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5Sensory Memory,
Short-Term Memory,and Working Memory
C H A P T E R
135
Some Questions We Will Consider
What Is Memory?
What Are the Purposes of Memory?
The Plan of This Chapter
Introduction to the Modal Model of Memory
What Is Sensory Memory?
The Sparklers Trail and the Projectors Shutter
Sperlings Experiment: Measuring the Visual IconHow Can We
Distinguish Between Short-Term
and Long-Term Memory?
The Serial-Position Curve
Demonstration: Remembering a List
Differences in Coding
Demonstration: Reading a Passage
Neuropsychological Evidence for Differences Between
STM and LTM Demonstration: Digit Span
Test Yourself 5.1
What Are the Properties of Short-Term Memory?
What Is the Capacity of Short-Term Memory?
What Is the Duration of Short-Term Memory?
Demonstration: Remembering Three Letters
Problems With the Modal Model
Demonstration: Reading Text and Remembering
Numbers
Working Memory: The Modern Approach to
Short-Term Memory
The Three Components of Working Memory
Operation of the Phonological Loop
Demonstration: Phonological Similarity Effect
Demonstration: Word-Length Effect
Demonstration: Repeating TheThe Visuospatial Sketch Pad
Status of Research on Working Memory
Working Memory and the Brain
The Delayed-Response Task in Monkeys
Neurons That Hold Information
Brain Imaging in Humans
Test Yourself 5.2
Think About It
Key Terms
CogLab: Apparent Movement; Partial Report; Serial Position;
Memory Span; Brown-Peterson; Phonological Similarity;
Irrelevant Speech Effect; Modality Effect; Operation
Span; Position Error; Sternberg Search; Suffix Effect
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Some Questions We Will Consider
Why can we remember a telephone number long enough to place a
call, but then we
forget it almost immediately? Is there a way to increase the
ability to remember things that have just happened?
Do we use the same memory system to remember things we have seen
and things wehave heard?
n n n
Everything in life is memory, save for the thin edge of the
present.
(Gazzaniga, 2000)
The thin edge of the present is what is happening right at this
moment, but a momentfrom now the present will become the past, and
some of the past will become stored inmemory. What you will read in
this chapter and the two that follow supports the idea
thateverything in life is memory and shows how our memory of the
past not only providesa record of a lifetime of events we have
experienced and knowledge we have learned, butcan also affect our
experience of what is happening right at this moment.
WHAT IS MEMORY?The definition of memoryprovides the first
indication of its importance in our lives:Memory is the processes
involved in retaining, retrieving, and using information about
stimuli,images, events, ideas, and skills after the original
information is no longer present.The fact thatmemory retains
information that is no longer present means that memory can serve
as aform of mental time travel, enabling us to bring back many
different things that havehappened in the past. We can use our
memory time machine to go back just a mo-mentto the words you read
at the beginning of this sentenceor many yearsto eventsas early as
a birthday party in early childhood.
What Are the Purposes of Memory?
Memory is important not only for recalling events from the
distant past, but also for deal-ing with day-to-day activities.
When I asked students in my cognitive psychology class tomake a Top
10 list of what they use memory for, they came up with over 30
differentuses, most of them related to day-to-day activities. The
top five items on their list, in-
volved remembering the following things.
1. material for exams2. their daily schedule
3. names
Chapter 5136
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Sensory Memory, Short-Term Memory, and Working Memory137
4. phone numbers5. directions to places
What would your list include? As a student, remembering material
for exams is prob-ably on your list, but it is likely that people
from different walks of life, such as businessexecutives,
construction workers, homemakers, nurses, or football players,
would createlists that would differ from the ones created by
college students in ways that reflect the de-mands of their
particular lives. Remembering the material that will be on the next
cogni-tive psychology exam might not make a football players list,
but remembering the play-book might.
One reason I ask students to create their memory list is to get
them to think about
how important memory is in their day-to-day lives. But the main
reason is to make themaware of how many important functions they
dontinclude on their lists, because they takethem for granted. A
few of these things include labeling familiar objects (you know
youare reading a book because of your past experience with books),
having conversations(you need memory to keep track of the flow of a
conversation), knowing what to do in arestaurant (you need to
remember a sequence of events, starting with being seated andending
with paying the check and leaving a tip), and finding your way to
class.
The list of things that depend on memory is an extremely long
one because just abouteverything we do depends on remembering what
we have experienced in the past. Butperhaps the most powerful way
to demonstrate the importance of memory is to consider
what happens to peoples lives when they lose their memory.
Consider, for example, thecase of Clive Wearing (Annenberg,
2000).
Wearing was a highly respected musician and choral director in
England who, in his40s, contracted viral encephalitis, which
destroyed parts of his temporal lobe that are im-portant for
forming new memories. Because of his brain damage, Wearing lives
totally
within the most recent one or two minutesof his life. He
remembers what just hap-pened and forgets everything else. Whenhe
meets someone, and the person leavesthe room and returns three
minutes later,
Wearing reacts as if he hadnt met the per-son earlier. Because
of his inability to formnew memories, he constantly feels he
has
just become conscious for the first time.This feeling is made
poignantly clear
by Wearings diary, which contains hun-dreds of entries like I
have woken up forthe first time and I am alive (Figure5.1). But
Wearing has no memory of ever
writing anything except for the sentence hehas just written.
When questioned about
Figure 5.1 Clive Wearings diary looked like this. Sometimes he
wouldcross out previous entries, because he could only remember
writing the
most recent entry.
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previous entries, Wearing acknowledges that they are in his
handwriting, but because hehas no memory for writing them, he
denies that they are his. It is no wonder that he isconfused, and
not surprising that he describes his life as being like death. His
loss of
memory has robbed him of his ability to participate in life in
any meaningful way, and heneeds to be constantly cared for by
others.
The Plan of This ChapterThe goal of this chapter is to begin
describing the basic principles of memory so we canunderstand both
cases like Clive Wearings and also the basic principles behind
normal
memory processes (Figure 5.2). We begin by describing a model of
memory that is calledthe modal model. This is an
information-processing model, which contains a number of
Chapter 5138
Working memory
and the brain
What are the stages of the modal
model?
Do STM and LTM have different
mechanisms?
What are the properties of STM?
Compare STM
and LTM mechanisms
Short-term
memory
Working
memory
The modal
model
How does working memory explain
short-term memory processes?
How does the brain hold information
in working memory?
Figure 5.2 Flow diagram for this chapter.
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stages, beginning with ones that hold information for only a
short time (sensory memoryand short-term memory) and ends with one
that can hold information for extremely longperiods of time
(long-term memory).
After introducing the modal model, we will consider evidence for
the idea that theshort-term and long-term components of the modal
model involve different mechanisms.
We then focus on the short-term component, first looking at
properties of short-termmemory and then at research that has led to
a more modern way of looking at the short-term stage of memory,
which is called working memory. Finally, we will describe
researchon where some of the mechanisms of working memory are
located in the brain. Thischapter therefore focuses mainly on the
short-term component of the memory system. In
Chapters 6 and 7 we will consider the longer-term
components.
Introduction to the Modal Model of MemoryIn 1968 Richard
Atkinson and Richard Shiffrin proposed a model of memory that
includedstages with different durations (Figure 5.3). The model has
been so influential that it iscalled the modal model of memory.The
various stages of the model are called the struc-tural features of
the model. There are three major structural features: (1) sensory
mem-
ory, an initial stage that holds information for seconds or
fractions of a second; (2) short-term memory (STM),which holds
information for only 1530 seconds; and (3) long-termmemory
(LTM),which can hold information for years or even decades.
Atkinson and Shiffrin also describe the memory system as
including controlprocesses,which are active processes that can be
controlled by the person and may differfrom one task to another. An
example of a control process is rehearsalrepeating a stim-ulus over
and over, as you might repeat a telephone number in order to hold
it in yourmind after looking it up in the phone book. Other
examples of control processes are (1)strategies you might use to
help make a stimulus more memorable, such as relating thenumbers in
a phone number to a familiar date in history, and (2) strategies of
attentionthat help you selectively focus on other information you
want to remember.
Sensory Memory, Short-Term Memory, and Working Memory139
Figure 5.3 Flow diagram for Atkinson and Shiffrins (1968) model
of memory. This model, which is described
in the text, is called the modal modelbecause of the huge
influence it has had on memory research.
InputSensorymemory
Short-termmemory
Long-termmemory
Output
Rehearsal: A control process
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To illustrate how the structural features and control processes
operate, lets considerwhat happens as Rachel looks up the number
for Mineos Pizza in the phone book (Figure5.4). When she first
looks at the book, all of the information that enters her eyes is
regis-
tered in sensory memory (Figure 5.4a). But Rachel focuses on the
number for Mineosusing the control process of selective attention,
so the number enters STM (Figure 5.4b)and Rachel uses the control
process of rehearsal to keep it there (Figure 5.4c).
