Timeline-Anchored Comments in Video-Based Learning: The Impact of Visual Layout and Content Depth

Many video sites or learning platforms allow real-time chatting or asynchronous commenting on specific time points during video lectures. Comments, as user-generated knowledge, facilitate social interaction but also affect cognitive learning. The visual layout of these comments can affect learners' attention and learning, but the effect has rarely been studied. This study compares two common layouts (embedded vs. separated) and considers the content depth of comments through a laboratory eye-tracking experiment involving 40 participants. The results suggest that, with both layouts, learners switched attention to the comments every 10 seconds and stayed focused for 1.3 seconds on average before returning attention to the video. With an embedded layout, learners switched attention more frequently to the comments and remembered more surface-level comments. With a separate layout presenting deep-level comments, learners searched for information faster and performed better on open-book quizzes. We outline the design implications of using timeline-anchored comments to promote online learning.