As you've already learned, very little of what happens to us in our everyday lives is encoded and stored as an episodic memory. Although we've focused on episodic memories, the same is true for semantic memories, which means that most of what we experience is neither encoded nor stored as explicit memories. Furthermore, even when we encode and store an explicit memory, over time, we eventually forget either part or all of it. In this section, you will learn about four theories of why we forget explicit memories.

Reconstruction Theory of Forgetting

The reconstruction theory of forgetting states that the forgetting of explicit memories occurs because the process of retrieval from the long-term store introduces inaccuracies in memory codes. Whenever we retrieve an explicit memory, we change its memory code to some extent by filling in gaps with information obtained from other sources (see the What Jennifer Saw web site for an example of this involving eyewitness testimony). The changed memory code will be returned to the long-term store until the next retrieval. Over time, the memory may become so transformed that it bears little resemblance to the information originally encoded.

Neisser and Harsch (1992) performed a study that provided support for reconstruction theory in a surprising way. These researchers took advantage of a highly publicized tragedy, the 1986 explosion of the space shuttle Challenger, to study flashbulb memories, which are defined as episodic memories of events that, because of their emotional intensity, are encoded in vivid detail. Mnay people believe that, because of the nature of flashbulb memories, they change very little over even long periods of time. It is argued that emotionally-intense events activate our attention to such an extent that these events are encoded in great detail. In short, the events are "burned into our memory," thereby resulting in a virtually photographic memory code. In recent years, similar claims have been made about memories of 9/11.

In order to test whether flashbulb memories actually occur, the day after the explosion of the space shuttle, Challenger, Neisser and Harsch (1992) asked students in an introductory-psychology course to fill out a questionnaire asking them to describe in detail the following information about the situation in which they first heard about the disaster:

• where they were
• how they found out
• who was with them
• what they were doing
• what time it was

Because the event had occurred only 24 hours before, their episodic memories should have been very accurate. Three years later, the researchers gave the same students a new copy of the questionnaire and asked them to answer again these questions. The students also were asked at that time to rate how confident they were in the accuracy of their memories three years after the events.

Neisser and Harsch (1992) then compared the first set of answers to the second set for each student. They discovered that only 3 of the 44 students (7%) showed perfect recall. Thirty students (68%) recalled memories that contained varying amounts of accurate and inaccurate details. And 11 students (25%) recalled memories that were completely inaccurate. As an illustration of the development of a completely inaccurate memory, one student initially provided the following response just 24 hours after the explosion:

I was in my religion class and some people walked in and started talking about [it]. I didn’t know any details except that it had exploded and the schoolteacher’s students had all been watching which I thought was so sad. (quoted in Ofshe & Watters, 1994, p. 39)

The schoolteacher mentioned was Christa McAuliffe, the first civilian to fly aboard a NASA spacecraft. Three years after giving this response, the same student provided a very different answer:

When I first heard about the explosion I was sitting in my freshman dorm room with my roommate and we were watching TV. It came on a news flash and we were both totally shocked. I was really upset and I went upstairs to talk to a friend of mine and then I called my parents. (p. 39)

Neisser and Harsch found that over 90% of the students had memories that contained at least one major inaccuracy. What is even more surprising is that those with completely inaccurate memories were just as confident in the accuracy of their memories as were those with completely accurate memories! For example, the student quoted above had complete confidence in the accuracy of her three-year-old memory — a memory that was false in virtually all details.

One semester after the second questionnaire was given, Neisser and Harsch (1992) asked the students to look at their answers to both questionnaires. The researchers expected that those who had misremembered the original event would realize their mistake after reading their responses to the first questionnaire. But not one student did. Although most were upset by the differences between the two sets of answers, their false memories did not change. They still felt certain that they remembered the event accurately, even after being shown incontrovertible evidence this was not the case. (For studies of "flashbulb memories" of the 9/11 attacks, see Talarico & Rubin, 2003 and Hirst, et al., 2009.)

Encoding-Specificity Theory of Forgetting

The encoding-specificity theory of forgetting states that forgetting is due to an inability of a retrieval cue to activate stored information because the retrieval cue is not associated with (is dissimilar to) the memory code. In order to activate a memory code, the stimulus that is serving as a retrieval cue must have some similarity to the memory code — it must, in some wa, be associated with the memory code for an individual. For example, a memory that is encoded in tactile form (such as a memory for how an unseen bump on your back feels) is not likely to be retrieved by a cue that is in visual form (such as a picture of that same bump).

As another example, let’s say that there is a particular woman in your class whom you know by sight. In this case, your long-term memory for her is encoded in a visual form (when you think of her, you see an image of her face). Now, let’s say that you get assigned to a group with this person and she calls you to discuss the group's assignment. In this case, your memory of her may not be retrieved because the retrieval cue is the sound of her voice, whereas the memory code is an image of her face. In other words, an auditory retrieval cue is unable to activate a visual memory code. In this sense, you have “forgotten” who she is.

There are more subtle examples of forgetting due to a mismatch between retrieval cues and memory codes. Let’s say that you have studied for a test primarily by memorizing word-for-word definitions of concepts (that is, by rote memorization of the definitions). Your memory codes for these definitions, therefore, would involve phonemic encoding. On a multiple-choice test, the retrieval cue would be the correct answer (presented as one of several choices). If the correct answer is worded exactly as it was presented in the textbook, you should have no difficulty choosing it because the form of the retrieval cue is identical to the form in which you encoded it. On the other hand, if the instructor gives an answer worded differently from the original definition — an answer that means the same thing — then the form of the retrieval cue is too dissimilar to your memory code: the retrieval cue involves a semantic code, not a phonemic code. After the test, you may even complain angrily: “I don’t know where he got those questions! I know the answers weren’t anywhere in the book or in my notes!” In a sense, you are correct; but the problem is in the way you studied instead of in what you studied. If, during your studying, you had encoded information by using elaborative rehearsal and, therefore, forming semantic memory codes, you would have been better able to choose the correct answers on the test.