After Rachel has dialed the phone number, she may forget it
because it has not beentransferred into long-term memory. However,
she decides to memorize the number sonext time she wont have to
look it up in the phone book. The process she uses to memo-rize the
number, a control process we will discuss in Chapter 6, transfers
the number into
long-term memory, where it is stored (Figure 5.4d). A few days
later, when Rachels urgefor pizza returns, she remembers the
number. This process of remembering informationthat is stored in
long-term memory is called retrieval because the information must
be re-trieved from LTM so it can reenter STM to be used (Figure
5.4e). Retrieval is anothercontrol process that we will describe in
Chapter 6.
One thing that becomes apparent from our example is that the
components of mem-ory do not act in isolation. Long-term memory is
essential for storing information but be-fore we can become aware
of this stored information, it must be moved into STM. STM
is where information resides as we are working with it, as
Rachel was doing when she firstlooked up the phone number and when
she later retrieved it from LTM.
We have described the broad outline of the model, but what about
the details? As wedelve deeper into the modal model, we will see
that each stage handles information dif-ferently, and that our
ability to remember depends on how these stages work together.
Webegin by describing sensory memory.
WHAT IS SENSORY MEMORY?Sensory memoryis the retention, for brief
periods of time, of the effects of sensory stim-ulation. We can
demonstrate this brief retention for the effects of visual
stimulation withtwo familiar examples: the trail left by a moving
sparkler and the experience of seeing afilm.
The Sparklers Trail and the Projectors ShutterIt is dark,
sometime around the Fourth of July, and you place a match to the
tip of asparkler. As sparks begin radiating from the hot spot at
the tip, you sweep the sparklerthrough the air, and create a trail
of light (Figure 5.5). Although it appears that this trail
iscreated by light left by the sparkler as you wave it through the
air, there is, in fact, no lightalong this trail. The lighted trail
is a creation of your mind because everywhere thesparkler goes you
retain a perception of its light for a fraction of a second. This
retention
of the perception of light in your mind is called the
persistence of vision.
Chapter 5140
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Sensory Memory, Short-Term Memory, and Working Memory141
Figure 5.4 What happens in different parts of Rachels memory as
she is (a and b) looking up the phone number,(c) calling the pizza
shop, and (d) memorizing the number.A few days later, (e) she
retrieves the number from long-
term memory to order pizza again. Darkened parts of the modal
model indicate which processes are activated foreach action that
Rachel takes.
Sensory STM LTM
All info on page
enters sensorymemory.
Sensory STM LTM
Focus on 555-5100.
It enters STM.
Sensory LTM
Rehearse the number
to keep it in STM whilemaking the phone call.
Sensory STM LTM
Storage
Store number in LTM.
Sensory STM LTM
Retrieve number from LTM.
It goes back to STM and isremembered.
(a)
(b)
(c)
(d)
(e)
STM
Remember numberto make call
Remember numberto make call again
Retrieval
Rehearsal555-5100555-5100555-5100
555-5100
Rehearsing
Memorizing
Retrieval
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Something similar happens while you are watching a film in a
darkened movie theater.You may see actions moving smoothly across
the screen, but what is actually projected isquite different. We
can appreciate what is happening on the screen by considering the
se-quence of events that occur as a film is projected. First, a
single film frame is positioned infront of the projector lens, and
when the projectors shutter opens, the image on the filmframe is
projected onto the screen. The shutter then closes, so the film can
move to thenext frame without causing a blurred image, and during
that time, the screen is dark.
When the next frame has arrived in front of the lens, the
shutter opens again, flashing thenext image onto the screen. This
process is repeated rapidly, 24 times per second, so 24still images
are flashed on the screen every second, with each image separated
by a briefperiod of darkness (see Table 5.1).
ApparentMovement
Chapter 5142
Figure 5.5 (a) A sparkler can cause a trail of light when it is
moved rapidly. (b) This trail occurs because theperception of the
light is briefly held in the mind.
Perceptual
trail
B
azukiMuhamm
ed/ReutersNewsmediaInc./
CORBIS
Table 5.1 PERSISTENCE OFVISION INFILM
What Happens? What Is on the Screen? What Do You Perceive?
Film frame 1 is projected. Picture 1 Picture 1
Shutter closes and film moves Darkness Picture 1 (persistence of
vision)to the next frame.
Shutter opens and film Picture 2 Picture 2*frame 2 is
projected.
*Note that the images appear so rapidly (24 per second) that you
dont see individual images, but see a moving image created by
the
rapid sequence of images.
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A person viewing the film sees the progression of still images
as movement anddoesnt see the dark intervals between the images
because the persistence of vision fills inthe darkness by retaining
the image of the previous frame. If the period between the im-
ages is too long, the mind cant fill in the darkness completely,
and you perceive a flicker-ing effect. This is what happened in the
early movies when the projectors flashed imagesmore slowly, causing
longer dark intervals. This is why these early films were called
flick-ers, a term that remains today, when we talk about going to
the flicks.
Sperlings Experiment: Measuring the Visual Icon
The persistence of vision effect that adds a trail to our
perception of moving sparklers andfills in the dark spaces between
frames in a film has been known since the early days ofpsychology
(Boring, 1942). This lingering of the visual stimulus in our mind
was studiedby Sperling (1960) in a famous experiment in which he
flashed an array of letters, like theone in Figure 5.6a, on the
screen for 50 milliseconds (50/1,000 sec) and asked his
partici-pants to report as many of the letters as possible. This
procedure was called the whole-report procedure because
participants were told to base their report on the whole
display.
Sperlings participants were able to report an average of only 4
or 5 of the 12 letters in
the display, but they often commented that they had seen all of
the letters at first, but theletters had faded away as they were
reporting them. What were the participants seeing be-fore the
letters faded? To answer this question, Sperling used the procedure
shown in Fig-ure 5.6b.
Sperling flashed an array of 12 letters as before, but
immediately after they were ex-tinguished he sounded a tone that
told the participant which row of letters to report. Ahigh-pitched
tone indicated that the participant should report the letters in
the top row, amedium-pitched tone signaled the middle row, and a
low-pitched tone signaled the bot-tom row. Note that since the
tones were presented afterthe letters were turned off,
theparticipants attention was directed not to the actual letters,
which were no longer pres-ent, but to whatever trace remained in
the participants mind after the letters were turnedoff. This
procedure was called the partial-report procedure because
participants wereasked to direct their attention to just part of
the display.
The results showed that no matter which row the participants
were instructed to re-port, they remembered an average of about 3.3
of the 4 letters (82 percent) in that row.
Starting with the fact that his participants were able to
remember 82 percent of he let-ters no matter which row they
reported, Sperling was able to calculate how many letterswere
available to participants from the entire 12-item display just
after the display wasturned off. Assuming that 82 percent of the
entire display was available, Sperlings cal-culation, 12 0.82 =
9.8, indicated that about 10 letters were available from the
wholedisplay.
We have already noted that Sperlings participants could report
only 4 or 5 letterswhen tested using the whole-report procedure
because as they were reporting these 4 or
5 letters, the other letters had faded. To determine the time
course of this fading, Sperling
Sensory Memory, Short-Term Memory, and Working Memory143
Partial Report
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Chapter 5144
(a) Whole report
X
A
C
M
F
D
X F
ZD
C
L
N
Z
T
B
P
X
A
C
M
F
D
L
N
Z
T
B
P
(b) Partial report
Tone immediate
Immediate tone
X
A
C
M
F
D
B
L
N
Z
T
B
P
(c) Partial reportTone delayed
DelayDelayed tone
Medium
Low
High
Medium
Low
High
X M
L T
Figure 5.6 Procedure for three of Sperlings (1960) experiments.
(a) Whole report procedure: Person saw all12 letters at once for 50
msec. and reported as many as he or she could remember. (b) Partial
report: Person
saw all 12 letters, as before, but immediately after they were
turned off, a tone indicated with row the person
was to report; (c) Partial report, delayed: Same as (b), but
with a short delay between extinguishing the letters
and presentation of the tone.
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repeated the partial-report procedure but instead of presenting
the cue tones immediatelyafter the letters were extinguished, he
delayed presentation of the tones so he could de-termine what a
person could report from each row at various times after the
display hadbeen extinguished (Figure 5.6c).
The result of the partial-report experiments showed that the
participants memorydropped rapidly, so that by 1 second after the
flash, they could report just slightly more
than 1 letter in a row, or a total of about 4 letters for all
three rowsthe same number ofletters they reported using the
whole-report technique. Figure 5.7 plots this result interms of the
number of letters available to the participants from the entire
display, whichSperling determined by multiplying the average number
of letters reported for 1 rowtimes 3.
Sperling concluded from these results that a short-lived sensory
memory registers allor most of the information that hits our visual
receptors but that this information decays
within less than a second. This brief sensory memory for visual
stimuli is called iconic
memoryor thevisual icon(icon means image), and corresponds to
the sensory memorystage of Atkinson and Shiffrins model. Other
research, using auditory stimuli, has shownthat sounds also persist
in the mind. This persistence of sound, which is called echoic
mem-ory, lasts for a few seconds after presentation of the original
stimulus (Darwin et al., 1972).
