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Georg Jahn, Papenmeier Frank, Huff Markus; Spatial Reference in Multiple Object Tracking. Journal of Vision 2010;10(7):310. doi: 10.1167/10.7.310.
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While tracking multiple targets simultaneously, the configuration in the scene as it is projected onto the picture plane provides stable spatial reference for tracking targets. Multiple object tracking in a 3D-scene is robust against smooth movements of the whole scene even without static reference objects (Liu et al., 2005) suggesting that targets and distractors provide enough configurational information. What is important, however, is continuous motion in the picture plane as revealed by the detrimental effect of abrupt viewpoint changes (Huff, Jahn, & Schwan, 2009). Abrupt viewpoint changes suddenly change the configuration of identically looking objects in the picture plane and yield it difficult to establish correspondence between object locations before and after the viewpoint change. The background in a 3D-scene can act as a static and visually distinct spatial reference to solve this correspondence problem. If the presence of a static background turns out to be beneficial, this would demonstrate that static reference objects are used to locate targets in MOT when the configuration of dynamic objects provides insufficient information. We report three experiments employing abrupt viewpoint changes, in which a checkerboard floor plane and a wireframe floor plane improved performance compared to a display lacking any static background. This floor plane effect was found when viewpoint changes of 20° occurred while two targets were tracked and while a single target was tracked. In contrast, tracking 3, 4, or 6 targets showed no benefit from the presence of a floor plane. We argue that targets are tracked as parts of a continuously changing configuration that provides spatial reference. Discontinuous changes create the need to use static reference objects for relocating targets. Our experiments have revealed narrow limits for relocating targets, which may generalize to other dynamic tasks, in which observers move and targets are not continuously in view.
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