Abstract
Common Fate is a Gestalt principle (Wertheimer (1923), in which static elements embedded in a static background are indistinguishable, but become instantly visible when they move synchronously. Our work is inspired by analysis tasks, where the goal is to find correlated groups of moving elements in environments where the background elements are also moving. Adapting the paradigm introduced by Treisman and Gelade (1980), we measured reaction time as a function of target area for static and moving dot patterns, which were embedded in either static or moving dot backgrounds. All target and background dots moved smoothly to a new random position every second, but the spatial-temporal movements of the 7 target dots were always synchronized. Reaction time for moving dots on a static background was fast, and constant, independent of the spatial area subtended by the target dots. When the background dots were also animated, however, reaction time increased linearly with the spatial area of the target pattern. In a second experiment, we varied the spatial configuration of the target pattern, to explore whether this bifurcation depended on Gestalt feature (good continuation vs. proximity) or on the experimental task (detection vs. identification). In all four conditions, the static background did not affect reaction time for the animated target, which did not change with target area. Moreover, performance was only marginally slower than for animated or static targets with no background at all. When the background was animated, reaction time increased linearly with target area for all four conditions. Percent correct, however, decreased more rapidly for identification tasks, suggesting greater interference from the moving background. Reaction time for a correlated group of target dots was independent of target array size for both detection and identification, but this parallel process breaks down with target area when the background dots are also animated.