September 2005
Volume 5, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2005
How many objects can you track? Evidence for a flexible tracking resource
Author Affiliations
  • George A. Alvarez
    Harvard University
  • Steven L. Franconeri
    University of British Columbia
Journal of Vision September 2005, Vol.5, 641. doi:10.1167/5.8.641
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      George A. Alvarez, Steven L. Franconeri; How many objects can you track? Evidence for a flexible tracking resource. Journal of Vision 2005;5(8):641. doi: 10.1167/5.8.641.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

The number of moving objects that can be tracked with attention is often reported to be 4, suggesting that there is a “structural limit” on tracking. We show that the tracking limit is not fixed, but depends systematically on the speed of the objects, such that at slow speeds observers can track 8 targets as well as a single target moving at a fast speed. Critically, the function relating the speed limit to the number of targets tracked is continuous, without any noticeable break in the 3-5 target range, suggesting that tracking accuracy is limited only by the amount of resources devoted to each target, not by a structural limitation. Method: Observers performed a multiple object tracking task in which they tracked 1–8 circles among a set of 16 identical moving circles. In session 1, observers adjusted the speed of the objects to find the maximum speed at which they could perfectly track the targets for 5 seconds. In session 2, we verified the accuracy of these settings by having observers track 1-8 targets moving at their “personal” speed limit for each number of targets. Results: With each increase in the number of targets, the speed limit decreased significantly. Moreover, the function was continuous, without any noticeable discontinuities in the 3–5 object range (r = .998 between speed and log of the number of targets). All speed settings were greater than zero indicating that on average observers estimated there was a speed at which they could perfectly track as many as 8 moving targets. It also appears that observers were able to accurately estimate their speed limits for tracking different numbers of targets, as tracking performance was near 100% for each number of targets in the second session and did not differ for different numbers of targets. Conclusion: These results are inconsistent with models that assume a fixed 4 object limit on tracking, and suggest that that tracking capacity is limited only by the amount of resources devoted to each target.

Alvarez, G. A. Franconeri, S. L. (2005). How many objects can you track? Evidence for a flexible tracking resource [Abstract]. Journal of Vision, 5(8):641, 641a, http://journalofvision.org/5/8/641/, doi:10.1167/5.8.641. [CrossRef]
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