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 Lefèvre Cesame-UCL

Is this yours ??

What happens with his car ???

Driving around in the country side

Eye movements Saccades Latency Position error

Eye movements bis Smooth pursuit Retinal slip

Interaction between saccades and pursuit

Saccade programming Position Time 0 . 9 0 . 9 0 . 1 S AMP PE S AMP PE RS = ⋅ = ⋅ + ⋅

Occlusions

Typical example

Tracking the invisible path

Conclusion : smooth pursuit • In one dimension, horizontal eye velocity decreases • Vectorial velocity decreases after occlusion onset but… • H and V components of eye velocity remain tightly coupled and can accelerate

Saccades During visually guided pursuit : correcting the position error During occlusions : target is invisible

Saccade programmation Visually guided saccades : S AMP 0 . 1 0 . 9 PE 0 . 1 RS = + ⋅ + ⋅ Predictive saccades (target is invisible) : S AMP 0 . 1 0 . 15 PE * 0 . 2 RS * = + ⋅ + ⋅

Conclusion : saccades (1) • In contrast with visually-guided saccades, predictive saccades do not correct position error • They are driven by the velocity error.

Saccade latency

Saccade latencies

First saccades

Ensuing saccades Inter-saccadic time

Ensuing saccades

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

Intro to modeling 0 . 1 0 . 9 0 . 1 S AMP PE RS = + ⋅ + ⋅

Modeling during occlusion S AMP 0 . 1 0 . 15 PE 0 . 2 RS = + ⋅ + ⋅

LATER model always on

"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

Wake up now…. It's finished…