Thus, sensory memory can register huge amounts of information
(perhaps all of theinformation that reaches the receptors), but it
retains this information for only seconds orfractions of a second.
There has been some debate regarding the purpose of this large
butrapidly fading store (Haber, 1983), but many cognitive
psychologists believe that the sen-
sory store is important for (1) collecting information to be
processed; (2) holding the
Sensory Memory, Short-Term Memory, and Working Memory145
Figure 5.7 Results of Sperlings (1960) partial-report
experiments. The decrease in performance is due to therapid decay
of iconic memory (called sensory memoryin the modal model).
(Reprinted from The Serial Position
Effect in Free Recall, by B. B. Murdoch, Journal of Experimental
Psychology, 64, pp. 482488. Copyright
1962 with permission from the American Psychological
Association. )
1.00.80.60.40.20
Delay of tone (sec)
2
4
6
8
10
12
Calculatednumberof
lettersavailabletoparticip
ant
Partialreport Whole
report
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information briefly while initial processing is going on; and
(3) filling in the blanks whenstimulation is intermittent. We now
turn to the next boxes in the modal model, short-term memory, and
long-term memory.
HOW CAN WE DISTINGUISH BETWEEN SHORT-TERM AND LONG-TERM
MEMORY?Short-term memory and long-term memory are the central parts
of the modal model.
When we described what happened in Rachels memory system as she
ordered a pizza, wesaw that there is a rich interaction between STM
and LTM. However, the way they are
represented as two separate boxes in the model implies that they
are two different typesof memory with different properties.
Certainly, our everyday experience seems to indicatethat there is
one type of memory for remembering telephone numbers you have
justlooked up in the phone book and another type for remembering
the phone number a fewdays later or remembering what you did last
summer. But could there be just one type ofmemory in which some
information decays rapidly and some remains for long periods?
Although this is a possibility, there is good evidence to
support the idea that STM andLTM are two different types of memory.
We begin describing this evidence by consider-
ing a classic experiment that measured the relationship between
a words position in a listand the chances that the word will be
remembered later.
The Serial-Position CurveHow well can you remember a list of
words? The following demonstration is based on aclassic experiment
in memory research (Murdoch, 1962).
Demonstration
Remembering a List
Get someone to read the stimulus list (see end of chapter, on p.
178) to you at a rate of about one
word every two seconds. Right after the last word, write down
all of the words you can remember.
You can analyze your results by noting how many words you
remembered from thefirst five entries on the list, the middle five,
and the last five. Did you remember more
words from the first or last five than from the middle?
Individual results vary widely, butwhen Murdoch did this experiment
on a large number of participants and plotted the per-centage
recall for each word versus the words position on the list, he
obtained the serial-position curve shown in Figure 5.8, which
indicates that memory is better for words atthe beginning or end of
the list.
Chapter 5146
Serial
Position
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To understand why the words position in the list should matter
lets first consider thebetter memory for words at the end of the
list. This is called the recency effectbecausethese are the words
that were presented most recently. One possible explanation for
thebetter memory for words at the end of the list is that the most
recently presented wordsare still in STM. To test this idea, Murray
Glanzer and Anita Cunitz (1966) repeated Mur-
dochs experiment but had their participants count backwards for
30 seconds right afterhearing the last word. This counting
prevented rehearsal and allowed time for informa-tion to be lost
from STM. The result was what we would predict: The delay caused by
thecounting eliminated the effect (Figure 5.9a). Glanzer and Cunitz
therefore concluded thatthe recency effect is due to storage of
recently presented items in STM.
But what about the words at the beginningof the list? Superior
memory for stimulipresented at the beginning of a sequence is
called the primacy effect.A possible explana-tion of the primacy
effect is that these words have been transferred to LTM. One piece
ofevidence supporting this idea is that the participants in Glanzer
and Cunitzs experimentcontinued to remember these words even after
they had finished counting backwards for30 seconds.
One reason that the words presented earlier in the list could
have been transferredinto LTM is that participants had more time to
rehearse them. Glanzer and Cunitiz testedthis idea by presenting
the list at a slower pace, so there was more time between each
wordand participants had more time to rehearse. Just as we would
expect if the primacy effect
Sensory Memory, Short-Term Memory, and Working Memory147
Figure 5.8 Serial-position curve (Murdoch, 1962). Notice that
memory is better for words presented at the be-ginning of the list
(primacy effect) and at the end (recency effect).
5 10 15 20
Serial position
20
40
60
80
100
Percentrecalled
Serial-position curve
Recencyeffect
Primaryeffect
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is due to rehearsal, increasing the time between each word
increased memory for the earlywords (see dotted curve in Figure
5.9b). Table 5.2 summarizes the results of the serial po-
sition experiments we have just described.
Chapter 5148
1 5 10 15
Serial position
Evidence that recency effect is due to STM
Evidence that primacy effect is due to LTM
20
30
40
50
60
70
Percentcorrect
No delay
30-sec delay eliminates
recency effect
1 5 10 15 20
Serial position
0
25
50
75
100
Percentcorrect
Short timebetween words
Longer timebetween wordsallows morerehearsal
(b)
(a)
Figure 5.9 Result of Glanzer and Cunitzs (1966) experiment. (a)
The serial-position curve has a normal re-
cency effect when the memory test is immediate (solid line), but
no recency effect occurs if the memory test isdelayed for 30
seconds (dashed line). (b) Memory for earlier words is better when
words are presented more
slowly (solid line). (Reprinted from Journal of Verbal Learning
and Verbal Behavior, 5, M. Glanzer et al., Two
Storage Mechanisms in Free Recall, pp. 351360 (Figures 1 &
2), copyright 1966, with permission from
Elsevier.)
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Differences in CodingAnother way to distinguish between STM and
LTM is to consider the way information iscoded in STM and LTM.
Codingrefers to the way information is represented. Remember,for
example, our discussion in Chapter 2 of how a persons face can be
represented by thepattern of firing of a number of neurons.
Determining how a stimulus is represented by thefiring of neurons
is a physiological approach to coding. We can also take a mental
approachto coding by asking how a stimulus or an experience is
represented in the mind. For exam-ple, imagine that you have just
finished listening to your cognitive psychology professorgive a
lecture. We can describe different kinds of mental coding that
occur for this experi-ence by considering some of the ways you
might remember what happened in class.
Imagining what your professor looks like, perhaps by conjuring
up an image in your
mind, is an example ofvisual coding. Remembering the sound of
your professors voice isan example of auditory coding, which is
called phonological coding. Finally, remember-ing what your
professor was talking about is an example of coding in terms of
meaning,
which is called semantic coding(see Table 5.3).Research on how
information is coded in memory has demonstrated all of these
kinds
of coding for both STM and LTM, but has shown that the most
common type of codingfor short-term memory is phonological coding
and the most common type of coding inlong-term memory is semantic
coding.
Sensory Memory, Short-Term Memory, and Working Memory149
Table 5.2 PRIMACY AND RECENCYEFFECTS
Effect Why Does It Occur? How Can It Be Changed?
Recency EffectBetter memory for words at the end Words are still
in STM. To decrease, test after waiting 30
of the serial-position curve. seconds after end of the list
soinformation is lost from STM
(see Figure 5.9a).
Primacy Effect
Better memory for words at the Words are rehearsed during To
increase, present the list morebeginning of the serial-position
curve. presentation of the list so slowly so there is more time
for
they get into LTM. rehearsal (see Figure 5.9b).
Table 5.3 TYPES OFCODING
Type of Coding Example
Visual Image of a person
Phonological Sound of the persons voice
Semantic Meaning of what the person is saying
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Coding in Short-Term Memory One of the early experiments that
investigated cod-ing in STM was done by R. Conrad in 1964. In
Conrads experiment, participants saw anumber of target letters
flashed briefly on a screen, and were told to write down the
let-
ters in the order they were presented. Conrad found that when
participants made errors,they were most likely to misidentify the
target letter as another letter thatsounded like thetarget. For
example, F was most often misidentified as S or X, two letters that
soundsimilar to F. Thus, even though the participantssaw the
letters, the mistakes they made
were based on the letterssound.From these results Conrad
concluded that the code for STM is phonological (based
on thesoundof the stimulus), rather than visual (based on the
appearance of the stimulus).This conclusion fits with our common
experience with telephone numbers. Even thoughour contact with them
in the phone book is visual, we usually remember them by repeat-ing
their sound over and over rather than by visualizing what the
numbers look like in thephone book (also see Wickelgren, 1965).
Do Conrads results mean that STM is always coded phonologically?
Not necessarily.Some tasks, such as remembering the details of a
diagram or an architectural floor plan, re-quire visual codes
(Kroll, 1970; Posner & Keele, 1967; Shepard & Metzler,
1971a). This useof visual codes in STM was demonstrated in an
experiment by Guojun Zhang and Herbert
Simon (1985), who presented Chinese language symbols to
native-speaking Chinese par-ticipants. The stimuli for this
experiment were radicals and characters (Figure 5.10a).
