ory most successfully when they relate it to things they already know (more on this point in Chapter 9 ).
From the dual-store perspective, control processes that enable storage in long-term memory take place in working memory. As we’ve seen, working memory has a limited capacity and can handle only so much information at one time. The result is that long-term memory storage occurs slowly, and a great deal of information is lost in the process. In essence, working memory is the bottleneck in the memory system: It prevents most information from ever getting into long-term memory.
Long-Term Memory
Long-term memory is perhaps the most complex component of the human memory system. As such, it has been studied more extensively than either the sensory register or working memory, and psychologists have offered numerous theories about its nature. I’ll give you an overview of it here and then describe its characteristics and relevant control processes in more depth in the following three chapters.
Characteristics of Long-Term Memory
Much of the content of long-term memory relates to the nature of how things are, were, or will be —knowledge often referred to as declarative knowledge . But it also includes knowledge about how to do things —knowledge known as procedural knowledge (e.g., J. R. Anderson, 1983a,
1995). Its capacity is obviously much larger than that of working memory, its forms of storage appear to be more flexible, and its duration is, of course, quite a bit longer.
Capacity As far as theorists can determine, the capacity of long-term memory is unlimited. In fact, as you’ll discover in Chapter 9 , the more information that’s already stored there, the easier it is to store additional information.
Forms of storage Information is probably encoded in long-term memory in a variety of ways. For example, language provides one basis for storing information, sensory images provide another, and nonverbal abstractions and meanings—general understandings of the world, if you will—provide still another. Over the long run, people rarely save information in the precise ways they encountered it in the environment. Rather than remember word-for-word sentences or precise mental images, people tend to remember the gist of what they see and hear, along with idiosyncratic interpretations and (often) minor or major distortions of reality.
Some of the knowledge in long-term memory is explicit knowledge , such that people can easily recall and explain it. But a great deal of it is, instead, implicit knowledge that affects peo- ple’s behavior even though they can’t consciously retrieve and inspect it. We’ll look closely at the nature of both explicit and implicit knowledge—as well as at the nature of both declarative and procedural knowledge—in Chapter 10 .
Another noteworthy characteristic of information in long-term memory is its interconnected- ness: Related pieces tend to be associated together. Virtually every piece of information in
long-term memory is probably directly or indirectly connected with every other piece. 11
Duration As you’ll learn in Chapter 11 , theorists disagree regarding the duration of long- term memory. Some theorists believe that once information is stored in long-term memory, it remains permanently, and thus any “forgetting” is simply a retrieval problem. In contrast, others
believe that information can disappear from long-term memory through a variety of forgetting processes—processes that may or may not kick in depending on how the information was initially stored and how often it’s used. Ultimately, although some information may remain in long-term memory for long periods, there’s probably no way to show conclusively that all
information stored there remains permanently. The question about the duration of long-term memory is still an open one, and the best we can say is that long-term memory’s duration is indefinitely long .
Speaking of retrieval from long-term memory, what was Edward C. Tolman’s middle name? Did you perhaps remember your friend Harry’s brother-in-law, Marvin Chace? Or did you think
of Tolman chacing his rats down their mazes? As you’ll discover in Chapter 11 , the more ways
that people store a piece of information in long-term memory, the better their chances of retriev- ing the information when they need it.
11 As you should recall from Chapter 2 , most neurons in the brain have synaptic connections with hundreds of other neurons. Presumably many of these synapses account for the organized nature of long-term memory.
Up to this point, we’ve been talking about the dual-store (three-component) model of memory almost as if it were Ultimate Truth. But not all psychologists agree that this model accurately represents how human memory functions. I myself sometimes wonder whether the three com- ponents are the distinctly different entities that the model portrays. For example, recall my ear- lier point that auditory information in the sensory store typically lasts for 2 or more seconds. Also recall how Baddeley’s phonological loop can maintain a list of spoken words in working
memory only to the extent that the list is short and consists of quickly pronounceable words—a list that can be repeated in, say, 2 to 4 seconds. In fact, Baddeley (2001) has suggested that audi- tory information stored in working memory tends to last only about 2 seconds unless it’s rehearsed. It’s possible, then, that maintenance rehearsal may in some cases act on and maintain information that’s actually in a sensory-register type of mechanism.
