Viewers rarely notice objects that enter or leave dynamic information displays without salience-boosting tricks

One primary motivation for studying object tracking is to inspire better designs of visual information displays that contain multiple moving points, such as air-traffic control displays, educational simulations, or dynamic data visualizations. Most studies focus on improving one metric within these moving displays: how many ‘targets’ can we track under different display conditions. But realistic displays also demand another task: noticing whether a moving object (e.g., an airplane, a particle, or a data point) enters or leaves the edges of that display, even when it is not actively tracked. How well would viewers spontaneously notice that event, and how can we help them improve? We set up dynamic displays where tracking two of 20 objects was the primary task, and noticing whether one object entered or left was a secondary task. When tracked objects left the display, people easily noticed them (94%), though they were far less likely to notice when untracked objects left (46%). We expected that noticing untracked objects entering or leaving would be difficult, so we tested a salience-boosting trick inspired by real-world information displays: including buffer areas around the display where entering or leaving objects would be temporarily spatially salient. For untracked objects, people were far better at noticing objects enter or leave when they passed through the outer buffer (75%) compared to when they did not (37%). Intriguingly, both with and without the buffer, it was easier to notice untracked objects entering the display (66%) than leaving (46%). In summary, the buffer around the edges of the display helped people notice entering or leaving untracked objects, validating a technique used by professional information designers. If our visual system provides an illusion of perceived detail by relying on heuristics and statistics, then real-world information displays must leverage the right tricks to guide viewers to important changes.