Radicalsare symbols that are part of the Chinese language and
that are not associated withany sound. Charactersconsist of a
radical plus another symbol, and do have a sound.
When participants were asked to reproduce a series of radicals
presented one after an-other, or a series of characters, they were
able to reproduce a string of 2.7 radicals, on the
Chapter 5150
Figure 5.10 (a) Examples of radicaland character stimuli for
Zhang and Simons (1985) coding experiment.
(b) Results showing evidence for visual coding (left bar) and
phonological coding (right bar).
(a) (b)
Radicals Characters
6
4
2Num
berrecalled
0
8
Greater recall whenphonological codingpossible
Recall based onvisual coding
Radical(no sound)
Character(has sound)
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average, and a string of 6.4 characters, on average (Figure
5.10b). The participants abil-ity to remember the radicals must be
due to visualcoding, since the radicals have no soundor meaning.
The participants superior memory for the characters is most likely
due to the
addition of phonological coding, since each character is
associated with a sound.Thus, information can be coded in STM both
visually and phonologically. In addi-
tion, there is also evidence for semantic coding in STM. This is
illustrated by an experi-ment in which Delos Wickens and coworkers
(1976) had three different groups of partic-ipants (the fruit
group, the meat group, and the professions group) listen to
three
words, count backwards for 15 seconds, and then remember the
three words. They didthis for a total of four trials, with
different words presented on each trial.
Table 5.4 shows the experimental design of Wickenss experiment
for the three groupsof participants. Looking down the fruit column
indicates that the fruit group was askedto remember names of fruits
for all four trials. The meat group was asked to remembermeats for
the first three trials and then was switched to fruit on trial 4,
and the professionsgroup was asked to remember professions for the
first three trials, and then was switchedto fruit on trial 4.
The results for these three groups are indicated in Figure 5.11.
There are two impor-tant things to notice about these results.
First, participants in three all groups remembered
about 87 percent of the words on trial 1 (Figure 5.11a), and the
performance for all threegroups dropped on trials 2 and 3 (Figures
5.11b and c), so by trial 3 they remembered onlyabout 30 percent of
the words. The decrease in performance on the second and third
trialsis caused by an effect called proactive interference
(PI)information learned previouslyinterferes with learning new
information.
The effect of proactive interference is illustrated by what
might happen when a fre-quently used phone number is changed.
Consider, for example, what might happen whenRachel calls the
number 521-5100, she had memorized for Mineos Pizza, only to get
a
recording saying that the phone number has been changed to
522-4100. Although Racheltries to remember the new number, she
makes mistakes at first because proactive interfer-ence is causing
her memory for the old number to interfere with her memory for the
new
Sensory Memory, Short-Term Memory, and Working Memory151
Table 5.4 WICKENSS EXPERIMENT DEMONSTRATING SEMANTIC CODING
INSTM
Groups
Fruit Meat Profession
Trial 1 banana, peach, apple salami, pork, chicken lawyer,
firefighter, teacher
Trial 2 plum, apricot, lime bacon, hot dog, beef dancer,
minister, executive
Trial 3 melon, lemon, grape hamburger, turkey, veal accountant,
doctor, editor
Trial 4 orange, cherry, pineapple orange, cherry, pineapple
orange, cherry, pineapple
(same category) (switch category) (switch category)
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number. The fact that the new number is similar to the old one
adds to the interferenceand makes it harder to remember the new
number.
The decrease in performance on trials 2 and 3 of Wickenss
experiment was caused byproactive interference because the new
items on each trial were from the same categoryas those on the
previous trials. Participants in the fruit group heard only names
of fruitsfor the first 3 trials, those in the meat group heard only
names of meats, and those in theprofessions group heard only names
of professions. But on the fourth trial, all of thegroups heard
names of fruits. Performance remained low for the participants who
hadbeen hearing the names of fruits because proactive interference
continued for that group,but performance increased for the
professions group because shifting to fruits eliminatedthe
proactive interference that had built up on trials 13 for the names
of professions (Fig-ure 5.11d). The resulting increase in
performance is called release from proactive inter-ference, or
release from PI.
Figure 5.11d also indicates that the release from PI is not as
pronounced for theswitch from meats to fruits because meats and
fruits are more similar to each other thanare professions and
fruits. Can you relate these results to Rachels problem in
remember-ing the new number for the pizza shop? Would the switch
have been easier or harder forRachel if the new phone number had
been very different from the old one?
What does release from PI tell us about coding in STM? The key
to answering thisquestion is to realize that the release from PI
that occurs in the Wickens experiment de-pends on the words
categories (fruits, meats, professions). Because placing words into
cat-
Chapter 5152
Figure 5.11 Results of Wickens et al.s (1976) proactive
inhibition experiment. (See Table 5.4 for design).(a) Initial
performance on trial 1. (b and c) On trials 2 and 3 performance for
all groups (professions, mean,
and fruit) drops due to proactive interference. (d) On trial 4,
performance recovers for the professions and
meat group due to release from proactive interference.
(a) Trial 1.
P MGroup
F
Percentrecalled 80
100
60
40
20
0
(b) Trial 2. More words in same categories.
P MGroup
F
Percentrecalled 80
100
60
40
20
0
Decrease due tobuildup of PI
(c) Trial 3. Words still in same category.
P MGroup
F
Percentrecalled 80
100
60
40
20
0
(d) Trial 4. Shift to fruit category for professions and meat.
No shift for fruit.
P MGroup
F
Percentrecalled 80
100
60
40
20
0
Release from PI
More PI
Meat
Fruit
Professions
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egories involves the meaningsof the words, the results of the
Wickens experiment demon-strate the operation ofsemantic codingin
STM.
Coding in Long-Term Memory Althoughsome semantic coding does
occur in STM, se-mantic coding is thepredominanttype of coding in
LTM. Semantic encoding is illustratedby the kinds of errors that
people make in tasks that involve LTM. For example, remem-bering
the word tree as bush would indicate that the meaning of the word
tree (ratherthan its visual appearance or the sound of saying tree)
is what was registered in LTM.
Jacqueline Sachs (1967) demonstrated the importance of meaning
in LTM by havingparticipants listen to a tape recording of a
passage like the one in the following demon-stration. Try this
yourself.
Demonstration
Reading a Passage
Read the following passage.
There is an interesting story about the telescope. In Holland, a
man named Lippershey was
an eyeglass maker. One day his children were playing with some
lenses. They discoveredthat things seemed very close if two lenses
were held about a foot apart. Lippershey began
experimenting and his spyglass attracted much attention. He sent
a letter about it to
Galileo, the great Italian scientist. Galileo at once realized
the importance of the discovery
and set about to build an instrument of his own.
Now cover up the passage and indicate which of the following
sentences is identical to a sentence
in the passage and which sentences are changed.
1. He sent a letter about it to Galileo, the great Italian
scientist.
2. Galileo, the great Italian scientist, sent him a letter about
it.
3. A letter about it was sent to Galileo, the great Italian
scientist.
4. He sent Galileo, the great Italian scientist, a letter about
it.
Which sentence did you pick? Sentence 1 is the only one that is
identical to one in thepassage. Many of Sachss participants (who
heard a passage about two times as long as the
one you read) correctly identified (1) as being identical and
knew that (2) was changed, buta number identified (3) and (4) as
matching one in the passage, even though the wording
was different. The participants apparently remembered the
sentences meaning and not itsexact wording.
But just as STM can be encoded in a few different ways, so can
LTM. For example,you use a visual code when you recognize someone
based on his or her appearance, andyou are using a phonological
code when you recognize them based on the sound of his orher
voice.
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Neuropsychological Evidence for Differences Between STM and
LTMIn Chapter 2 we saw that a technique used in neuropsychology is
identifying dissocia-
tionssituations in which one function is absent but others are
present. This techniquehas been used in memory research to
differentiate between STM and LTM by studyingpeople with brain
damage that has affected one of these functions while sparing the
other.
People With Functioning STM but Poor LTM Clive Wearing, the
musician who losthis memory due to viral encephalitis, is an
example of a person who has a functioningSTM but is unable to form
new LTMs. Another case of functioning STM but absentLTM is the case
of H.M., who became one of the most famous cases in
neuropsychology
when surgeons removed his hippocampus (see Figure 5.12) in an
attempt to eliminateepileptic seizures that had not responded to
other treatments (Scoville & Milner, 1957).