Furthermore, a number of theorists have argued that working memory and long-term memory are actually different aspects of a single (rather than dual) storage mechanism. Others have chal-
lenged a related idea: that active, conscious processing in working memory is really necessary for storage in long-term memory. We now look at some of the evidence related to each of these issues.
Are Working Memory and Long-Term Memory Really Different?
Let’s return to the serial learning curve described in the Chapter 7 . Given a list of items to remember, people can more easily recall the first few items in the list (the primacy effect) and the
last few items (the recency effect) than the middle items (to refresh your memory, look once again
at Figure 7.8). Using a dual-store model of memory to explain this curve (e.g., Norman, 1969), we might say that people process the first few items sufficiently to store them in long-term memory, and they continue to hold the last few items in working memory after the entire list has been presented. They lose many of the middle items because they don’t have enough time to process them adequately before later items “bump them out” of working memory. Supporting this interpretation is the finding that when presentation rate is slowed down (allowing for more processing in working memory), the primacy effect increases, and when processing is prevented, the primacy effect disappears (Glanzer & Cunitz, 1966; L. R. Peterson & Peterson, 1962). In contrast, the recency effect seems to be more affected by the recall interval: The longer that recall of the list is delayed—decreasing the likelihood that any items are still in working memory—the less people are able to remember items at the end of the list (Glanzer & Cunitz, 1966; Horn, 2008; Postman & Phillips, 1965).
Yet other research studies have cast doubt on the idea that the recency effect necessarily reflects the use of a working memory separate from long-term memory (R. G. Crowder, 1993; R. L. Greene, 1986; Öztekin, Davachi, & McElree, 2010; Wickelgren, 1973). For example, in a study by Thapar and Greene (1993), college students viewed a series of words presented two at a time on a computer screen; they also performed a 20-second distractor task (mentally adding a series of digits) after each pair of words. The students remembered the last few words in the list much better than the middle words, even though—thanks to the distractor task— none of the
words could possibly have still been in working memory. Considering results such as these, theorists have suggested that the serial learning curve can be explained as easily by a single-store model as by a dual-store model. One possible explanation is that items in a list are easier to remember if they’re distinctive in some way. Items near the end of the list might be more memorable
because of their positions: A learner may specifically identify a word as “the last one” or “the next- to-last one” (R. L. Greene, 1986; Unsworth, Heitz, & Parks, 2008; R. K. Wagner, 1996). A second possibility is simply that forgetting occurs rapidly at first and then slowly tapers off—a pattern that has been observed for many different species and many different tasks (J. R. Anderson, 1995; Wickelgren, 1973; Wixted & Ebbesen, 1991). From this perspective, the recency effect may be the result of the fact that the last items of a list haven’t yet undergone that rapid decay.
Another source of evidence that’s been used to support the dual-store model is the finding that encoding seems to be somewhat different in working memory versus long-term memory, with the former being heavily dependent on verbatim auditory encoding and latter being more likely to involve gist and general meanings that are often nonverbal in nature. Yet forms of encoding in the two components overlap quite a bit. For instance, information in working memory sometimes takes the form of general meanings (Shulman, 1971, 1972), and information in long-term mem- ory sometimes takes an acoustic form (Intons-Peterson, Russell, & Dressel, 1992; T. O. Nelson & Rothbart, 1972; Reisberg, 1992). Furthermore, even the initial encoding of information (which presumably takes place in working memory) often draws on knowledge in long-term memory right from the get-go (P. A. Kirschner, Sweller, & Clark, 2006). For example, people recognize words in print more quickly when the words are embedded in a meaningful context (Rayner, Foorman, Perfetti, Pesetsky, & Seidenberg, 2001). And they recognize spoken words much more quickly when the words are common ones they use every day (R. K. Wagner, 1996).
