135
CogLab: Partial Report; Brown-Peterson; Memory
Span; Phonological Similarity Effect; Apparent
Movement; Irrelevant Speech Effect; Modality Effect;
Operation Span; Position Error; Sternberg Search
5
Short-Term and
Working Memory
What Is Memory?
The Purposes of Memory
The Modal Model of Memory
Sensory Memory
The Sparkler’s Trail and the Projector’s Shutter
Sperling’s Experiment: Measuring the Visual Icon
Short-Term Memory
What Is the Duration of Short-Term Memory?
Demonstration: Remembering Three Letters
What Is the Capacity of Short-Term Memory?
Demonstration: Digit Span
How Is Information Coded in Short-Term Memory?
Test Yourself 5.1
Working Memory: The Modern Approach
to Short-Term Memory
Demonstration: Reading Text and Remembering Numbers
The Phonological Loop
Demonstration: Phonological Similarity Effect
Demonstration: Word-Length Effect
Demonstration: Articulatory Suppression
The Visuospatial Sketch Pad
Demonstration: Holding a Verbal Stimulus in the Mind
Demonstration: Holding a Spatial Stimulus in the Mind
The Central Executive
Update on the Working Memory Model: Addition
of the Episodic Buffer
Working Memory and the Brain
The Delayed-Response Task in Monkeys
Neurons That Hold Information
Brain Imaging in Humans
Something to Consider: Working Memory
in American Sign Language
Test Yourself 5.2
Chapter Summary
Think About It
If You Want to Know More
Key Terms
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? (139)
Is there a way to increase the ability to
remember things that have just happened?
(149)
Do we use the same memory system to remember
things we have seen and things
we have heard? (155)
•
•
•
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136 Chapter 5
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 moment
from now the present will become the past, and some of the past will become stored
in memory. What you will read in this chapter and the two that follow supports the idea
that “everything in life is memory” and shows how our memory of the past not only provides
a record of a lifetime of events we have experienced and knowledge we have learned,
but can also affect our experience of what is happening right at this moment.
What Is Memory?
The definition of memory provides 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 Purposes of Memory
The fact that memory retains information that is no longer present means that we can
use our memory as a “time machine” to go back just a moment—to the words you read
at the beginning of this sentence—or many years—to events as early as a childhood
birthday party. This “mental time travel” afforded by memory can place you back in a
situation, so you feel as though you are reliving it, even to the extent of experiencing
feelings that were occurring long ago. But memory goes beyond reexperiencing events.
We also use memory to remember what we need to do later in the day, to remember
facts we have learned, and to use skills we have acquired.
If you were asked to create a “Top 10” list of what you use memory for, what would
you include? When I ask my students to do this, most of their items relate to day-to-day
activities. The top five items on their list involved remembering the following things.
1. Material for exams
2. Their daily schedule
3. Names
4. Phone numbers
5. Directions to places
Remembering material for exams is probably high on most students’ lists, but it is
likely that people from different walks of life, such as business executives, construction
workers, homemakers, or politicians, would create lists that differ from the ones created
by college students in ways that reflect the demands of their particular lives. Remembering
the material that will be on the next cognitive psychology exam would be an unlikely
entry on a construction worker’s list, but remembering the procedure for framing
a house might be on that list.
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137Short-Term and Working Memory
One reason I ask students to create a “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
them aware of how they don’t include many important functions on their lists, because
they take them for granted. A few of these things include labeling familiar objects (you
know you are 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 a restaurant (you need to remember a sequence of events, starting with
being seated and ending with paying the check), and finding your way to class.
The list of things that depend on memory is an extremely long one because just
about everything we do depends on remembering what we have experienced in the past.
But perhaps the most powerful way to demonstrate the importance of memory is to
consider what happens to people’s lives when they lose their memory. Consider, for example,
the case of Clive Wearing (Annenberg, 2000; D. Wearing, 2005).
Wearing was a highly respected musician and choral director in England who, in
his 40s, contracted viral encephalitis, which destroyed parts of his temporal lobe that
are important for forming new memories. Because of his brain damage, Wearing lives
totally within the most recent one or two minutes of his life. He remembers what just
happened and forgets everything else. When he meets someone, and the person leaves
the room and returns three minutes later, Wearing reacts as if he hadn’t met the person
earlier. Because of his inability to form new memories, he constantly feels he has just
become conscious for the first time.
This feeling is made poignantly clear by Wearing’s diary, which contains hundreds
of entries like “I have woken up for the first time” and “I am alive” (Figure 5.1). But
Wearing has no memory of ever writing anything except for the sentence he has just
written. When questioned about previous entries, Wearing acknowledges that they are
in his handwriting, but because he has no memory for writing them, he denies that they
are his. It is no wonder that he is confused, 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 he needs to be constantly cared for by others.
■ Figure 5.1 Clive Wearing’s
diary looked like this.
Sometimes he would cross
out previous entries because
he could only remember writing
the most recent entry.
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138 Chapter 5
In this chapter we will begin describing the basic principles of memory so we can
understand both cases like Clive Wearing’s and also the basic principles behind normal
memory processes (Figure 5.2). We begin by describing a model of memory we
introduced in Chapter 1 called the modal model (see p. 20). After describing the modal
model, we will focus on the short-term components of the model, first looking at properties
of sensory memory and short-term memory 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 research on where some of the mechanisms of
working memory are located in the brain.