The encoding-specificity principle states that the ability of a retrieval cue to facilitate (aid) the retrieval of a stored memory depends on the degree to which it is associated with (is similar to) the memory code. Thus, how individuals encode information in working memory for transfer to long-term memory will affect their ability to retrieve this information later. In order to do your best on tests, you should elaboratively rehearse information in working memory so that you can form complex semantic memory codes. Semantic codes are superior for two reasons:

• they allow for a more enduring long-term memory code;
• they allow a greater number of retrieval cues to activate the memory code.

Interference Theory of Forgetting

The interference theory of forgetting states that forgetting is due to an inability of a retrieval cue to activate a desired memory code because it overlaps with (is similar to) other memory codes. In short, we confuse different but similar memories and, hence, have difficulty retrieving one of them without also retrieving others, which then get confused with it. For example, if you've moved a lot in recent years, you may have trouble remembering your current address because it is similar to your old addresses.

There are two ways that interference can cause the forgetting of an explicit memory:

• Proactive interference: old information interferes with the retrieval of new information;
• Retroactive interference: new information interferes with the retrieval of old information.

For example, I often have trouble learning the names of my current students because I keep getting them confused with the names of former students: the older names make it hard for me to remember the new names (proactive interference: interference that goes from the past forward to the present). I also often have difficulty remembering the names of former students because the names of my current students gets confused with them (retroactive interference: interference that goes backwards from the present to the past). In general, interference is greatest when the competing items are similar in some way — the more similar, the greater the interference. If a student's name is unique — for example, if one of my students is named Viola, which is an unusual name in the early 21st-century United States — I am more likely to remember it. On the other hand, common student names (such as John Hernandez and James Harris) are likely to interfere with one another and, hence, be difficult to remember.

There are limits to interference. In fact, we often find that learning similar information in two different courses can help you to better remember the information. Such facilitation of learning is probably much more common than interference. Why isn’t interference occurring in this situation? Well, it is, but it depends on what we are testing for. We probably would see interference if I asked you in which of these two courses you had learned a particular item of information. But of course, no one asks you such questions on a test. Your teachers simply want you to learn the material, not also remember in which class you learned it. Thus, if you are learning similar material in two classes — or even better, if you can elaborate on what you are learning and find similarities yourself — then your learning of the material is improved.

In general, interference is an important cause of forgetting only when we learn similar items of information that we need to keep separate in our minds for later retrieval. For example, parking in the lot outside of school each and every day can cause problems when you are trying to remember exactly where you parked today: you probably keep getting this confused with where you parked during the past week. Nevertheless, parking in the same lot each day also facilitates your learning of other material. For example, you probably have learned a great deal about where you are most likely to find an open space at a particular time.

Defensive Theory of Forgetting

The defensive theory of forgetting states that forgetting is due to the transfer of a memory code from the preconscious level to the unconscious level because recall of the memory causes too much anxiety. In other words, this theory states that a person transforms an explicit memory into an implicit one when the memory distresses him or her. According to this theory, people do this because, if they no longer are aware of the memory, then their anxiety (distress) disappears. For example, if you had seen one of your parents temporarily become very ill when you were a young child, your memory for this event, even after the parent had recovered, may have caused you a great deal of anxiety. If you were not able to cope at this time with the memory of this event, then you would have felt severe anxiety whenever you recalled it. At this point, according to defensive theory, you may have transformed the explicit memory into an implicit one by using what we will call defensive forgetting. If you do not now remember certain traumatic events from your childhood, events that you know happened (because others told you that they did), defensive theory suggests that defensive forgetting may be the cause. Because of its importance in the history of psychiatry and clinical psychology, the evidence for and against defensive forgetting will be discussed in Sections 6-15 and 6-16.

Study Questions for Section 6-14

1. What is the cause of forgetting according to reconstruction theory?
2. What is an example from your own life of forgetting because of reconstruction?
3. What do you think may be a good way to prevent forgetting due to the reconstruction of memory codes? (NOTE: I did not talk about this.)
4. How would you define the concept of "flashbulb memory" in your own words?
5. What is an example of a flashbulb memory not mentioned in the reading (perhaps one that you've experienced)?
6. What was studied by Neisser and Harsch (1992) and how did they study it?
7. What were the results of the study by Neisser and Harsch (1992) and how did they interpret these results?
8. When participants in the study by Neisser and Harsch (1992) were shown that their 3-year-old recollections were incorrect, what did they do?
9. What is the cause of forgetting according to encoding-specificity theory?
10. What is an example from your own life of forgetting because of a mismatch between a retrieval cue and the way in which a memory was encoded?
11. What is the best way to form a memory code that can be activated by a broad range of retireval cues?
12. What is the cause of forgetting according to interference theory?
13. What is an example from your own life of forgetting something due to interference?
14. What is the best way to prevent forgetting caused by confusing similar information stored in long-term memory? (NOTE: I did not talk about this.)
15. What is the cause of forgetting according to the defensive theory of forgetting?
16. What is a possible example of defensive forgetting from your own life?

Go to Quiz 6-14 questions

Go to Readings Section 6-15