Still another body of evidence that has been used on both sides of the debate comes from peo- ple who have undergone certain brain injuries or neurosurgical procedures. Sometimes these indi- viduals show an impairment of one kind of memory without a corresponding loss of function in the other (R. C. Atkinson & Shiffrin, 1968; Eysenck & Keane, 1990; R. K. Wagner, 1996; Zechmeister & Nyberg, 1982). Some individuals can recall events experienced before a brain trauma but are unable to retain new experiences. Such a disability may suggest either (1) a problem with working memory while long-term memory remains intact (a dual-store explanation) or (2) a problem in general storage processes (a single-store explanation). Other individuals with brain injuries can recall new experiences long enough to talk briefly about them but can’t remember them a few min- utes later or at any point thereafter. These might be cases in which (1) working memory is function- ing but new information seemingly cannot be transferred into long-term memory (a dual-store explanation) or (2) general retrieval processes have been impaired (a single-store explanation).
To some degree, working memory and long-term memory processes seem to depend on differ- ent parts of the brain (Nee, Berman, Moore, & Jonides, 2008; Zola-Morgan & Squire, 1990). And different areas of the brain are active when people are trying to recall items from the beginning versus end of a serial list (Talmi, Grady, Goshen-Gottstein, & Moscovitch, 2005). Even so, as noted in Chapter 2 , most learning and thinking tasks—even very simple ones—tend to involve many parts of
the brain. Certainly different parts of the brain specialize in different tasks, but a human learner is likely to rely on many parts regardless of the learning or memory task at hand (e.g., Nee et al., 2008).
Is Conscious Thought Necessary for Long-Term Memory Storage?
In the dual-store model, information must go through working memory before it can be stored in long-term memory. Working memory is, by definition, an active, conscious mechanism. It would seem, then, that a learner would have to be actively involved in storing virtually anything in long-term memory. This isn’t always the case, however. Some kinds of information—once they’ve captured a person’s attention—seem to be automatically stored in long-term memoryeven if not specifically selected for further processing (Frensch & Rünger, 2003; Zacks, Hasher, & Hock, 1986). For example, consider this question:
Which word occurs more frequently in English— bacon or pastrami?
You probably had no difficulty answering correctly that bacon is the more frequently occurring
word. Hasher and Zacks (1984) found that people could easily answer such questions about the frequency of events even though they’d never been concerned about counting them. Similarly, people could answer questions about where various events occurred without having intention- ally processed this information. Such automatic storage of frequency information and locations begins quite early in life and may help to establish a knowledge base on which future learning can build (Siegler & Alibali, 2005).
Much of this seemingly nonconsciously processed information becomes implicit (rather than explicit) knowledge. Quite possibly, the brain learns—and stores information in long-term memory—in at least two distinctly different ways. One is a very conscious way in which working memory plays an active role. Another is a more basic, “thoughtless” way that involves formation of simple stimulus–stimulus and stimulus–response associations similar to those of which behavior- ists speak (Bachevalier, Malkova, & Beauregard, 1996; Frensch & Rünger, 2003; D. J. Siegel, 1999).
Complicating the picture even further is the possibility that thinking itself may sometimes occur outside the confines of working memory. A series of studies by Dijksterhuis, Nordgren, and their colleagues indicates that complex problems—those involving far more information than work- ing memory’s limited capacity can handle—are often more effectively addressed when people don’t actively think about them for a period of time (Dijksterhuis & Nordgren, 2006; Strick, Dijksterhuis, & van Baaren, 2010). Even when not consciously mulling over a complex problem, these researchers suggest, people may be slowly analyzing the problem, determining which aspects of the problem are more and less important to take into account, imprecisely estimating particular quantities, and integrating problem-relevant information into an overall summary. The result is that a complex problem is sometimes better solved when it remains outside of working memory’s limited-capacity limelight for a while. The products of such nonconscious thinking are often implicit and hard to put a finger on. For instance, people might describe them as “intuition” or a “gut feeling” that they can’t easily explain (Dijksterhuis & Nordgren, 2006, p. 105; also see Bargh & Morsella, 2008).
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LTERNATIVEV
IEWS OFH
UMANM
EMORYIn attempts to address weaknesses of the dual-store model, some theorists have offered alterna- tive models. Here we’ll look at two of them: a levels-of-processing model and an activation model. Both of these theories emphasize cognitive processes involved in human memory rather than the possible structures that may comprise it.