Introduction to Long-Term Memory
Distinctions Between LTM and STM
Demonstration: Serial Position
Demonstration: Reading a Passage
Types of Long-Term Memory
Declarative Memory
Episodic and Semantic Memory
The Separation of Episodic and Semantic Memories
Connections Between Episodic and Semantic Memories
Implicit Memory
Repetition Priming
Method: Repetition Priming
Method: Recognition and Recall
Procedural Memory
An Example of Implicit Memory in Everyday Experience
How Does Information Become Stored
in Long-Term Memory?
Maintenance Rehearsal and Elaborative Rehearsal
Levels-of-Processing Theory
Demonstration: Remembering Lists
Method: Varying Depth of Processing
Transfer-Appropriate Processing
Additional Factors That Aid Encoding
Demonstration: Reading a List
Test Yourself 6.1
How Are Memories Stored in the Brain?
Information Storage at the Synapse
Forming Memories in the Brain: The Fragility
of New Memories
Forming Memories in the Brain: The Process
of Consolidation
Memory for Emotional Stimuli
How Do We Retrieve Information
From Long-Term Memory?
Retrieval Cues
Method: Cued Recall
Encoding Specificity
State-Dependent Learning
176
What Memory Research Tells Us About Studying
Elaborate and Generate
Organize
Associate
Take Breaks
Match Learning and Testing Conditions
Something to Consider: Are Memories Ever
“Permanent”?
Method: Fear Conditioning
Test Yourself 6.2
Chapter Summary
Think About It
If You Want to Know More
Key Terms
CogLab: Serial Position; Implicit Learning; Levels of
Processing; Encoding Specificity; Suffix Effect; Von
Restorff Effect
6
Long-Term Memory:
Basic Principles
Some Questions We Will Consider
What is the best way to store information in
long-term memory? (196)
How is it possible that a lifetime of experiences
and accumulated knowledge can be
stored in neurons? (207)
What are some techniques we can use to help
us get information out of long-term memory
when we need it? (215)
•
•
•
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177Long-Term Memory: Basic Principles
Jimmy G. had been admitted to the Home for the Aged, accompanied by a transfer
note that described him as “helpless, demented, confused, and disoriented.” As neurologist
Oliver Sacks talked with Jimmy about events of his childhood, his experiences
in school, and his days in the Navy, Sacks noticed that Jimmy was talking as if he were
still in the Navy, even though he had been discharged 10 years earlier. Sacks (1985) recounts
the rest of his conversation with Jimmy as follows:
“What year is this, Mr. G?” I asked, concealing my perplexity under a casual
manner.
“Forty-five, man. What do you mean?” He went on, “We’ve won the war, FDR’s
dead, Truman’s at the helm. There are great times ahead.”
“And you, Jimmy, how old would you be?” Oddly, uncertainly, he hesitated a moment,
as if engaged in calculation. “Why, I guess I’m nineteen, Doc. I’ll be twenty
next birthday.” Looking at the gray-haired man before me, I had an impulse for which
I have never forgiven myself—it was, or would have been, the height of cruelty had
there been any possibility of Jimmy’s remembering it.
“Here,” I said, and thrust a mirror toward him. “Look in the mirror and tell me
what you see. Is that a nineteen-year-old looking out from the mirror?”
He suddenly turned ashen and gripped the sides of the chair. “Jesus Christ,” he
whispered. “Christ, what’s going on? What’s happened to me? Is this a nightmare?
Am I crazy? Is this a joke?”—and he became frantic, panicky.
“It’s okay, Jim,” I said soothingly. “It’s just a mistake. Nothing to worry about.
Hey!” I took him to the window. “Isn’t this a lovely spring day. See the kids there
playing baseball?” He regained his color and started to smile, and I stole away, taking
the hateful mirror with me.
Two minutes later I reentered the room. Jimmy was still standing by the window,
gazing with pleasure at the kids playing baseball below. He wheeled around as I
opened the door, and his face assumed a cheery expression.
