Psychological Review 1968, Vol. 75, No. 6, 522-536

TOWARD A THEORY OF MEMORY AND ATTENTION 1DONALD A. NORMAN University of California, San Diego A theoretical structure is described to account for a variety of phenomena encountered in the study of perception, attention, and memory. A storage system is proposed which has 2 different modes of activation : a temporary excitation, called short-term or primary storage, and a permanent excitation, called long-term or secondary storage. The storage is assumed to be organized so that access to stored information can be made directly from a sensory code. Thus, the initial interpretation of sensory events can be performed automatically, allowing attention to be directed to events on the basis of their meaning and momentary psychological pertinence. A retrieval process is described to handle the problem of deciding when an item that is recovered from storage is that which was sought. The output from storage is accepted as valid only if it can lead back naturally to the original query of memory. If it cannot, the retrieval process continues, using the initial query together with each intermediate output to guide the direction of search.

Usually the word "memory" means the remembrance of a past event, but in that remembrance may things are involved. To be remembered, information must first be acquired, then retained in a storage system, and, finally, be retrieved when sought. To understand memory we must understand all of its stages. In order to construct a comprehensive picture of the processes of remembering, we must select our theories from experimental and theoretical studies of perception, attention, memory, and information processing systems. Some of these studies provide us with incomplete information, some of these theories may be wrong, and

some are not necessarily relevant to human behavior. Yet it is possible to organize theories of the various components into one consistent structure which, even if not accurate, may be of some use in guiding further thinking and exploration. The purpose of this paper is to form a comprehensive theory of attention, storage, and retrieval which is consistent with existing data. Three different stages or processing are described. First, an attention mechanism is described which selects among the various sources of sensory information only after they have activated their representation in storage. The process of choosing among sources is, thus, com1 Supported by Research Grant NBO7454 bined with the process of interpreting from the National Institute of Neurological each input. Second, a storage system Diseases and Blindness, United States Public is described which may be activated Health Service. Many people have made temporarily (short-term or primary substantial comments about earlier versions of this paper. In particular, the author memory) or more permanently (longwishes to thank Donald Broadbent, Anthony term or secondary memory). Third.it Deutsch, Ralph Haber, Peter Lindsay, Molly is proposed that retrieval occurs Potter, and Nancy Waugh. Obviously, the through repeated queries of the storways in which their suggestions have been followed may not always be satisfactory to age system until a satisfactory output is obtained. all of these people.522

MEMORY AND ATTENTION All the proposals of this paper are speculative, some are difficut to document, and critical experimental tests are either difficult to do or not yet possible. Hopefully, these proposals will elicit further discussion and research. Because of the ways in which each of the proposed stages of processing interacts with the other it is not possible to discuss one stage without first discussing them all. Thus, in the sections that follow, first each of the theoretical ideas is discussed briefly, then, when the major points have been mentioned, we return to discuss each process in more detail and specific experimental predictions. In this paper most emphasis is directed towards the types of operations and situations encountered in the study of memory and divided attention, with very little mention of sensory or perceptual tasks. This distinction is made primarily to simplify the discussion, for although these other areas are not discussed explicitly, much of what follows will have important implications for them. In particular, it should be emphasized that the problems of interest here are the ways that meaning and context interact with the perception, storage, and retrieval of sensory information. Thus, we start the story after a good deal of physiological operations have already been performed on information received at the sense organs. Indeed, for visual information, we might consider that the present story begins where the visual information storage (Sperling, 1967) or iconic storage (Neisser, 1967) leaves off. Selection and Attention A common framework for theories of attention is that man's capacity to process information is limited. The manner in which this limitation acts has been the subject of much debate, with

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different theorists taking different views. The basic problem is this. Suppose that we are presented with two different verbal messages simultaneously and asked to perform some task (such as shadowing) on the material of one message. We find that we are unable to recall many of the features of the other, nonattended message (Cherry, 1953) and have little memory for any of the words (Moray, 1959), unless the shadowing task itself was momentarily disrupted when the second message was presented (Mowbray, 1964). These results alone would imply that there was only a single channel of attention, which accepted the material contained in one message and rejected the information in the other. This is not the case, for it turns out that we are able to switch our attention from one message to another when it is important to do so (Gray & Wedderburn, 1960; Treisman, I960, 1964a, 1964b). Obviously, we would not know when important information had arrived on rejected channels unless we had performed some analyses on them: Therefore, we would like the selection mechanism to analyze arriving signals well enough to allow for efficient selection among them without using any of the limited processing of the attention mechanism itself. The problem of specifying the properties of selection could be resolved if the initial analysis of the signal were performed automatically, without any need for sophisticated cognitive processes. When we say that a signal has been interpreted, presumably we mean that the physical characteristics of the signal have been matched with those of some representation which is stored in memory. This representation guides us to information stored about the meaning of the signal. The problem, therefore, is to determine how this in-

