The long-term store can be described in terms of the same characteristics used to describe the sensory and short-term stores: the levels of awareness at which long-term memories are stored; the duration of long-term memories; the capacity of the long-term store; the encoding of long-term memories; and the causes of forgetting of long-term memories. The first characteristic will be discussed in this section. The remaining characteristics will be discussed in several of the sections that follow.

Levels of Awareness of Long-Term Memories

We can think of the ability to attend to information stored in the memory system as involving a continuum from conscious to preconscious to unconscious (see Figure 1). By definition, only memory codes in the short-term store are at the conscious level. Therefore, according to the information-processing approach, memory codes in the long-term store are, by definition, outside of conscious awareness, and we cannot become aware of them until they are transferred from the long-term store to the short-term store.

Figure 1. Levels of awareness and the ease or difficulty of attending to mental content at each level

As you know from your own experience, some long-term memories are relatively easy to retrieve (that is, to bring to the conscious level), such as the day and time of your favorite television show. The preconscious level of awareness contains memory codes that are relatively easy to attend to. On the other hand, other long-term memories are much more difficult to retrieve, such as (perhaps) the name of your second-grade teacher. The unconscious level of awareness contains memory codes that are very difficult or impossible to attend to. In order to bring long-term memories to the conscious level, they must be attended to, which causes them to be transferred to the short-term store. Unconscious long-term memory codes that are unable to enter the short-term store still may affect conscious cognitions, emotions, and behaviors (perhaps by being transferred to unconscious components of working memory).

An explicit memory is a long-term memory about a fact or life event that can be attended to and, hence, consciously remembered. For example, your conscious memory of what you were doing five minutes ago involves the activation of a preconscious long-term memory code. Explicit memories sometimes are referred to as declarative memories because they are memories that can be stated or "declared" to others (Squire & Zola, 1996). An implicit memory is a long-term memory about a fact, life event, skill, or response that cannot be attended to and, hence, cannot be consciously remembered. The presence of an implicit memory is indicated by its effect on conscious cognitions, emotions, or behaviors. For example, memories of responses learned through classical and operant conditioning are implicit because they involve learned mental events or learned behaviors that are evoked directly by environmental events (that is, without the need for conscious remembering). Implicit memories sometimes are referred to as nondeclarative memories because they are memories that cannot be declared to others.

The case of H. M. can help us to understand better the distinction between explicit and implicit memories (Schacter, 1987). As we saw in Section 6-7, it was very difficult for Henry to learn new information because of his problems with anterograde amnesia. Scoville and Milner (1957) provided some examples of this:

Ten months ago [Henry's] family moved from their old house to a new one a few blocks away on the same street; he still has not learned the new address, though remembering the old one perfectly, nor can he be trusted to find his way home alone. Moreover, he does not know where objects in continual use are kept; for example, his mother still has to tell him where to find the lawn mower, even though he may have been using it only the day before. She also states that he will do the same jigsaw puzzles day after day without showing any practice effect and that he will read the same magazine over and over again without finding their contents familiar. This patient has even eaten luncheon in front of one of us [Brenda Milner] without being able to name, a mere half-hour later, a single item of food he had eaten; in fact, he could not remember having eaten luncheon at all. (p. 14)

Nevertheless, there were some things he could learn and remember quite well. For example, he was tested often over many years in the same room at the Massachusetts Institute of Technology. When walking down the hall to the testing room, he would claim that he did not know where the room was, yet he would make the correct turns leading to it. He seemed to know approximately where the room was, but he did not know that he knew this, which suggests that he did not have amnesia for all types of information. Although Henry did not have an explicit memory for the location of the testing room, he did have an implicit memory, allowing him to walk there without knowing consciously how to do this. In general, Henry was unable to form new explicit memories but was able to form new implicit memories.

