Is motion extrapolation employed in multiple object tracking ? Tracking as a low - level , non - predictive function q Brian

In a series of five experiments, we investigated whether visual tracking mechanisms utilize prediction when recovering multiple reappearing objects. When all objects abruptly disappeared and reappeared mid-trajectory, it was found that (a) subjects tracked better when objects reappeared at their loci of disappearance than when they reappeared in their extrapolated trajectories, (b) disappearance episodes ranging from 150 to 900 ms had virtually no differential effect on performance, (c) tracking deteriorated monotonically as a function of displacement magnitude during disappearance, and (d) tracking did not depend on whether objects moved in predictable paths. Even objects that reappeared backward in their trajectories were tracked dramatically better than objects that reappeared in their extrapolated trajectories. When all objects disappeared and reappeared in ways that implicated the presence of an occluder (i.e., with occlusion and disocclusion cues along fixed contours), tracking again was not predictive, and performance deteriorated with increased displacement. When objects reappeared predictably in 75% of trials, they were still tracked better when they reappeared at 0010-0285/$ see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.cogpsych.2005.12.001 q Special thanks to Sharanya Chandrasekar and Amir Amirrezvani for help in programming, and Brian Scholl for suggesting the technique to make objects gradually occlude and disocclude. We also thank Todd Horowitz and David Fenscik for helpful discussions on object tracking. We additionally appreciate the input of the Visual Attention Lab, including Vidal Annan, John Dennis, Charles King, Alan Kugel, and Carly Leonard. Last, but not least, we are grateful for the advice of Rob Gordon and two anonymous reviewers. This paper constitutes the first author’s Cognitive Science Certificate project and is supported by NIMH Grant 1R01-MH60924 to Z.W.P. * Corresponding author. Present address: UCLA Department of Psychology, 1285 Franz Hall, Box 951563, Los Angeles, CA 90095-1563, USA. E-mail address: [email protected] (B.P. Keane). B.P. Keane, Z.W. Pylyshyn / Cognitive Psychology 52 (2006) 346–368 347 their points of disappearance. Theoretical implications of a non-predictive multiple object tracking mechanism are discussed. 2005 Elsevier Inc. All rights reserved.