One, Two, Three, Infinity: How Many Memory Systems Are There?

Bruce W. A. Whittlesea

Simon Fraser University

The evidence for multiple memory systems arises from two convergent sources. Behavioural investigations have demonstrated dissociations between important functions, such as between remembering and knowing, or between explicit and implicit tasks. Further, neuropsychological investigations have demonstrated dissociations between intact and impaired persons, and observations of differential involvement of brain subsystems in different tasks. The promise of this approach was the identification of a manageably small number of independent memory subsystems, serving different aspects of memorial function. A problem for this approach is that there are many more dissociable functions than have been taken into account. The logic of dissociation would lead to positing a very large number of independent and semi-independent subsystems of memory; and as the number of postulated systems increases, their descriptive and explanatory power decreases. A further problem is the analysis of tasks. Typifying tasks by their overt demands (e.g., implicit versus explicit) is dangerous, because people often satisfy those demands by indirect means. Similarly, typifying tasks as implicit or explicit by their outcomes is dangerous, partly because of circularity and partly because similar patterns of outcome can result from different causes. A consequent problem is that observation of a correlation between brain activity and performance in some task is often of ambiguous significance. A third problem is that, beside the pattern of dissociation that forms the basis of the separate systems account, there is also a pattern of synergy across major functions at a deeper level of analysis, such that, for example, the explicit, reflective tasks of remembering and knowing can be understood as the product of unconscious attributional processes based on implicit, nonreflective processes such as skills, habits and priming. I propose a unitary framework for understanding memory, based on two primary assumptions: the preservation of particular experiences and the construction of new experiences, based on the production and evaluation of cognitive, perceptual and sensorimotor performance.