The subject of human memory has fascinated thinkers and scientists throughout recorded history. What people remember, and how they remember it, has an impact on every aspect of life. The performance of the simplest, everyday tasks is based on the ability to recall how they are done, and new information and experiences can only be fully assimilated if a framework of past experience exists. Despite its overwhelming importance, however, human memory was, for centuries, only a matter for speculation. It was not until the late nineteenth century that the empirical study of memory began. As successive theories of memory were proposed, they were subjected to testing. Whether the proposed theories were confirmed or denied by the testing, the results inevitably suggested new paths for investigation, and further theorizing. After over one hundred years of study and experiment, no definitive description of the operations of human memory has yet been formulated. Instead, the past century of investigation has produced increasingly refined conceptualizations of the structure and processes of human memory, and an ever-increasing number of empirical facts that must be taken into account by any new theory.
Memory can be approached from two different perspectives--processes or structure--which are intimately intertwined. In both approaches, certain basic explanatory concepts have come to be generally accepted, and these "important commonalities" come as close as is currently possible to "a generally accepted theory that provides a framework and direction for research" (Estes, 1987, p. 14). In the first approach, it is the processes of memory that are the subject of investigation. These processes have generally been understood along the lines of a basic model of encoding (entry), retention (storage), and retrieval (remembering). The other, structural, approach consists of the search for the "functionally separable components of the memor...