Memory (Encoding, Storage, Retrieval)

By Kathleen B. McDermott and Henry L. Roediger III

Washington University in St. Louis

“Memory” is a single term that reflects a number of different abilities: holding information briefly while
working with it (working memory), remembering episodes of one’s life (episodic memory), and our
general knowledge of facts of the world (semantic memory), among other types. Remembering episodes
involves three processes: encoding information (learning it, by perceiving it and relating it to past
knowledge), storing it (maintaining it over time), and then retrieving it (accessing the information when
needed). Failures can occur at any stage, leading to forgetting or to having false memories. The key to
improving one’s memory is to improve processes of encoding and to use techniques that guarantee
effective retrieval. Good encoding techniques include relating new information to what one already
knows, forming mental images, and creating associations among information that needs to be
remembered. The key to good retrieval is developing effective cues that will lead the rememberer back
to the encoded information. Classic mnemonic systems, known since the time of the ancient Greeks and
still used by some today, can greatly improve one’s memory abilities.

Learning Objectives

• Define and note differences between the following forms of memory: working memory, episodic
memory, semantic memory, collective memory.

• Describe the three stages in the process of learning and remembering.

• Describe strategies that can be used to enhance the original learning or encoding of information.

• Describe strategies that can improve the process of retrieval.

• Describe why the classic mnemonic device, the method of loci, works so well.

Introduction

In 2013, Simon Reinhard sat in front of 60 people in a room at Washington University, where he
memorized an increasingly long series of digits. On the first round, a computer generated 10 random
digits—6 1 9 4 8 5 6 3 7 1—on a screen for 10 seconds. After the series disappeared, Simon typed them
into his computer. His recollection was perfect. In the next phase, 20 digits appeared on the screen for
20 seconds. Again, Simon got them all correct. No one in the audience (mostly professors, graduate
students, and undergraduate students) could recall the 20 digits perfectly. Then came 30 digits, studied
for 30 seconds; once again, Simon didn’t misplace even a single digit. For a final trial, 50 digits appeared
on the screen for 50 seconds, and again, Simon got them all right. In fact, Simon would have been happy
to keep going. His record in this task—called “forward digit span”—is 240 digits!
In some ways memory is like file drawers where you store mental information. Memory is also a series of
processes: how does that information get filed to begin with and how does it get retrieved when
needed? [Image: M Cruz, https://goo.gl/DhOMgp, CC BY-SA 4.0, https://goo.gl/SWjq94]

When most of us witness a performance like that of Simon Reinhard, we think one of two things: First,
maybe he’s cheating somehow. (No, he is not.) Second, Simon must have abilities more advanced than
the rest of humankind. After all, psychologists established many years ago that the normal memory span
for adults is about 7 digits, with some of us able to recall a few more and others a few less (Miller, 1956).
That is why the first phone numbers were limited to 7 digits—psychologists determined that many errors
occurred (costing the phone company money) when the number was increased to even 8 digits. But in
normal testing, no one gets 50 digits correct in a row, much less 240. So, does Simon Reinhard simply
have a photographic memory? He does not. Instead, Simon has taught himself simple strategies for
remembering that have greatly increased his capacity for remembering virtually any type of material—
digits, words, faces and names, poetry, historical dates, and so on. Twelve years earlier, before he started
training his memory abilities, he had a digit span of 7, just like most of us. Simon has been training his
abilities for about 10 years as of this writing, and has risen to be in the top two of “memory athletes.” In
2012, he came in second place in the World Memory Championships (composed of 11 tasks), held in
London. He currently ranks second in the world, behind another German competitor, Johannes Mallow.
In this module, we reveal what psychologists and others have learned about memory, and we also
explain the general principles by which you can improve your own memory for factual material.

