Cognitive Psychology and Its Implications, Ch. 7

Human Memory:

Retention and Retrieval

Popular fiction frequently has some protagonist who is unable to recall some critical

memory—either because of some head injury, repression of some traumatic

experience, or just because the passage of time has seemed to erase the memory.

The critical turning event in the story occurs when the protagonist is able to recover

the memory—perhaps because of hypnosis, clinical treatment, returning to an old

context, or (particularly improbable) being hit on the head again. Although our everyday

struggles with our memory are seldom so dramatic, we all have had experiences

with memories that are just at the edge of availability. For instance, try remembering

the name of someone who sat beside you in class in grade school or a teacher of a

class. Many of us can picture the person but will experience a real struggle with retrieving

that person’s name—a struggle at which we may or may not succeed. This chapter

will answer the following questions: • How does memory for information fade with the passage of time? • How do other memories interfere with the retrieval of a desired memory? • How can other memories support the retrieval of a desired memory? • How does a person’s internal and external context influence the recall

of a memory? • How can our past experiences influence our behavior without our being able

to recall these experiences?

•Are Memories Really Forgotten?

Figure 7.1 repeats Figure 6.1, identifying the prefrontal and temporal structures

that have proved important in studies of memory. This chapter will focus more

on the temporal (and particularly the hippocampal) contributions to memory,

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Are Memories Really Forgotten? | 177

which play a major role in retention of memory. One of the earliest studies of

the role of the temporal cortex in memory seemed to provide evidence that

forgotten memories are still there even though we cannot retrieve them. As part

of a neurosurgical procedure, Penfield (1959) electrically stimulated portions of

patients’ brains and asked them to report what they experienced (patients were

conscious during the surgery, but the stimulation technique was painless). In

this way, Penfield determined the functions of various portions of the brain.

Stimulation of the temporal lobes led to reports of memories that patients

were unable to report in normal recall, such as events from childhood. This

seemed to provide evidence that much of what seems forgotten is still stored

in memory. Unfortunately, it is hard to know whether the patients’ memory

reports were accurate because there is no way to verify whether the reported

events actually occurred. Therefore, although suggestive, the Penfield experiments

are generally discounted by memory researchers.

A better experiment, conducted by Nelson (1971), also indicates that forgotten

memories still exist. He had participants learn a list of 20 paired associates,

each consisting of a number for which the participant had to recall a

noun (e.g. 43-dog). The subjects studied the list and were tested on it until

they could recall all the items without error. Participants returned for a retest

2 weeks later and were able to recall 75% percent of the associated nouns when

cued with the numbers. However, interest focused on the 25% that they could

no longer recall—were these items really forgotten? Participants were given

new learning trials on the 20 paired associates. The paired associates they had

missed were either kept the same or changed. For example, if a participant had

learned 43-dog but failed to recall the response dog to 43, he or she might now

be trained on either 43-dog (unchanged) or 43-house (changed). Participants

were tested after studying the new list once. If the participants had lost all

memory for the forgotten pairs, there should have been no difference between

recall of changed and unchanged pairs. However, participants correctly recalled

78% of the unchanged items formerly missed, but only 43% of the changed items.

FIGURE 7.1 The brain structures

involved in the creation and

storage of memories. Prefrontal

regions are responsible for

the creation of memories. The

hippocampus and surrounding

structures in the temporal

cortex are responsible for the

permanent storage of these

memories.

Brain Structures

Prefrontal regions

active when information

is retrieved

Hippocampal regions

(internal) active during

retrieval

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This large advantage for unchanged items indicates that participants had retained

some memory of the original paired associates, even though they had been unable

to recall them initially.

Sometimes we can recognize things we cannot recall. So, Nelson (1978) also

conducted a similar test involving recognition rather than recall. Four weeks

after the initial learning phase, participants failed to recognize 31% of the

paired associates they had learned. As in the previous experiment, Nelson asked

participants to relearn the missed items. For half the stimuli, the responses were

changed; for the other half, they were left unchanged. After one relearning trial,

participants recognized 34% of the unchanged items but only 19% of the

changed items. Thus, even when participants failed this sensitive recognition

test, however, it appears that a record of the item was still in memory—the

evidence again being that relearning was better for the unchanged pairs than

for the changed ones.

These experiments do not prove that everything is remembered. They show

only that appropriately sensitive tests can find evidence for remnants of some

memories that appear to have been forgotten. In this chapter, we will discuss

first how memories become less available with time, then some of the factors

that determine our success in retrieving these memories.

Even when people appear to have forgotten memories, there is evidence that

they still have some of these memories stored.

•The Retention Function

The processes by which memories become less available are extremely regular,

and psychologists have studied their mathematical form. Wickelgren did some

of the most systematic research on memory retention functions, and his data

are still used today. In one recognition experiment (Wickelgren, 1975), he presented

participants with a sequence of words to study and then examined the

probability of their recognizing the words after delays ranging from 1 min to

14 days. Figure 7.2 shows performance as a function of delay. The performance

measure Wickelgren used is called d (pronounced d-prime), which is derived

from the probability of recognition. Wickelgren interpreted it as a measure of

memory strength.

Figure 7.2 shows that this measure of memory systematically deteriorates

with delay. However, the memory loss is negatively accelerated—that is, the rate

of change gets smaller and smaller as the delay increases. Figure 7.2b replots

the data as the logarithm of the performance measure versus the logarithm

of delay. Marvelously, the function becomes linear. The log of performance is

a linear function of the log of the delay T; that is,

where A is the value of the function at 1 min [log(1) = 0] and b is the slope

of the function in Figure 7.2b, which happens to be 0.30 in this case.

log d¿ = A - b log T

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This equation can be transformed to

where c _ 10A and is 3.62 in this case. That is, these performance measures are

power functions of delay. In a review of research on forgetting, Wixted and

Ebbesen (1991) concluded that retention functions are generally power functions.

This relationship is called the power law of forgetting. Recall from Chapter

6 that there is also a power law of learning: Practice curves are described by

power functions. Both functions are negatively accelerated, but with an important

difference. Whereas practice functions show diminishing improvement

with practice, retention functions show diminishing loss with delay.

A very dramatic example of the negative acceleration in retention function

was produced by Bahrick (1984), who looked at participants’ retention of English-

Spanish vocabulary items anywhere from immediately to 50 years after they

had completed courses in high school and college. Figure 7.3 plots the number

of items correctly recalled out of a total of 15 items as a function of the logarithm

of the time since course completion. Separate functions are plotted for

students who had one, three, or five courses. The data show a slow decay of

knowledge combined with a substantial practice effect. In Bahrick’s data, the

retention functions are nearly flat between 3 and 25 years (as would be predicted

by a power function), with some further drop-off from 25 to 49 years (which is

more rapid than would be predicted by a power function). Bahrick (personal

communication, circa 1993) suspects that this final drop-off is probably related

to physiological deterioration in old age.

There is some evidence that the explanation for these decay functions may

be found in the associated neural processes. Recall from Chapter 6 that longterm

potentiation (LTP) is an increase in neural responsiveness that occurs as a

reaction to prior electrical stimulation.We saw that LTP mirrors the power law

d¿ = cT-b

The Retention Function | 179

(a) (b)

1.0

2.0

Delay, T (days)

3.62T −0.321

Measure of retention (d ʹ)

10 15 20 1

1.0

2.0

3.0

4 7 15 30 50 1 2 4 71014

Minutes

log d ʹ

Days

log T

FIGURE 7.2 Results from Wickelgren’s experiment to discover a memory retention function.

(a) Success at word recognition, as measured by d’, as a function of delay T. (b) The data

by Memory & Cognition.)

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of learning. Figure 7.4 illustrates some data from Raymond & Redman (2006)

that shows a decrease in LTP in the rat hippocampus with delay. Plotted there

are three conditions—a control condition that received no LTP, a condition

that received just a single stimulation to induce LTP, and another condition that

received 8 such stimulations.While the level LTP is greater in the condition with

8 stimulations than 1 (a learning effect), both conditions show a drop off with

delay. The smooth lines in the figure represent the best-fitting power functions

180 | Human Memory: Retention and Retrieval

Completion

14 38

log (time+1) (months)

Five courses

Test score

69 114 175 301 415 596

Three courses

One course

FIGURE 7.3 Results from Bahrick’s experiment that measured participants’ retention over

various time periods of English-Spanish vocabulary items. The number of items correctly

recalled out of a total of 15 items is plotted as a function of the logarithm of the time

Psychological Association.)

180

1 TBS

8 TBS

No TBS

150

120

−30

Minutes

EPSC (% change)

0 30 60 90 120

FIGURE 7.4 From Raymond and Redman (2006), 1 or 8 theta-burst stimulations (TBS) are

presented at 10 minutes in the experiment. The changes in ESPC (excitatory postsynaptic

current—a measure of LTP) are plotted as a function of time. Also, a control condition is

presented that received no TBS. The two lines represent best-fitting power functions.

Anderson7e_Chapter_07.qxd 8/20/09 9:47 AM Page 180

and show that maintenance of LTP has the form of a power function. Thus, the

time course of this neural forgetting mirrors the time course of behavioral forgetting,

just as the neural learning function mirrors the behavioral learning

function. In terms of the strength concept introduced in Chapter 6, the assumption

is that the strength of the memory trace decays with time. The data

on LTP suggest that this strength decay involves changes in synaptic strength.

