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Chapter 5
Short-Term and Working Memory
Some Questions to 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 heard?
Is there a relationship between memory
capacity and intelligence?
What Is Memory?
• Memory: processes involved in retaining,
retrieving, and using information about
stimuli, images, events, ideas, and skills after
the original information is no longer present
Modal Model of Memory
• Atkinson and Shiffrin (1968)
• Computer as a model for human cognition
• Memory is an integrated system that
processes information
– Acquire, store, and retrieve information
– Components of memory do not act in isolation
• Memory has a limited capacity
– Limited space
– Limited resources
– Limited time
Caption: 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
Modal Model of Memory
• Control processes: active processes that can
be controlled by the person
– Rehearsal
– Strategies used to make a stimulus more
– Strategies of attention
Caption: 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.
Modal Model of Memory: Sensory Memory
• Short-lived sensory memory registers all or
most information that hits our visual receptors
– Information decays very quickly
• Persistence of vision: retention of the
perception of light
– Sparkler’s trail of light
– Frames in film
Modal Model of Memory: Sensory Memory
• Holds large amount of information for a short
period of time
– Collects information
– Holds information for initial processing
– Fills in in the blank
Modal Model of Memory: Sensory Memory
• Measuring the capacity and duration of
sensory memory (Sperling, 1960)
– Array of letters flashed quickly on a screen
– Participants asked to report as many as
Modal Model of Memory: Sensory Memory
• Whole report: participants asked to report as
many as could be seen
– Average of 4.5 out of 12 letters (37.5%)
Modal Model of Memory: Sensory Memory
• Partial report: participants heard tone that told
them which row of letters to report
– Average of 3.3 out of 4 letters (82.5%)
– Participants could report any of the rows
Modal Model of Memory: Sensory Memory
• Delayed partial report: presentation of tone
delayed for a fraction of a second after the
letters were extinguished
– Performance decreases rapidly
Caption: Results of Sperling’s (1960) partial report experiments. The
decrease in performance is due to the rapid decay of iconic
memory (sensory memory in the modal model).
Modal Model of Memory: Short-Term Memory
• Stores small amounts of information for a
brief duration
• Includes both new information received from
the sensory stores and information recalled
from long-term memory
Modal Model of Memory: Short-Term Memory
• Measuring the duration of short-term memory
– Read three letters, then a number
– Begin counting backwards by three’s
– After a set time, recall three letters
Modal Model of Memory: Short-Term Memory
• After three seconds of counting, participants
performed at 80%
• After 18 seconds of counting, participants
performed at 10%
Modal Model of Memory: Short-Term Memory
• Short-term memory, when rehearsal is
prevented, is about 15-20 seconds
Modal Model of Memory: Short-Term Memory
• Proactive interference (PI): occurs when
information learned previously interferes with
learning new information
Caption: 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 with a delay of 18 seconds
between presentation and test. These data are based on the average
performance over many trials. (b) Analysis of Peterson and Peterson’s
results by Keppel and Underwood, showing little decrease in performance
if only the first trial is included.
Modal Model of Memory: Short-Term Memory
• Capacity of short-term memory
– Digit span: how many digits a person can
• Typical result: 5-8 items
• But what is an item?
Modal Model of Memory: Short-Term Memory
• Chunking: small units can be combined into
larger meaningful units
– Chunk is a collection of elements strongly
associated with one another but weakly
associated with elements in other chunks
Modal Model of Memory: Short-Term Memory
• Ericcson et al. (1989)
– Trained a college student with average
memory ability to use chunking
• S.F. had an initial digit span of 7
– After 230 one-hour training sessions, S.F.
could remember up to 79 digits
• Chunking them into meaningful units
Modal Model of Memory: Short-Term Memory
• Chase and Simon (1973)
– Memory for chess pieces on a board
– Chess masters and beginners
– Pieces positioned for a real chess game or
randomly positioned
Caption: 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.
Modal Model of Memory: Short-Term Memory
• How is information coded in STM?
– Coding: the way information is represented
– Physiological: how stimulus is represented
by the firing of neurons
– Mental: how stimulus or experience is
represented in the mind
Modal Model of Memory: Short-Term Memory
• Auditory coding – Conrad (1964)
– Participants briefly saw target letters and
were asked to write them down
– Errors most often occurred with letters that
sounded alike
– STM is auditory
Modal Model of Memory: Short-Term Memory
• Visual coding – Della Sala (1999)
– Presented visual information that is difficult
to verbalize
– Participants could recreate patterns of up
to 9 items
– STM is also visual
Modal Model of Memory: Short-Term Memory
• Semantic coding – Wickens et al. (1976)
– Participants listened to three words, counted
backwards for 15 seconds, and attempted to
recall the three words
• Four trials, different words on each trial
Modal Model of Memory: Short-Term Memory
• On trial 4, participants memorized words from a
different category
– Release from PI: memory increased
– Participants used meaning of the words in
their processing
– STM is also semantic
Caption: Results of Wickens et al.’s (1976) proactive inhibition experiment. (a)
Fruit group, showing reduced performance on trials 2, 3, and 4 caused at
least partially by proactive interference (indicated by dark points). (b)
Professions group, showing reduced performance on trials 2 and 3 but
improved performance on trial 4. The increase in performance on trial 4
represents a release from proactive interference caused by the change of
category from professions to fruits.