“Hiya, Doc!” he said. “Nice morning! You want to talk to me—do I take this
chair here?” There was no sign of recognition on his frank, open face.
“Haven’t we met before, Mr. G?” I said casually.
“No, I can’t say we have. Quite a beard you got there. I wouldn’t forget you, Doc!”
. . .
“You remember telling me about your childhood, growing up in Pennsylvania,
working as a radio operator in a submarine? And how your brother is engaged to a
girl from California?”
“Hey, you’re right. But I didn’t tell you that. I never met you before in my life.
You must have read all about me in my chart.”
“Okay,” I said. “I’ll tell you a story. A man went to his doctor complaining of
memory lapses. The doctor asked him some routine questions, and then said, ‘These
lapses. What about them?’ ‘What lapses?’ the patient replied.”
“So that’s my problem,” Jimmy laughed. “I kinda thought it was. I do find myself
forgetting things, once in a while things that have just happened. The past is clear,
though.” (Sacks, 1985, p. 14)
Jimmy G. suffers from Korsakoff’s syndrome, a condition caused by a prolonged
deficiency of vitamin B1, usually as a result of chronic alcoholism. The deficiency leads
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178 Chapter 6
to the destruction of areas in the frontal and temporal lobes, which causes severe impairments
in memory. The damage to Jimmy G.’s memory makes it impossible for him
to assimilate or retain new knowledge. He cannot recognize people he has just met, follow
a story in a book, find his way to the corner drugstore, or solve problems that take
more than a few moments to figure out. Jimmy’s problem is similar to Clive Wearing’s,
from Chapter 5. He is unable to form new long-term memories, and his reality therefore
consists of some memories from long ago plus what has happened within the last 30–
60 seconds.
There are countless movies that feature a character
with memory loss. In some movies, a character
loses his or her memory for everything in their past,
including their identity, but is able to form new
memories. This is what happened to Gregory Peck’s
character in the 1945 classic Spellbound, which was
directed by Alfred Hitchcock. In other movies, the
main character has trouble forming new memories.
For example, Lenny, the fictional character played
by Guy Pearce in Memento (2000), had a problem
like Clive Wearing’s and Jimmy G’s, but it was
apparently not as severe, because he was able to
function in the outside world, although with some
difficulty. To compensate for his inability
to form new memories, Lenny
recorded his experiences with a Polaroid
camera and had key facts tattooed onto
his body (Figure 6.1). Although Lenny’s
problem was identified in the movie as
a loss of short-term memory, his shortterm
memory was fine, because he could
remember what had just happened to him.
His problem was that he couldn’t form
new long-term memories.
In 50 First Dates, Drew Barrymore
plays a woman who has a memory problem
that occurs only in the movies—she
remembers what is happening to her on a
given day, but when she wakes up the next
morning she can’t remember anything
that happened on that day. The fact that
her memory “resets” every morning seems
not to bother Adam Sandler, who falls
in love with her, either in spite of or because of her
memory problems.
The following are some other movies in
which memory loss plays a crucial role: Anastasia
(1956; Ingrid Bergman); Dead Again (1991; Emma
Thompson); Goundhog Day (1993; Bill Murray); The
Long Kiss Goodnight (1996; Geena Davis); Who Am
I? (1998; Jackie Chan); The Bourne Identity (2002;
Matt Damon); Paycheck (2003; Ben Affleck); Eternal
Sunshine of the Spotless Mind (2004; Jim Carrey/Kate
Winslet). (See Think About It on page 231 for more
on memory loss in the movies.)
Memory Loss in the Movies
©CORBISSYGMA
■ Figure 6.1 Guy Pearce’s character, Lenny, from the film Memento.
To deal with his memory problem, he had key facts he wanted to
remember tattooed on his body.