The operation eliminated H.M.s seizures, but unfortunately also
eliminated his abil-ity to form new LTMs. Thus, the outcome of
H.M.s case is similar to that of Clive Wear-ings, except Clive
Wearings brain damage was caused by disease and H.M.s was causedby
surgery. H.M.s unfortunate situation occurred because in 1953 the
surgeons did notrealize that the hippocampus is crucial for the
formation of LTMs. Once they realized thedevastating effects of
removing the hippocampus, H.M.s operation was never
repeated.However, H.M. has been studied for over 50 years and has
taught us a great deal aboutmemory. The property of H.M.s memory
that is important for distinguishing betweenSTM and LTM is the
demonstration that it is possible to lose the ability to form
newLTMs while still retaining STM. This loss of one ability while
the other remains intact isa single dissociation. To determine a
double dissociation we need to find another person
who has the opposite problem (i.e., good LTM, poor STM).
Chapter 5154
Frontalcortex
Prefrontalcortex
Amygdala
Hippocampus
Figure 5.12 Cross-section of the brain showing some of the key
structures that are involved in memory.
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People With Functioning LTM but Poor STM T. Shallice and
Elizabeth Warrington(1970) describe K.F., a patient with normal LTM
but poor STM. One indication of K.Fsproblems with STM is her
reduced digit spanthe number of digits a person can re-
member. You can determine your digit span by doing the following
demonstration.
Demonstration
Digit Span
Using an index card or piece of paper, cover all of the numbers
below. Move the card down to un-
cover the first string of numbers. Read the numbers, cover them
up, and then write them down.
Then move the card to the next string and repeat this procedure
until you begin making errors.The longest string you are able to
reproduce without error is your digit span.
2149
39678
649784
7382015
84261432
4823928075852981637
If you succeeded in remembering the longest string of digits,
you have a digit span of10. The typical span is between 5 and 8
digits. Patient K.F. had a digit span of 2 and, inaddition, the
recency effect in her serial-position curve, which is associated
with STM,
was reduced.Table 5.5, which indicates which aspects of memory
are impaired and which are intact
for Clive Wearing, H.M., and K.F., demonstrates that a double
dissociation exists forSTM and LTM. In Chapter 2 we saw that this
means that the two functions are caused bydifferent mechanisms,
which act independently.
The evidence we have described involving coding, the
serial-position curve, andneuropsychological case studies provides
good reasons to differentiate between STM andLTM. We will see that
this distinction has proven to be an extremely valuable way to
ap-proach the study of memory. In the remainder of this chapter we
will describe the prop-
erties of STM and then focus on working memory, which is an
updated way of looking atshort-term memory.
Sensory Memory, Short-Term Memory, and Working Memory155
Memory
Span
Table 5.5 A DOUBLE DISSOCIATION FORSTM AND LTM
STM LTM
Clive Wearing and H.M. OK Impaired
K.F. Impaired OK
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Test Yourself 5.1
1. Why can we say that memory is life? Answer this question by
considering whatmemory does for people with the ability to
remember, and what happens when thisability is lost, as in cases
like Clive Wearing (p. 137).
2. Describe Atkinson and Shiffrins modal model of memory both in
terms of its struc-ture (the boxes connected by arrows) and the
control processes. Then describe howeach part of the model comes
into play when you decide you want to order pizza butcant remember
the phone number of the pizzeria.
3. What do seeing the trail left by a moving sparkler and
watching a film have in com-
mon? How are both related to the modal model of memory?4.
Sperling showed that we can see 9 or 10 out of 12 letters right
after they are brieflyflashed, but we can report only about 4 of
these letters just a short time later. How didhe show this? How is
this result related to the modal model?
5. The idea that there are two different types of memoryone
short-term and the otherlong-termis supported by experiments that
measured the serial-position curve andby experiments that
investigated the form of the memory code. Describe these
exper-iments and the reasoning behind them.
6. The proactive interference experiment described in the
chapter is presented as evi-dence for a particular type of coding
in short-term memory. What type of coding wasdemonstrated? Why does
the conclusion hold for STM, even though the experimenttook much
longer than the 3060 seconds that information is usually held in
STM?
7. Studying the behavior of people with brain damage has
provided further evidence forthe idea of two types of memory.
Describe the cases of Clive Wearing, H.M., and K.F.in terms of
their symptoms and how we can draw general conclusions about
memoryfrom these symptoms. Why can we draw stronger conclusions
about memory by con-sidering more than one case?
WHAT ARE THE PROPERTIES OF SHORT-TERM MEMORY?As we think about
memory, considering both what psychologists have learned about it
and
how we use it every day, it is easy to downplay the importance
of STM compared to LTM.In my class survey of the uses of memory, my
students focused almost entirely on howmemory enables us to hold
information for long periods, such as remembering
directions,peoples names, or material that might appear on an exam.
Certainly, our ability to storeinformation for long periods is
important, as attested by cases such as H.M. and Clive
Wearing, whose inability to form LTMs makes it impossible for
them to function inde-pendently. But, as we will see, STM (and
working memory) is also crucial for normalfunctioning. Consider,
for example, the following sentence.
Chapter 5156
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The human brain is involved in everything we know about the
important things in life,like football.
How do we understand this sentence? First, the beginning of the
sentence is stored inSTM. Then we read the rest of the sentence and
determine the overall meaning by com-paring the information at the
end of the sentence to the information at the beginning.
But what if we couldnt hold the beginning of the sentence in
STM? If the informationin the first phrase faded before you
completed the sentence, you might think that the topicof the
sentence is football and wouldnt realize that the sentence is
really about the brain.
Holding small amounts of information for brief periods is the
basis of a great deal ofour mental life. Everything we think about
or know at a particular moment in time in-
volves STM because short-term memory is our window on the
present. (Remember fromFigure 5.4e that Rachel remembered the phone
number of the pizzeria by transferring itfrom LTM to STM.) Early
research on STM focused on answering the following twoquestions:
(1) How much information can STM hold? and (2) How long can STM
holdthis information?
What Is the Capacity of Short-Term Memory?
One measure of the capacity of STM is the digit span of 58 items
(or more for some peo-ple). A famous paper by George Miller (1956),
who was one of the pioneers in the devel-opment of modern cognitive
psychology, begins with the title The Magical NumberSeven, Plus or
Minus Two, and goes on to present evidence that we can hold 59
itemsin our short-term memory.
One of the things Miller grapples with in his discussion of STM
is the problem ofdefining exactly what an item is. Although the
answer to this question might seem obvi-ous if we simply consider
the memory span for digits, it becomes more complicated when
we consider trying to remember the following words: team, noise,
room, crowd, training,screening, football, film.
How many units are there in this list? There are 8 words, but if
we group them differ-ently, they can form the following 4 pairs:
football team, training film, crowd noise, screen-ing room. We can
take this one step further by arranging these groups of words into
onesentence: Thefootball teamviewed the training film about crowd
noise, in thescreening room.
Is this stimulus 8 items, 4 items, or 1 item? Miller introduced
the concept of chunking
to describe the fact that small units (like words) can be
combined into larger meaningfulunits, like phrases or sentences. A
chunkhas been defined as a collection of elements thatare strongly
associated with one another but are weakly associated with elements
in otherchunks (Gobet et al., 2001). Thus the word noise is
strongly associated with the word crowdbut is not as strongly
associated with the other words, such asfilm or room.
Research has shown that chunking in terms of meaning can
increase our ability tohold information in STM. Thus, we can recall
a sequence of 58 unrelated words, but ar-ranging the words to form
a meaningful sentence so that the words become more strongly
Sensory Memory, Short-Term Memory, and Working Memory157
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associated with one another increases the memory span to 20
words or more (Butterworthet al., 1990).
K. Anders Ericcson and coworkers (1980) demonstrated an effect
of chunking by
showing how a college student with average memory ability was
able to achieve amazingfeats of memory. Their participant, S.F.,
was asked to repeat strings of random digits that
were read to him. Although S.F. had a typical memory span of 7
digits, after 230 one-hoursessions, he was able to repeat sequences
of up to 79 digits without error. How did he doit? S.F. used
chunking to recode the digits into larger units that formed
meaningful se-quences. For example, 3492 became 3 minutes and 49
point 2 seconds, near world-record mile time, and 893 became 89
point 3, very old man. This example illustrateshow STM and LTM can
interact with each other, because S.F., who was a runner,
created
his chunks based on his knowledge of running times that were
stored in LTM.Another example of chunking that is based on an
interaction between STM and LTM
is an experiment by William Chase and Herbert Simon (1973a,
1973b) in which theyshowed chess players pictures of chess pieces
on a chess board for 5 seconds. The chessplayers were then asked to
reproduce the positions they had seen. Chase and Simon com-pared
the performance of a chess master who had played or studied chess
for over 10,000hours to the performance of a beginner who had less
than 100 hours of experience. The
results, shown in Figure 5.13a, show that the chess master
placed 16 pieces out of 24 cor-rectly on his first try, compared to
just 4 out of 24 for the beginner. Moreover, the masterrequired
only four trials to reproduce all of the positions exactly, whereas
even after seventrials the beginner was still making errors.
Chapter 5158
Figure 5.13 Results of Chase and Simons (1973a, 1973b) chess
memory experiment. (a) Master is better atreproducing actual game
positions. (b) Masters performance drops to level of beginner when
pieces are
arranged randomly.