The Modal Model of Memory
The modal model of memory, which was proposed by Richard Atkinson and Richard
Shiffrin (1968), is shown in Figure 5.3. As we noted in Chapter 1, this model, which was
proposed 40 years ago, is too simple to explain many of the things that have been discovered
about memory since the model was proposed, but it does provide a way to introduce
many of the basic principles of memory. We will, therefore, use the modal model
as our starting point, and will update the model later in this and subsequent chapters.
■ Figure 5.2
Flow diagram for
this chapter.
PCR
Working memory
and the brain
• What are the stages of the modal
model?
• What are the properties of STM?
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?
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139Short-Term and Working Memory
The stages of the modal model are called the structural features of the model. There
are three major structural features:
1. Sensory memory is an initial stage that holds all incoming information for
seconds or fractions of a second.
2. Short-term memory (STM) holds 5–7 items for about 15–30 seconds. We
will be describing the characteristics of short-term memory in this chapter.
3. Long-term memory (LTM) can hold a large amount of information for
years or even decades. We will describe long-term memory in Chapters
6 and 7.
Atkinson and Shiffrin also describe the memory system as including control processes,
which are active processes that can be controlled by the person and may differ
from one task to another. An example of a control process is rehearsal—repeating a
stimulus over and over, as you might repeat a telephone number in order to hold it in
your mind 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
the numbers in a phone number to a familiar date in history, and (2) strategies of
attention that help you selectively focus on other information you want to remember.
To illustrate how the structural features and control processes operate, let’s consider
what happens as Rachel looks up the number for Mineo’s Pizza in the phone book (Figure
5.4). When she first looks at the book, all of the information that enters her eyes
is registered in sensory memory (Figure 5.4a). But Rachel focuses on the number for
Mineo’s using 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 been
transferred into long-term memory. However, she decides to memorize the number so
next time she won’t have to look it up in the phone book. The process she uses to memorize
the number, a control process we will discuss in Chapter 6, transfers the number
■ Figure 5.3 Flow diagram for Atkinson and Shiffrin’s (1968) model of memory. This model, which is
described in the text, is called the modal model because of the huge influence it has had on memory
research.
Input
Sensory
memory
Short-
term
memory
Long-
term
memory
Output
Rehearsal: A control processt by PDF Splitter
140
■ Figure 5.4 What happens in different parts of Rachel’s 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 for each action that Rachel takes.
Sensory STM LTM
All info on page
enters sensory
memory.
Sensory STM LTM
Focus on 555-5100.
It enters STM.
Sensory LTM
Rehearse the number
to keep it in STM while
making the phone call.
Sensory STM LTM
Storage
Awareness
Store number in LTM.
Sensory STM LTM
Retrieve number from LTM.
It goes back to STM and is
remembered.
(a)
(b)
(c)
(d)
(e)
STM
Remember number
to make call
Remember number
to make call again
Retrieval
Rehearsal
555-5100
555-5100
555-5100
555-5100
Rehearsing
Memorizing
Retrieval
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141Short-Term and Working Memory
into long-term memory, where it is stored (Figure 5.4d). A few days later, when Rachel’s
urge for pizza returns, she remembers the number. This process of remembering information
that is stored in long-term memory is called retrieval because the information
must be retrieved from LTM so it can reenter STM to be used (Figure 5.4e).
One thing that becomes apparent from our example is that the components of memory
do not act in isolation. Long-term memory is essential for storing information, but
before we can become aware of this stored information, it must be moved back into STM.
We will now consider each component of the model, beginning with sensory memory.
Sensory Memory
Sensory memory is the retention, for brief periods of time, of the effects of sensory
stimulation. We can demonstrate this brief retention for the effects of visual stimulation
with two familiar examples: the trail left by a moving sparkler and the experience
of seeing a film.
The Sparkler’s Trail and the Projector’s Shutter
It is dark, sometime around the Fourth of July, and you place a match to the tip of a
sparkler. As sparks begin radiating from the hot spot at the tip, you sweep the sparkler
through the air, and create a trail of light (Figure 5.5). Although it appears that this trail
is created by light left by the sparkler as you wave it through the air, there is, in fact,
no light along this trail. The lighted trail is a creation of your mind, which retains a
■ Figure 5.5 (a) A sparkler can cause a trail of light when it is moved rapidly. (b) This trail occurs
because the perception of the light is briefly held in the mind.
Perceptual
trail
©BazukiMuhammad/ReutersNewsmediaInc./CORBIS
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142 Chapter 5
perception of the sparkler’s light for a fraction of a second. This retention of the perception
of light in your mind is called the persistence of vision.
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
is quite different. We can appreciate what is happening on the screen by considering
the sequence of events that occur as a film is projected. First, a single film frame
is positioned in front of the projector lens, and when the projector’s shutter opens, the
image on the film frame is projected onto the screen. The shutter then closes, so the
film can move to the next 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 the next image onto the screen. This process is repeated rapidly,
24 times per second, so 24 still images are flashed on the screen every second, with each
image separated by a brief period of darkness (see Table 5.1).
A person viewing the film sees the progression of still images as movement and
doesn’t see the dark intervals between the images because the persistence of vision fills
in the darkness by retaining the image of the previous frame. If the period between the
images is too long, the mind can’t fill in the darkness completely, and you perceive a
flickering effect. This is what happened in the early movies when the projectors flashed
images more slowly, causing longer dark intervals. This is why these early films were
called “flickers,” a term that remains today, when we talk about going to the “flicks.”
Sperling’s Experiment: Measuring the Visual Icon
The persistence of vision effect that adds a trail to our perception of moving sparklers
and fills in the dark spaces between frames in a film has been known since the early days
of psychology (Boring, 1942). This lingering of the visual stimulus in our mind was
studied by Sperling (1960) in a famous experiment in which he flashed an array of letters,
like the one in Figure 5.6a, on the screen for 50 milliseconds (ms; 50/1,000 second)
and asked his participants to report as many of the letters as possible. This part of the
Table 5.1 Persistence of Vision in Film
What Is on
What Happens? the Screen? What Do You Perceive?
