The eye-tracking method was used to assess the influence of detailed, colorful illustrations on reading behaviors and learning outcomes. Based on participants' subjective ratings in a pre-study, we selected eight one-page human anatomy lessons. In the main study, participants learned these eight human anatomy lessons; four were accompanied by detailed illustrations, and the other four were accompanied by simplified illustrations. Participants completed a comprehension test and an evaluation questionnaire after reading each lesson. The results showed that detailed and simplified illustrations were equally effective in terms of learning outcomes. Eye-tracking data indicated that the detailed illustrations attracted attention in the initial learning stage and received more visual attention during the overall learning process. Notably, correlation analysis revealed that spending a greater proportion of time re-inspecting the simplified illustration was associated with higher test performances. By contrast, greater proportion of time spent re-inspecting the detailed illustration was not significantly correlated with learning outcomes. The results suggest that detailed illustrations could influence the learning process, and may support learning differently compared with simplified illustrations.