(a) Actual game positions (b) Random placement
Master Beginner
12
8
4Correctplacements
0
16
Master Beginner
12
8
16
4Correctplacements
0
No advantage formaster if can't chunk
Master does betterbecause can chunkbased on game positions
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We know that the masters superior performance was caused by
chunking because itoccurred only when the chess pieces were
arranged in positions from a real chess game.
When the pieces were arranged randomly, however, the chess
master performed as poorly
as the beginner (Figure 5.13b). Chase and Simon concluded that
the chess masters ad-vantage was due not to a more highly developed
short-term memory, but to his ability togroup the chess pieces into
meaningful chunks. Because the chess master had stored manyof the
patterns that occur in real chess games in LTM, he saw the layout
of chess piecesnot in terms of individual pieces but in terms of 4
to 6 chunks, each made up of a group ofpieces that formed familiar,
meaningful patterns. When the pieces were arranged ran-domly, the
familiar patterns were destroyed and the chess masters advantage
vanished(also see DeGroot, 1965; Gobet et al., 2001).
Chunking is an essential feature of STM because it enables this
limited capacity sys-tem to deal with the large amount of
information involved in many of the tasks we per-form every day,
such as chunking letters into words as you read this, remembering
the firstthree numbers of familiar telephone exchanges as a unit,
and transforming long conver-sations into smaller units of
meaning.
What Is the Duration of Short-Term Memory?How long does
information stay in short-term memory if we are prevented from
rehears-ing it? In a famous experiment carried out independently by
John Brown (1958) in Eng-land and Lloyd Peterson and Margaret
Peterson (1959) in the United States, participants
were given a task similar to the one in the following
demonstration.
Demonstration
Remembering Three Letters
You will need another person to serve as a participant in this
experiment. Tell the person that you
are going to read them three letters followed by a number. Once
they hear the number they should
start counting backwards by 3s from that number, and then when
you say Recall they should
write down the three letters that they heard at the beginning.
Once they start counting, time 20
seconds and say Recall. Note their accuracy and repeat this
procedure for a few more trials,
using a new set of letters and a new three-digit number on each
trial.
Trial 1: B F T 100
Trial 2: Q S D 96
Trial 3: K H J 104
Trial 4: L W G 50
Trial 5: C M Y 52
Trial 6: Z F H 75
Trial 7: F N C 120
Sensory Memory, Short-Term Memory, and Working Memory159
Brown-Peterson
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Peterson and Peterson found that their participants were able to
remember about 80percent of the letters after a 3-second delay
(left bar in Figure 5.14a), but could rememberan average of only 10
percent of the three-letter groups after an 18-second delay (right
barin Figure 5.14a). Peterson and Peterson initially interpreted
this result as demonstratingthat STM decays within 18 seconds.
According to this interpretation, participants forgotthe letters
because of the passage of time. However, when Keppel and Underwood
(1962)looked closely at Peterson and Petersons results, they found
that if they just considered
the participants performance on the first trial, there is little
falloff between the 3-secondand the 18-second delay (Figure 5.14b).
However, when they analyzed the results for thethird trial, they
began seeing a drop-off in performance between the 3-second and the
18-second delay (Figure 5.14c).
The fact that memory for the letters becomes worse after a
number of trials (also seeWaugh & Norman, 1965) suggests that
the difficulty may have been caused by proactiveinterference.
[Remember from our description of Wickenss experiment (see Figure
5.11and Table 5.4) that proactive interference occurs when material
that was presented earlier
interferes with memory for new information.] The rapid fading of
memory observed inBrowns and Peterson and Petersons experiments was
therefore actually caused not bydecay, but by interference.
What does it mean that the reason for the decrease in memory is
proactive interfer-ence, rather than decay? Because there is a
great deal of interference in our everyday ex-perience, it doesnt
really matter that PI causes the memory decrease, and we can still
con-clude that the effective duration of STM, when rehearsal is
prevented, is about 1520
seconds.
Chapter 5160
Figure 5.14 Results of Peterson and Petersons (1959) duration of
STM experiment. (a) The result originallypresented by Peterson and
Peterson, showing a large drop in memory for letters for a delay of
18 seconds be-
tween presentation and test; (b) analysis of Peterson and
Petersons results by Keppel and Underwood, showing
little decrease in performance on trial 1, and (c) more decrease
by trial 3.
3 18
50
Percentcorrect
0
100
Delay
3 18
50
100
Percentcorrect
0
Delay
3 18
50
100
0
Percentcorrect
Delay
(a) Average performanceover many trials
(b) First-trial performance (c) Third-trial performance
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Problems With the Modal ModelAtkinson and Shiffrins model of
memory has served the study of memory well because by
breaking the process of memory into stages, it generated a huge
amount of research oneach stage and on how the stages interact with
one another. There are, however, some re-sults that pose problems
for the model. The model does not account for how a personsuch as
K.F. who had a very small digit span could have poor STM but normal
LTM. Ac-cording to the model, all information must pass through STM
to reach LTM. But howcould this work for K.F., if her STM is
defective? Shallice and Warrington (1970), whostudied K.F.,
suggested that the Atkinson and Shiffrin model is oversimplified
and thatperhaps there may be another pathway that enables
information to enter LTM without
passing through STM.In addition, other research has shown that
STM is not just a single process but con-
sists of a number of different processes, perhaps corresponding
to the way information iscoded into STM (remember that there is
evidence for visual, phonological, and semanticencoding in STM;
Freedman & Martin, 2001). Some of the most influential evidence
forthis idea has been provided by Alan Baddeley, who has shown that
the short-term processconsists of a number of specialized
components.
One of the first experiments that suggested that the short-term
process consists of a
number of components was the observation by Baddeley and Hitch
(1974) that undersome conditions participants could do two tasks at
once. You can demonstrate this to
yourself with the following demonstration.
Demonstration
Reading Text and Remembering Numbers
Keep these numbers in your mind (7, 1, 4, 9) as you read the
following passage.
Baddeley reasoned that if STM had a limited storage capacity of
about the length of a tele-
phone number, filling up the storage capacity should make it
difficult to do other tasks that
depend on STM. But he found that participants could hold a short
string of numbers in their
memory while carrying out another task, such as reading or even
solving a simple word
problem. How are you doing with this task? What are the numbers?
What is the gist of what
you have just read?
Because Baddeleys participants were able to read while
simultaneously rememberingnumbers, he concluded that the short-term
process must consist of a number of compo-nents that can function
separately. In the foregoing example, the digit span task in
which
you held numbers in your memory is handled by one component
while comprehendingthe paragraph is handled by another component.
Based on results such as this, Baddeleydecided that the name of the
short-term process should be changed from short-term
memory to working memory.
Sensory Memory, Short-Term Memory, and Working Memory161
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WORKING MEMORY: THE MODERN APPROACH TO SHORT-TERM MEMORY
Baddeley (2000) definesworking memoryas follows: Working memory
is a limited capacitysystem for temporary storage and manipulation
of information for complex tasks such as compre-hension, learning,
and reasoning. From this definition we can see that working memory
dif-fers from STM in two ways:
1. Working memory consists of a number of parts.2. Its function
is not just to brieflystore information but to manipulate
information
to help us carry out complex cognitive tasks.
Thus, the emphasis of the working memory concept is not on how
information is brieflyretained but on how information is
manipulated to achieve complex cognitions such asthinking and
comprehension (Baddeley, 2000).
The Three Components of Working MemoryWorking memory
accomplishes the manipulation of information through the action
ofthree components: thephonological loop, the visuospatial sketch
pad, and the central executive(Figure 5.15).
The Phonological Loop The phonological loop holds verbal and
auditory informa-tion. Thus, when you are trying to remember a
telephone number or a persons name, orto understand what your
cognitive psychology professor is talking about, you are using
your phonological loop (Figure 5.16a). This loop is divided into
two parts:
1. Storagea place that holds the memory trace. The trace fades
in about 2 sec-
onds unless it is refreshed by rehearsal. This is the passive
part of the phonologi-cal loop.
2. Rehearsalthe part of the phonological loop responsible for
the repetition thatrefreshes the memory trace. This is the active
part of the phonological loop.
Chapter 5162
Figure 5.15 Diagram of the three main components of Baddeley and
Hitchs (1974; Baddleley, 2000) model of
working memory: the phonological loop, the visuospatial sketch
pad, and the central executive.
Storage(passive)
Rehearsal(active)
Phonologicalloop
Baddeley's working memory model
Centralexecutive
Visualinformation
Spatialinformation
Visuospatialsketch pad
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The Visuospatial Sketch Pad Thevisuospatial sketch pad holds
visual and spatialinformation. When you form a picture in your mind
or do tasks like solving a puzzle orfinding your way around campus,
you are using your visuospatial sketch pad (Figure5.16b). As you
can see from the diagram, the phonological loop and the
visuospatial sketchpad are attached to the central executive.
