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How can we track a target when it is occluded ?
Jean-Jacques Orban de Xivry Philippe Lefèvre
Cesame-UCL
How can we track a target when it is occluded ? Jean-Jacques Orban - - PowerPoint PPT Presentation
How can we track a target when it is occluded ? Jean-Jacques Orban - - PowerPoint PPT Presentation
How can we track a target when it is occluded ? Jean-Jacques Orban de Xivry Philippe Lefvre Cesame-UCL Is this yours ?? What happens with his car ??? Driving around in the country side Eye movements Saccades Latency Position error Eye
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What happens with his car ???
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Driving around in the country side
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Eye movements
Saccades
Position error Latency
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Eye movements bis
Smooth pursuit
Retinal slip
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Interaction between saccades and pursuit
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Saccade programming
PE S AMP ⋅ = 9 . RS PE S AMP ⋅ + ⋅ = 1 . 9 .
Position Time
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Occlusions
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Typical example
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Tracking the invisible path
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Conclusion : smooth pursuit
- In one dimension, horizontal eye velocity
decreases
- Vectorial velocity decreases after
- cclusion onset but…
- H and V components of eye velocity
remain tightly coupled and can accelerate
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Saccades
During visually guided pursuit : correcting the position error During occlusions : target is invisible
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Saccade programmation
Visually guided saccades :
RS PE S AMP ⋅ + ⋅ + = 1 . 9 . 1 .
Predictive saccades (target is invisible) :
* 2 . * 15 . 1 . RS PE S AMP ⋅ + ⋅ + =
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Conclusion : saccades (1)
- In contrast with visually-guided saccades,
predictive saccades do not correct position error
- They are driven by the velocity error.
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Saccade latency
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Saccade latencies
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First saccades
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Ensuing saccades
Inter-saccadic time
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Ensuing saccades
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Conclusion : saccades (2)
- Saccadic system seems to be always
- active. As soon as a saccade is over, a
decision process is reinitiated for the next saccade
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Intro to modeling
RS PE SAMP ⋅ + ⋅ + = 1 . 9 . 1 .
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Modeling during occlusion
RS PE S AMP ⋅ + ⋅ + = 2 . 15 . 1 .
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LATER model always on
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"Behind the trees"
- H and V components remain coupled
- Saccades do not correct for position error
- Position error plays a minor role in the
programming of saccades but velocity error has a major one
- Saccadic system is always active and
saccadic latency can be explained by a cascade of LATER processes
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