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Storage Much research, as well as our introspections, supports the notion that the storage of events has at least two different modes of operation: a transient mode for immediate memories and a permanent mode for long-term memories. Our immediate memories of events are perfectly clear and complete, as far as we can tell. Yet within a few seconds they fade to the point where they are but a bare outline of the actual happening. Recovering an event that has just been experienced is a far different operation from recovering one from the past. One process is automatic and apparently effortless; the other requires much mental work. The difference in the quality of a very recent memory from that of a long past one so impressed William James that he thought they ought not to be described in similar ways. The one he called "primary"; the other, "secondary." Primary memory consists of those events in the span of consciousness itself; it provides a continuous link to the present moment of time. Recent evaluation of this description is provided by Waugh and Norman (1965). Although logically there appear to be two storage systems, they need not be physically different. A theory that requires two separate physical storages could be called a "box" theory; this implies that material is temporarily stored in one box (primary storage) before 2 The phrases "location in storage" and it can be transferred to the other. The "the address of the information" should be in- trouble with such a theory lies in the terpreted to mean that however information assumed separation between the two is represented in human storage, there is some systems. Perceptual recognition of systematic method of getting access to it. words and of familiar sensory inputs is The method of getting to any particular stored representation is called its address. almost immediate. The recognition of There may be several addresses for each particular sensory inputs requires, at stored representation, but according to the the least, that we be able to find some present theory, only one representation for representation of the inputs in secondeach address. No implication should be If the box theory is to drawn about the actual method, form, or ary storage. specificity of storage from the use of these hold, there must be sufficient interconphrases. nections between the storages to allow

terpretation can be performed automatically. One solution to the problem of automating the interpretation process is to let the initial access to storage be based entirely on the sensory features of the signal. This means that the initial analysis of the input consists of a simple, linear progression of operations: First the signal is transduced from its physical form into some physiological representation; then, various transformations and operations extract special features of the signal; finally, the special features uniquely determine the address in human storage at which the signal representation is found.2 Full interpretation of the signal requires a knowledge of the context in which it was presented, but it is clear that the starting point of any analysis must come from the simple matching of the signal with its stored representation. The process described here is similar to that involved in finding information in a dictionary. First, the physical form of the item (i.e., the ordering of its letters) determines the address of the information relevant to the interpretation of the item (i.e., the location of the definitions in the dictionary). The proper interpretation may still be ambiguous, however, because several possible alternatives might be available. To clear up the ambiguity we must add information about context and expectations. We return to this point later.

MEMORY AND ATTENTION a comparison of the just-perceived sensory events with the collection of previously experienced perceptions. This intercommunication must be so direct and complete that formal distinctions between the two storage systems become difficult to make. In fact, with sufficiently complex interactions, the two systems become equivalent to one. It seems better to say simply that there appear to be operational differences between the storage systems and to avoid the problem of physical representation for a while. Several features of primary storage imply a strong relationship between primary and secondary memories. For one, the capacity of primary memory seems to be determined by the number of meaningful units within it, rather than by the duration or length of the physical representation of the items (Craik, 1967; Miller, 1956; Waugh & Norman, 1965). For another, errors in immediate memory for verbal material appear to be acoustically related to the correct items, even if the items were originally presented visually (Conrad, 1964). Neither of these features would be observed unless the items in primary storage had already been transformed from a form which reflected their physical properties into a representation which depended upon information which could only be contained in secondary storage. There are a number of differences, as well as similarities, between information stored in the two systems, aside from the obvious features already mentioned. For example, retention of material in primary storage is affected by acoustical similarity among the items which are to be retained, whereas in secondary memory, semantic similarity has the same effect (Baddeley, 1966). A picture of a dual-process storage system is easy to devise. Let secondary and primary storage be different

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properties of the same physical device. Initial activation of the storage causes temporary traces to appear which dissipate unless some action is taken to maintain them. This activity is primary memory. Permanent changes in storage occur when there has been prior activation of temporary (primary) traces and, probably, cognitive action as well: for example, selection, attention, and rehearsal. Thus primary and secondary storage use the same physical structures. As a result, they exhibit some of the same logical properties. Primary storage will have quite different temporary phenomena than secondary storage, however. Because primary traces are continually changing whereas secondary traces are passive and permanent, the two storage modes may appear to have quite different retrieval properties. Primary and secondary storage do not necessarily represent the only type of storage used in processing information. Any analysis of complex dataprocessing devices indicates the need for numerous storage devices. Temporary storage mechanisms are needed to maintain the results of intermediate steps of analyses. Small "buffer" memories are needed at each interface of peripheral equipment to the central system to improve the efficiency of operations. Although these concepts can be criticized as being relevant solely to the computer technology from which they derive, it is more likely that the need for numerous types of temporary memory systems is a true general property of any large scale system. In the system postulated here, it is quite likely that some form of sensory storage would improve performance by maintaining an image of the signal during the time required to match the input with its corresponding stored representation. In terms of this paper, Sperling's visual information storage

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FIG. 1. An outline of selection and attention. (Sensory inputs,