The Central Executive The central executive is where the major
work of workingmemory occurs. The central executive pulls
information from long-term memory and co-ordinates the activity of
the phonological loop and visuospatial sketch pad by focusing
onspecific parts of a task and switching attention from one part to
another. For example,imagine that you are driving in a strange
city, and a friend in the passenger seat is reading
you directions to a restaurant. As your phonological loop takes
in the verbal directions,your sketch pad is helping you visualize a
map of the streets leading to the restaurant (Fig-ure 5.17). These
two kinds of information are coordinated and combined by the
centralexecutive to create a coherent episode that we might title
Finding the Restaurant.
As we describe working memory, keep in mind that it is a
hypothesis about how themind works that needs to be tested by doing
experiments. A number of experiments havebeen conducted to test the
idea that the phonological loop and visuospatial sketch pad
deal
with different types of information.
Sensory Memory, Short-Term Memory, and Working Memory163
Figure 5.16 Tasks handled by components of working memory. (a)
The phonological loop handles language.Reading is shown here, but
the phonological loop also handles information that is received
verbally, as when lis-
tening to someone speak. (b) The visuospatial sketch pad handles
visual and spatial information.
(a) (b)
Reading
Visuospatialsketch pad
Phonologicalloop
Puzzle
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Operation of the Phonological LoopThree phenomena support the
idea of a system specialized for language: the
phonologicalsimilarity effect, the word-length effect, and
articulatory suppression.
Phonological Similarity Effect The phonological similarity
effectoccurs when let-ters or words that sound similar are
confused. Remember Conrads experiment in whichhe showed that people
often confuse similar-sounding letters, such as T and P. Con-rad
interpreted this result to support the idea of phonological coding
in STM. In pres-ent-day terminology Conrads result would be
described as a demonstration of thephonological similarity effect
that occurs as words are processed in the phonologicalloop of
working memory. Here is another demonstration of the phonological
similarityeffect:
Chapter 5164
Figure 5.17 Tasks processed by the phonological loop (hearing
directions) and visuospatial sketch pad(visualizing the route)
being coordinated by the central executive.
verbal and visual information
Phonologicalloop
Visuospatialsketch pad
Go leftat the
secondcorner
PhonologicalSimilarity
Effect
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Demonstration
Phonological Similarity Effect
Task 1: Slowly read the following words. Look away and count to
15. Then write them down.
mac, can, cap, man, map
Task 2: Now do the same thing for these words.
pen, pay, cow, bar, rig
Which of the two tasks was more difficult? Many people find that
they confuse thesimilar-sounding words in Task 1 and that it is
easier to remember the different-soundingwords in Task 2. This
confusion of words in Task 1 is an example of the phonological
sim-ilarity effect.
Word-Length Effect Theword-length effectrefers to the finding
that memory forlists of words is better for short words than for
long words.
Demonstration
Word-Length Effect
Task 1: Read the following words, look away, and then write down
the words you remember.
beast, bronze, wife, golf, inn, limp, dirt, star
Task 2: Now do the same thing for the following list.
alcohol, property, amplifier, officer, gallery, mosquito,
orchestra, bricklayer
Each list contains eight words but according to the word-length
effectthe second list will be more difficult to remember because
the words arelonger. Results of an experiment by Baddeley and
coworkers (1984) thatillustrate this advantage for short words is
shown in Figure 5.18. The
word-length effect occurs because the larger words fill up the
capacityof the phonological loop, and so rehearsal is less
effective for the longer
words because of the extra time needed to rehearse them.The
limited capacity of the loop explains the initially surprising
find-
ing that American children have a larger digit span than Welsh
children.Before you conclude that American children are smarter
than Welshchildren, consider that the names of numbers in Welsh
(un, dau, tri, ped-
war, pump, chwech . . .) are longer than the names of the
numbers in
Sensory Memory, Short-Term Memory, and Working Memory165
Shortwords
Longwords
50
Percentcorrectrecall
0
100
Normal word-length effect
Figure 5.18 How word length af-fects memory, showing that recall
is
better for short words (Baddeley et
al., 1984).
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English (one, two, three, four, five, six . . .). Since it takes
longer to pronounce Welsh num-bers, fewer can be held in the
phonological loop, and the memory span for these numbersis
therefore less (Ellis & Hennelly, 1980).
In another study of memory for verbal material, Baddeley and
coworkers (1975)found that people are able to remember the number
of items that they can pronounce inabout 1.52.0 seconds (also see
Schweickert & Boruff, 1986). Try counting out loud, asfast as
you can, for two seconds. According to Baddeley, the number you
reach should beclose to your digit span.
Ar ti cula tory Suppressi on A phenomenon called articulatory
suppressionoccurswhen a person repeats an irrelevant sound such as
the while hearing words to remem-
ber. Saying the, the, the, the . . . impairs memory for the
words by interfering with op-eration of the phonological loop
(Baddeley et al., 1984; Murray, 1968). The followingdemonstration,
which is based on an experiment by Baddeley and coworkers (1984),
illus-trates an effect of articulatory suppression:
Demonstration
Repeating TheTask 1: Repeat the word the out loud (i.e., the,
the, the . . .) as you read the following
list. Then turn away and recall as many words as you can.
automobile mathematics
apartment syllogism
basketball Catholicism
Task 2: Now do the same thing for the following list.
story ant towel
car coffee swing
According to the word-length effect, the second list should be
easier to recall than thefirst because the words are shorter (see
Figure 5.18). Remember that one of the advan-tages of shorter words
is that they leave more space in the phonological loop for
rehearsal.
However, Baddeley et al. (1984) showed that articulatory
suppression caused by sayingthe, the, the . . . reduces performance
on both lists and reduces the advantage for shortwords (Figure
5.19a). This occurs because repeating the, the, the . . . prevents
rehearsalin the phonological loop (Figure 5.19b).
What about the effect of saying the, the, the . . . on the
phonological similarity ef-fect, in which similar sounding words
are confused? If participants heara list of words
while saying the, the, the . . ., the phonological similarity
effect still occurs because eventhough the phonological loop is
dealing with the, the, the . . ., asking participants to
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listen to the words causes the words to enter the phonological
loop directly (Figure 5.20a).Once in the phonological loop these
words can be confused based on their sound, so thephonological
similarity effect still occurs.
Sensory Memory, Short-Term Memory, and Working Memory167
Figure 5.19 (a) Saying the, the, the . . . abolishes the
word-length effect, so there is little difference in per-formance
for short words and long words (Baddeley et al., 1984). (b) Diagram
of how working memory explains
this result by proposing that saying the, the, the . . . reduces
rehearsal in the phonological loop.
(a) (b)
Short
words
Long
words
50
Percentcorrect
recall
0
100
Articulatorysuppression
the, the,the . . .
Phonologicalloop
Visuospatialsketch pad
Reduces rehearsal
advantage forshort words
Figure 5.20 Working memory and the effect of saying the, the,
the . . . on the phonological similarity effect.(a) Phonological
similarity effect still occurs for spoken words because listening
causes words to enter phono-
logical loop directly. (b) The effect does not occur for
visually presented words because they are prevented from
being recoded verbally in the phonological loop.
the,the,the . . .
Phonological
loopVisuospatialsketch pad
Blocked from changing tophonological code by the, the, the . .
.
Pear,Bear,Tear
Spoken words enterphonological loop directly
Effect of saying the, the, the . . .
the,the,the . . .
Phonological
loop
Visuospatial
sketch pad
Pear,Bear,
Tear
(a) Phonological similarity effect occurs if words are heard (b)
No phonological similarity effect if words are read
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However, if participants reada visually presented list of words
while saying the, the,the . . ., the phonological similarity effect
does notoccur, because the words are initiallyregistered in the
visuospatial sketch pad and saying the, the, the . . . prevents
them frombeing changed to a phonological code by the phonological
loop (Figure 5.20b). Withouta phonological code, similar-sounding
words cant be confused based on their sound sothe phonological
similarity effect is eliminated. Table 5.6 summarizes the effects
of sayingthe, the, the . . . on the phonological similarity
effect.
The Visuospatial Sketch PadWhen we discussed divided attention
in Chapter 4 (see page 113), we described some ex-periments by Lee
Brooks (1968) in which participants were asked to do two tasks at
once.
In one experiment, participants were asked to indicate whether
each word in a sentencethey had memorized was a noun by either
sayingyesor no (task 1), or by pointing to Yor
Nin a visual display (task 2) like the one in Figure 4.18 (see
Figure 5.21a). In another ex-periment, participants were asked to
indicate whether each corner of a block letter Fthat they were
imagining was an outside corner by either sayingyesor no (task 3)
or point-ing to YorN(task 4) (see Figure 5.21b).
