fixated
8visual 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!
9quasi-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
10Double Saccade Experiment
time
11remapping
- 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
12frontal 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
13superior 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
14basal 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
15The Full Dominey Model
- DCEP-Damped Change in Eye Position
- 7a/LIP-Oculomotor Region of Posterior Parietal
Cortex
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