Varieties of Memory

To be a good chess player you have to learn to increase working memory so you can plan ahead for
several offensive moves while simultaneously anticipating - through use of memory - how the other
player could counter each of your planned moves. [Image: karpidis, https://goo.gl/EhzMKM, CC BY-SA
2.0, https://goo.gl/jSSrcO]

For most of us, remembering digits relies on short-term memory, or working memory—the ability to hold
information in our minds for a brief time and work with it (e.g., multiplying 24 x 17 without using paper
would rely on working memory). Another type of memory is episodic memory—the ability to remember
the episodes of our lives. If you were given the task of recalling everything you did 2 days ago, that
would be a test of episodic memory; you would be required to mentally travel through the day in your
mind and note the main events. Semantic memory is our storehouse of more-or-less permanent
knowledge, such as the meanings of words in a language (e.g., the meaning of “parasol”) and the huge
collection of facts about the world (e.g., there are 196 countries in the world, and 206 bones in your
body). Collective memory refers to the kind of memory that people in a group share (whether family,
community, schoolmates, or citizens of a state or a country). For example, residents of small towns often
strongly identify with those towns, remembering the local customs and historical events in a unique way.
That is, the community’s collective memory passes stories and recollections between neighbors and to
future generations, forming a memory system unto itself.

Psychologists continue to debate the classification of types of memory, as well as which types rely on
others (Tulving, 2007), but for this module we will focus on episodic memory. Episodic memory is usually
what people think of when they hear the word “memory.” For example, when people say that an older
relative is “losing her memory” due to Alzheimer’s disease, the type of memory-loss they are referring to
is the inability to recall events, or episodic memory. (Semantic memory is actually preserved in early-
stage Alzheimer’s disease.) Although remembering specific events that have happened over the course
of one’s entire life (e.g., your experiences in sixth grade) can be referred to as autobiographical memory,
we will focus primarily on the episodic memories of more recent events.

Three Stages of the Learning/Memory Process

Psychologists distinguish between three necessary stages in the learning and memory
process: encoding, storage, and retrieval (Melton, 1963). Encoding is defined as the initial learning of
information; storage refers to maintaining information over time; retrieval is the ability to access
information when you need it. If you meet someone for the first time at a party, you need to encode her
name (Lyn Goff) while you associate her name with her face. Then you need to maintain the information
over time. If you see her a week later, you need to recognize her face and have it serve as a cue to
retrieve her name. Any successful act of remembering requires that all three stages be intact. However,
two types of errors can also occur. Forgetting is one type: you see the person you met at the party and
you cannot recall her name. The other error is misremembering (false recall or false recognition): you
see someone who looks like Lyn Goff and call the person by that name (false recognition of the face). Or,
you might see the real Lyn Goff, recognize her face, but then call her by the name of another woman you
met at the party (misrecall of her name).

Whenever forgetting or misremembering occurs, we can ask, at which stage in the learning/memory
process was there a failure?—though it is often difficult to answer this question with precision. One
reason for this inaccuracy is that the three stages are not as discrete as our description implies. Rather,
all three stages depend on one another. How we encode information determines how it will be stored
and what cues will be effective when we try to retrieve it. And too, the act of retrieval itself also changes
the way information is subsequently remembered, usually aiding later recall of the retrieved
information. The central point for now is that the three stages—encoding, storage, and retrieval—affect
one another, and are inextricably bound together.

Encoding

Encoding refers to the initial experience of perceiving and learning information. Psychologists often study
recall by having participants study a list of pictures or words. Encoding in these situations is fairly
straightforward. However, “real life” encoding is much more challenging. When you walk across campus,
for example, you encounter countless sights and sounds—friends passing by, people playing Frisbee,
music in the air. The physical and mental environments are much too rich for you to encode all the
happenings around you or the internal thoughts you have in response to them. So, an important first
principle of encoding is that it is selective: we attend to some events in our environment and we ignore
others. A second point about encoding is that it is prolific; we are always encoding the events of our
lives—attending to the world, trying to understand it. Normally this presents no problem, as our days are
filled with routine occurrences, so we don’t need to pay attention to everything. But if something does
happen that seems strange—during your daily walk across campus, you see a giraffe—then we pay close
attention and try to understand why we are seeing what we are seeing.