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179Long-Term Memory: Basic Principles
The severe disabilities suffered by Jimmy G. and Clive Wearing illustrate the importance
of being able to retain information about what has happened in the past. The
purpose of this chapter is to begin looking at how long-term memory operates. We will
do this by following the plan shown in Figure 6.2. First we introduce LTM by looking
at how it interacts with STM/working memory, and how it differs from STM. We then
describe the types of LTM, how information becomes stored in LTM, and the physiological
mechanisms responsible for this storage. Finally, we will describe some of the
factors involved in retrieving information from LTM. The principles introduced in this
chapter lay the groundwork for the next chapter, in which we will continue our discussion
of LTM by considering everyday applications of memory and why we make errors
of memory.
Introduction to Long-Term Memory
One way to describe LTM is as an “archive” of information about past events in our
lives and knowledge we have learned. What is particularly amazing about this storage
is how it stretches from just a few moments ago to as far back as we can remember. The
•What are some ways that information gets
into LTM?
Types of
LTM
Introduction to
LTM
Getting information
into LTM
Physiology of
LTM storage
Retrieving information
from LTM
•What are the different types of LTM?
•How does LTM interact with working memory?
•How does LTM differ from STM?
•How are memories stored in neurons and in
the brain?
•How do we get information out of LTM?
•How can we apply our knowledge of memory
to studying?
■ Figure 6.2 The
flow diagram for
this chapter.
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180 Chapter 6
large time span of LTM is illustrated in Figure 6.3, which shows what a student who has
just taken a seat in class might be remembering about events that occurred at various
times in the past.
His first recollection—that he has just sat down—would be contained in his shortterm/working
memory because it happened within the last 30 seconds. But everything
before that—from his recent memory that 5 minutes ago he was walking to class, to a
memory from 10 years earlier of the elementary school he had attended in the third
grade—is part of long-term memory.
Although all of these memories are contained in LTM, they aren’t all the same.
More-recent memories tend to be more detailed, and much of this detail and often the
specific memories themselves fade with the passage of time and as other experiences accumulate.
Thus, on October 1, 2006, this person would probably not remember the details
of what happened while walking to class on October 1, 2005, but would remember
some of the general experiences from around that time. One of the things that we will
be concerned with in this chapter and the next one is why we retain some information
and lose other information.
But simply considering LTM as an “archive” that retains information from the past
leaves out an important function of LTM. LTM works closely with working memory to
help create our ongoing experience. Consider, for example, what happens when Tony’s
friend Cindy says, “Jim and I saw the new James Bond movie last night” (Figure 6.4). As
Tony’s working memory is holding the exact wording of that statement in his mind, it
is simultaneously accessing information from long-term memory, which helps him understand
what Cindy is saying. Tony’s ability to understand the sentence depends on retrieving,
from LTM, the meanings of each of the words that make up the sentence. His
I remember
my elementary
school
I started
college
Jim and I
went to the
football game
I went
shopping for
clothes
I was
walking to
class
30 sec
ago
5 minYesterdayLast
week
One
year ago
10
years ago
LTM STM
I just
sat down.
■ Figure 6.3 Long-term memory covers a span that stretches from about 30 seconds ago to your
earliest memories. Thus, all of this student’s memories, except the memory “I just sat down,” would be
classified as long-term memories.
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181Long-Term Memory: Basic Principles
LTM also contains a great deal of additional information about movies, James Bond,
and Cindy. Although Tony might not consciously think about all of this information
(after all, he has to pay attention to the next thing that Cindy is going to tell him), it is
all there in his LTM and adds to his understanding of what he is hearing and his interpretation
of what that might mean.
LTM therefore provides both an archive that we can refer to when we want to remember
events from the past, and a wealth of background information that we are constantly
consulting as we use working memory to make contact with what is happening
at a particular moment.
Distinctions Between LTM and STM
The interplay between what is happening in the present and information from the past,
which we described in the interaction between Tony and Cindy, is based on the distinction
between STM and LTM that was the centerpiece of the modal model of memory
(see p. 138). Beginning in the 1960s, a great deal of research was conducted that was
designed to distinguish between short-term processes (called short-term memory at the
time) and long-term memory. This distinction was studied in a classic experiment by
B. B. Murdoch, Jr. (1962), which is illustrated by the following demonstration:
Jim and I saw
the new James
Bond movie.