Film frame 1 is projected. Picture 1 Picture 1
Shutter closes and film moves to Darkness Picture 1 (persistence of vision)
the next frame.
Shutter opens and film frame 2 Picture 2 Picture 2*
is projected.
*Note that the images appear so rapidly (24 per second) that you don’t see individual images, but see a moving image
created by the rapid sequence of images.
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143Short-Term and Working Memory
(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 report
Tone delayed
Delay
Delayed tone
Medium
Low
High
Medium
Low
High
X M
L T
■ Figure 5.6 Procedure for three of Sperling’s (1960) experiments. (a) Whole report method: Person
saw all 12 letters at once for 50 ms 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
which row the person was to report. (c) Delayed partial report: Same as (b), but with a short delay
between extinguishing the letters and presentation of the tone.
experiment used the whole report method because participants were asked to report
as many letters as possible from the whole matrix. When they did this they were able to
report an average of 4.5 out of the 12 letters.
At this point Sperling could have concluded that because the exposure was brief,
participants saw only an average of 4.5 of the 12 letters. However, there is another possibility:
Perhaps participants saw most of the letters immediately after they were presented,
but their perception faded rapidly as they were reporting the letters, so by the
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144 Chapter 5
time they had reported 4–5 letters, they could no longer see the matrix or remember
what had been there.
Sperling devised the partial report method to determine which of these two possibilities
is correct. In this technique, he flashed the matrix for 50 ms, as before, but
immediately after it was flashed, he sounded one of the following cue tones, to indicate
which row of letters the participants were to report (Figure 5.6b):
High-pitched: Top row
Medium-pitched: Middle row
Low-pitched: Bottom row
Note that because the tones were presented after the letters were turned off, the participant’s
attention was directed not to the actual letters, which were no longer present, but
to whatever trace remained in the participant’s mind after the letters were turned off.
When the cue tones directed participants to focus their attention onto one of the
rows, they correctly reported an average of about 3.3 of the 4 letters (82 percent) in
that row. Because participants saw an average of 82 percent of the letters no matter which
row was cued, Sperling concluded that the correct description of what was happening
was that immediately after the display was presented, participants saw an average of
82 percent of the letters in the whole display, but were not able to report all of these letters
because they rapidly faded as the initial letters were being reported.
Sperling then did an additional experiment to determine the time course of this fading.
For this experiment, Sperling devised a delayed partial report method in which
the presentation of cue tones was delayed for a fraction of a second after the letters were
extinguished (Figure 5.6c).
The result of the delayed partial report experiments was that when the cue tones
were delayed for about half a second after the flash, participants were able to report only
slightly more than 1 letter in a row, or a total of about 4 letters for all three rows—the
same number of letters they reported using the whole-report technique. Figure 5.7 plots
this result in terms of the number of letters available to the participants from the entire
display, as a function of time following presentation of the display. This graph indicates
that immediately after a stimulus is presented, all or most of the stimulus is available
for perception. This is sensory memory. Then, over the next second, sensory memory
fades, until by 1 second, less than 5 of the 12 letters in the matrix can be reported. Note
that this corresponds to the number of letters that were reported in the whole report
technique.
Sperling concluded from these results that a short-lived sensory memory registers
all or 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 memory or the visual icon (icon means “image”), and corresponds to the sensory
memory stage of Atkinson and Shiffrin’s model. Other research, using auditory
stimuli, has shown that sounds also persist in the mind. This persistence of sound,
which is called echoic memory, lasts for a few seconds after presentation of the original
stimulus (Darwin et al., 1972).
Partial
Report
Partial
Report
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145Short-Term and Working Memory
Thus, sensory memory can register huge amounts of information (perhaps all of
the information that reaches the receptors), but it retains this information for only seconds
or fractions of a second. There has been some debate regarding the purpose of
this large but rapidly fading store (Haber, 1983), but many cognitive psychologists believe
that the sensory store is important for (1) collecting information to be processed;
(2) holding the information briefly while initial processing is going on; and (3) filling in
the blanks when stimulation is intermittent.
Sperling’s experiment is important not only because it reveals the capacity of sensory
memory (large) and its duration (brief), but also because it provides yet another
demonstration of how clever experimentation can reveal extremely rapid cognitive processes
that we are usually unaware of. (See the discussion of illusory conjunctions in
Chapter 3, page 67, for another example of how cognitive psychologists studied a rapid
process that occurs without our awareness.)
Short-Term Memory
Whatever you are thinking about right now, or remember from what you have just read,
is in your short-term memory. As we will see shortly, most of this information is eventually
lost, with only some of it reaching the more permanent store of long-term memory.
Because of the brief duration of STM, it is easy to downplay its importance compared to
LTM. In my class survey of the uses of memory, my students focused almost entirely on
how memory enables us to hold information for long periods, such as remembering directions,
people’s names, or material that might appear on an exam. Certainly, our abil-
1.00.80.60.40.20
Delay of tone (sec)
2
4
6
8
10
12
Calculatednumberof
lettersavailabletoparticipant
Partial
report Whole
report
■ Figure 5.7 Results of Sperling’s (1960) partial report experiments. The decrease in performance is
due to the rapid decay of iconic memory (called sensory memory in the modal model).
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146 Chapter 5
ity to store information for long periods is important, as attested by cases such as Clive
Wearing’s, whose inability to form LTMs makes it impossible for him to function independently.
