This study explored the effects of prior knowledge (high vs. low; HPK and LPK) and concept-map structure (hierarchical vs. network; HS and NS) on disorientation, cognitive load, and learning from non-linear documents on "the infection process of a retrograde virus (HIV)". Participants in the study were 24 adults. Overall subjective ratings of disorientation and cognitive load, as well as detailed analysis of eye movement and navigation data were used. The results showed that LPK learners gained equal factual knowledge from the HS and NS concept maps, gained more conceptual knowledge from the HS concept map, and had to invest less mental effort in the posttest after learning with the HS concept map. On the other hand, HPK learners gained more factual knowledge from the HS concept map than from the NS concept map, and gained equal conceptual knowledge from both concept-map structures. Also, LPK learners experienced higher disorientation during learning with the NS concept map than the HS map, whereas no differential effect of concept-map structure was found for HPK learners. Both LPK and HPK learners invested less mental effort in processing the HS concept map. The eye tracking and navigation data provided more detailed insight into these findings. (Contains 1 figure and 2 tables.)