Another example of this is described in a case study from the early twentieth century (Sacks, 1995). One day in 1911, a neurologist by the name of Edouard Claparéde took his medical students on rounds. One of Claparéde's patients was a man with severe anterograde amnesia similar to Henry's. In order to demonstrate to his students the man's memory disturbance, Claparéde placed a pin between his fingers, which he stuck in the man's palm after reaching to shake his hand. Within a minute or two after this event, the man was unable to remember why his hand hurt: he had no explicit memory of the incident. He did, however, develop a classically conditioned fear response that made up an implicit memory of the incident. The existence of the implicit memory was demonstrated the next day when the patient, although unable to recall consciously the preceding day's visit, refused to shake hands with Claparéde. In this case, the CS was the sight of Claparéde’s hand and the CR was the anxiety elicited by the sight of Claparéde’s hand, which led the patient to refuse to shake his doctor's outstretched hand.

Retrieval Cues

In order for a long-term memory code (whether explicit or implicit) to affect an individual's conscious cognitions, emotions, and behaviors, the individual must experience a retrieval cue, which is a stimulus that activates a long-term memory code. Retrieval cues are necessary because long-term memories are not stored at the conscious level and, hence, their memory codes must be activated by something first. If the memory code is an explicit (preconscious) one, the retrieval cue will cause a conscious memory to be retrieved. If the memory code is an implicit (unconscious) one, the retrieval cue will cause changes in conscious cognitions, emotions, and/or behaviors (as in the case of Claparéde’s patient). Retrieval cues activate long-term memory codes because they are, in some way, associated with these memories. For example, if you want to retrieve explicit memories of the names of your friends from third grade, standing in your third-grade classroom and seeing a class picture from third grade might be adequate retrieval cues (perhaps even bringing back a flood of memories from that time period). Or perhaps, while eating waffles one day, you suddenly think of a friend from childhood. As you think more about this friend, you remember the time you stayed overnight at his house and ate waffles for breakfast the following morning. In this example, the waffles were a retrieval cue because they were associated with an explicit memory of your childhood friend and an event from that time period.

Smells and tastes seem to be especially good retrieval cues for explicit memories of long-ago life events. Marcel Proust (Mar•sell Proost, 1871–1922), the French novelist and essayist, described the retrieval of an especially intense and vivid childhood memory in his novel, In Search of Lost Time (À la Recherche du Temps Perdu):

The other evening, having come in chilled, by the snow, and not being able to get warm, as I had started to read in my room under the lamp, my old cook offered to make tea, which I never drink. And chance had it that she brought me some slices of toast. I dipped the toast into my mouth and having the sensation against my palate of its sogginess permeated with the taste of tea, I felt a disturbance, scents of geraniums and orange trees, a feeling of extraordinary light, of happiness; I stayed motionless, fearing a single movement could interrupt what was happening in me, which I did not understand, but still concentrating on this taste of dunked bread, which seemed to produce such wonders, when suddenly the shaken partitions of my memory caved in, and it was the summers I spent in the country house I mentioned which burst into my consciousness, with their mornings, and drawing with them the procession, the nonstop charge of happy hours. Then I remembered: every day when I was dressed, I went down into the room of my grandfather, who had just awakened me and was drinking his tea. He used to dunk a rusk and give it to me. (quoted in Hilts, 1995, p. 77)

As an adult, the taste of toast dipped in tea was a retrieval cue for a memory that had not been recalled in many years — a memory of summers spent at a relative’s house. The memory's powerful impact was caused by its vivid perceptual details and the strong emotions evoked by these. Most remembrances, however, are not so clear and striking. Retrieval cues (such as the several choices you read on an item from a multiple-choice test) are more likely to activate memories of general knowledge or fuzzy memories of past life events.

Another example of a retrieval cue involves the common experience of having to return to the place in which you recently had thought of something in order to remember what that thought was. Perhaps while you were in your bedroom one afternoon, for example, you decided to drive to the grocery store and pick up a few things. You remembered that your car keys were in the kitchen and, so, you started to walk down the hallway towards the kitchen. Halfway there, however, you forgot why you were going to the kitchen. At that point, it is likely that you stopped, turned around, and returned to the bedroom. Once back in the room, you looked around and remembered suddenly that you had been walking to the kitchen to get your car keys. In this example, the perceptions making up your experience of the bedroom served as a retrieval cue for the memory.