But, as we will see, STM (and working memory, which we will describe later)
is also crucial for normal functioning. Consider, for example, the following sentence.
The human brain is involved in everything we know about the important things in
life, like music and dancing.
How do we understand this sentence? First, the beginning of the sentence is stored in
STM. We then read the rest of the sentence and determine the overall meaning by comparing
the information at the end of the sentence to the information at the beginning.
But what if we couldn’t hold the beginning of the sentence in STM? If the information
in the first phrase faded before you completed the sentence, you might think that the
topic of the sentence is music and dancing and wouldn’t realize that the sentence is really
about the brain.
Holding small amounts of information for brief periods is the basis of a great deal
of our mental life. Everything we think about or know at a particular moment in time
involves STM because short-term memory is our window on the present. (Remember
from Figure 5.4e that Rachel became aware of the pizzeria’s phone number by transferring
it from LTM to STM.) Early research on STM focused on answering the following
two questions: (1) What is the duration of STM? and (2) How much information
can STM hold?
What Is the Duration of Short-Term Memory?
John Brown (1958) in England and Lloyd Peterson and Margaret Peterson (1959)
in the United States carried out experiments to determine the duration of STM. In
their experiments 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 three letters followed by a number. Once the person hears the
number he or she should start counting backward by 3’s from that number, and then when
you say “Recall,” the person should write down the three letters heard at the beginning.
Once the person starts counting, time 20 seconds and say, “Recall.” Note the 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.
Peterson and Peterson found that their participants were able to remember about
80 percent of the letters after a 3-second delay (left bar in Figure 5.8a), but could remember
an average of only 10 percent of the three-letter groups after an 18-second
Brown-
Peterson
Brown-
Peterson
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147Short-Term and Working Memory
delay (right bar in Figure 5.8a). Peterson and Peterson initially interpreted this result as
demonstrating that participants forgot the letters because their memory trace decayed
during the 18 seconds. However, when G. Keppel and Benton Underwood (1962) looked
closely at Peterson and Peterson’s results, they found that if they considered the participants’
performance on just the first trial, there is little falloff between the 3-second
and the 18-second delay (Figure 5.8b). However, when they analyzed the results for the
third trial, they began seeing a drop-off in performance between the 3-second and the
18-second delay (Figure 5.8c).
Why would memory become worse after a few trials? Keppel and Underwood suggested
that the drop-off in memory was due not to decay of the memory trace, as Peterson
and Peterson had proposed, but to proactive interference (PI)—interference
that occurs when information that was learned previously interferes with learning new
information.
The effect of proactive interference is illustrated by what might happen when a
frequently used phone number is changed. Consider, for example, what might happen
when Rachel calls the number she had memorized for Mineo’s Pizza, 521-5100, only to
get a recording saying that the phone number has been changed to 522-4100. Although
Rachel tries to remember the new number, she makes mistakes at first because proactive
interference is causing her memory for the old number to interfere with her memory
for the new number. The fact that the new number is similar to the old one adds to the
interference and makes it harder to remember the new number.
What does it mean that the reason for the decrease in memory is proactive interference,
rather than decay? From the point of view of understanding the basic mecha■
Figure 5.8 Results of Peterson and Peterson’s (1959) duration of STM experiment. (a) The result
originally presented by Peterson and Peterson, showing a large drop in memory for letters for a delay of
18 seconds between presentation and test; (b) analysis of Peterson and Peterson’s 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 performance
over many trials
(b) First-trial performance (c) Third-trial performance
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148 Chapter 5
nisms underlying memory, it is important to know that interference is a basic mechanism
of forgetting. From the point of view of our everyday life experience, it is easy to
see that interference is happening constantly, as one event follows the next (and even
when nothing is “happening,” we are usually thinking about something). The outcome
of this constant interference is that the effective duration of STM, when rehearsal is
prevented, is about 15–20 seconds.
What Is the Capacity of Short-Term Memory?
Information is not only lost rapidly from STM, but there is a limit to how much information
can be held there. One measure of this capacity is provided by the digit span—
the number of digits a person can remember.
Digit Span 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
uncover the first string of numbers. Read the numbers, cover them up, and then write them
down in the correct order. 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.
2 1 4 9
3 9 6 7 8
6 4 9 7 8 4
7 3 8 2 0 1 5
8 4 2 6 1 4 3 2
4 8 2 3 9 2 8 0 7
5 8 5 2 9 8 1 6 3 7
If you succeeded in remembering the longest string of digits, you have a digit span of
10. The typical span is between 5 and 8 digits.
According to measurements of digit span, the capacity of STM is 5–8 items. But
what exactly is an item? George Miller (1956) considered this question in a famous paper
titled “The Magical Number Seven, Plus or Minus Two.” Miller expanded the definition
of an item beyond digits by considering how we remember words and combinations
of words. Consider, for example, trying to remember the following words: monkey, child,
wildly, zoo, jumped, city, ringtail, young. How many units are there in this list? There are
8 words, but if we group them differently, they can form the following 4 pairs: ringtail
monkey, jumped wildly, young child, city zoo. We can take this one step further by arranging
these groups of words into one sentence: The ringtail monkey jumped wildly for the young
child at the city zoo.
Memory
Span
Memory
Span
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149Short-Term and Working Memory
Chunking Is the sentence about the child watching a monkey at the zoo 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 meaningful units, like phrases, or even
larger units, like sentences, paragraphs, or stories. A chunk has been defined as a collection
of elements that are strongly associated with one another but are weakly associated
with elements in other chunks (Gobet et al., 2001). In our example the word ringtail is
strongly associated with the word monkey but is not as strongly associated with the other
words, such as child or jumped.
