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David E. Fencsik, Todd S. Horowitz, Skyler S. Place, Sarah B. Klieger, Jeremy M. Wolfe; Target tracking during interruption in the multiple-object tracking task. Journal of Vision 2005;5(8):28. doi: 10.1167/5.8.28.
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Observers can successfully track a subset of independently moving identical objects in a multiple-object tracking task, even if all objects disappear for a 300–500 ms gap. How observers reacquire targets following such a gap reveals what kinds of information they maintain for moving objects. With identical objects, only two types of information are available: location and trajectory. In Experiment 1, objects disappeared and then reappeared at one of three locations: the point of disappearance (“stay” condition”), the position predicted by continued motion during the gap (“forward”), or the position predicted if the object had reversed direction during the gap (“reverse”). We found that tracking accuracy in the stay condition was superior to both the forward and reverse conditions, which were equivalent, supporting the use of location information in target reacquisition. Experiment 2 replicated Experiment 1, but with a condition in which objects disappeared one at a time. In this case, tracking accuracy in the forward condition, while still worse than in the stay condition, was now superior to that in the reverse condition. In Experiment 3, objects always reappeared in the forward position. In the motion condition, objects moved before they disappeared. In the static condition, they were stationary before the gap but reappeared in the forward position. Tracking performance was better in the motion condition. Experiments 2 and 3 support the use of trajectory information in target reacquisition. Taken together, the results indicate that the visual system maintains both types of information about tracked objects, selectively favoring one or the other in reacquisition depending on the nature of the task. More speculatively, we suggest that there may be two distinct mechanisms: one for general task-postponement during simultaneous offset (see Horowitz et al., VSS 2004), and the other for maintaining object continuity during single-object disappearance or occlusion.
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