The concept of retrieval cue helps to explain why using elaborative rehearsal to encode information in working memory is the best strategy for creating easily accessible and stable long-term memories. When we elaboratively encode information, a memory code is created that can be activated by a larger number of retrieval cues because elaborative rehearsal creates a number of links to information already stored in the long-term store. For example, if you encoded the name of the behaviorist, John Watson, in terms of his later career as an advertising executive (see here), you may be unable to answer a test question asking you to "name the famous behaviorist who studied the conditioning of fear in Little Albert." A memory code created through the use of elaborative rehearsal, however, probably would allow you to answer this question easily since a larger number of retrieval cues would activate the memory code associated with John Watson. Furthermore, the greater the number of possible retrieval cues created by elaborative rehearsal, the more likely it becomes that the memory will be retrieved often, which creates a stronger and more durable memory code.

Mental Events as Retrieval Cues

There is evidence that mental states can serve as retrieval cues. For example, state-dependent memory is said to occur when people are better able to retrieve information learned while in a particular mental state, such as a state of consciousness or a mood state, when they are again in that same mental state. For example, if you study for your test while drinking a few beers, you may do better on the test if you have a few beers while taking it. Before you put this strategy into action, however, you should be aware that you will do much better on the test if you are sober both while studying for the test and while taking the test. Nonetheless, some research on state-dependent memory suggests that, if you are slightly intoxicated while studying, then you may do a bit better if you are slightly intoxicated while taking the test.

A concept that is related to, but distinct from, state-dependent memory is the mood-congruence effect. The mood-congruence effect is an increased tendency to recall life events that are consistent with one's present mood rather than life events that are inconsistent with that mood. When you are happy, for example, you are more likely to recall positive experiences from your past (such as the time you found a twenty-dollar bill) than you are to recall negative experiences (such as the time you lost a twenty-dollar bill). In other words, research on the mood-congruence effect suggests that your present mood state may serve as a retrieval cue for long-term memories formed when you were in the same mood state in the past.

The mood-congruence effect implies that it may not be a good idea to trust too much the negative memories of depressed, anxious, or distressed people because they would be expected to more easily recall negative than positive long-term memories. In fact, they may even make past events sound more negative than they really were:

Researchers have documented ... that people tend naturally to reconstruct the past in terms of their present circumstances, exaggerating the degree of earlier misfortune and trauma if they currently are feeling bad, minimizing it if they are feeling good. Findings from various studies — of Gulf War veterans, car accident victims, witnesses to school shootings, international peacekeepers — are remarkably consistent in this regard. They show that individuals with more severe symptoms of anxiety and depression remember a traumatic event as being worse when they are asked about it a second time many months, or even years, after the first. Those with fewer symptoms, however, tended to recall the event as less harrowing than they had previously described it. (Sommers & Satel, 2005, p. 155)

If you have known for a long time a normally happy person who is currently depressed, you may be amazed at how many positive memories he or she seems to be forgetting. There is no need to worry, however. As soon as the person's mood improves, there should be an increase in the number of positive memories retrieved.

Study Questions for Section 6-10

1. At what level(s) of awareness is the long-term store?
2. What are the two major types of memory in the long-term store and what levels of awareness are they associated with?
3. In what ways are explicit and implicit memories similar to and different from each other?
4. What are some examples of explicit memories from your own life?
5. What are some examples of implicit memories not mentioned in the reading?
6. Why would it be very difficult to think of examples of implicit memories from your own life?
7. What does the case of H. M. (and other similar cases) tell us about brain structures important for the formation of explicit and implicit memories?
8. How would you define in your own words the concept of "retrieval cue"?
9. What are some examples of retrieval cues not mentioned in the reading?
10. Why are retrieval cues necessary in order to get information out of the long-term store?
11. Why is a particular stimulus able to act as a retrieval cue for a particular memory?
12. When a retrieval cue activates an explicit memory code in the long-term store, what happens to the explicit memory code (that is, where does it "go" according to the standard model of memory)?
13. How would you define state-dependent memory in your own words?
14. What is an example of state-dependent memory not mentioned in the reading?
15. How would you define "mood-congruence effect" in your own words?
16. What is an example of the mood-congruence effect from your own life?
17. How would the mood-congruence effect limit what a psychotherapist can learn about a client's past life?
18. Why should you be skeptical when a happy person tells you that his life has always been wonderful?

Go to Quiz 6-10 questions

Go to Readings Section 6-11