this particular chapter has lots of references of studies done on the matter.

In reviewing the results of these and other experiments, the editors of a 1996 book on hypertext and cognition wrote that, since hypertext “imposes a higher cognitive load on the reader,” it’s no surprise “that empirical comparisons between paper presentation (a familiar situation) and hypertext (a new, cognitively demanding situation) do not always favor hypertext.” But they predicted that, as readers gained greater “hypertext literacy,” the cognition problems would likely diminish. 20 That hasn’t happened. Even though the World Wide Web has made hypertext commonplace, indeed ubiquitous, research continues to show that people who read linear text comprehend more, remember more, and learn more than those who read text peppered with links.