The important result for our purposes is that for both of these
experiments the taskwas easier if the stimulus that participants
was holding in their mind and the operation
they were performing on that stimulus involved
differentcapacities. Thus, in the first ex-periment, in which the
stimulus was verbal(a memorized sentence), thespatial task (task
2)
was easier, but in the second experiment, in which the stimulus
was spatial(an imaginedletter), the verbal task (task 3) was
easier. We can explain these results in terms of thephonological
loop and the visuospatial sketch pad by recognizing that verbal
tasks dependon the phonological loop and spatial tasks depend on
the visuospatial sketch pad. Thus,for task 1 in the first
experiment, when the stimulus and task were both verbal (Figure
Chapter 5168
Table 5.6 EFFECT OFSAYING THE, THE, THE . . . ON THE
PHONOLOGICALSIMILARITYEFFECT FORAUDITORY ANDVISUAL
PRESENTATIONS
Presentation Effect?
Auditory No(hear word list) Phonological similarity
effect still occurs
(see Figure 5.20a)
Visual Yes
(read a word list) Phonological similarity effect no longer
occurs
(see Figure 5.20b)
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5.22a), the phonological loop was overloaded and the task became
difficult. But for task 2in the first experiment, when the stimulus
was verbal and the task was spatial (Figure5.22b), the loop and
sketch pad shared responsibility and the task became easier.
Figures5.22c and d show the spatial stimulus in the sketch pad for
tasks 3 and 4 of experiment 2.Fill in the tasks and results for
each diagram to match the information in Figure 5.21b.
All of these demonstrations show that working memory is set up
to process phono-logical and visual-spatial information separately
so it can handle differenttypes of infor-mation that are presented
simultaneously, but that working memory has trouble handling
similartypes of information that are presented
simultaneously.Before leaving the loop and the sketch pad, lets
consider an experiment by M. A.
Brandimonte and coworkers (1992) that illustrates the principles
we have been discussingin a different way. Brandimonte briefly
presented a picture of an object like the one in Fig-ure 5.23a and
then briefly presented a picture of part of the object, as in
Figure 5.23b. Theparticipants task was to subtract the second
picture from the first and indicate what the newpicture
represented. Remember that the pictures were not present while the
participants
Sensory Memory, Short-Term Memory, and Working Memory169
Figure 5.21 Summary of the results of Brookss (1968) experiment
described in Chapter 4. (a) The tasks in-volving the verbal
stimulus.Task (2), which involves a spatial response, is easier.
(b) The tasks involving the
spatial stimulus.Task (3), which involves a verbal response, is
easier.
John ran to the store to buy some oranges
(a) Verbal stimulus
Task 1: Saying yes or no
Task 2: Pointing to Y or N in Figure 4.18
(b) Spatial stimulus
Visualize F and indicate whether each corner is outside by:
Memorize sentence and indicate whether each word is a noun
by:
Easier
(spatial task)
Easier
(verbal task) Task 3: Saying yes or no
Task 4: Pointing to Y or N
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Chapter 5170
Figure 5.22 The results of Brookss (1968) experiments from
Figure 5.21, explained in terms of workingmemory. When the stimulus
is verbal, (a) task 1, which requires a verbal response, is
difficult because the
phonological loop has to process both the verbal stimulus and
verbal response. (b) Task 2, which requires a
visual response, is easier because processing is divided between
the phonological loop and the visuospatial
sketch pad. (c and d) Fill in these diagrams for tasks 3 and 4
in Figure 5.21b.
Remembersentence+
Sayyes
Phonologicalloop
Visuospatialsketch pad
(a) Task 1
Remembersentence
Pointto
yes
(b) Task 2: Easier
(c) Task 3: You fill in the task and result
(d) Task 4: You fill it in
Overload
d h b k h b h d b d h
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carried out the subtraction task so the subtraction had to be
done in theirminds. In the example in Figure 5.23, the initial
picture is a piece of candy,and after subtraction, it becomes a
fish. Brandimonte then had another
group of participants do the same task while saying la, la, la.
. . .Based on what you know about operation of the phonological
loopand visuospatial sketch pad, how do you think saying la, la, la
. . .
would affect participants performance on the subtraction task?
One wayto answer this question is to reason that saying la, la, la
. . . would notaffect participants performance because the words
la, la, la . . . areprocessed by the phonological loop and the
visual images are processedby the visuospatial sketch pad, so they
wouldnt interfere with one an-
other. However, as it turns out, saying the words
improvedparticipantsperformance on the subtraction task.
Why did the la, la, la group do better? The key to answering
thisquestion is to realize that in the first part of the experiment
there are two
ways that the participants can memorize the objects. They can
name them(verbal coding) so the object in Figure 5.23a would become
the wordcandy, or they can create visual images of them (visual
coding) so theobject would be a picture in the participants
minds.
The working memory diagram in Figure 5.24 shows that saying
la,la, la . . . fills up the phonological loop and so prevents the
image in Fig-ure 5.23a from being coded phonologically.
Consequently, the partici-pants must code the objects visually in
the sketch pad (Figure 5.24). Be-cause the subtraction task in the
second part of the experiment is easier
when starting with a visual image, being forced to use the
sketch pad im-proves performance. Thus, the Brandimonte experiment
shows how per-
formance can be enhanced when activity in one component of
working memory forcesparticipants to use the system that is most
well-suited to the task.
Sensory Memory, Short-Term Memory, and Working Memory171
(a)
(b)
Figure 5.23 Stimuli used inBrandimonte et al.s (1992) exper-
iment. (a) The initial stimulus;
(b) part that the participant is
asked to mentally subtract from
the initial stimulus. (Reprinted
from Influence of Short-Term
Memory Codes on Visual Image
Processing: Evidence from Image
Transformation Tasks, by M.A.
Brandimonte, Journal of Experi-
mental Psychology: Learning,
Memory and Cognition, 18, pp.
157165. Copyright 1992 with
permission from the American
Psychological Association.)
Figure 5.24 Explanation of the Brandimonte result in terms of
working memory. Saying la, la, la . . . , preventsthe initial
stimulus from being recoded verbally by the phonological loop.
Therefore, it must be coded visually by
the visuospatial sketch pad.
la, la,la, la,
la
Phonologicalloop
Visuospatialsketch pad
Phonological codinginto candy prevented
Must becodedvisually
St t f R h W ki M
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Status of Research on Working MemoryOne of the characteristics
of a good theory is that it suggests new experiments. Atkinsonand
Shiffrins modal model did this, and so has Baddeleys working memory
model. But
just as Baddeleys early observations led to a rethinking of the
STM part of the modalmodel, other observations (including some made
by Baddeley) have raised questions aboutthe working memory
model.
For example, there are patients with brain damage whose memory
spans have been re-duced to just one or two digits, indicating that
the phonological loop is severely impaired.However, these same
patients can repeat back sequences of 5 or 6 words if the words
forma sentence (Vallar & Baddeley, 1984; Wilson & Baddeley,
1988). How can this memory
for sentences occur if the phonological loop is impaired? One
possibility is that perhapslong-term memory (which is not impaired
in these patients) helps out for meaningful ma-terial like
sentences. Results such as these have led Baddeley (2000) to
propose that thereare additional components in the working memory
system that communicate closely withlong-term memory. It is likely
that future research on working memory will be concerned
with the connection between working memory and long-term memory
(see Ericsson &Kintsch, 1995).
More research is also needed to better determine how the central
executive works.
You may have noticed that we said little about the central
executive. One reason for this isbecause the central executives
task of coordinating and controlling the two subsystems is
very complex, and only recently have researchers begun studying
the ways that the cen-tral executive operates (see Andrade, 2001;
Baddeley, 1996).
WORKING MEMORY AND THE BRAINEarly physiological studies of the
short-term component of memory demonstrated thatbehaviors that
depended on working memory can be disrupted by damage to specific
areasof the brain, especially the prefrontal cortex (PF cortex; see
Figure 5.12). The PF cortexreceives inputs from the sensory areas,
which are involved in processing incoming visualand auditory
information. It also receives signals from areas involved in
carrying out ac-tions and is connected to areas in the temporal
cortex that are important for forming long-term memories (see
Figure 2.3 for location of the temporal lobe). Thus the wiring
dia-
gram of the PF cortex is exactly what we would expect for the
operation of a memorysystem like working memory that has to take
incoming information from the environmentand pass some of this
information on to longer-term storage.
The Delayed-Response Task in MonkeysEarly work on the physiology
of working memory used a task called the delayed-responsetask,which
required a monkey to hold information in working memory during a
delay pe-
riod. Figure 5.25 shows the setup for this task. The monkey sees
a food reward in one of
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two food wells. Both wells are then covered, a screen is lowered
during a delay, and then thescreen is raised and the monkey obtains
the food if it reaches for the correct food well.
Monkeys can be trained to accomplish this task but if their PF
cortex is removed, theirperformance drops to chance level so they
pick the correct food well only about half of thetime. This result
supports the idea that the PF cortex is important for holding
informa-tion for brief periods of time. In fact, it has been
suggested that one reason we can de-scribe the memory behavior of
very young infants (younger than about 8 months of age)as out of
sight, out of mind (so when an object that the infant can see is
then hiddenfrom view, the infant behaves as if the object no longer
exists) is that their frontal an