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Brian Levinthal, Steven Franconeri; Grouping by common fate occurs for only one group at a time. Journal of Vision 2010;10(7):1177. doi: 10.1167/10.7.1177.
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© ARVO (1962-2015); The Authors (2016-present)
Grouping allows the visual system to link separate regions of the visual field into a single unit for some types of processing. Although much past work examines when grouping will occur, and the relative strength of different types of grouping, less is known about the mechanism that causes the separate regions to become linked. We present a series of experiments demonstrating that a type of motion-based grouping, often called “common fate,” may be driven by selection of a common motion vector among the grouped objects. Selecting in a spatially global manner for the motion vector currently exhibited by one object should also activate other objects that exhibit the same pattern of motion, affording the shape created by the group, as well as a feeling that objects ‘go together’. This account makes a counter-intuitive prediction, that only one motion vector, and hence one common fate group, can be created at a time. Participants performed a search for a common fate group among non-common fate groups. Displays contained four pairs of moving dots, where one dot per pair was constrained to a small region near fixation, the other was located in the periphery. Among the four dot-pairs, one to four were locked in common motion, and we measured response times for participants to find at least one synchronized dot pair. Search slopes were highly serial (∼750ms/pair), but were flat when one motion vector was precued. We propose that selection of an object's motion vector is a prerequisite for grouping by common fate, but this vector selection can group an unlimited number of objects sharing a pattern of motion.
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