The study of learning and memory has greatly expanded during the last two decades. Instead of limiting themselves to highly constrained, rather artificial laboratory experiments, cognitive psychologists have begun studying tasks more closely related to daily life, such as memory for places, names and faces, testimony of eye-witnesses, and memorization of songs, poems and stories. They have found that many, if not most, such activities involve the construction and storage of complex structures in memory. For example, the evidence suggests that we store in our memories not only individual words, but also an inventory of longer expressions, which are used to increase fluency in oral discourse. In addition, we organize stories and autobiographical memories into complex units which affect their subsequent recall. In this process, events that are not causally related to the goals in a story do not fit well into these memory structures and thus are not usually well recalled. Likewise, events with similar structures, or similar roles in larger structures, are likely to be confused in recall.