Thus, there may be a direct relationship between the concept of strength

defined at the behavioral level and strength defined at the neural level.

The idea that memory traces simply decay in strength with time is one of

the common explanations of forgetting; it is called the decay theory of forgetting.

We will review one of the major competitors of this theory next: the

interference theory of forgetting.

The strength of a memory trace decays as a power function of the retention

interval.

•How Interference Affects Memory

The discussion to this point might lead one to infer that the only factor affecting

loss of memories is the passage of time. However, it turns out that retention is

strongly impacted by another factor: interfering material. Much of the original

research on interference involved the learning of paired associates. The interest

focused on how the learning of one list of paired associates would affect the

memory for another list. In the typical interference experiment, two critical

groups are defined (Table 7.1). The A–D experimental group learns two lists of

paired associates, the first list designated A–B and the second designated A–D.

These lists are so designated because they share common stimuli (the A terms).

For example, among the pairs that the participants study in the A–B list might

be cat-43 and house-61, and in the A–D list cat-82 and house-37. The C–D control

group also first studies the A–B list but then studies a completely different

second list, designated C–D, which does not contain the same stimuli as the first

list. For example, in the second C–D list, participants might study bone-82 and

cup-37. After learning their respective second lists, both groups are retested for

memory of their first list, in both cases the A–B list. Often, this retention test is

administered after a considerable delay, such as 24 hours or a week. In general,

the A–D group does not do as well as the C–D group with respect

either to rate of learning of the second list or to retention of the

original A–B list (see Keppel, 1968, for a review). Such experiments

provide evidence that learning the A–D list interferes with retention

of the A–B list and causes it to be forgotten more rapidly.

More generally, research has shown that it is difficult to maintain

multiple associations to the same items. It is harder both to learn

new associations to these items and to retain the old ones if new

associations are learned. These results might seem to have rather

dismal implications for our ability to remember information. They

How Interference Affects Memory | 181

TABLE 7.1

Experimental and Control Groups Used

in a Typical Interference Experiment

A–D Experimental C–D Control

Learn A–B Learn A–B

Learn A–D Learn C–D

Test A–B Test A–B

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would appear to imply that it would become increasingly difficult to learn new

information about a concept. Every time we learned a new fact about a friend,

we would be in danger of forgetting an old fact about that person. Fortunately,

there are important additional factors that counteract such interference. Before

discussing these factors, however, we need to examine in more detail the basis for

such interference effects. It turns out that a rather different experimental paradigm

has been helpful in identifying the cause of the interference effects.

Learning additional associations to an item can cause old ones to be forgotten.

The Fan Effect: Networks of Facts

Referring back to the activation equation in Chapter 6, the interference effects

we have studied can be understood in terms of the amount of activation that

spreads to stimulate a memory structure. The basic idea is that when participants

are presented with a stimulus such as cat, activation will spread from it to

all of its associates. There is a limit, however, to the amount of activation that

can spread from a source; the more things associated with that source, the less

the activation that will spread to any particular memory structure. In one

experiment illustrating these ideas (Anderson, 1974a), I asked participants to

memorize 26 facts, of the form A person is in a location. Some persons were

paired with only one location, and some locations with only one person. Other

persons were paired with two locations, and other locations with two persons.

For instance, suppose that participants studied these sentences:

1. The doctor is in the bank. (1-1)

2. The fireman is in the park. (1-2)

3. The lawyer is in the church. (2-1)

4. The lawyer is in the park. (2-2)

Each statement is followed by two numbers, reflecting the number of facts associated

with the person and the location. For instance, sentence 3 is labeled 2-1

because its person occurs in two sentences (sentences 3 and 4) and its location

in one (sentence 3). Participants were drilled on this material until they knew it

well. Before beginning the reaction-time phase, participants were able to recall

all the locations associated with a particular person (e.g., doctor) and all the

persons associated with a particular location (e.g., park). Thus, unlike the interference

experiments reviewed earlier, all the material was memorized, and interest

focused on the speed with which it could be retrieved. After memorizing

the material, participants were presented with sentences and had to judge

whether they recognized the sentences from the study set. These studied sentences

were mixed in with new sentences created by re-pairing people and locations

from the study set. The reaction times involving sentences such as those

listed above are displayed in Table 7.2, which classifies the data as a function of

the number of facts associated with a person and a location. As can be seen,

recognition time increases as a function of both the number of facts studied

about the person and the number of facts studied about the location. The slowdown

in recall is not much more than a hundred milliseconds, but such effects

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can add up in situations like taking a time-pressure test. Taking a little more

time to answer each question can mean not finishing the test.

These interference effects can be explained by applying the concept of spreading

activation to propositional networks (described in Chapter 5). Figure 7.5

shows the network representation for sentences 1 through 4. By applying the

activation concept to this representation, we can account for the increase in

reaction time. Consider how the participant might recognize a test sentence

such as A lawyer is in the park. According to the spreading-activation theory,

recognizing this proposition involves the following discrete steps:

1. Presentation of the test sentence activates the representation of the terms

lawyer, in, and park in this network. These are the sources of activation.

2. Activation spreads from these sources along the various paths leading

from the nodes. A critical assumption is that these sources have a fixed

capacity for emitting activation; thus, the more paths there are leading

from a source, the less activation will go down any one path.

3. Activation coming down various paths converges at proposition nodes.

These activations sum to produce an overall level of activation of the

proposition node.

4. The proposition is recognized in an amount of time that is inversely

related to its level of activation.

So, given a structure like that shown in Figure 7.5,

participants should be slower to recognize a fact

involving lawyer and park than one involving doctor

and bank because more paths emanate from

the first set of concepts. That is, in the lawyer and

park case, two paths point from each of the concepts

to the two propositions in which each was

studied, whereas only one path leads from each

of the doctor and bank concepts. The increase in

reaction time related to an increase in the number

of facts associated with a concept is called the fan

effect. It is so named because the increase in reaction

time is related to an increase in the fan

How Interference Affects Memory | 183

TABLE 7.2

Results of an Experiment to Demonstrate the Fan Effect

Mean Recognition Time for Sentences (s)

Number of Sentences about a Specific Person

Number of Sentences

Using a Specific Location 1 2

1 1.11 1.17

2 1.17 1.22

Lawyer Subject Location

Doctor Bank

Park

Relation

Subject

Church Fireman

Subject Relation

Relation

Location

Location Subject

Location

FIGURE 7.5 A network

representation of four sentences

used in the experiment of

Anderson (1974a) demonstrating

how spreading activation works.

The sentences are The doctor is

in the bank; The fireman is in

the park; The lawyer is in the

church; and The lawyer is in

the park.

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of facts emanating from the network representation

of the concept.

In an fMRI brain-imaging study, Sohn et al.

(2003) looked at the response in the prefrontal

cortex during the verification of such facts. They

contrasted high-fan sentences (in which the items

appeared in many other sentences) with low-fan

sentences (in which the items appeared in few

sentences). Figure 7.6 compares the hemodynamic

response in the two conditions and shows that

there is greater response in the high-fan condition.

Note that there is a higher hemodynamic response

in the condition where there is lower activation of

the concepts. One might have expected lower concept

activation to map onto weakened hemodynamic

response. However, the prefrontal structures

must work harder to retrieve the memory in conditions of lower activation.

As we will see throughout the later chapters of this text, in which we look

at higher mental processes like problem solving, more difficult conditions are

associated with higher metabolic expenditures, reflecting the greater mental

work required in these conditions.

The more facts associated with a concept, the slower is retrieval of any one

of the facts.

The Interfering Effect of Preexisting Memories

Do such interference effects occur with material learned outside of the laboratory?

As one way to address this question, Lewis and Anderson (1976)

investigated whether the fan effect could be obtained with material the participant

knew before the experiment.We had participants learn fantasy facts about

public figures; for example, Napoleon Bonaparte was from India. Participants

studied from zero to four such fantasy facts about each public figure. After

learning these “facts,” they proceeded to a recognition test phase, in which they

saw three types of sentences: (1) statements they had studied in the experiment;

(2) true facts about the public figures (such as Napoleon Bonaparte was an

emperor); and (3) statements about the public figures that were false both in the

experimental fantasy world and in the real world. Participants had to respond

to the first two types of facts as true and to the last type as false.

Figure 7.7 presents participants’ reaction times in making these judgments as

a function of the number (or fan) of the fantasy facts studied about the person.

Note that reaction time increased with fan for all types of facts. Also note that

participants responded much faster to actual facts than to experimental facts.

The advantage of actual facts can be explained by the observation that these true

facts would be much more strongly encoded in memory than the fantasy facts.

The most important result to note in Figure 7.7 is that the more fantasy facts

participants learned about an individual such as Napoleon Bonaparte, the longer

184 | Human Memory: Retention and Retrieval

0 1

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

2 3 4

Time from stimulus onset (s)

Increase in BOLD response (%)

5 6 7 8

High fan

Low fan

FIGURE 7.6 Differential

hemodynamic response in the

prefrontal cortex during the

retrieval of low-fan and high-fan

sentences. The increase in BOLD

response is plotted against the

time from stimulus onset. (After

Sohn et al., 2003. Adapted by permission

Academy of Sciences.)