• Jim is the guy Cindy met
three weeks ago.
• James Bond is 007.
• I saw that movie. It had some
good explosions.
• Cindy is a big James Bond fan.
• From what I know about
relationships it seems as if
they like each other.
Cindy Tony
She went to
the movie
with Jim.
STM LTM
LTM
STM
■ Figure 6.4 Tony’s STM, which is dealing with the present, and his LTM, which contains knowledge
relevant to what is happening, work together as Cindy tells him something.
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182 Chapter 6
Demonstration
Serial Position
Get someone to read the stimulus list (see end of chapter, on p. 234) to you at a rate of
about one word every 2 seconds. Right after the last word, write down all of the words you
can remember.
You can analyze your results by noting how many words you remembered from the
first five entries on the list, the middle five, and the last five. Did you remember more
words from the first or last five than from the middle? Individual results vary widely,
but when Murdoch did this experiment on a large number of participants and plotted
the percentage recall for each word versus the word’s position on the list, he obtained a
function called the serial-position curve.
Serial-Position Curve Murdoch’s serial-position curve, shown in Figure 6.5, indicates that
memory is better for words at the beginning of the list and at the end of the list. Superior
memory for stimuli presented at the beginning of a sequence is called the primacy
effect. A possible explanation of the primacy effect is that participants had time
to rehearse these words and transfer them to LTM. According to this idea, participants
begin rehearsing the first word right after it is presented, and because no other words
Serial
Position
Serial
Position
5 10 15 20
Serial position
20
40
60
80
100
Percentrecalled
Serial-position curve
Recency
effect
Primacy
effect
■ Figure 6.5 Serial-position curve (Murdoch, 1962). Notice that memory is better for words presented
at the beginning of the list (primacy effect) and at the end (recency effect). (Reprinted from “The
Serial Position Effect in Free Recall,” by B. B. Murdoch, Jr., Journal of Experimental Psychology, 64,
pp. 482–488. Copyright © 1962 with permission from the American Psychological Association.)
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183Long-Term Memory: Basic Principles
have been presented, it receives 100 percent of the person’s attention. When the second
word is presented, attention becomes spread over two words, and so on, so as additional
words are presented less rehearsal is possible for later words.
Murray Glanzer and Anita Cunitz (1966) tested the idea that rehearsal of the early
words might lead to better memory by presenting the list at a slower pace, so there was
more time between each word and participants had more time to rehearse. Just as we
would expect if the primacy effect is due to rehearsal, increasing the time between each
word increased memory for the early words (see dashed curve in Figure 6.6a). (Addi-
1 5 10 15
Serial position
Evidence that recency effect is due to STM
20
30
40
50
60
70
Percentcorrect
No delay
30-sec delay eliminates
recency effect
Evidence that primacy effect is due to LTM
1 5 10 15 20
Serial position
0
25
50
75
100
Percentcorrect
Short time
between words
Longer time
between words
allows more
rehearsal
(a)
(b)
■ Figure 6.6 Result of
Glanzer and Cunitz’s (1966)
experiment. (a) The solid curve
is the serial position curve from
Figure 6.5. The dashed curve
occurred when the words were
presented more slowly. (b) The
serial-position curve has a
normal recency effect when
the memory test is immediate
(solid line), but no recency
effect occurs if the memory
test is delayed for 30 seconds
(dashed line). (Reprinted from
Journal of Verbal Learning and
Verbal Behavior, 5, M. Glanzer
& A. R. Cunitz, “Two Storage
Mechanisms in Free Recall,”
pp. 351–360, Figures 1 & 3,
Copyright © 1966, with permission
from Elsevier.)
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184 Chapter 6
tional explanations have been proposed to explain memory for the middle words. See
Neath & Suprenant, 2003, for details.)
