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Reem Alzahabi, Matthew Cain; Ensemble Perception during Multiple Object Tracking. Journal of Vision 2020;20(11):122. doi: https://doi.org/10.1167/jov.20.11.122.
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© ARVO (1962-2015); The Authors (2016-present)
Multiple object tracking studies consistently reveal attentive tracking limits of approximately 3–5 items (Pylyshyn & Storm, 1988). In addition, we know of several cognitive phenomena that are subject to changes in processing due to grouping, such as improvements in visual working memory (Li, Qian, & Liang, 2018). Yet, there has been little systematic work investigating the role of grouping on multiple object tracking ability, and more specifically, in identifying the heuristics that lead to the formation and perception of ensembles within dynamic contexts. The current study addresses the following questions: (1) Is tracking capacity impacted by the number of items the group is composed of? (2) To what extent do inter-object spacing and common fate contribute to the perception of moving groups of objects? (3) Does the perception of common fate rely on the rigidity of the group? That is, to what extent can the individuated objects within a group deviate from the group’s overall motion and the group still be perceived as a group? In experiment 1, we manipulated group size (2, 4, or 8 objects) and tracking load (4– 32 objects) and found that tracking capacity estimates were on average, 4 groups of objects, regardless of the number of items a group is composed of. In experiment 2, we manipulated inter-object spacing, while maintaining a constant common fate trajectory. We found that tracking performance declined as inter-object spacing increased. In experiment 3, we manipulated the jitter of individual objects within a group, such that eccentricities of movement spanned increasing distances. We found that tracking performance declined as jitter eccentricities expanded and common fate was increasingly disrupted. Our data contribute to our overall understanding of multiple object tracking as it applies to groups of objects and characterizes the properties that determine the formation and perception of object ensembles.
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