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they took to recognize a fact that they already knew about the individual; for example,

Napoleon Bonaparte was an emperor. Thus, we can produce interference

with preexperimental material. For further research on this topic, see Peterson

and Potts (1982).

Material learned in the laboratory can interfere with material learned

outside of the laboratory.

The Controversy over Interference and Decay

We have seen two mechanisms that can produce forgetting: decay of trace

strength and interference from other memories. There has been some speculation

in psychology that what appears to be decay may really reflect interference. That

is, the reason memories appear to decay over a retention interval is that they are

interfered with by additional memories that the participants have learned. This

speculation led to research that studied whether material was better retained over

an interval during which participants slept or one during which they were awake.

The reasoning was that there would be fewer interfering memories learned during

sleep. Ekstrand (1972) reviewed a great deal of research consistent with the

conclusion that less is forgotten during the period of sleep.However, it seems that

the critical variable is not sleep but rather the time of day during which material

is learned. Hockey, Davies, and Gray (1972) found that participants better remembered

material that they learned at night, even if they were kept up during

the night and slept during the day. It seems that early evening is the period of

How Interference Affects Memory | 185

Number of fantasy facts learned (fan)

Reaction time (ms)

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

1 2 3 4

False

Experimental true

Actual true

FIGURE 7.7 Results from Lewis and Anderson’s study to

investigate whether the fan effect could be obtained using

material participants knew before the experiment. The task

was to recognize true and fantasy facts about a public

figure and to reject statements that contained neither true

nor fantasy facts. Participants’ reaction times in making

these judgments are plotted as a function of the number

(or fan) of the fantasy facts studied. The time participants

took to make all three judgments increased as they learned

more fantasy facts. (After Lewis and Anderson, 1976. Adapted by

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highest arousal (at least for typical undergraduate participants) and that retention

is best for material learned in a high arousal state. See Anderson (2000) for

a review of the literature on effects of time of day.

There has been a long-standing controversy in psychology about whether

retention functions, such as those illustrated in Figures 7.2 and 7.3, reflect decay

in the absence of any interference or reflect interference from unidentified

sources. Objections have been raised to decay theories because they do not

identify the psychological factors that produce the forgetting but rather assert

that forgetting occurs spontaneously with time. It may be possible, however,

that there is no explanation of decay at the purely psychological level. The

explanation may be physiological, as we saw with respect to the LTP data (see

Figure 7.4). Thus, it seems that the best conclusion, given the available data, is

that both interference and decay effects contribute to forgetting.

Forgetting results both from decay in trace strength and from interference

from other memories.

Redundancy Protects Against Interference

There is a major restriction on the situations in which interference effects are

seen: Interference occurs only when one is learning multiple pieces of information

that have no intrinsic relationship to one another. In contrast, interference

does not occur when the information is somewhat redundant. An experiment by

Bradshaw and Anderson (1982) illustrates the contrasting effects of redundant

versus irrelevant information. These researchers looked at participants’ ability

to learn some little-known information about famous people. In the single condition,

they had participants study just one fact:

Newton became emotionally unstable and insecure as a child.

In the irrelevant condition, they had participants learn a target fact plus two

unrelated facts about the individual:

Locke was unhappy as a student at Westminster.

plus

Locke felt fruits were unwholesome for children.

Locke had a long history of back trouble.

In the relevant condition, participants learned two additional facts that were

causally related to the target fact:

Mozart made a long journey from Munich to Paris.

plus

Mozart wanted to leave Munich to avoid a romantic entanglement.

Mozart was intrigued by musical developments coming out of Paris.

Participants were tested for their ability to recall the target facts immediately

after studying them and after a week’s delay. They were presented with names

such as Newton, Mozart, and Locke and asked to recall what they had studied.

Table 7.3 displays the results. Comparing the irrelevant condition with the single

condition, we see the standard interference effect: Recall was worse when there

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were more facts to be learned about an item.

However, the conclusion is quite different when

we compare the relevant condition to the single

condition. Here, particularly at a week’s delay,

recall was better when the participant had to

learn additional facts causally related to the

target facts.

To understand why the effects of interference

are eliminated or even reversed when

there is redundancy among the materials to be

learned requires that we move on to discussing

the retrieval process and, in particular, the role

of inferential processes in retrieval.

Learning redundant material does not interfere with a target memory

and may even facilitate the target memory.

•Retrieval and Inference

Often, when people cannot remember a particular fact, they are able to retrieve

related facts and so infer the target fact on the basis of the related facts. For example,

in the case of the Mozart facts just discussed, even if the participants

could not recall that Mozart made a long journey from Munich to Paris, if they

could retrieve the other two facts, they would be able to infer this target fact.

There is considerable evidence that people make such inferences at the time of

recall. They seem unaware that they are making inferences but rather think that

they are recalling what was actually studied.

Bransford, Barclay, and Franks (1972) reported an experiment that demonstrates

how inference can lead to incorrect recall. They had participants study

one of the following sentences:

1. Three turtles rested beside a floating log, and a fish swam beneath them.

2. Three turtles rested on a floating log, and a fish swam beneath them.

Participants who had studied sentence 1 were later asked whether they had

studied this sentence:

3. Three turtles rested beside a floating log, and a fish swam beneath it.

Not many participants thought they had studied this sentence. Participants

who had studied sentence 2 were tested with

4. Three turtles rested on a floating log, and a fish swam beneath it.

The participants in this group judged that they had studied sentence 4 much

more often than participants in the other group judged that they had studied

sentence 3. Of course, sentence 4 is implied by sentence 2, whereas sentence 3 is

not implied by sentence 1. Thus, participants thought that they had actually

studied what was implied by the studied material.

Retrieval and Inference | 187

TABLE 7.3

The Contrasting Effects of Relevant and Irrelevant Information

Recall (%)

Condition Immediate Recall Recall at 1 Week

Single fact 92 62

Irrelevant facts 80 45

Relevant facts 94 73

by the Journal of Verbal Learning and Verbal Behavior.

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A study by Sulin and Dooling (1974) illustrates how inference can bias participants’

memory for a text. They asked participants to read the following passage:

Carol Harris’s Need for Professional Help

Carol Harris was a problem child from birth. She was wild, stubborn, and violent.

By the time Carol turned eight, she was still unmanageable. Her parents

were very concerned about her mental health. There was no good institution

for her problem in her state. Her parents finally decided to take some action.

They hired a private teacher for Carol.

A second group of participants read the same passage, except that the name

Helen Keller was substituted for Carol Harris.1 A week after reading the passage,

participants were given a recognition test in which they were presented with a

sentence and asked to judge whether it had occurred in the passage they read

originally. One of the critical test sentences was She was deaf, dumb, and blind.

Only 5% of participants who read the Carol Harris passage accepted this

sentence, but a full 50% of the participants who read the Helen Keller version

thought they had read the sentence. This is just what we would expect. The second

group of participants had elaborated the story with facts they knew about

Helen Keller. Thus, it seemed reasonable to them at test that this sentence had

appeared in the studied material, but in this case their inference was wrong.

We might wonder whether an inference such as She was deaf, dumb, and blind

was made while the participant was studying the passage or only at the time of

the test. This is a subtle issue, and participants certainly do not have reliable intuitions

about it. However, a couple of techniques seem to yield evidence that the

inferences are being made at test. One method is to determine whether the inferences

increase in frequency with delay.With delay, participants’ memory for the

studied passage should deteriorate, and if they are making inferences at test, they

will have to do more reconstruction, which in turn will lead to more inferential

errors. Both Dooling and Christiaansen (1977) and Spiro (1977) found evidence

for increased inferential intrusions with increased delay of testing.

Dooling and Christiaansen used another technique with the Carol Harris

passage to show that inferences were being made at test. They had the participants

study the passage and then told them a week later, just before test, that

Carol Harris really was Helen Keller. In this situation, participants also made

many inferential errors, accepting such sentences as She was deaf, dumb, and

blind. Because they did not know that Carol Harris was Helen Keller until test,

they must have made the inferences at test. Thus, it seems that participants do

make such reconstructive inferences at time of test.

In trying to remember material, people will use what they can remember

to infer what else they might have studied.

Plausible Retrieval

In the foregoing analysis, we spoke of participants as making errors when they

recalled or recognized facts that were not explicitly presented. In real life,

188 | Human Memory: Retention and Retrieval

1 Helen Keller was well known to participants of the time, famous for overcoming both deafness and blindness

as a child.

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however, such acts of recall often would not be regarded as errors but as intelligent

inferences. Reder (1982) has argued that much of recall in real life involves

plausible inference rather than exact recall. For instance, in deciding that Darth

Vader was evil in Star Wars, a person does not search memory for the specific

proposition that Darth Vader was evil, although it may have been directly

asserted in the movie. The person infers that Darth Vader was evil from memories

about the Stars Wars movies.

Reder has demonstrated that people will display very different behavior,

depending on whether they are asked to engage in exact retrieval or plausible

retrieval. She had participants study passages such as the following:

The heir to a large hamburger chain was in trouble. He had married a lovely

young woman who had seemed to love him. Now he worried that she had

been after his money after all. He sensed that she was not attracted to him.

Perhaps he consumed too much beer and French fries. No, he couldn’t give up

the fries. Not only were they delicious, he got them for free.

