There are many aspects of cognitive processing that occur without awareness. In higher-level cognition, the influence of statistical co-occurrences on the accessibility of concepts is one of the most important aspects of implicit processing. For example, it has long been known that prior presentation of a word that is semantically related to a second word can speed the recognition of that word (e.g., Neely, 1976). In addition, exposure to a particular word or association can facilitate access to that word or association in the future (Jacoby, Toth, & Yonelinas, 1993; Squire, 1987). In addition, actions that are taken frequently in particular contexts become associated with those contexts in ways that create habits that can be executed without awareness of the relationship between the environment and the behavior (Logan, 1988; Schneider & Shiffrin, 1977).