A giraffe in the context of a zoo or

its natural habitat may register as nothing more than ordinary, but put it in another setting - in the
middle of a campus or a busy city - and its level of distinctiveness increases dramatically. Distinctiveness
is a key attribute to remembering events. [Image: Colin J Babb, https://goo.gl/Cci2yl, CC BY-SA 2.0,
https://goo.gl/jSSrcO]
Right after your typical walk across campus (one without the appearance of a giraffe), you would be able
to remember the events reasonably well if you were asked. You could say whom you bumped into, what
song was playing from a radio, and so on. However, suppose someone asked you to recall the same walk
a month later. You wouldn’t stand a chance. You would likely be able to recount the basics of a typical
walk across campus, but not the precise details of that particular walk. Yet, if you had seen a giraffe
during that walk, the event would have been fixed in your mind for a long time, probably for the rest of
your life. You would tell your friends about it, and, on later occasions when you saw a giraffe, you might
be reminded of the day you saw one on campus. Psychologists have long pinpointed distinctiveness—
having an event stand out as quite different from a background of similar events—as a key to
remembering events (Hunt, 2003).

In addition, when vivid memories are tinged with strong emotional content, they often seem to leave a
permanent mark on us. Public tragedies, such as terrorist attacks, often create vivid memories in those
who witnessed them. But even those of us not directly involved in such events may have vivid memories
of them, including memories of first hearing about them. For example, many people are able to recall
their exact physical location when they first learned about the assassination or accidental death of a
national figure. The term flashbulb memory was originally coined by Brown and Kulik (1977) to describe
this sort of vivid memory of finding out an important piece of news. The name refers to how some
memories seem to be captured in the mind like a flash photograph; because of the distinctiveness and
emotionality of the news, they seem to become permanently etched in the mind with exceptional clarity
compared to other memories.

Take a moment and think back on your own life. Is there a particular memory that seems sharper than
others? A memory where you can recall unusual details, like the colors of mundane things around you,
or the exact positions of surrounding objects? Although people have great confidence in flashbulb
memories like these, the truth is, our objective accuracy with them is far from perfect (Talarico & Rubin,
2003). That is, even though people may have great confidence in what they recall, their memories are
not as accurate (e.g., what the actual colors were; where objects were truly placed) as they tend to
imagine. Nonetheless, all other things being equal, distinctive and emotional events are well-
remembered.

Details do not leap perfectly from the world into a person’s mind. We might say that we went to a party
and remember it, but what we remember is (at best) what we encoded. As noted above, the process of
encoding is selective, and in complex situations, relatively few of many possible details are noticed and
encoded. The process of encoding always involves recoding—that is, taking the information from the
form it is delivered to us and then converting it in a way that we can make sense of it. For example, you
might try to remember the colors of a rainbow by using the acronym ROY G BIV (red, orange, yellow,
green, blue, indigo, violet). The process of recoding the colors into a name can help us to remember.
However, recoding can also introduce errors—when we accidentally add information during encoding,
then remember that new material as if it had been part of the actual experience (as discussed below).
Although it requires more effort, using images and associations can improve the process of recoding.
[Image: psd, https://goo.gl/9xjcDe, CC BY 2.0, https://goo.gl/9uSnqN]

Psychologists have studied many recoding strategies that can be used during study to improve retention.
First, research advises that, as we study, we should think of the meaning of the events (Craik & Lockhart,
1972), and we should try to relate new events to information we already know. This helps us form
associations that we can use to retrieve information later. Second, imagining events also makes them
more memorable; creating vivid images out of information (even verbal information) can greatly improve
later recall (Bower & Reitman, 1972). Creating imagery is part of the technique Simon Reinhard uses to
remember huge numbers of digits, but we can all use images to encode information more effectively.
The basic concept behind good encoding strategies is to form distinctive memories (ones that stand out),
and to form links or associations among memories to help later retrieval (Hunt & McDaniel, 1993). Using
study strategies such as the ones described here is challenging, but the effort is well worth the benefits
of enhanced learning and retention.