Research has shown that chunking in terms of meaning can increase
our ability to hold information in STM. Thus, we can recall a
sequence of 5–8 unrelated words, but arranging the words to form a
meaningful sentence so that the words become more strongly associated
with one another increases the memory span to 20 words or more
(Butterworth et 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 amazing feats 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 extensive
training (230 one-hour sessions), he was able to repeat sequences of
up to 79 digits without error. How did he do it? S.F. used chunking to
recode the digits into larger units that formed meaningful sequences.
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 illustrates an interaction between STM and LTM, because
S.F., who was a runner, created some of 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 provided by an experiment by William Chase
and Herbert Simon (1973a, 1973b) in which they showed chess players
pictures of chess pieces on a chessboard for 5 seconds. The chess
players were then asked to reproduce the positions they had seen.
Chase and Simon compared the performance of a chess master who
had played or studied chess for over 10,000 hours to the performance
of a beginner who had less than 100 hours of experience. The results,
shown in Figure 5.9a, show that the chess master placed 16 pieces out
of 24 correctly on his first try, compared to just 4 out of 24 for the beginner.
Moreover, the master required only four trials to reproduce all
of the positions exactly, whereas even after seven trials the beginner
was still making errors.
We know that the master’s superior performance was caused by
chunking because it occurred only when the chess pieces were arranged
in positions from a real chess game. When the pieces were arranged
randomly, the chess master performed as poorly as the begin■
Figure 5.9 Results of Chase and
Simon’s (1973a, 1973b) chess memory
experiment. (a) The chess master
is better at reproducing actual game
positions. (b) Master’s performance
drops to level of beginner when
pieces are arranged randomly.
(a) Actual game positions
Master Beginner
12
8
4
Correctplacements
0
16
Master does better
because can chunk
based on game positions
(b) Random placement
Master Beginner
12
8
16
4
Correctplacements
0
No advantage for
master if can't chunk
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150 Chapter 5
ner (Figure 5.9b). Chase and Simon concluded that the chess master’s advantage was
due not to a more highly developed short-term memory, but to his ability to group the
chess pieces into meaningful chunks. Because the chess master had stored many of the
patterns that occur in real chess games in LTM, he saw the layout of chess pieces not
in terms of individual pieces but in terms of 4 to 6 chunks, each made up of a group of
pieces that formed familiar, meaningful patterns. When the pieces were arranged randomly,
the familiar patterns were destroyed, and the chess master’s advantage vanished
(also see DeGroot, 1965; Gobet et al., 2001).
Chunking is an essential feature of STM because it expands the capacity of STM
so it can handle 5–8 chunks rather than just 5–8 items. This enables the limited-capacity
STM to deal with the large amount of information involved in many of the tasks we
perform every day, such as chunking letters into words as you read this, remembering
the first three numbers of familiar telephone exchanges as a unit, and transforming
long conversations into smaller units of meaning.
How Is Information Coded in Short-Term Memory?
Coding refers to the way information is represented. Remember, for example, our discussion
in Chapter 2 of how a person’s face can be represented by the pattern of firing of a
number of neurons. Determining how a stimulus is represented by the firing of neurons
is a physiological approach to coding. We can also take a mental approach to coding
by asking how a stimulus or an experience is represented in the mind. For example,
imagine that you have just finished listening to your cognitive psychology professor give
a lecture. We can describe different kinds of mental coding that occur for this experience
by considering some of the ways you might remember what happened in class.
Remembering the sound of your professor’s voice is an example of auditory coding.
Imagining what your professor looks like, perhaps by conjuring up an image in
your mind, is an example of visual coding. Finally, remembering what your professor
was talking about is an example of coding in terms of meaning, which is called semantic
coding (see Table 5.2).
Auditory Coding One of the early experiments that investigated coding in STM was done
by R. Conrad in 1964. In Conrad’s experiment, participants saw a number of target
letters flashed briefly on a screen and were told to write down the letters in the order
Table 5.2 Types of Coding
Type of Coding Example
Auditory Sound of the person’s voice
Visual Image of a person
Semantic Meaning of what the person is saying
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151Short-Term and Working Memory
they were presented. Conrad found that when participants made errors, they were most
likely to misidentify the target letter as another letter that sounded like the target. For
example, “F” was most often misidentified as “S” or “X,” two letters that sound similar
to “F.” Thus, even though the participants saw the letters, the mistakes they made were
based on the letters’ sounds.
From these results Conrad concluded that the code for STM is auditory (based
on the sound of the stimulus), rather than visual (based on the visual appearance of the
stimulus). This conclusion fits with our common experience with telephone numbers.
Even though our contact with them in the phone book is visual, we usually remember
them by repeating their sound over and over rather than by visualizing what the numbers
look like in the phone book (also see Wickelgren, 1965).
Visual Coding Some tasks, such as remembering the details of a diagram or an architectural
floor plan, require visual codes (Kroll, 1970; Posner & Keele, 1967; Shepard &
Metzler, 1971). This use of 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 participants. The stimuli for this experiment were “radicals”
and “characters” (Figure 5.10a). Radicals are symbols that are part of the Chinese language
and that are not associated with any sound. Characters consist of a radical plus
another symbol, and do have a sound.
When participants were asked to reproduce a series of radicals presented one after
another, or a series of characters, they were able to reproduce a string of 2.7 radicals, on
the average, and a string of 6.4 characters, on average (Figure 5.10b). The participants’
ability to remember the radicals must be due to visual coding because the radicals have
■ Figure 5.10 (a) Examples of radical and character stimuli for Zhang and Simon’s (1985) coding
experiment. (b) Results showing evidence for visual coding (left bar) and auditory coding (right bar).