Then she had participants judge sentences such as

1. The heir married a lovely young woman who had seemed to love him.

2. The heir got his French fries from his family’s hamburger chain.

3. The heir was very careful to eat only healthy food.

The first sentence was studied; the second was not studied, but is plausible; and

the third was neither studied nor plausible. Participants in the exact condition

were asked to make exact recognition judgments, in which case they were to

accept the first sentence and reject the second two. Participants in the plausible

condition were to judge whether the sentence

was plausible given the story, in which case they

were to accept the first two and reject the last.

Reder tested participants immediately after

studying the story, 20 min later, or 2 days later.

Reder was interested in judgment time for

participants in the two conditions, exact versus

plausible. Figure 7.8 shows the results from her

experiment, plotted as the average judgment

times for the exact condition and the plausible

condition as a function of delay. As might be

expected, participants’ response times increased

with delay in the exact condition. However, the

response times actually decreased in the plausible

condition. They started out slower in the

plausible condition than in the exact condition,

but this trend was reversed after 2 days. Reder

argues that participants respond more slowly in

the exact condition because the exact traces are

getting weaker. A plausibility judgment, however,

does not depend on any particular trace

and so is not similarly vulnerable to forgetting.

Retrieval and Inference | 189

none 20 min

Reaction time (s)

Delay

2.40

2.60

3.00

2.80

3.20

2 days

Exact recall

Plausible retrieval

FIGURE 7.8 Results from Reder’s experiment showing that people

display different behavior depending on whether they are asked to

engage in exact retrieval or plausible retrieval of information. The

time required to make exact versus plausible recognition judgments

of sentences is plotted as a function of delay since study of a story.

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Participants respond faster in the plausible condition with delay because they

no longer try to use inefficient exact retrieval. Instead they use plausibility,

which is faster.

Reder and Ross (1983) compared exact versus plausible judgments in another

study. They had participants study sentences such as

Alan bought a ticket for the 10:00 a.m. train.

Alan heard the conductor call, “All aboard.”

Alan read a newspaper on the train.

Alan arrived at Grand Central Station.

They manipulated the number of sentences that participants had to study

about a particular person such as Alan. Then they looked at the times participants

took to recognize sentences such as

1. Alan heard the conductor call, “All aboard.”

2. Alan watched the approaching train from the platform.

3. Alan sorted his clothes into colors and whites.

In the exact condition, participants had to judge whether the sentence had

been studied. So, given the foregoing material, participants would accept test

sentence 1 and reject test sentences 2 and 3. In the plausible condition, participants

had to judge whether it was plausible that Alan was involved in the activity,

given what they had studied. Thus, participants would accept sentences 1 and 2

and reject sentence 3.

In the exact condition, Reder and Ross found that participants’ response

times increased when they had studied more facts about Alan. This is basically

a replication of the fan effect discussed earlier in the chapter. In the plausible

condition, however, participants’ response times decreased when they had

learned more facts about Alan. The more facts they knew about Alan, the more

ways there were to judge a particular fact to be plausible. Thus, plausibility

judgment did not have to depend on retrieval of a particular fact.

People will often judge what plausibly might be true rather than try

to retrieve exact facts.

The Interaction of Elaboration and Inferential Reconstruction

In Chapter 6, we discussed how people tend to display better memories if they

elaborate the material being studied.We also discussed how semantic elaborations

are particularly beneficial. Such semantic elaborations should facilitate the process

of inference by providing more material from which to infer. Thus, we expect

elaborative processing to lead to both an increased recall of what was studied and

an increase in the number of inferences recalled. An experiment by Owens,

Bower, and Black (1979) confirms this prediction. Participants studied a story that

followed the principal character, a college student, through a day in her life: making

a cup of coffee in the morning, visiting a doctor, attending a lecture, shopping

for groceries, and attending a party. The following is a passage from the story:

Nancy went to see the doctor. She arrived at the office and checked in with the

receptionist. She went to see the nurse, who went through the usual procedures.

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Then Nancy stepped on the scale and the nurse recorded her weight. The doctor

entered the room and examined the results. He smiled at Nancy and said,

“Well, it seems my expectations have been confirmed.”When the examination

was finished,Nancy left the office.

Two groups of participants studied the story. The only difference between the

groups was that the theme group had read the following additional information

at the beginning:

Nancy woke up feeling sick again and she wondered if she really were pregnant.

How would she tell the professor she had been seeing? And the money

was another problem.

College students who read this additional passage characterized Nancy as an unmarried

student who is afraid she is pregnant as a result of an affair with a college

professor. Participants in the neutral condition, who had not read this opening

passage, had no reason to suspect that there was anything special about Nancy.

We would expect participants in the theme condition to make many more themerelated

elaborations of the story than participants in the neutral condition.

Participants were asked to recall the story 24 hours after studying it. Those

in the theme condition introduced a great many more inferences that had not

actually been studied. For instance, many participants reported that the doctor

told Nancy she was pregnant. Intrusions of this variety are expected if participants

reconstruct a story on the basis of their elaborations. Table 7.4 reports

some of the results from the study. As can be seen, many more inferences were

added in recall for the theme condition than for the neutral condition. A second

important observation, however, is that participants in the theme condition

also recalled more of the propositions they had actually studied. Thus,

because of the additional elaborations these participants made, they were able

to recall more of the story.

We might question whether participants really benefited from their elaborations,

because they also misrecalled many things that did not occur in the story.

However, it is wrong to characterize the intruded inferences as errors. Given the

theme information, participants were perfectly right to make inferences and

to recall them. In a nonexperimental setting, such as recalling information for

an exam, we would expect these participants to recall such inferences as easily

as material they had actually read.

Retrieval and Inference | 191

TABLE 7.4

The Interactive Effects of Elaboration and Inference

Number of Propositions Recalled

Theme Condition Neutral Condition

Studied propositions 29.2 20.3

Inferred propositions 15.2 3.7

Cognition.

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When participants elaborate on material while studying it, they tend to

recall more of what they studied and also tend to recall the inferences that

they did not study but made themselves.

Eyewitness Testimony and the False-Memory Controversy

The ability to elaborate on and make inferences from information, both while it

is being studied and when our recall is being tested, is essential to using our

memory successfully in everyday life. Inferences made while studying material

allow us to extrapolate from what we actually heard and saw to what is probably

true.When we hear that someone found out in a doctor’s visit that she was

pregnant, it is a reasonable inference that she was told so by the doctor. So such

inferences usually lead to a much more coherent and accurate understanding of

the world. There are circumstances, however, in which we need to be able to

separate what we actually saw and heard from our inferences. The difficulty of

doing so can lead to harmful false memories; the Gargoil example above is only

the tip of the iceberg.

One situation in which it is critical to separate inference from actual experience

is in eyewitness testimony. It has been shown that eyewitnesses are often

inaccurate in the testimony they give, even though jurors accord it high weight.

One reason for the low accuracy is that people confuse what they actually

observed about an incident with what they heard from other sources. Loftus

192 | Human Memory: Retention and Retrieval

this commercial, all 15 of his participants recalled that

“gargling with Gargoil Antiseptic helps prevent colds,”

although this assertion was clearly not

made in the commercial. The Federal Trade

Commission explicitly forbids advertisers

from making false claims, but does the

Listerine ad make a false claim? In a

landmark case, the courts ruled against

Warner-Lambert, makers of Listerine, for

implying false claims in this commercial.

As a corrective action the court ordered

Warner-Lambert to include in future advertisements

the disclaimer “contrary to

prior advertising, Listerine will not help

prevent colds or sore throats or lessen

their severity.” They were required to

continue this disclaimer until they had

expended an amount of money equivalent to their prior

10 years of advertisement.

Implications

How have advertisers used knowledge of cognitive psychology?

Advertisers often capitalize on our tendency to embellish

what we hear with plausible inferences. Consider the

following portion of an old Listerine

commercial:

“Wouldn’t it be great,” asks the mother, “if

you could make him cold proof? Well, you

can’t. Nothing can do that.” [Boy sneezes.]

“But there is something that you can do that

may help. Have him gargle with Listerine

Antiseptic. Listerine can’t promise to keep

him cold free, but it may help him fight off

colds. During the cold-catching season, have

him gargle twice a day with full-strength

Listerine. Watch his diet, see he gets plenty

of sleep, and there’s a good chance he’ll have

fewer colds, milder colds this year.”

A verbatim text of this commercial,

with the product name changed to “Gargoil,” was used in

an experiment conducted by Harris (1977). After hearing

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Retrieval and Inference | 193

(1975, 1996; Loftus, Miller, & Burns, 1978) showed that subsequent information

can change a person’s memory of an observed event. In one study, for

instance, Loftus asked participants who had witnessed a traffic accident about

the car’s speed when it passed a Yield sign. Although there was no Yield sign,

many participants subsequently remembered having seen one, confusing the

question they were asked with what they had actually seen. Another interesting

example involves the testimony given by John Dean about events in the Nixon

White House during the Watergate cover-up (Neisser, 1981). After Dean testified

about conversations in the Oval Office, it was discovered that Nixon had

recorded these conversations. Although Dean was substantially accurate in gist,

he confused many details, including the order in which these conversations

took place.