Superior memory for stimuli presented at the end of a sequence is called the recency
effect. One possible explanation for the better memory for words at the end of
the list is that the most recently presented words are still in STM. To test this idea,
Glanzer and Cunitz had their participants count backward for 30 seconds right after
hearing the last word of a list. This counting prevented rehearsal and allowed time for
information to be lost from STM. The result was what we would predict: The delay
caused by the counting eliminated the effect (dashed curve in Figure 6.6b). Glanzer
and Cunitz therefore concluded that the recency effect is due to storage of recently presented
items in STM (Table 6.1).
But what is the evidence that short-term/working memory and long-term memory
are separate processes? After all, there could be only one process that handles memories
for both recent events and later events. We will now see how neuropsychological
evidence has shown that STM/working memory and LTM are, in fact, two separate
processes.
Neuropsychological Evidence In Chapter 2 we introduced the technique of determining
dissociations, which is used to draw conclusions from case studies of brain-damaged
patients (see Method: Neuropsychology, p. 43). This technique has been used in memory
research to differentiate between STM and LTM by identifying people with brain
damage that has affected one of these functions while sparing the other. We will see
that studies of patients have established a double dissociation between STM and LTM.
That is, there are some patients with functioning STM who can’t form new LTMs and
other patients who have poor STM but functioning LTM. Taken together, these two
types of patients establish a double dissociation, which indicates that STM and LTM
operate independently and are served by different mechanisms.
In Chapter 5 we described Clive Wearing, the musician who lost his memory
due to viral encephalitis and who has a functioning STM but is unable to form new
Table 6.1 Primacy and Recency Effects
Effect Why Does It Occur? How Can It Be Changed?
Primacy Effect
Better memory for words at Words are rehearsed during To increase, present the list more
the beginning of the serial- presentation of the list, so slowly, so there is more time for
position curve. they get into LTM. rehearsal (see Figure 6.6a).
Recency Effect
Better memory for words at Words are still in STM. To decrease, test after waiting
the end of the serial-position 30 seconds after end of the list, so
curve. information is lost from STM (see
Figure 6.6b).
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185Long-Term Memory: Basic Principles
LTMs. Another case of functioning STM but absent LTM is the case of H.M., who
became one of the most famous cases in neuropsychology when surgeons removed his
hippocampus (see Figure 5.24) in an attempt to eliminate epileptic seizures that had not
responded to other treatments (Scoville & Milner, 1957).
The operation eliminated H.M.’s seizures, but unfortunately also eliminated his
ability to form new LTMs. Thus, the outcome of H.M.’s case is similar to that of Clive
Wearing’s, except Clive Wearing’s brain damage was caused by disease, and H.M.’s was
caused by surgery. H.M.’s unfortunate situation occurred because in 1953 the surgeons
did not realize that the hippocampus is crucial for the formation of LTMs. Once they
realized the devastating effects of removing the hippocampus, H.M.’s operation was
never repeated. However, H.M. has been studied for over 50 years and has taught us
a great deal about memory. The property of H.M.’s memory that is important for distinguishing
between STM and LTM is the demonstration that it is possible to lose the
ability to form new LTMs while still retaining STM.
There are also people with the opposite problem: normal LTM but poor STM.
Patient K.F.’s problem with STM was indicated by her reduced digit span—the number
of digits she could remember (see p. 148; Shallice & Warrington, 1970). Whereas the
typical span is between 5 and 8 digits, K.F. had a digit span of 2 and, in addition, the
recency effect in her serial-position curve, which is associated with STM, was reduced.
Even though K.F.’s STM was greatly impaired, she had a functioning LTM, as indicated
by her ability to form and hold new memories of events in her life. (See Think
About It on page 231 for more on K.F.)
Table 6.2, which indicates which aspects of memory are impaired and which are
intact for Clive Wearing, H.M., and K.F., demonstrates that a double dissociation exists
for STM and LTM. We can conclude, therefore, that STM and LTM are caused by different
mechanisms, which can act independently.
Coding in Long-Term Memory We can also distinguish between STM and LTM by comparing
the way information is coded by the two systems. In Chapter 5 we saw that auditory,
visual, and semantic coding can occur for STM. LTM can also involve each of
these types of coding. For example, you use visual coding in LTM when you recognize
someone based on his or her appearance, auditory coding when you recognize a person
based on the sound of his or her voice, and semantic coding when you remember the
general gist or meaning of something that happened in the past.
