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Piers Howe, Natalie Incledon, Daniel Little; REVISITING TARGET MERGING IN MULTIPLE OBJECT TRACKING (MOT). Journal of Vision 2012;12(9):456. doi: https://doi.org/10.1167/12.9.456.
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Introduction: What counts as an object for the purposes of MOT? Tracking accuracy substantially decreases in MOT when each target is joined via a connector to a distractor, an effect known as target merging (Scholl et al., 2001). This occurs because each conjoined target-distractor pair is perceived as a single, indivisible object. Altering the connector used influences the degree of target merging and provides an opportunity to investigate the nature of visual objecthood in MOT. However, the Scholl et al. (2001) study had a potential confound: The target-distractor pairs continuously changed length, which in itself has been found to disrupt tracking (VanMarle & Scholl, 2003). Our experiments addressed this issue. Method & Results: In the baseline condition, the target-distractor pairs were not conjoined (i.e. a standard MOT paradigm). Tracking accuracy was high. The bars condition was identical to the baseline condition except that each target-distractor pair was conjoined by a solid bar. Tracking accuracy was greatly reduced even though the target-distractor pairs did not change length. The luminance condition was identical to the bars condition except that luminance differences were used to make the targets distinct from the connecting bars. Tracking accuracy was still much lower than in the baseline condition. In the dumbbells and pie-shaped conditions the connecting bars were altered in a way that was expected to abolish target-merging effects (Scholl et al., 2001). Surprisingly, tracking accuracy was still much less than in the baseline condition. In the occlusion condition, the centres of the connecting bars were occluded. Tracking accuracy was again much poorer than in the baseline condition. Conclusion: We found that target merging effects occurred even when the length of the target-distractor pairs was held constant. In fact, the effects were more robust than previously reported, occurring even when the targets were made perceptually distinct from the connecting bars.
Meeting abstract presented at VSS 2012
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