Another case of memory confusion that has produced a great deal of recent

notoriety concerns the controversy about the so-called false-memory

syndrome. This controversy involves cases where individuals claim to recover

memories of childhood sexual abuse that they had suppressed (Schacter,

2001).Many of these recovered memories occur in the process of therapy, and

some memory researchers have questioned whether these recovered memories

ever happened and hypothesized that they might have been created by

the strong suggestions of the therapists. For instance, one therapist said to

patients, “You know, in my experience, a lot of people who are struggling with

many of the same problems you are, have often had some kind of really

painful things happen to them as kids—maybe they were beaten or molested.

And I wonder if anything like that ever happened to you?” (Forward & Buck,

1988, p. 161). Given the evidence we have reviewed about how people will put

information together to make inferences about what they should remember,

one could wonder if the patients who heard this might remember what did

not happen.

A number of researchers have shown that it is possible to create false memories

by use of suggestive interview techniques. For instance, Loftus and Pickerall

(1995) had adult participants read four stories from their childhood written by

an older relative—three were true, but one was a false story about being lost in

the mall at age 5. After reading the story, about 25% of participants claimed to

remember the event of being lost in a mall. Ceci, Loftus, Leichtman, and Bruck

(1995) were similarly able to create false memories in 3- to 6-year-old children.

The process by which we distinguish between memory and imagination is quite

fragile, and it is easy to become confused about the source of information. Of

course, it would not be ethical to try to plant false memories about something

so traumatic as sexual abuse, and there are questions (e.g., Pope, 1996) about

whether it is possible to create false memories as awful as those involving childhood

sexual abuse.

There is an intense debate about how much credibility should be given to

recovered memories of childhood abuse. Although there is a temptation to want

to come to either the simple conclusion that all reports of recovered memories

of abuse should be believed or the conclusion that all should be discounted, it

does not appear to be so simple. There are cases of recovered memories of abuse

that seem to have strong documentation (Sivers, Schooler, and Freyd, 2002) and

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there are cases where the alleged victims of such abuse have subsequently

retracted and said they were misled in their memories (Schacter, 2001).

Serious errors of memory can occur because people fail to separate what they

actually experienced from what they inferred, imagined, or were told.

False Memories and the Brain

Recently, researchers have developed the ability to explore the neural basis of

false memories. They have used a less exotic example than getting people to

believe they had been lost in the mall. In a Deese-Roediger-McDermott

paradigm originally invented by Deese (1959) and elaborated by Roediger and

McDermott (1995), participants study lists of words. One list might contain

thread, pin, eye, sewing, sharp, point, prick, thimble, haystack, thorn, hurt, injection,

syringe, cloth, knitting; a second list might contain bed, rest, awake, tired,

dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn, drowsy. In a

later test, participants are shown a series of words and must decide whether

they have studied those words. There are three types of words:

True (e.g., sewing, awake)

False (e.g., needle, sleep)

New (e.g., door, candy)

The true items were in the lists; the false ones are strongly associated with items

in the list but were not on the list; and the new ones are unrelated to items on

the list. Participants accept most of the true items and reject most of the new

ones, but they have difficulty in rejecting the false items. In one study, Cabeza,

Rao,Wagner, Mayer, and Schacter (2001) found that 88% of the true items and

only 12% of the new items were accepted, but 80% of the false items were also

accepted—almost as many as the true items.

Cabeza et al. examined the activation patterns that these different types of

words produced in the cortex. Figure 7.9 illustrates such activation profiles in

the two hippocampal structures. In the hippocampus proper, true words and

false words produced almost identical fMRI responses, which were stronger

than the responses produced by the new words. Thus, these hemodynamic responses

appear to match up pretty well with the behavioral data where participants

cannot discriminate between true items and false items. However, in the

parahippocampal gyrus, an area just adjacent to the hippocampus, both false

and new items produced identical weak responses, whereas the true items produced

a larger hemodynamic response. The parahippocampus is more closely

connected to sensory regions of the brain, and Cabeza et al. suggested that it

retains the original sensory experience of seeing the word, whereas the hippocampus

maintains a more abstract representation and this is why true items

produce a larger hemodynamic response. Schacter (e.g., Dodson & Schacter,

2002a, 2000b) has suggested that people can be trained to pay more attention

to these distinctive sensory features and so improve their resistance to false

memories. As one application, distinctiveness training can be used to help

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elderly patients who have particular difficulty with false memories. For instance,

older adults sometimes find it hard to remember whether they have seen

something or just imagined it (Henkel, Johnson, & DeLeonardis, 1998).

The hippocampus responds to false memories with as high activation as it

responds to true memories and so fails to discriminate between what was

experienced and what was imagined.

Retrieval and Inference | 195

Hippocampus

Image number

True

False

New

(a)

Normalised MR signal

−1.5

−1.0

−0.5

0.5

1.0

2 3 4 5

True

False

New

(b)

Normalised MR signal

−1.5

−1.0

−0.5

0.5

1.0

Image number

Parahippocampal gyrus

1 2 3 4 5

FIGURE 7.9 Results from the fMRI study by Cabeza et al. of activation patterns produced

by participants’ judgments of true, false, and new items on a previously learned word list.

(a) Bilateral hippocampal regions were more activated for true and false items than for

new items, with no difference between the activations for true and false items. (b) A left

posterior parahippocampal region (the parahippocampal gyrus) was more activated for

true items than for false and new items, with no difference between the activations for

Academy of Sciences.)

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•Associative Structure and Retrieval

The spreading activation theory described in Chapter 6 implies that we can

improve our memory by providing prompts that are closely associated with a

particular memory. You may find yourself practicing this technique when you

try to remember the name of an old classmate. You may prompt your memory

with names of other classmates or memories of things you did with that

classmate. Often, the name does seem to come to mind as a result of such efforts.

An experiment by Tulving and Pearlstone (1966) provides one demonstration

of this technique. They had participants learn lists of 48 words that contained

categories such as dog, cat, horse, and cow, which form a domestic mammal

category. Participants were asked to try to recall all the words in the list. They

displayed better memory for the word lists when they were given prompts such

as mammal, which served to cue memory for members of the categories.

The Effects of Encoding Context

Among the cues that can become associated with a memory are cues from the

context in which the memory was formed. If such contextual cues could be

revived when the memory was being tested, a person would have additional

ways to reactivate the target memory. There is ample evidence that context can

greatly influence memory. This section will review some of the ways in which

this influence can occur. Context effects are often referred to as encoding effects

because the context is affecting what is encoded into the memory trace that

records the event.

Smith, Glenberg, and Bjork (1978) performed an experiment that showed

the importance of physical context. In their experiment, participants learned

two lists of paired associates on different days and in different physical settings.

On day 1, participants learned the paired associates in a windowless room in a

building near the University of Michigan campus. The experimenter was neatly

groomed, dressed in a coat and a tie, and the paired associates were shown on

slides. On day 2, participants learned the paired associates in a tiny room with

windows on the main campus. The experimenter was dressed sloppily in a flannel

shirt and jeans (it was the same experimenter, but some participants did not

recognize him) and presented the paired associates via a tape recorder. A day

later, participants were tested for their recall of half the paired associates in one

setting and half in the other setting. They could recall 59% of the list learned in

the same setting as they were tested, but only 46% of the list learned in the

other setting. Thus, it seems that recall is better if the context during test is the

same as the context during study.

Perhaps the most dramatic manipulation of context was performed by

Godden and Baddeley (1975). They had divers learn a list of 40 unrelated words

either on the shore or 20 feet under the sea. The divers were then asked to recall

the list either in the same environment or in the other environment. Figure 7.10

displays the results of this study. Participants clearly showed superior memory

when they were asked to recall the list in the same environment in which

they studied it. So, it seems that contextual elements do get associated with

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memories and that memory is improved when

participants are provided with these contextual

elements when being tested. This result actually has

serious implications for diver instruction, because

most of the instructions are given on dry land but

must be recalled under water.

The degree to which such contextual effects are

obtained has proved to be quite variable from experiment

to experiment (Roediger & Guynn, 1996).

Fernandez and Glenberg (1985) reported a number

of failures to find any context dependence; and

Saufley, Otaka, and Bavaresco (1985) reported a

failure to find such effects in a classroom situation.

Eich (1985) argued that the magnitude of such contextual

effects depends on the degree to which the

participant integrates the context with the memories.

In his experiment, he read lists to two groups

of participants. In one condition, participants were

instructed to imagine the referents of the nouns

alone (e.g., imagine a kite in the sky); in the other,

they were asked to imagine the referents integrated

with the context (e.g., imagine a kite on the table in the corner of the room).

Eich found a much larger effect of a change of context when participants were

instructed to imagine the referent integrated with the context.

Bower, Monteiro, and Gilligan (1978) showed that emotional context can

have the same effect as physical context. They instructed participants to learn

two lists. For one list, they hypnotically induced a positive state by having participants

review a pleasant episode in their lives; for the other, they hypnotically

induced a negative state by having participants review a traumatic event. A later

recall test was given under either a positive or a negative emotional state (again

hypnotically induced). Better memory was obtained when the emotional state

at test matched the emotional state at study.2

Not all research shows such mood-dependent effects. For instance, Bower

and Mayer (1985) failed to replicate the Bower et al. (1978) result. Eich and

Metcalfe (1989) found that mood-dependent effects tend to be obtained only

when participants integrate their memories at study with the mood information.

Thus, like the effects of physical context, mood-dependent effects occur

only in special study situations.

