SPLTRAK Abstract Submission
Center-looking suggests grouping rather than separate attentional foci in multiple object tracking
Christina L. Blaxton, Hilda M. Fehd, Adriane E. Seiffert
Department of Psychology, Vanderbilt University

Previous research has shown that, when asked to track multiple moving targets among identical distractors, people often look at the center of the group of targets (Fehd & Seiffert, 2008, Cognition). There are two possible explanations for the center-looking tendency. One possibility is that targets are grouped first and then attention and gaze are directed toward the group. The other possibility is that separate attentional foci are directed toward each target and gaze settles in the center as the equidistant point. To test these hypotheses, we biased attention to one target over the others to measure whether gaze would shift from the center toward the more-attended target. Participants tracked three targets moving among distractors for 5 seconds and attempted to select the targets at the end of each trial. Experiment 1 manipulated attention with a goal-driven approach by giving participants points for correct target selections. To bias attention, one target was worth more points than the other two. Experiment 2 took a stimulus-driven approach by varying the contrast of the targets.  To bias attention, one target was a different contrast (either higher or lower) than the other two. The results showed that participants were significantly more accurate at selecting the target that was worth more points (Exp. 1; t(11) = 3.2, p <.01) and the target with unique contrast (Exp. 2; t(10) = 2.549, p <.05) than the other targets, suggesting that the manipulations of attention were successful. However, participants continued to look at the center of the group of targets in both experiments, rather than off-center towards the more-attended target. These observations provide no support for the theory that people allocate weighted attentional foci to targets, but are consistent with the conclusion that tracking multiple objects involves attending to targets as a group.