(a) (b)
Radicals Characters
6
4
2
Numberrecalled
0
8
Greater recall when
auditory coding
possible
Recall based on
visual coding
Radical
(no sound)
Character
(has sound)
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152 Chapter 5
no sound or meaning. The participants’ superior memory for the characters is most
likely due to the addition of auditory coding because each character is associated with a
sound. Thus, both visual and auditory coding can be involved in STM.
Semantic Coding There is also evidence for semantic coding in STM. This is illustrated
by an experiment by Delos Wickens and coworkers (1976). Table 5.3 shows the experimental
design for Wickens’ experiment. He used three different groups of participants—a
“professions” group, a “meat” group, and a “fruit” group. Participants in each
group listened to three words (for example, banana, peach, apple for the fruit group),
counted backward for 15 seconds, and then attempted to recall the three words. They
did this for a total of four trials, with different words presented on each trial.
The basic idea behind this experiment was to first create a decrease in memory
for all three groups by starting Trials 2 and 3 with different words from the same category
as was presented in Trial 1 (to cause proactive interference, which we discussed
on page 147). This result is shown in Figure 5.11, which indicates that participants in all
three groups remembered about 87 percent of the words on Trial 1 (Figure 5.11a), and
the performance for all three groups dropped on Trials 2 and 3 (Figures 5.11b and c), so
by Trial 3 they remembered only about 30 percent of the words.
The crucial trial in the experiment was Trial 4, because on this trial all three groups
were presented with names of fruits. From Figure 5.11d we can see that performance remained
low for the fruit group because proactive interference continued for that group.
But something different happened for the other two groups. Performance increased for
the meat group and the professions group because shifting to fruits eliminated the proactive
interference that had built up on Trials 1–3 for the names of meats and professions.
The resulting increase in performance is called release from proactive interference,
or release from PI. Figure 5.11d also indicates that the release from PI is not
as pronounced for the switch from meats to fruits because meats and fruits are more
similar to each other than are professions and fruits.
What does release from PI tell us about coding in STM? The key to answering this
question is to realize that the release from PI that occurs in the Wickens experiment
Table 5.3 Wickens’ Experiment Demonstrating Semantic Coding in STM
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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153Short-Term and Working Memory
depends on the words’ categories (fruits, meats, professions). Because placing words into
categories involves the meanings of the words, the results of the Wickens experiment
demonstrate the operation of semantic coding in STM.
Test Yourself 5.1
1. Why can we say that “memory is life”? Answer this question by considering what
memory does for people with the ability to remember, and what happens when this
ability is lost, as in cases like Clive Wearing’s.
2. Describe Atkinson and Shiffrin’s modal model of memory both in terms of its structure
(the boxes connected by arrows) and the control processes. Then describe how
each part of the model comes into play when you decide you want to order pizza but
can’t remember the pizzeria’s phone number.
3. Describe sensory memory and Sperling’s experiment in which he measured the capacity
and duration of sensory memory.
4. Is memory lost from STM by decay or by interference? Be sure you understand the
Peterson and Peterson experiment and Keppel and Underwood’s interpretation of
it. What is the time span of STM?
5. What is the capacity of STM, and how is it influenced by chunking?
6. Describe evidence supporting auditory, visual, and semantic coding of STM.
■ Figure 5.11 Results of Wickens et al.’s (1976) proactive inhibition experiment. (See Table 5.3 for
design). (a) Initial performance on Trial 1. (b and c) On Trials 2 and 3, performance for all groups (professions,
meat, 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 M
Group
F
Percentrecalled
80
100
60
40
20
0
(b) Trial 2. More words in
same categories.
P M
Group
FPercentrecalled
80
100
60
40
20
0
Decrease due to
buildup of PI
(c) Trial 3. Words still in
same category.
P M
Group
F
Percentrecalled
80
100
60
40
20
0
(d) Trial 4. Shift to fruit
category for professions
and meat. No shift for fruit.
P M
Group
F
Percentrecalled
80
100
60
40
20
0
Release from PI
More PI
Meat
Fruit
Professions
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154 Chapter 5
Working Memory: The Modern Approach to Short-Term Memory
In Chapter 1 we noted that models are used in cognitive psychology to organize data
that has been generated in many experiments and also to pose questions to be answered
by additional experiments. By these criteria, the modal model has been one of the most
useful models in cognitive psychology, because it explains a great deal of data and has
resulted in thousands of experiments. But as happens with most models, new results
emerge that can’t be easily explained by the model. This leads either to revision of the
model or proposal of an entirely new one.
In the case of the short-term memory components of the modal model, new results
prompted Alan Baddeley and Graham Hitch (1974) to propose that STM be replaced
by working memory—a mechanism that consists of a number of specialized components.
One of the main results that led to the proposal of working memory was the observation
that under some conditions participants could do two tasks at once. You can see
this for yourself by doing 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
telephone 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 Baddeley’s participants were able to read while simultaneously remembering
numbers, he concluded that the short-term process must consist of a number of
components that can function separately. In the demonstration, the digit span task in
which you held numbers in your memory was handled by one component while comprehending
the paragraph was handled by another component. Based on results such
as this, Baddeley decided the name of the short-term process should be changed from
short-term memory to working memory.