Working Memory
• Similar concept to short-term memory
• Working memory (WM): limited capacity system
for temporary storage and manipulation of
information for complex tasks such as
comprehension, learning, and reasoning
Working Memory
• Working memory differs from STM
– STM is a single component
– WM consists of multiple parts
Working Memory
• Working memory differs from STM
– STM holds information for a brief period of
– WM is concerned with the processing and
manipulation of information that occurs during
complex cognition
Caption: 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
Phonological Loop
• Phonological similarity effect
– Letters or words that sound similar are
Phonological Loop
• Word-length effect
– Memory for lists of words is better for short
words than for long words
– Takes longer to rehearse long words and to
produce them during recall
Phonological Loop
• Articulatory suppression
– Prevents one from rehearsing items to be
• Reduces memory span
• Eliminates word-length effect
• Reduces phonological similarity effect for
reading words
Visuospatial Sketch Pad
• Brooks (1968)
– Memorize sentence and then consider each
word (mentally)
– Response is either
• Phonological: say “yes” if it is a noun and
“no” if it is not
• Visuospatial: point to Y if word is a noun
and N if word is not
Visuospatial Sketch Pad
• Pointing was easier than speaking
• Task (memorize sentence) involved the
phonological loop
• Pointing response involved the visuospatial
sketch pad
• Verbal response involved the phonological loop
• Conducting two verbal tasks overloaded the
phonological loop
Visuospatial Sketch Pad
• Brooks (1968)
– Visualize a capital letter F, starting at the top
left corner
– Response is either
• Phonological: say “out” if it is an exterior
corner and “in” if it is an interior corner
• Visuospatial: point to “out” if it is an exterior
corner and “in” if it is an interior corner
Visuospatial Sketch Pad
• Speaking was easier than pointing
• Task (visualize a capital letter) involved the
visuospatial sketch pad
• Pointing response involved the visuospatial
sketch pad
• Verbal response involved the phonological loop
• Conducting two visuospatial tasks overloaded
the visuospatial sketch pad
Visuospatial Sketch Pad
• Results show that if the task and the response
draw on the same WM component, performance
is worse than if the task and the response are
distributed between WM components
Working Memory
• WM is set up to process different types of
information simultaneously
• WM has trouble when similar types of
information are presented at the same time
The Central Executive
• Attention controller
– Focus, divide, switch attention
• Controls suppression of irrelevant information
Episodic Buffer
• Backup store that communicates with LTM and
WM components
• Hold information longer and has greater
capacity than phonological loop or visuospatial
sketch pad
Caption: Baddeley’s revised working memory model, which contains
the original three components plus the episodic buffer.
WM and the Brain
• Prefrontal cortex responsible for processing
incoming visual and auditory information
– Monkeys without a prefrontal cortex have
difficulty holding information in WM
WM and the Brain
• Funahashi et al. (1989)
– Single cell recordings from monkey’s
prefrontal cortex during a delay-response
WM and the Brain
• Neurons responded when stimulus was flashed
in a particular location and during delay
• Information remains available via these neurons
for as long as they continue firing
Caption: Results of an experiment showing the response of neurons
in the monkey’s PF cortex during an attentional task. Neural
responding is indicated by an asterisk (*). (a) A cue square is
flashed at a particular position, causing the neuron to respond. (b)
The square goes off , but the neuron continues to respond during
the delay. (c) The fixation X goes off , and the monkey
demonstrates its memory for the location of the square by moving
its eyes to where the square was
WM and the Brain
• Areas in frontal lobe, parietal lobe, and
cerebellum are involved in WM
Caption: Some of the areas in the cortex that have been shown by
brain imaging research to be involved in working memory. The
colored dots represent the results of more than 60 experiments
that tested working memory for words and numbers (red), objects
(blue), spatial location (orange), and problem-solving (green).
WM and the Brain: Individual Differences
• Vogel et al. (2005)
• Determined participants’ WM
– High-capacity WM group
– Low-capacity WM group
• Shown either simple or complex stimuli
• Measured ERP responses
Caption: Results of the Vogel et al. (2005) experiment. The key
finding is that performance is about the same when only the red
rectangles are present (left pair of bars); although adding the two
blue rectangles has little effect for the high-capacity participants, it
causes an increase in the response for the low-capacity
participants (right pair of bars).
WM and the Brain: Individual Differences
• Vogel et al. (2005)
• Results
– High-capacity participants were more efficient
at ignoring the distractors