Perhaps a more robust effect is mood congruence, the fact that it is easier to

remember happy memories when one is in a happy state and sad memories when

Associative Structure and Retrieval | 197

Dry

Learning environment

Mean number of words recalled

Wet

Wet recall environment

Dry recall environment

FIGURE 7.10 Results of a study by Godden and Baddeley to

investigate the effects of context on participants’ recall of words.

The mean number of words recalled is plotted as a function of

the environment in which learning took place. Participants recalled

word lists better in the same environment in which they were

learned. (After Godden & Baddeley, 1975. Adapted by permission of the publisher.

2 As an aside, it is worth commenting that, despite popular reports, the best evidence is that hypnosis per se

does nothing to improve memory (see Hilgard, 1968; M. Smith, 1982; Lynn, Lock, Myers, & Payne, 1997),

although it can help memory to the extent that it can be used to re-create the contextual factors at the time

of test.However,much of a learning context can also be re-created by nonhypnotic means, such as through

free association about the circumstances of the event to be remembered (e.g., Geiselman, Fisher,Mackinnon,

& Holland, 1985).

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one is in a sad state.Mood congruence is an effect of

the content of the memories rather than the emotional

state of the participant during study. For instance,

Teasdale and Russell (1983) had participants

learn a list of positive, negative, and neutral words in

a normal state. Then, at test, they induced either

positive or negative states. Their results, illustrated

in Figure 7.11, show that participants recalled more

of the words that matched their mood at test.When

a particular mood is created at test, elements of that

mood will prime memories that share these elements.

Thus, mood elements can prime both memories

whose content matches the mood, as in the

Teasdale and Russell experiment, and memories that

have such mood elements integrated as part of the

study procedure (as in Eich & Metcalfe, 1989).

A related phenomenon is state-dependent

learning. People find it easier to recall information if

they can return to the same emotional and physical

state they were in when they learned the information.

For instance, it is often casually claimed that

when heavy drinkers are sober, they are unable to

remember where they hid their alcohol when drunk, and when drunk they are

unable to remember where they hid their money when sober. In fact, some experimental

evidence does exist for this state dependency of memory with respect to

alcohol, but the more important factor seems to be that alcohol has a general debilitating

effect on the acquisition of information (Parker, Birnbaum, & Noble,

1976). Marijuana has been shown to have similar state-dependent effects. In one

experiment (Eich, Weingartner, Stillman, & Gillin, 1975), participants learned a

free-recall list after smoking either a marijuana cigarette or an ordinary cigarette.

Participants were tested 4 hours later—again after smoking either a marijuana

cigarette or a regular cigarette. Table 7.5 shows the results from this study. Two effects

were seen, both of which are typical of research on the effects of psychoactive

drugs on memory. First, there is a state-dependent effect reflected by better recall

198 | Human Memory: Retention and Retrieval

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Mood state at test

Words recalled

Elation Depression

Positive words

Neutral words

Negative words

FIGURE 7.11 Results from

Teasdale and Russell’s study of

mood congruence. The number

of words recalled from a

previously studied list is plotted

against the mood state at test.

Participants recalled more of

the words that matched their

mood at test. (From Teasdale &

Russell, 1983. Reprinted by permission

Psychological Society.)

TABLE 7.5

State-Dependent Learning: The Effects of Drugged State at Study and at Test

At Test (% correct)

Ordinary Marijuana

At Study Cigarette Cigarette Average

Ordinary cigarette 25 20 23

Marijuana cigarette 12 23 18

and Verbal Behavior.

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when the state at test matched the state at study. Second, there is an overall higher

level of recall when the material was studied in a nonintoxicated state.

People show better memory if their external context and their internal states

are the same at the time of study and the time of the test.

The Encoding-Specificity Principle

Memory for material to be learned can also depend heavily on the context of

other material to be learned in which it is embedded. Consider a recognitionmemory

experiment by D. M. Thompson (1972). Thompson’s participants

studied pairs of words such as sky blue. Participants were told that they were

responsible only for the second item of the pair—in this case blue; the first word

represented context. Later, they were tested by being presented with either blue or

sky blue. In both cases, they were asked whether they had originally seen blue. In

the single-word case, they recognized blue 76% of the time, whereas in the pair

condition their recognition rate was 85%. Thus, even though they were tested

only for blue, their memories were better in the context of the other word.

A series of experiments (e.g., Tulving & Thompson, 1973;Watkins & Tulving,

1975) has dramatically illustrated how memory for a word can depend on how

well the test context matches the original study context. There were three

phases to the experiment:

1. Original study:Watkins and Tulving had participants learn pairs of

words such as train-black and told them that they were responsible only

for the second word, referred to as the to-be-remembered word.

2. Generate and recognize: Participants were given words such as white and

asked to generate four free associates to the word. So, a participant might

generate snow, black, wool, and pure. The stimuli for the task were chosen

to have a high probability of eliciting the to-be-remembered word. For

instance, white has a high probability of eliciting black. Participants were

then told to indicate which of the four associates they generated was the

to-be-remembered word they had studied in the first phase. In cases

where the to-be-remembered word was generated, participants correctly

chose it only 54% of the time. Because participants were always forced to

indicate a choice, some of these correct choices must have been lucky

guesses. Thus, true recognition was even lower than 54%.

3. Cued recall: Participants were presented with the original context words

(e.g., train) and asked to recall the to-be-remembered words (i.e., black).

Participants recalled 61% of the words—higher than their recognition

rate without any correction for guessing.Moreover,Watkins and Tulving

found that 42% of the words recalled had not been recognized earlier

when the participants gave them as free associates.3

Recognition is usually superior to recall. Thus, we would expect that if participants

could not recognize a word, they would be unable to recall it. Usually,

Associative Structure and Retrieval | 199

3 A great deal of research has been done on this phenomenon. For a review, read Nilsson and Gardiner (1993).

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we expect to do better on a multiple-choice test than on a recall-the-answer

test. Experiments such as the one just described provided very dramatic reversals

of such standard expectations. The results can be understood in terms of

the similarity of the test context to the study context. The test context with the

word white and its associates was quite different from the context in which

black had originally been studied. In the cued-recall test context, by contrast,

participants were given the original context (train) with which they had studied

the word. Thus, if the contextual factors are sufficiently weighted in favor of

recall, as they were in these experiments, recall can be superior to recognition.

Tulving interprets these results as illustrating what he calls the encodingspecificity

principle: The probability of recalling an item at test depends on the

similarity of its encoding at test to its original encoding at study.

People show better word memory if the words are tested in the context of the

same words with which they were studied.

•The Hippocampal Formation and Amnesia

In Chapter 6, we discussed the fictional character Leonard, who suffered amnesia

resulting from hippocampal damage. A large amount of evidence points to

the great importance of the hippocampal formation, a structure embedded

within the temporal cortex, for the establishment of permanent memories.

In animal studies (typically rats or primates; for a review, see Eichenbaum &

Bunsey, 1995; Squire, 1992), it has been shown that lesions in the hippocampal

formation produce severe impairments in the ability to learn new associations,

particularly those that require remembering combinations or configurations of

elements. Damage to the hippocampal area also produces severe amnesia

(memory loss) in humans. One of the most studied amnesic patients is known

as HM.4 In 1953 when he was 27 years old, large parts of his temporal lobes

were surgically removed to cure epilepsy. He had one of the most profound

amnesias ever recorded and was studied for decades. He had normal memories

of his life up to the age of 16 but forgot most of 11 years before the surgery.

Moreover, he was almost totally unable to remember new events. He appeared

in many ways as a normal person with a clear self-identity, but his identity was

largely as the person he was when he was 16 where his memories stopped

(although he realized he is older and had learned some general facts about the

world). His surgical operation involved complete removal of the hippocampus

and surrounding structures, and this is considered the reason for his profound

memory deficits (Squire, 1992).

Only rarely is there a reason for surgically removing the hippocampal formation

from humans. However, for various reasons, humans can suffer severe

damage to this structure and the surrounding temporal lobe. One common

200 | Human Memory: Retention and Retrieval

4 Henry Gustav Molaison recently died at the age of 82. His obituary is available at http://www.nytimes

.com/2008/12/05/us/05hm.html.

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cause is a severe blow to the head, but other frequent causes include brain

infections (such as encephalitis) and chronic alcoholism, which can result in a

condition called Korsakoff syndrome. Such damage can result in two types of

amnesia: retrograde amnesia, which refers to the loss of memory for events

that occurred before the injury, and anterograde amnesia, which refers to an

inability to learn new things.