Baddeley (2000b) defines working memory as follows: Working memory is a
limited-capacity system for temporary storage and manipulation of information for
complex tasks such as comprehension, learning, and reasoning. From this definition we
can see that working memory differs from STM in two ways:
1. Short-term memory is a single component, whereas working memory consists
of a number of parts.
2. Short-term memory is concerned mainly with holding information for a
brief period of time, whereas working memory is concerned with the manipulation
of information that occurs during complex cognition.
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155Short-Term and Working Memory
Thus, working memory is concerned not just with how memory operates, but with how
information is processed in the service of various forms of cognition, such as problem
solving, thinking, attention, and language (Baddeley, 2000b).
Working memory accomplishes the manipulation of information through the action
of three components: the phonological loop, the visuospatial sketch pad, and the central
executive (Figure 5.12).
● The phonological loop holds verbal and auditory information. Thus, when
you are trying to remember a telephone number or a person’s name, or to
understand what your cognitive psychology professor is talking about, you
are using your phonological loop (Figure 5.13a).
■ Figure 5.12 Diagram of the three main
components of Baddeley and Hitch’s (1974;
Baddeley, 2000) model of working memory:
the phonological loop, the visuospatial sketch
pad, and the central executive.
Verbal and
auditory
information
Phonological
loop
Baddeley's working memory model
Central
executive
Visual and
spatial
information
Visuospatial
sketch pad
■ Figure 5.13 Tasks handled by components of working memory. (a) The phonological loop handles
language. Reading is shown here, but the phonological loop also processes information that is received
verbally, as when listening to someone speak. (b) The visuospatial sketch pad processes visual and
spatial information.
(a) (b)
Reading
Visuospatial
sketch pad
Phonological
loop
Puzzle
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156 Chapter 5
● The visuospatial sketch pad holds visual and spatial
information. When you form a picture in your mind
or do tasks like solving a puzzle or finding your way
around campus, you are using your visuospatial sketch
pad (Figure 5.13b). As you can see from the diagram,
the phonological loop and the visuospatial sketch pad
are attached to the central executive.
● The central executive is where the major work of
working memory occurs. The central executive pulls
information from long-term memory and coordinates
the activity of the phonological loop and visuospatial
sketch pad by focusing on specific parts of a task and
switching attention from one part to another. One of
the main jobs of the central executive is to decide how
to divide attention between different tasks. For example,
imagine you are driving in a strange city, and a
friend in the passenger seat is reading you directions to
a restaurant while the news is being broadcast on the
car radio. As your phonological loop takes in the verbal
directions, your sketch pad is helping visualize a map of
the streets leading to the restaurant (Figure 5.14), and
the central executive is coordinating and combining
these two kinds of information. In addition, the central
executive might be helping you focus your attention on the directions and
ignore the messages from the radio.
As we describe working memory, keep in mind that it is a hypothesis about how the
mind works that needs to be tested by experiments. A number of experiments have been
conducted to illustrate how the phonological loop and visuospatial sketch pad work in
different situations.
The Phonological Loop
Three phenomena support the idea of a system specialized for language: the phonological
similarity effect, the word-length effect, and articulatory suppression.
Phonological Similarity Effect The phonological similarity effect occurs when letters or
words that sound similar are confused. Remember Conrad’s experiment in which he
showed that people often confuse similar-sounding letters, such as “T” and “P.” Conrad
interpreted this result to support the idea of auditory coding in STM. In present-day
terminology Conrad’s result would be described as a demonstration of the phonological
similarity effect, which occurs as words are processed in the phonological loop of working
memory. Here is another demonstration of the phonological similarity effect:
Phonological
Similarity
Effect
Phonological
Similarity
Effect
■ Figure 5.14 Tasks processed by the
phonological loop (hearing directions; listening
to the radio) and visuospatial sketch pad
(visualizing the route) being coordinated by
the central executive.
Visuospatial
sketch pad
Phonological
loop
Central executive coordinates
verbal and visual information
Go left
at the
second
corner
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157Short-Term and Working Memory
Demonstration
Phonological Similarity Effect
Task 1: Slowly read the following letters. Look away and count to 15. Then write them down.
g, c, b, t, v, p
Task 2: Now do the same thing for these letters.
f, l, k, s, y, g
Which of the two tasks was more difficult? Many people find that they confuse
the similar-sounding letters in Task 1 and sometimes report similar-sounding letters
that weren’t present, like d, e, or z. In contrast, it is easier to remember the differentsounding
letters in Task 2. This confusion of the letters in Task 1 is an example of the
phonological similarity effect.
Word-Length Effect The word-length effect occurs when memory for lists 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, brick-
layer
Each list contains eight words, but according to the word-length effect
the second list will be more difficult to remember because the words
are longer. Results of an experiment by Baddeley and coworkers (1984)
that illustrate this advantage for short words are shown in Figure 5.15.
The word-length effect occurs because it takes longer to rehearse the
long words and to produce them during recall.
The word-length effect explains the initially surprising finding that
American children have a larger digit span than Welsh children. Before
you conclude that American children are smarter than Welsh children,
consider that the names of numbers in Welsh (un, dau, tri, pedwar,
pump, chwech . . .) are longer than the names of the numbers in English
(one, two, three, four, five, six . . .). Because it takes longer to pronounce
■ Figure 5.15 How word length
affects memory, showing that recall
is better for short words (Baddeley
et al., 1984).
Short
words
Long
words
50
Percentcorrectrecall
0
100
Normal word-length effect
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158 Chapter 5
Welsh numbers, fewer can be held in the phonological loop, and the memory span for
these numbers is 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 in
about 1.5–2.0 seconds (also see Schweickert & Boruff, 1986). Try counting out loud, as
fast as you can, for 2 seconds. According to Baddeley, the number of words you can say
should be close to your digit span. (Note, however, that some researchers have proposed
that the word-length effect does not occur under some conditions. See Lovatt et al.,
2000, 2002).
