What kind of influence does the structure of an educational hypermedia system have on the way its users understand its contents and organize the knowledge they acquire through its browsing? In this article, this already much discussed question, situated at the boundary between semiotics and cognitive science, is revisited in the light of results from a recent experiment. Forty undergraduate students participated in this experiment, which required them to retrieve answers to four questions in a 160-node educational hypermedia system. A structured interview followed the task, to evaluate the knowledge acquired by the subjects, based on their answers to the four questions. The transcripts of their answers were analyzed using an original content analysis method, based on the identification of key referents and the relationships connecting them in the subject's discourse. Results show effects of the way information is hierarchized and contextualized within the system on the subjects' discourse organization. They tend to confirm the view that considers hypermedia as systems whose node-and-link structure modulate semantic relationships (stressing a part of them and dimming the others) within the body of knowledge they present, resulting in qualitative differences in the user's schematic network of representations of the system. (Contains 9 tables and 8 figures.)