We emphasized earlier that encoding is selective: people cannot encode all information they are
exposed to. However, recoding can add information that was not even seen or heard during the initial
encoding phase. Several of the recoding processes, like forming associations between memories, can
happen without our awareness. This is one reason people can sometimes remember events that did not
actually happen—because during the process of recoding, details got added. One common way of
inducing false memories in the laboratory employs a word-list technique (Deese, 1959; Roediger &
McDermott, 1995). Participants hear lists of 15 words, like door, glass, pane, shade, ledge, sill, house,
open, curtain, frame, view, breeze, sash, screen, and shutter. Later, participants are given a test in which
they are shown a list of words and asked to pick out the ones they’d heard earlier. This second list
contains some words from the first list (e.g., door, pane, frame) and some words not from the list
(e.g., arm, phone, bottle). In this example, one of the words on the second list is window, which—
importantly—does not appear in the first list, but which is related to other words in that list. When
subjects were tested with the second list, they were reasonably accurate with the studied words (door,
etc.), recognizing them 72% of the time. However, when window was on the test, they falsely recognized
it as having been on the list 84% of the time (Stadler, Roediger, & McDermott, 1999). The same thing
happened with many other lists the authors used. This phenomenon is referred to as the DRM (for
Deese-Roediger-McDermott) effect. One explanation for such results is that, while students listened to
items in the list, the words triggered the students to think about window, even though window was
never presented. In this way, people seem to encode events that are not actually part of their
experience.

Because humans are creative, we are always going beyond the information we are given: we
automatically make associations and infer from them what is happening. But, as with the word
association mix-up above, sometimes we make false memories from our inferences—remembering the
inferences themselves as if they were actual experiences. To illustrate this, Brewer (1977) gave people
sentences to remember that were designed to elicit pragmatic inferences. Inferences, in general, refer to
instances when something is not explicitly stated, but we are still able to guess the undisclosed
intention. For example, if your friend told you that she didn’t want to go out to eat, you may infer that
she doesn’t have the money to go out, or that she’s too tired. With pragmatic inferences, there is
usually one particular inference you’re likely to make. Consider the statement Brewer (1977) gave her
participants: “The karate champion hit the cinder block.” After hearing or seeing this sentence,
participants who were given a memory test tended to remember the statement as having been, “The
karate champion broke the cinder block.” This remembered statement is not necessarily
a logical inference (i.e., it is perfectly reasonable that a karate champion could hit a cinder block without
breaking it). Nevertheless, the pragmatic conclusion from hearing such a sentence is that the block was
likely broken. The participants remembered this inference they made while hearing the sentence in place
of the actual words that were in the sentence (see also McDermott & Chan, 2006).

Encoding—the initial registration of information—is essential in the learning and memory process.
Unless an event is encoded in some fashion, it will not be successfully remembered later. However, just
because an event is encoded (even if it is encoded well), there’s no guarantee that it will be remembered
later.
Storage

Memory traces, or engrams, are NOT perfectly preserved recordings of past experiences. The traces are
combined with current knowledge to reconstruct what we think happened in the past. [Simon
Bierdwald, https://goo.gl/JDhdCE, CC BY-NC-SA 2.0, https://goo.gl/jSSrcO]

Every experience we have changes our brains. That may seem like a bold, even strange, claim at first, but
it’s true. We encode each of our experiences within the structures of the nervous system, making new
impressions in the process—and each of those impressions involves changes in the brain. Psychologists
(and neurobiologists) say that experiences leave memory traces, or engrams (the two terms are
synonyms). Memories have to be stored somewhere in the brain, so in order to do so, the brain
biochemically alters itself and its neural tissue. Just like you might write yourself a note to remind you of
something, the brain “writes” a memory trace, changing its own physical composition to do so. The basic
idea is that events (occurrences in our environment) create engrams through a process of consolidation:
the neural changes that occur after learning to create the memory trace of an experience. Although
neurobiologists are concerned with exactly what neural processes change when memories are created,
for psychologists, the term memory trace simply refers to the physical change in the nervous system
(whatever that may be, exactly) that represents our experience.
Although the concept of engram or memory trace is extremely useful, we shouldn’t take the term too
literally. It is important to understand that memory traces are not perfect little packets of information
that lie dormant in the brain, waiting to be called forward to give an accurate report of past experience.
Memory traces are not like video or audio recordings, capturing experience with great accuracy; as
discussed earlier, we often have errors in our memory, which would not exist if memory traces were
perfect packets of information. Thus, it is wrong to think that remembering involves simply “reading out”
a faithful record of past experience. Rather, when we remember past events, we reconstruct them with
the aid of our memory traces—but also with our current belief of what happened. For example, if you
were trying to recall for the police who started a fight at a bar, you may not have a memory trace of who
pushed whom first. However, let’s say you remember that one of the guys held the door open for you.
When thinking back to the start of the fight, this knowledge (of how one guy was friendly to you) may
unconsciously influence your memory of what happened in favor of the nice guy. Thus, memory is a
construction of what you actually recall and what you believe happened. In a phrase, remembering is
reconstructive (we reconstruct our past with the aid of memory traces) not reproductive (a perfect
reproduction or recreation of the past).

