Multiple Object Tracking through Occlusion
 
 
This page contains some sample demonstrations from the following paper:
Scholl, B. J., & Pylyshyn, Z. W. (1999). Tracking multiple items through occlusion: Clues to visual objecthood. Cognitive Psychology, 38, 259-290.
The demonstrations are provided as Quicktime movies, which can be downloaded or viewed directly in most web-browsers. (To download a free Quicktime player, go here.) These movies are a bit large and choppy, but they should be sufficient to illustrate the basic conditions. If the movies seem too choppy or if the lines are not drawn smoothly, try downloading the movies and playing them off your local hard drive.  
 
We have used the multiple object tracking task to explore the factors which mediate the maintenance of dynamic object tokens over time, representing a portion of the world not only as an object, but as that object -- i.e. as the same object from some earlier time-slice. Spatiotemporal continuity appears to play a major role here, but we have demonstrated that this system also recognizes and makes allowances for occlusion. We have demonstrated that multiple objects can be easily tracked through occlusion (even when the occluders are invisible or 'virtual'!), but that this allowance for occlusion does not reflect a simple robust tolerance for any interruption in spatiotemporal continuity. For example, tracking performance is impaired when items are present on the visual field at the same times and to the same degrees as in the occlusion conditions, but disappear and reappear by imploding and exploding into and out of existence, instead of accreting and deleting along a fixed contour.  
 
No Occlusion (baseline; with repulsion-defined trajectories (244 KB)  
Occlusion (312 KB)  
Virtual Occlusion (232 KB)  
Implosion/Explosion (208 KB)