Although some semantic coding does occur in STM, semantic coding is the predominant
type of coding in LTM. Semantic encoding is illustrated by the kinds of errors
Table 6.2 A Double Dissociation for STM and LTM
STM LTM
Clive Wearing and H.M. OK Impaired
K.F. Impaired OK
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186 Chapter 6
that people make in tasks that involve LTM. For example, remembering the word “tree”
as “bush” would indicate that the meaning of the word “tree” (rather than its visual appearance
or the sound of saying “tree”) is what was registered in LTM.
Jacqueline Sachs (1967) demonstrated the importance of meaning in LTM by having
participants listen to a tape recording of a passage like the one in the following
demonstration.
Demonstration
Reading a Passage
Read the following passage:
There is an interesting story about the telescope. In Holland, a man named Lippershey
was an eyeglass maker. One day his children were playing with some lenses. They
discovered that things seemed very close if two lenses were held about a foot apart.
Lippershey began experimenting and his “spyglass” attracted much attention. He sent
a letter about it to Galileo, the great Italian scientist. Galileo at once realized the importance
of the discovery and set about to build an instrument of his own.
Now cover up the passage and indicate which of the following sentences is identical to
a sentence in the passage and which sentences are changed.
1. He sent a letter about it to Galileo, the great Italian scientist.
2. Galileo, the great Italian scientist, sent him a letter about it.
3. A letter about it was sent to Galileo, the great Italian scientist.
4. He sent Galileo, the great Italian scientist, a letter about it.
Which sentence did you pick? Sentence 1 is the only one that is identical to one
in the passage. Many of Sachs’s participants (who heard a passage about two times
as long as the one you read) correctly identified (1) as being identical and knew that
(2) was changed. However, a number of people identified (3) and (4) as matching one
in the passage, even though the wording was different. These participants apparently
remembered the sentence’s meaning and not its exact wording. The finding that specific
wording is forgotten but the general meaning can be remembered for a long time has
been confirmed in many experiments. Semantic coding in LTM is important not only
for remembering stories, but events from the past as well.
Types of Long-Term Memory
So far, we have been discussing LTM in general. But researchers have found it useful
to distinguish between different types of LTM. The most basic division of LTM is
between declarative memory and implicit memory. Declarative memory is our conscious
recollection of events we have experienced or facts we have learned. Implicit (or nondeclarative)
memory is memory that occurs when a past experience influences behavior,
but we are not aware of the experience that is influencing the behavior (Figure 6.7).
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187Long-Term Memory: Basic Principles
LONG-TERM MEMORY
DECLARATIVE
(conscious)
Semantic
(facts,
knowledge)
Procedural
memory
Episodic
(personal
events)
IMPLICIT
(not conscious)
Repetition
priming
■ Figure 6.7 Long-term memory
can be divided into declarative
memory and implicit memory. We
can also distinguish between
two types of declarative memory,
episodic and semantic. There are a
number of different types of implicit
memory. Two of the main types are
repetition priming and procedural
memory.
Declarative Memory
Most memory researchers distinguish between two types of declarative memory. Episodic
memory is memory for personal events in our lives. For example, remembering
visiting your grandfather’s house when you were 10 is an example of episodic memory.
Semantic memory involves facts and knowledge, such as knowledge about how an automobile
engine works or the names of famous modern painters.
Episodic and Semantic Memory
When we say that episodic memory is memory for events and semantic memory is memory
for facts, we are distinguishing between these two types of memory based on the
types of information remembered. Endel Tulving (1985) has, however, suggested that
episodic and semantic memory can also be distinguished based on the type of experience
associated with each (also see Gardiner, 2001; Wheeler et al., 1997).
