This study tested whether seeing others' typed messages while viewing video lectures affected learners' attention and learning performance. Participants viewed one of three versions of a video lecture: (a) conventional video lecture as control; (b) video lecture with others' programmed messages appearing onscreen when the instructor was giving demonstrations on course content; (c) video lecture with others' programmed messages appearing onscreen when the instructor was posing questions. In Experiment 1, participants viewed video lectures without pause and could not post messages themselves. Eye tracking data revealed that although seeing others' messages did not decrease learners' attention to the learning content in the video, greater attention to others' messages was associated with lower retention. Furthermore, learners who viewed the conventional video lecture showed higher transfer than those who viewed either of the video lectures that included others' messages. In Experiment 2, participants viewed self-paced lectures and could post messages themselves. Experiment 2 duplicated the results of Experiment 1 in a realistic educational setting. Overall, these findings suggest that seeing others' messages during a video lecture has negative effects on learners' attention and learning.