Articulatory Suppression A phenomenon called articulatory suppression occurs when a
person is prevented from rehearsing items to be remembered by repeating an irrelevant
sound such as “the” (“the, the, the, . . .”) (Baddeley, 2000b; Baddeley et al., 1984; Murray,
1968). Articulatory suppression has three effects: (1) it reduces the memory span;
(2) it eliminates the word-length effect; and (3) it reduces the phonological similarity effect
for reading words.
Articulatory suppression reduces memory span because speaking interferes with
rehearsal. The following demonstration, which is based on an experiment by Baddeley
and coworkers (1984), illustrates this effect of articulatory suppression:
Demonstration
Articulatory Suppression
Task 1: Read following list. Then turn away and recall as many words as you can.
dishwasher, hummingbird, engineering, hospital, homelessness, reasoning
Task 2: Read the following list while repeating the word “the” out loud (i.e., “the, the,
the . . .”). Then turn away and recall as many words as you can.
automobile, apartment, basketball, mathematics, syllogism, catholicism
Articulatory suppression occurs when remembering the second list becomes harder because
repeating the, the, the overloads the phonological loop.
Baddeley and coworkers (1984) also found that repeating “the, the, the . . .” not only
reduces the ability to remember lists of words, but it also eliminates the word-length
effect (Figure 5.16a). According to the word-length effect, a list of one-syllable words
should be easier to recall than a list of longer words because the shorter words leave
more space in the phonological loop for rehearsal. However, eliminating rehearsal by
saying “the, the, the . . .” eliminates this advantage for short words (Figure 5.16b).
Saying “the, the, the . . .” also reduces the phonological similarity effect for words
that are read. Normally words that are read are initially represented in the visuospatial
sketch pad, and then this information is transferred to the phonological loop. However,
saying “the, the, the . . .” prevents this information from being transferred to the phonological
loop because the phonological loop is engaged (Figure 5.17). Thus, similart
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159Short-Term and Working Memory
sounding words can’t be confused based on their sound, so the phonological similarity
effect is eliminated.
The Visuospatial Sketch Pad
We have seen that operation of the phonological loop can explain performance on verbal
tasks. We also saw, in the example that involved saying “the, the, the . . .” while reading
words, that it is necessary to consider the visuospatial sketch pad to explain situations
in which visual stimuli are involved. We will now consider a series of experiments by
Lee Brooks (1968) involving tasks that either both depend on the phonological loop or
(a) (b)
Short
words
Long
words
50
Percentcorrectrecall
0
100
Articulatory
suppression
the, the,
the . . .
Phonological
loop
Visuospatial
sketch pad
Reduces rehearsal
advantage for
short words
■ Figure 5.16
(a) Saying “the, the,
the . . .” abolishes the
word-length effect, so
there is little difference
in performance 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.
the,
the,
the . . .
Phonological
loop
Visuospatial
sketch pad
No transfer to phonological
loop because loop is engaged
Pear,
Bear,
Tear
Effect of saying “the, the, the”
on reading words
Phonological
loop is engaged
Words registered
here
■ Figure 5.17 Effect of
saying “the, the, the . . .” on
reading words. The phonological
similarity effect does not
occur for visually presented
words because the phonological
loop is engaged with
processing “the, the, the. . . .”
This prevents visual stimuli
from being recoded verbally in
the phonological loop.
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160 Chapter 5
that can be shared between the phonological loop and the visuospatial
sketch pad. The following demonstration is based on one
of Brooks’ tasks:
Demonstration
Holding a Verbal Stimulus in the Mind
Task 1: Memorize the sentence below, and then without looking at
it, consider each word in order and say “yes” if it is a noun and “no”
if it isn’t a noun.
John ran to the store to buy some oranges.
Task 2: Memorize the sentence below, and then use Figure 5.18
to indicate whether each word is a noun. As you remember each
word in the order it appears in the sentence, point to the Y if the
word is a noun and to the N if it isn’t (move down a row in the display
in Figure 5.18 for each new word).
The bird flew out the window to the tree.
Did you notice any difference in the difficulty of these two
tasks? Participants in Brooks’s (1968) experiment, on which this
demonstration is based, found it easier when they pointed to Y
or N than when they said yes or no. We can explain this result
in terms of working memory and the visuospatial sketch pad by recognizing that verbal
tasks depend on the phonological loop and spatial tasks depend on the visuospatial
sketch pad. Thus, for the first task, when the stimulus and task were both verbal (Figure
5.19a), the phonological loop was overloaded and the task became difficult. But for
the second task, when the stimulus was verbal and the task was spatial (Figure 5.19b), the
processing was distributed between the loop and sketch pad, and the task became easier.
We can also demonstrate the effect of distributing processing across the loop and sketch
pad by asking a person to hold a spatial stimulus in his or her mind, as in the following
demonstration:
Demonstration
Holding a Spatial Stimulus in the Mind
Task 3: Visualize the F in Figure 5.20. Then look away from the figure, and while visualizing
the F in your mind, start at the upper left corner (the one marked with the *) and, moving
around the outline of the F in a clockwise direction in your mind, point to Y in Figure 5.18
for an outside corner, and N for an inside corner.
■ Figure 5.18 Response matrix for the
“Holding a Verbal Stimulus in the Mind”
demonstration. (From Brooks, 1968.)
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
N
N
N
N
Y
N
N
N
N
N
N
N
Y
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