Spotlights

The paper contributes a novel technique that can improve user performance in skim reading. Users typically use a continuous-rate-based scrolling technique to skim works such as longer Web pages, e-books, and PDF files. However, visual attention is compromised at higher scrolling rates because of motion blur and extraneous objects with overly brief exposure times. In response, we present Spotlights. It complements the regular continuous technique at high speeds (2--20 pages/s). We present a novel design rule informed by theories of the human visual system for dynamically selecting objects and placing them on transparent overlays on top of the viewer. This improves the quality of visual processing at high scrolling rates by 1) limiting the number of objects, 2) ensuring minimal processing time per object, and 3) keeping objects static to avoid motion blur and facilitate gaze deployment. Spotlights was compared to continuous scrolling in two studies using long documents (200+ pages). Comprehension levels for long documents were comparable with those in continuous-rate-based scrolling, but Spotlights showed significantly better scrolling speed, gaze deployment, recall, lookup performance, and user-rated comprehension.