The defining property of the experience of episodic memory is that it involves mental
time travel. When we are having an episodic memory we are traveling back in time
to reconnect with events that happened in the past. For example, I can travel back in
my mind to 1996 to remember cresting the top of a mountain near the California coast
for the first time and seeing the Pacific Ocean far below, stretching into the distance. I
remember sitting in the car, seeing the ocean, saying “Wow!” to my wife who was sitting
next to me, and some of the emotions I was experiencing. Tulving describes this
experience of episodic memory as self-knowing or remembering, with the idea that
remembering always involves mental time travel. Note, however, that putting oneself
back in a situation through mental time travel does not guarantee that the memory is
accurate. As we will see in the next chapter, memories of events from our past do not
always correspond to what actually happened.
In contrast to the mental time travel property of episodic memory, the experience of
semantic memory involves accessing knowledge about the world that does not have to be
tied to any specific personal experience. This knowledge can be things like facts, vocabulary,
numbers, and concepts. When we experience semantic memory, we are not traveling
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188 Chapter 6
back to a specific experience in our past, but we are experiencing things we are familiar
with and know about. For example, I know many facts about the Pacific Ocean—where
it is located, that it is big, that if you travel west from San Francisco you end up in Japan.
All of these things are semantic memories. Tulving describes the experience of semantic
memory as knowing, with the idea that knowing does not involve mental time travel.
The distinctions between episodic and semantic memory are summarized in Table
6.3. We will now consider the evidence that supports the idea that episodic and semantic
memories are served by different mechanisms.
The Separation of Episodic and Semantic Memories
It is possible to classify some memories as episodic and others as semantic, but is there
any evidence to support the idea that there are two types of long-term memory that are
served by different mechanisms? Neuropsychological research on people with different
kinds of brain damage provides evidence for these differences.
Neuropsychological Evidence We first consider the case of K.C., who at the age of 30 rode
his motorcycle off a freeway exit ramp and suffered severe damage to his hippocampus
and surrounding structures (Rosenbaum et al., 2005). Because of this injury, K.C. lost
his episodic memory—he can no longer relive any of the events of his past. He can,
however, remember that certain things happened. For example, K.C. knows that his
brother died—an event that occurred 2 years before the accident. He is not, however,
aware of experiencing things such as hearing about the circumstances of his brother’s
death, where he was when he heard about it, or what happened at the funeral. K.C. also
remembers facts like where the eating utensils are located in the kitchen and the difference
between a strike and a spare in bowling. Thus, K.C. has lost the episodic part of
his memory, but his semantic memory is largely intact.
A person whose brain damage resulted in symptoms opposite to those experienced
by K.C. is an Italian woman who was in normal health until she suffered an attack of
encephalitis at the age of 44 (DeRenzi et al., 1987). The first signs of a problem were
headaches and a fever, which were later followed by hallucinations lasting for 5 days.
When she returned home after a 6-week stay in the hospital, she had difficulty recogTable
6.3 Episodic and Semantic Memory
Type of Consciousness
Memory Information Characteristics (Tulving)
Episodic Personally experienced “Mental time travel” that revisits Self-knowing
events past experiences
Semantic Facts, knowledge about Knowledge, without mental Knowing
the world time travel
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189Long-Term Memory: Basic Principles
nizing familiar people; she had trouble shopping because she
couldn’t remember the meaning of words on the shopping list
or where things were in the store; and she could no longer
recognize famous people or recall facts such as the identity of
Beethoven or the fact that Italy was involved in World War II.
All of these are semantic memories.
Despite this severe impairment of memory for semantic
information, the woman’s episodic memory for events in her
life was preserved. She could remember what she had done during the day and things
that had happened weeks or months before. Table 6.4 summarizes the two cases we
have described. These cases, taken together, demonstrate a double dissociation between
episodic and semantic memory, which supports the idea that memory for these two different
types of information probably involves different mechanisms.
Although the double dissociation shown in Table 6.4 supports the idea of separate
mechanisms for semantic and episodic memory, not all researchers agree that a double
dissociation has been demonstrated, and so research continues on how brain damage
affects LTM. (See Squire & Zola-Morgan, 1998, and Tulving & Markowitsch, 1998,
for further discussion of this evidence.) There is, however, evidence from brain imaging
experiments that retrieving episodic and semantic memories activates different areas of
the brain.