In the case of a blow to the head, the amnesia often is not permanent but

displays a particular pattern of recovery. Figure 7.12 displays the pattern of

recovery for a patient who was in a coma for 7 weeks following a closed head

injury. Tested 5 months after the injury, the patient showed total anterograde

amnesia—he could not remember what had happened since the injury. He

also displayed total retrograde amnesia for the 2 years preceding the injury and

substantial disturbance of memory beyond that. When tested 8 months after

The Hippocampal Formation and Amnesia | 201

Trauma

Coma

7 weeks

Examination

Gross disturbance

of memory back

to infancy

RA, total: 2 years AA, total:

not fixed

Trauma

Coma

7 weeks

Coma

7 weeks

Examination

RA, partial:

4 years patchy

memory

RA, total: 1 year

RA, total:

2 weeks

Memory normal Memory

precise

A few

memories

recalled

AA, total:

3 months

AA, total:

3.5 months

Examination

23 weeks

Residual permanent memory loss

(a)

(b)

(c)

FIGURE 7.12 The pattern of a patient’s recovery from amnesia caused by a closed head injury:

(a) after 5 months; (b) after 8 months; (c) after 16 months. RA _ retrograde amnesia;

W. H. Freeman.)

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the injury, the patient showed some ability to remember new experiences, and

the period of total retrograde amnesia had shrunk to 1 year. When tested

16 months after injury, the patient had full ability to remember new events

and had only a permanent 2-week period before the injury about which he

could remember nothing. It is characteristic that retrograde amnesia is for

events close in time to the injury and that events just before the injury are

never recovered. In general, anterograde and retrograde amnesia show this

pattern of occurring and recovering together, although in different patients

either the retrograde or the anterograde symptoms can be more severe.

A number of striking features characterize cases of amnesia. The first is that

anterograde amnesia can occur along with some preservation of long-term

memories. This was particularly the case for HM, who remembered many things

from his youth but was unable to learn new things. The existence of such cases

indicates that the neural structures involved in forming new memories are

distinct from those involved in maintaining old ones. It is thought that the hippocampal

formation is particularly important in creating new memories and

that old memories are maintained in the cerebral cortex. It is also thought that

events just prior to the injury are particularly susceptible to retrograde amnesia

because they still require the hippocampus for support. A second striking feature

of these amnesia cases is that the memory deficit is not complete and there

are certain kinds of memories the patient can still acquire. This feature will be

discussed in the next section on implicit and explicit memory. A third striking

feature of amnesia is that patients can remember things for short periods but

then forget them. Thus, HM would be introduced to someone and told the

person’s name, would use that name for a short time, and would then forget it

after a half minute. Thus, the problem in anterograde amnesia is retaining the

memories for more than 5 or 10 seconds.

Patients with damage to the hippocampal formation show both retrograde

amnesia and anterograde amnesia.

•Implicit versus Explicit Memory

So far, this chapter has mainly focused on memories to which people have conscious

access. However, some of the most interesting research in the field of

memory focuses on memories that we are not aware that we have. Occasionally,

we will become aware that we know things that we cannot describe. One example

that some people can relate to is memory for the keyboard of a keyboard.

Many accomplished typists cannot recall the arrangement of the keys except by

imagining themselves typing. Clearly, their fingers know where the keys are, but

they just have no conscious access to this knowledge. Such implicit memory

demonstrations highlight the significance of retrieval conditions in assessing

memory. If we asked the typists to tell us where the keys are, we would conclude

they had no knowledge of the keyboard. If we tested their typing, we would conclude

that they have perfect knowledge. This section discusses such contrasts, or

dissociations, between explicit and implicit memory. In the keyboard example

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above, explicit memory shows no knowledge, while

implicit memory shows total knowledge. Explicit

memory is the term used to describe knowledge

that we can consciously recall. Implicit memory is

the term used to describe knowledge that we cannot

consciously recall but that nonetheless manifests

itself in our improved performance on some task.

Cases of total dissociation of implicit and explicit

knowledge, such as the typing example, are

rare with normal individuals. Such cases are more

common in patients who suffer from certain amnesias.

Amnesic patients display implicit memories of

many experiences that they cannot consciously recall.

For instance, Graf, Squire, and Mandler (1984)

compared amnesic versus normal participants with

respect to their memories for a list of words such as

banana. After studying these words, participants

were asked to recall them. The results are shown in

Figure 7.13. Amnesic participants did much worse

than normal participants. Then participants were

given a word-completion task. They were shown the

first three letters of a word they had studied and

were asked to make an English word out of it.

For instance, they might be asked to complete

ban______. There is less than a 10% probability that

participants can generate the word (banana) they

studied by chance alone, but the results show that

participants in both groups were coming up with the studied word more than

50% of the time. Moreover, there was no difference between the amnesic and

normal participants in the word-completion task. So, the amnesic participants

clearly did have memory for the word list, although they could not gain conscious

access to that memory in a free-recall task. Rather, they displayed implicit

memory in the word-completion task. The patient HM had also been shown to

be capable of implicit learning. For example, he was able to improve on various

perceptual-motor tasks from one day to the next, although each day he had no

memory of the task from the previous day (Milner, 1962).

Amnesic patients often cannot consciously recall a particular event but will

show in implicit ways that they have some memory for the event.

Implicit versus Explicit Memory in Normal Participants

A great deal of research (for reviews, read Schacter, 1987; Richardson-Klavehn &

Bjork, 1988) has looked at dissociations between implicit and explicit memory in

normal individuals. It is often not possible with this population to obtain the

dramatic dissociations we see in amnesic individuals, who show no conscious

memory but normal implicit memory. It has been possible, however, to demonstrate

that certain variables have different effects on tests of explicit memory than

Implicit versus Explicit Memory | 203

Amnesic

Normal

Participants

Word completion

Words recalled (%)

Word recall

FIGURE 7.13 Results from an experiment by Graf, Squire, and

Mandler comparing the ability of amnesic patients and normal

participants to recall words studied versus the ability to complete

fragments of words studied. Amnesic participants did much worse

than normal participants on the word-recall task, but there was

no difference between the amnesic and normal participants in the

word-completion task. (From Graf, Squire, & Mandler, 1984. Reprinted by

Learning, Memory, and Cognition.)

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on tests of implicit memory. For instance, Jacoby

(1983) had participants just study a word such

as woman alone (the no-context condition),

study it in the presence of an antonym manwoman

(the context condition), or generate the

word as an antonym (the generate condition). In

this last condition, participants would see manand

have to say woman. Jacoby then tested the

participants in two ways, which were designed to

tap either explicit memory or implicit memory.

In the explicit memory test, participants were

presented with a list of words, some studied and

some not, and asked to recognize the old words.

In the implicit memory test, participants were

presented with one word from the list for a brief

period (40 ms) and asked to identify the word.

Figure 7.14 shows the results from these two

tests as a function of study condition.

Performance on the explicit memory test was

best in the condition that involved more semantic

and generative processing—consistent with earlier research we reviewed on elaborative

processing. In contrast, performance on the implicit perceptual identification

test got worse. All three conditions showed better perceptual identification

than would have been expected if the participants had not studied the word at all

(only 60% correct perceptual identification). This enhancement of perceptual

recognition is referred to as priming. Jacoby argues that participants show greatest

priming in the no-context condition because this is the study condition in which

they had to rely most on a perceptual encoding to identify the word. In the generate

condition, participants did not even have a word to read.5 Similar contrasts

have been shown in memory for pictures: Elaborative processing of a picture will

improve explicit memory for the picture but not affect perceptual processes in its

identification (e.g., Schacter, Cooper, Delaney, Peterson, and Tharan, 1991).

In another experiment, Jacoby and Witherspoon (1982) wondered whether

participants would display more priming for words they could recognize than

for words they could not. Participants first studied a set of words. Then, in one

phase of the experiment, they had to try to recognize explicitly whether or not

they had studied the words. In another phase, participants had to simply say

what word they had seen after a very brief presentation. Participants showed

better ability to identify the briefly presented words that they had studied than

words they had not studied. However, their identification success was no different

for words they had studied and could recognize than for words they had

studied but could not recognize. Thus, exposure to a word improves normal

participants’ ability to perceive that word (success of implicit memory), even

when they cannot recall having studied the word (failure of explicit memory).

204 | Human Memory: Retention and Retrieval

No context

Recognition judgment

(explicit memory)

Context

Experimental condition

Correct judgment (%)

Generate

Perceptual identification

(implicit memory)

FIGURE 7.14 Results from

Jacoby’s experiment

demonstrating that certain

variables have different effects

on tests of explicit memory

than on tests of implicit

memory. The ability to recognize

a word in a memory test versus

the ability to identify it in a

perceptual test is plotted as a

function of how the word was

originally studied. (From Jacoby,

1983. Reprinted by permission of the

Learning and Verbal Behavior.)

5 Not all research has found better implicit memory in the no-context condition.However, all research finds

an interaction between study condition and type of memory test. See Masson and MacLeod (1992) for

further discussion.

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Research comparing implicit and explicit memory suggests that the two types

of memory are realized rather differently in the brain.We have already noted that

amnesiacs with hippocampal damage show rather normal effects in studies of

priming, whereas they can show dramatic deficits in explicit memory. Research

with the drug midazolam has produced similar results in normal patients.

Midazolam is used for sedation in patients undergoing surgery. It has been noted

(Polster,McCarthy, O’Sullivan, Gray, & Park, 1993) that it produces severe anterograde

amnesia for the period of time it is in a patient’s system, although the patient

functions normally during that period. Participants given the drug just before

studying a list of words showed greatly impaired explicit memory for the words

they studied but intact priming for these words (Hirshman, Passannante, & Arndt,

2001).Midazolam has its effect on the neurotransmitters that are found throughout

the brain but which are particularly abundant in the hippocampus and prefrontal

cortex. The explicit memory deficits it produces are consistent with the association

of the hippocampus and the prefrontal cortex with explicit memory. Its lack of

implicit memory effects suggests that implicit memories are stored elsewhere.

Neuroimaging studies suggest that implicit memories are stored in the cortex.

