During the last 15 years, there have been some efforts to extend the use of eye - tracking to researching reading in complex contexts, such as the reading of multiple documents. The research community involved in this extension has been interested in higher - order comprehensio n processes occurring in complex reading contexts, such as sourcing, defined as the processes of attending to, representing, evaluating, and using available or accessible information about the sources of textual content. In this article, we argue that exte nding eye - tracking research to investigate more complex reading contexts has been made without critically reflecting on its validity in those contexts . Specifically, because eye - tracking captures automatic as well as conscious processes, it is currently an open question how consistently eye - tracking captures the strategic sourcing processes that take place during multiple document reading, in particular when using real documents that include salient source information that may attract bottom - up fixations. I n contrast, subjective methods , such as interviews , mainly target conscious processes, and may th erefore be a more valid and generalizable measure of strategic sourcing activities . W e compared sourcing indicators based on eye - tracking measures to sourcing indicated by a post - reading interview. Results suggest ed that curren t eye - tracking indices of sourcin g are not universally valid measures, and that simpler methods, such as asking readers whether they paid attention to source information , may be more suite d to assess strategic sourcing during multiple document reading.