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Michael N. Tombu, Adriane E. Seiffert; Moons in orbit: How are targets distinguished from distractors in multiple-object tracking?. Journal of Vision 2007;7(9):579. doi: 10.1167/7.9.579.
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People can track a subset of moving objects amongst distractors; a skill believed to be mediated by attentional processes. Multiple-object tracking (MOT) studies have provided insights into how objects are attended and represented. However, with most MOT tasks several factors presumably important to tracking performance such as eccentricity, target-target and target-distractor proximity vary unpredictably across time, making it difficult to pinpoint the specific causes of tracking failures. The goal of this study was to investigate the extent to which manipulations of speed, target-distractor proximity and the number of distractors affect common stages of processing. In order to do so, we designed a MOT display consisting of several groups of dots rotating about two axes: one at the center of each group, another at the center of the display. The display is similar to a solar system, such that the dots look like moon and planets rotating about each other in orbit about a star. The main benefit of this design is that speed, proximity and the number of distractors can be manipulated independent of one another and largely free of confounds, thus allowing for a more systematic investigation. We were particularly interested in determining whether target designation, presumably modulated by proximity and speed, was independent of distractor suppression, presumably affected by the number of distractors in the display. According to additive factors logic, if two manipulations affect independent stages of processing their effects should be additive, whereas if they affect a common processing stage, their effects should interact. Our results showed that, whereas proximity and number of distractors were additive, speed and proximity interacted. Performance was sharply impaired by speed increases when the dots were grouped closer than when they were far apart. These results suggest that distractors suppression and target designation occur at different stages of processing in MOT.
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