As we have discussed, there is increased hippocampal activity when memories

are explicitly retrieved (Schacter & Badgaiyan, 2001). During priming, in

contrast, there is often decreased activity in cortical regions. For instance, in one

fMRI study (Koutstaal et al., 2001), priming produced decreased activation in visual

areas responsible for the recognition of pictures. The decreased activation

that we see with priming reflects the fact that it is easier to recognize the primed

items. It is as if their representation has been strengthened in the cortex.

A general interpretation of these results would seem to be that new explicit

memories are formed in the hippocampus; but with experience, this information

is transferred to the cortex. That is why hippocampal damage does not

eliminate old memories formed before the damage. The permanent knowledge

deposited in the cortex includes such information as word spelling and what

things look like. These cortical memories are strengthened when they are

primed and become more available in a later retest.

New explicit memories are built in hippocampal regions, but old knowledge

can be implicitly primed in cortical structures.

Procedural Memory

Implicit memory is defined as memory without conscious awareness. By this

definition, rather different things can be considered implicit memories. Sometimes,

implicit memories involve perceptual information relevant to recognizing

the words. These memories result in the priming effects we saw in experiments

such as Jacoby’s. In other cases, implicit memories involve knowledge about

how to perform tasks. A classic example of such an implicit memory involves

procedural knowledge, such as riding a bike. Most of us have learned to ride a

bike but have no conscious ability to say what it is we have learned.Memory for

such procedural knowledge is spared in amnesic individuals.

An experiment by Berry and Broadbent (1984) involved a procedural learning

task with a more cognitive character than riding a bike. They asked participants

Implicit versus Explicit Memory | 205

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to try to control the output of a hypothetical sugar factory

(which was simulated by a computer program) by manipulating

the size of the workforce. Participants would see the month’s

sugar output of the factory in thousands of tons (e.g., 6,000 tons)

and then have to choose the next month’s workforce in hundreds

of workers (e.g., 700). They would then see the next month’s

output of sugar (e.g., 8,000 tons) and have to pick the workforce

for the following month. Table 7.6 shows a series of interactions

with the hypothetical sugar factory. The goal was to keep sugar

production within the range of 8,000 to 10,000 tons.

One can try to infer the rule relating sugar output to labor

force in Table 7.6; it is not particularly obvious. The sugar output

in thousands of tons (S) was related to the workforce input in

hundreds (W), and the previous month’s sugar output in thousands

of tons (S1), by the following formula: S _ 2 _W_ S1.

(In addition, a random fluctuation of 1,000 tons of sugar is

sometimes added, and S and W stay within the bounds of 1

to 12.) Oxford undergraduates were given 60 trials at trying to

control the factory. Over those 60 trials, they got quite good at

controlling the output of the sugar factory. However, they were

unable to state what the rule was and claimed they made their

responses on the basis of “some sort of intuition” or because it “felt right.”

Thus, participants were able to acquire implicit knowledge of how to operate

such a factory without acquiring corresponding explicit knowledge. Amnesic

participants have also been shown to be capable of learning this information

(Phelps, 1989).

In recent years, sequence learning (Curran, 1995) has become a major

model for study of the nature of procedural memory, including its realization

in the brain. There are a number of sequence-learning models, but in the basic

procedure, a participant observes a sequence of lights flash and must press corresponding

buttons. For instance, there may be four lights with a button under

each, and the task is to press the buttons in the same order as the lights flash.

The typical manipulation is to introduce a repeating sequence of lights and

contrast how much faster participants can press the keys in this sequence than

when the lights are random. For instance, in the original Nissen and Bullemer

(1987) study, the repeating sequence might be 4-2-3-1-3-2-4-3-2-1. People are

faster at the repeated sequence. There has been much interest in whether participants

are aware that there is a repeating sequence. In some experiments, they

are aware of the repetition; but in many others, they are not. They tend not to

notice the repeating sequence when the experimental pace is fast or when they

are performing some other secondary task. Participants are faster at the repeated

sequence whether they are aware of it or not.

It does not appear that the hippocampus is critical to developing proficiency

in the repeated sequence, because amnesiacs show an advantage for the repeated

sequence, as do normal patients with pharmacologically induced amnesia. On

the other hand, a set of subcortical structures, collectively called the basal ganglia

(see Figure 1.8), does appear to be critical for sequence learning. It had long

206 | Human Memory: Retention and Retrieval

TABLE 7.6

Procedural Memory: An Illustrative Series of

Inputs and Outputs for a Hypothetical Sugar

Factory

Workforce Input Sugar Output (tons)

(W) (S)

700 8,000

900 10,000

800 7,000

1,000 12,000

900 6,000

1,000 13,000

1,000 8,000

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been known that the basal ganglia are critical to motor control, because it is

damage to these structures that produces the deficits associated with Huntington’s

and Parkinson’s diseases, which are characterized by uncontrolled movements.

However, there are rich connections between the basal ganglia and the

prefrontal cortex, and it is now known that the basal ganglia are important in

cognitive functions. They have been shown to be active during the learning of a

number of skills, including sequence learning (Middleton & Strick, 1994). One

advantage of sequence learning is that it is a cognitive skill one can teach to nonhuman

primates and so perform detailed studies of its neural basis. Such primate

studies have shown that the basal ganglia are critical to early learning of a

sequence. For instance, Miyachi, Hikosaka, Miyashita, Karadi, and Rand (1997)

were able to retard early sequential learning in monkeys by injecting their basal

ganglia with a chemical that temporally inactivated it. Other neural structures

appear to be involved in sequence learning as well. For instance, similar chemical

inactivation of structures in the cerebellum retards later learning of a sequence.

All in all, the evidence is pretty compelling that procedural learning involves

structures different from those involved in explicit learning.

Procedural learning is another type of implicit learning and is supported

by the basal ganglia.

•Conclusions: The Many Varieties of Memory

in the Brain

Squire (1987) proposed that there are many different varieties of memory.

Figure 7.15 reproduces his classification. The major distinction is between

explicit and implicit memory, which he calls declarative memory and nondeclarative

memory. Declarative memory basically refers to factual memories we

can explicitly recall. It appears that the hippocampus is particularly important

Conclusions: The Many Varieties of Memory in the Brain | 207

Memory

Semantic

(facts )

Episodic

(events)

Procedural skills

(e.g., motor,

perceptual,

cognitive )

Priming

( perceptual,

semantic )

Conditioning Nonassociative

(habituation,

sensitization )

Declarative Nondeclarative

FIGURE 7.15 The varieties of memory proposed by Squire. (From Squire, 1987. Reprinted by permission

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for the establishment of declarative memories. Within the declarative memory

system, there is a distinction between episodic and semantic memory. Episodic

memories include information about where and when they were learned. For

example, a memory of a particular newscast can be considered an episodic

memory. This chapter and the previous Chapter 6 have discussed these kinds of

memories. Semantic memories, discussed in Chapter 5, reflect general knowledge

of the world, such as what a dog is or what a restaurant is.

Figure 7.15 makes it clear that there are many kinds of nondeclarative, or

implicit, memory.We have just completed a discussion of procedural memories

and the critical role of the basal ganglia and cerebellum in their formation.We

also talked about priming and the fact that priming seems to entail changes to

cortical regions directly responsible for processing the information involved.

There are other kinds of learning that we have not discussed but that are particularly

important in studies of animal learning. These include conditioning,

habituation, and sensitization, all of which have been demonstrated in species

ranging from sea slugs to humans. Evidence suggests that such conditioning in

mammals involves many different brain structures (Anderson, 2000). Many

different brain structures are involved in learning, and these different brain

structures support different kinds of learning.

208 | Human Memory: Retention and Retrieval

1. One of the exceptions to the decay of memories with time

is the “reminiscence bump” (Berntsen & Rubin, 2002)—

people show better memory for events that occurred in

their late teens and early 20s than for memories earlier

or later.What might be the explanation of this effect?

2. The story is told about David Starr Jordan, an ichthyologist

(someone who studies fish), who was the first

president of Stanford University. He tried to remember

the names of all the students but found that whenever

he learned the name of a student, he forgot the name

of a fish. Does this seem a plausible example of interference

in memory?

3. Do the false memories created in the Deese-Roediger-

McDermott paradigm reflect the same sort of underlying

processes as false memories of childhood

events?

4. It is sometimes recommended that students study for

an exam in the same room that they will be tested in.

According to the study of Eich (1985; see discussion on

p. 197), how would one have to study to make this an

effective procedure? Would this be a reasonable way

to study for an exam?

5. Squire’s classification in Figure 7.15 would seem to

imply that implicit and explicit memories involve different

memory systems and brain structures—one called

declarative and the other, nondeclarative. However,

Reder, Park, and Keiffaber (2009) argue that the same

memory system and brain structures sometimes display

memories that we are consciously aware of and others of

which we are not.How could one determine whether

implicit and explicit memory correspond to different

memory systems?

Questions for Thought

Key Terms

amnesia

anterograde amnesia

decay theory

declarative memory

Deese-Roediger-

McDermott paradigm

dissociations

encoding-specificity

principle

explicit memory

fan effect

false-memory syndrome

implicit memory

interference theory

Korsakoff syndrome

mood congruence

power law of forgetting

priming

procedural knowledge

retrograde amnesia

state-dependent learning