Psychologists refer to the time between learning and testing as the retention interval. Memories can
consolidate during that time, aiding retention. However, experiences can also occur that undermine the
memory. For example, think of what you had for lunch yesterday—a pretty easy task. However, if you
had to recall what you had for lunch 17 days ago, you may well fail (assuming you don’t eat the same
thing every day). The 16 lunches you’ve had since that one have created retroactive interference.
Retroactive interference refers to new activities (i.e., the subsequent lunches) during the retention
interval (i.e., the time between the lunch 17 days ago and now) that interfere with retrieving the specific,
older memory (i.e., the lunch details from 17 days ago). But just as newer things can interfere with
remembering older things, so can the opposite happen. Proactive interference is when past memories
interfere with the encoding of new ones. For example, if you have ever studied a second language, often
times the grammar and vocabulary of your native language will pop into your head, impairing your
fluency in the foreign language.

Retroactive interference is one of the main causes of forgetting (McGeoch, 1932). In the
module Eyewitness Testimony and Memory Biases http://noba.to/uy49tm37 Elizabeth Loftus describes
her fascinating work on eyewitness memory, in which she shows how memory for an event can be
changed via misinformation supplied during the retention interval. For example, if you witnessed a car
crash but subsequently heard people describing it from their own perspective, this new information may
interfere with or disrupt your own personal recollection of the crash. In fact, you may even come to
remember the event happening exactly as the others described it! This misinformation effect in
eyewitness memory represents a type of retroactive interference that can occur during the retention
interval (see Loftus [2005] for a review). Of course, if correct information is given during the retention
interval, the witness’s memory will usually be improved.

Although interference may arise between the occurrence of an event and the attempt to recall it, the
effect itself is always expressed when we retrieve memories, the topic to which we turn next.

Retrieval

Endel Tulving argued that “the key process in memory is retrieval” (1991, p. 91). Why should retrieval be
given more prominence than encoding or storage? For one thing, if information were encoded and
stored but could not be retrieved, it would be useless. As discussed previously in this module, we encode
and store thousands of events—conversations, sights and sounds—every day, creating memory traces.
However, we later access only a tiny portion of what we’ve taken in. Most of our memories will never be
used—in the sense of being brought back to mind, consciously. This fact seems so obvious that we rarely
reflect on it. All those events that happened to you in the fourth grade that seemed so important then?
Now, many years later, you would struggle to remember even a few. You may wonder if the traces of
those memories still exist in some latent form. Unfortunately, with currently available methods, it is
impossible to know.

Psychologists distinguish information that is available in memory from that which is accessible (Tulving &
Pearlstone, 1966). Available information is the information that is stored in memory—but precisely how
much and what types are stored cannot be known. That is, all we can know is what information we can
retrieve—accessible information. The assumption is that accessible information represents only a tiny
slice of the information available in our brains. Most of us have had the experience of trying to
remember some fact or event, giving up, and then—all of a sudden!—it comes to us at a later time, even
after we’ve stopped trying to remember it. Similarly, we all know the experience of failing to recall a fact,
but then, if we are given several choices (as in a multiple-choice test), we are easily able to recognize it.
We can't know the entirety of what is in our memory, but only that portion we can actually retrieve.
Something that cannot be retrieved now and which is seemingly gone from memory may, with different
cues applied, reemerge. [Image: Ores2k, https://goo.gl/1du8Qe, CC BY-NC-SA 2.0, https://goo.gl/jSSrcO]

What factors determine what information can be retrieved from memory? One critical factor is the type
of hints, or cues, in the environment. You may hear a song on the radio that suddenly evokes memories
of an earlier time in your life, even if you were not trying to remember it when the song came on.
Nevertheless, the song is closely associated with that time, so it brings the experience to mind.