Brain Imaging Evidence Evidence for separate mechanisms has also been provided by the
results of brain imaging experiments. Brian Levine and coworkers (2004) had participants
keep diaries of audiotaped descriptions of everyday events (example: “It was
the last night of our Salsa dance class. . . . People were dancing all different styles of
Salsa. . . .”), and facts drawn from their world knowledge (“By 1947, there were 5,000
Japanese Canadians living in Toronto”).
When the participants later listened to these descriptions while in an MRI scanner,
the everyday experiences elicited retrieval of episodic memories, and the facts elicited
retrieval of semantic memories. The results were complicated, because many brain areas
were involved, but the overall conclusion of this study was that retrieving episodic and
semantic memories causes overlapping but different patterns of brain activity. Other
research comparing brain activity during episodic and semantic retrieval has also found
differences between the areas activated by episodic and semantic memory (Cabeza &
Nyberg, 2000; Duzel et al., 1999; Nyberg et al., 1996).
Connections Between Episodic and Semantic Memories
The distinctions between episodic and semantic memories have been extremely useful
for understanding memory mechanisms. But although we can distinguish between
episodic and semantic memory, we can also show that there are connections between
them.
Table 6.4 Dissociations of
Episodic and Semantic Memory
Semantic Episodic
K.C. OK Poor
Italian woman Poor OK
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190 Chapter 6
Episodic Memories Can Be Lost, Leaving Only Semantic First consider how we acquire the
knowledge that makes up our semantic memories. Sitting in the sixth grade, you learn
about how the U.S. government works. Then in the seventh grade you look back and
remember what was going on in class as you were learning about U.S. government.
Placing yourself back in the class and remembering what was happening is episodic
memory. Later, in college, you still remember the information you learned in the sixth
grade and may even know that you learned about U.S. government in the sixth grade.
However, if you have lost the episodic component of this memory and can no longer remember
the specific day you were sitting there in class, you are experiencing a semantic
memory. This example illustrates that the knowledge that makes up semantic memories
is initially attained through a personal experience that could be the basis of an episodic
memory, but that memory for this experience often fades, leaving only semantic
memory.
This kind of “morphing” from episodic to semantic memory can also occur for personal
experiences. For example, consider graduating from high school. This is an important
event in many people’s lives, and one that they may remember for many years.
It is likely that many of the readers of this book can clearly place themselves at their
high school graduation. Memory for many of the details of this event may, however,
fade over the years, until many years later, not enough of the details remain to achieve
the mental time travel required for episodic memory. Nonetheless, semantic memory
remains, if the person knows the year they graduated, the high school they graduated
from, and other facts associated with their graduation.
Semantic Memory Can Be Enhanced If Associated With Episodic Memory Semantic memories
that have personal significance, which are called personal semantic memories, are
easier to remember than semantic memories that are not personally significant. For example,
knowledge about the facts associated with your high school graduation would be
personal semantic memories because your high school graduation has personal significance
for you. Robyn Westmacott and Morris Moscovitch (2003) showed that participants
have better recall for names of public figures such as actors, singers, and politicians
whom they associated with personal experiences. For example, you would be more
likely to recall the name of a popular singer in a memory test if you had attended one of
his or her concerts than if you had just read about the singer in magazines.
Semantic Memory Can Influence Our Experience by Influencing Attention Consider this situation:
Steven and Seth are watching a football game. The quarterback takes the snap,
is rushed hard, and flips the ball over the oncoming linemen for a completion. Later,
Seth remembers the details of the play, which was a pass over the left side, but the play
doesn’t stand out for Stephen. Seth remembers the play because his semantic memory,
which contains knowledge about football, caused him to direct his attention to what
various players were doing as the play unfolded. Thus, Seth’s semantic memory helped
direct his attention, so he formed memories about specific plays, but Stephen just remembered
that there were running plays and passing plays (Figure 6.8).
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