This chapter reviews many of the studies claiming to demonstrate implicit learning in such paradigms. It assesses evidence for the inaccessibility of knowledge acquired about sequential structures and looks at whether such knowledge is associated with distinct properties of storage and retrieval. Although Pierre Perruchet’s findings seem to provide clear support for an exemplar-based account, Cleeremans has recently suggested that it is possible that a combination of both abstraction and exemplar-based processing is taking place. Lewicki introduced the matrix scanning task, in which subjects are asked to view a succession of frames and to indicate, by pressing a button, which of several quadrants of a frame contained a target digit. Importantly, unaware subjects showed just as strong a Hebb effect as those claiming to be aware. The subjective test of awareness was a set of questions that began with general items and became increasingly more specific.