The general principle that underlies the effectiveness of retrieval cues is the encoding specificity
principle (Tulving & Thomson, 1973): when people encode information, they do so in specific ways. For
example, take the song on the radio: perhaps you heard it while you were at a terrific party, having a
great, philosophical conversation with a friend. Thus, the song became part of that whole complex
experience. Years later, even though you haven’t thought about that party in ages, when you hear the
song on the radio, the whole experience rushes back to you. In general, the encoding specificity principle
states that, to the extent a retrieval cue (the song) matches or overlaps the memory trace of an
experience (the party, the conversation), it will be effective in evoking the memory. A classic experiment
on the encoding specificity principle had participants memorize a set of words in a unique setting. Later,
the participants were tested on the word sets, either in the same location they learned the words or a
different one. As a result of encoding specificity, the students who took the test in the same place they
learned the words were actually able to recall more words (Godden & Baddeley, 1975) than the students
who took the test in a new setting.

One caution with this principle, though, is that, for the cue to work, it can’t match too many other
experiences (Nairne, 2002; Watkins, 1975). Consider a lab experiment. Suppose you study 100 items; 99
are words, and one is a picture—of a penguin, item 50 in the list. Afterwards, the cue “recall the picture”
would evoke “penguin” perfectly. No one would miss it. However, if the word “penguin” were placed in
the same spot among the other 99 words, its memorability would be exceptionally worse. This outcome
shows the power of distinctiveness that we discussed in the section on encoding: one picture is perfectly
recalled from among 99 words because it stands out. Now consider what would happen if the
experiment were repeated, but there were 25 pictures distributed within the 100-item list. Although the
picture of the penguin would still be there, the probability that the cue “recall the picture” (at item 50)
would be useful for the penguin would drop correspondingly. Watkins (1975) referred to this outcome as
demonstrating the cue overload principle. That is, to be effective, a retrieval cue cannot be overloaded
with too many memories. For the cue “recall the picture” to be effective, it should only match one item
in the target set (as in the one-picture, 99-word case).

To sum up how memory cues function: for a retrieval cue to be effective, a match must exist between
the cue and the desired target memory; furthermore, to produce the best retrieval, the cue-target
relationship should be distinctive. Next, we will see how the encoding specificity principle can work in
practice.

Psychologists measure memory performance by using production tests (involving recall) or recognition
tests (involving the selection of correct from incorrect information, e.g., a multiple-choice test). For
example, with our list of 100 words, one group of people might be asked to recall the list in any order (a
free recall test), while a different group might be asked to circle the 100 studied words out of a mix with
another 100, unstudied words (a recognition test). In this situation, the recognition test would likely
produce better performance from participants than the recall test.

We usually think of recognition tests as being quite easy, because the cue for retrieval is a copy of the
actual event that was presented for study. After all, what could be a better cue than the exact target
(memory) the person is trying to access? In most cases, this line of reasoning is true; nevertheless,
recognition tests do not provide perfect indexes of what is stored in memory. That is, you can fail to
recognize a target staring you right in the face, yet be able to recall it later with a different set of cues
(Watkins & Tulving, 1975). For example, suppose you had the task of recognizing the surnames of
famous authors. At first, you might think that being given the actual last name would always be the best
cue. However, research has shown this not necessarily to be true (Muter, 1984). When given names such
as Tolstoy, Shaw, Shakespeare, and Lee, subjects might well say that Tolstoy and Shakespeare are famous
authors, whereas Shaw and Lee are not. But, when given a cued recall test using first names, people
often recall items (produce them) that they had failed to recognize before. For example, in this instance,
a cue like George Bernard ________ often leads to a recall of “Shaw,” even though people initially failed
to recognize Shaw as a famous author’s name. Yet, when given the cue “William,” people may not come
up with Shakespeare, because William is a common name that matches many people (the cue overload
principle at work). This strange fact—that recall can sometimes lead to better performance than
recognition—can be explained by the encoding specificity principle. As a cue, George Bernard _________
matches the way the famous writer is stored in memory better than does his surname, Shaw, does (even
though it is the target). Further, the match is quite distinctive with George Bernard ___________, but the
cue William _________________ is much more overloaded (Prince William, William Yeats, William
Faulkner, will.i.am).

The phenomenon we have been describing is called the recognition failure of recallable words, which
highlights the point that a cue will be most effective depending on how the information has been
encoded (Tulving & Thomson, 1973). The point is, the cues that work best to evoke retrieval are those
that recreate the event or name to be remembered, whereas sometimes even the target itself, such
as Shaw in the above example, is not the best cue. Which cue will be most effective depends on how the
information has been encoded.

Whenever we think about our past, we engage in the act of retrieval. We usually think that retrieval is an
objective act because we tend to imagine that retrieving a memory is like pulling a book from a shelf,
and after we are done with it, we return the book to the shelf just as it was. However, research shows
this assumption to be false; far from being a static repository of data, the memory is constantly
changing. In fact, every time we retrieve a memory, it is altered. For example, the act of retrieval itself
(of a fact, concept, or event) makes the retrieved memory much more likely to be retrieved again, a
phenomenon called the testing effect or the retrieval practice effect (Pyc & Rawson, 2009; Roediger &
Karpicke, 2006). However, retrieving some information can actually cause us to forget other information
related to it, a phenomenon called retrieval-induced forgetting (Anderson, Bjork, & Bjork, 1994). Thus
the act of retrieval can be a double-edged sword—strengthening the memory just retrieved (usually by a
large amount) but harming related information (though this effect is often relatively small).

As discussed earlier, retrieval of distant memories is reconstructive. We weave the concrete bits and
pieces of events in with assumptions and preferences to form a coherent story (Bartlett, 1932). For
example, if during your 10th birthday, your dog got to your cake before you did, you would likely tell that
story for years afterward. Say, then, in later years you misremember where the dog actually found the
cake, but repeat that error over and over during subsequent retellings of the story. Over time, that
inaccuracy would become a basic fact of the event in your mind. Just as retrieval practice (repetition)
enhances accurate memories, so will it strengthen errors or false memories (McDermott, 2006).
Sometimes memories can even be manufactured just from hearing a vivid story. Consider the following
episode, recounted by Jean Piaget, the famous developmental psychologist, from his childhood:

One of my first memories would date, if it were true, from my second year. I can still see, most clearly,
the following scene, in which I believed until I was about 15. I was sitting in my pram . . . when a man
tried to kidnap me. I was held in by the strap fastened round me while my nurse bravely tried to stand
between me and the thief. She received various scratches, and I can still vaguely see those on her face. . .
. When I was about 15, my parents received a letter from my former nurse saying that she had been
converted to the Salvation Army. She wanted to confess her past faults, and in particular to return the
watch she had been given as a reward on this occasion. She had made up the whole story, faking the
scratches. I therefore must have heard, as a child, this story, which my parents believed, and projected it
into the past in the form of a visual memory. . . . Many real memories are doubtless of the same order.
(Norman & Schacter, 1997, pp. 187–188)

Piaget’s vivid account represents a case of a pure reconstructive memory. He heard the tale told
repeatedly, and doubtless told it (and thought about it) himself. The repeated telling cemented the
events as though they had really happened, just as we are all open to the possibility of having “many real
memories ... of the same order.” The fact that one can remember precise details (the location, the
scratches) does not necessarily indicate that the memory is true, a point that has been confirmed in
laboratory studies, too (e.g., Norman & Schacter, 1997).

Putting It All Together: Improving Your Memory

A central theme of this module has been the importance of the encoding and retrieval processes, and
their interaction. To recap: to improve learning and memory, we need to encode information in
conjunction with excellent cues that will bring back the remembered events when we need them. But
how do we do this? Keep in mind the two critical principles we have discussed: to maximize retrieval, we
should construct meaningful cues that remind us of the original experience, and those cues should
be distinctive and not associated with other memories. These two conditions are critical in maximizing
cue effectiveness (Nairne, 2002).

So, how can these principles be adapted for use in many situations? Let’s go back to how we started the
module, with Simon Reinhard’s ability to memorize huge numbers of digits. Although it was not obvious,
he applied these same general memory principles, but in a more deliberate way. In fact, all mnemonic
devices, or memory aids/tricks, rely on these fundamental principles. In a typical case, the person learns
a set of cues and then applies these cues to learn and remember information. Consider the set of 20
items below that are easy to learn and remember (Bower & Reitman, 1972).

1. is a gun. 11 is penny-one, hot dog bun.

2. is a shoe. 12 is penny-two, airplane glue.

3. is a tree. 13 is penny-three, bumble bee.

4. is a door. 14 is penny-four, grocery store.

5. is knives. 15 is penny-five, big beehive.

6. is sticks. 16 is penny-six, magic tricks.

7. is oven. 17 is penny-seven, go to heaven.

8. is plate. 18 is penny-eight, golden gate.

9. is wine. 19 is penny-nine, ball of twine.

10. is hen. 20 is penny-ten, ballpoint pen.

It would probably take you less than 10 minutes to learn this list and practice recalling it several times
(remember to use retrieval practice!). If you were to do so, you would have a set of peg words on which
you could “hang” memories. In fact, this mnemonic device is called the peg word technique. If you then
needed to remember some discrete items—say a grocery list, or points you wanted to make in a
speech—this method would let you do so in a very precise yet flexible way. Suppose you had to
remember bread, peanut butter, bananas, lettuce, and so on. The way to use the method is to form a
vivid image of what you want to remember and imagine it interacting with your peg words (as many as
you need). For example, for these items, you might imagine a large gun (the first peg word) shooting a
loaf of bread, then a jar of peanut butter inside a shoe, then large bunches of bananas hanging from a
tree, then a door slamming on a head of lettuce with leaves flying everywhere. The idea is to provide
good, distinctive cues (the weirder the better!) for the information you need to remember while you are
learning it. If you do this, then retrieving it later is relatively easy. You know your cues perfectly (one is
gun, etc.), so you simply go through your cue word list and “look” in your mind’s eye at the image stored
there (bread, in this case).

This peg word method may sound strange at first, but it works quite well, even with little training
(Roediger, 1980). One word of warning, though, is that the items to be remembered need to be
presented relatively slowly at first, until you have practice associating each with its cue word. People get
faster with time. Another interesting aspect of this technique is that it’s just as easy to recall the items in
backwards order as forwards. This is because the peg words provide direct access to the memorized
items, regardless of order.

How did Simon Reinhard remember those digits? Essentially he has a much more complex system based
on these same principles. In his case, he uses “memory palaces” (elaborate scenes with discrete places)
combined with huge sets of images for digits. For example, imagine mentally walking through the home
where you grew up and identifying as many distinct areas and objects as possible. Simon has hundreds
of such memory palaces that he uses. Next, for remembering digits, he has memorized a set of 10,000
images. Every four-digit number for him immediately brings forth a mental image. So, for example, 6187
might recall Michael Jackson. When Simon hears all the numbers coming at him, he places an image for
every four digits into locations in his memory palace. He can do this at an incredibly rapid rate, faster
than 4 digits per 4 seconds when they are flashed visually, as in the demonstration at the beginning of
the module. As noted, his record is 240 digits, recalled in exact order. Simon also holds the world record
in an event called “speed cards,” which involves memorizing the precise order of a shuffled deck of
cards. Simon was able to do this in 21.19 seconds! Again, he uses his memory palaces, and he encodes
groups of cards as single images.

Many books exist on how to improve memory using mnemonic devices, but all involve forming
distinctive encoding operations and then having an infallible set of memory cues. We should add that to
develop and use these memory systems beyond the basic peg system outlined above takes a great
amount of time and concentration. The World Memory Championships are held every year and the
records keep improving. However, for most common purposes, just keep in mind that to remember well
you need to encode information in a distinctive way and to have good cues for retrieval. You can adapt a
system that will meet most any purpose.