Short-term and
Working Memory
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Definition of memory
• The processes involved in retaining,
retrieving, and using information about
stimuli, images, events, ideas and skills after
the original information is no longer present.
• Important implications of this definition:
– Memory includes learning
– Memory involves a variety of processes that can
function with autonomy
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Importance of memory
• Obviously being able to remember past
experiences and learned skills is important for
ability to make decisions, etc. in the present
• Memory also important in predicting the
future. Much of what we know about the
future results from our knowledge of the past
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Stage theory of memory
• External  sensory  short-term  long-term
stimuli
memory
memory
memory
• Attention and sensory memory covered in the
previous section
• Now we turn to the study of short-term memory
(STM) and then later to the more encompassing
working memory
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Limited capacity ofSTM
• Miller (1956) proposed the magic number 7 +
2
• We can only receive, process, and retrieve
approximately 7 pieces of information at a
time
• His study asked people to recall in order lists
of numbers of varying length
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Overcoming this limitation
• Chunking – organizing or grouping
individual pieces of information into a
single “chunk”
• 18005551212
• 1-800-555-1212
• Today referred to as recoding 1,8,0,0 is
recoded as 1-800. 4 pieces of
information is recoded into 2 pieces
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Recoding
• Recoding can occur in STM if there is the
time and mental resources available to
reorganize the information
• Using long-term memory to recode
information – mnemonic devices
– Using a well learned strategy to recode
information
– An example is verbally recoding information
because language usage is over learned
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How accurate is this magic
number 7+
• It is accurate for relatively simple
information groups digits, words, etc.
• Not as accurate for more complex
information
– Example: with 3 or 4 word phrases the
magic number becomes 3 to 5
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Decay from STM
• Brown-Peterson task:
– Subjects shown three letters and then a 3 digit
number
– Subjects told to count backwards from the number
given by 3’s until asked to recall the letters
– Counting backwards prevented the rehearsal of
the letters
– Results:
• 3 second delay – little over 50% retained
• 9 second delay – little over 20% retained
• 18 second delay – less than 10% retained
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Interpretation of BrownPeterson
• Memory loss in STM is the result of
decay; “the memory trace decays”
without rehearsal
• STM different than long-term because it
was believed that forgetting in long-term
memory results from interference
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Can intereference occur in
STM?
• Could the counting backwards have actually
interfered with memory – not just preventing
rehearsal
• Reexamination of Brown and Peterson data (Keppel
and Underwood (1962))
• Waugh and Normal (1965) – Was the memory loss
the result of the passage of time- more loss as more
time passed
Or was increasing the amount of counting backwards
interfering with retention?
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Keppel and Underwood (1962)
• They saw that on the first trial, memory
performance was nearly perfect
• As subjects participated in more trials their
performance declined
• Their conclusion: previous trials interfered
with later trials – proactive interference
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Release from proactive
interference
• Changing the nature of the items to be remembered
reverses the decline in performance due to proactive
interference
• Wickens et al, 1963
– Two groups of subjects given 3 trials following the BrownPeterson task (letters) - Memory performance declined with
each trial
– Control group given a 4th trial using letters
– Experimental group switched to remembering digits
– Experimental group, but not control group, performed
perfectly; they were released from proactive interference
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Waugh and Norman (1965)
• Subjects verbally presented with lists of
16 digits – some lists were presented at
a rate of 1 digit per second others at 4
digits per second
• The last digit was the repeat of an
earlier digit. Subjects asked to write
down the digit that followed the earlier
digit. 4, 2, 6,8, 9, 2 correct answer is 6
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Waugh and Norman (1965)
• One group of lists took 16 seconds to present the
other group took 4 seconds
• If decay causes loss of information from short-term
memory, the 16 second group should remember less
because more time would have passed before they
responded
• Problem for decay theory was there was no
difference between groups. With no interference
performance was the same
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New decay theory
• Interference theory appears to fit the
data better than decay theory
• Active decay in a special situation –
subjects switch from one task to another
and must “forget” the previous
instructions
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Altmann and Gray (2002)
• Subjects shown one number at a time 1, 2, 3, 4 or 6,
7, 8, 9.
• 1 group of trials asked is the number odd or even?
• 2nd group of trials asked is the number from the group
of large numbers or small numbers?
• One group of subjects were switched very frequently,
the other infrequently
• Frequently switched group had faster reaction times
and were more accurate
• Conclusion: forgetting previous decision rule was
faster in this group because they needed to
remember the new rule – old info actively decayed
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Recall and the serial position
effect
• Present subjects with a list of 20, 30 or 40
items 1 every second, and ask them to recall
them in order.
• Primacy effect – more of the 1st items
presented are remembered
• Recency effect – more of the final items are
remembered
• 1st items rehearsed long enough to get in
long-term memory; last items still in STM
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Recall and the serial position
effect II
• Glanzer and Cunitz (1966)
• Same study except subjects told to count
backwards after list given
– Recency effect disappeared, not primacy
• Glanzer (1972)
• Again same study except subjects given 3, 6,
or 9 seconds between each item – longer to
rehearse
– Increase in primacy effect, no increase in recency
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Purpose of STM
• Rehearsal important part of STM
– Rehearsal maintains a memory trace for a
short period of time
– Rehearsal helps transfer information from
STM to LTM
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Retrieving information from
STM
• Donder’s reaction time studies – 1880’s
• Subtractive tasks
– A - a simple reflex – see light-push button
– B – decision + reflex – see blue light- push button
– see red light don’t push button
– C – decision + choice + reflex – see blue light
push button 1 – see red light - push button 2
– How long does it take to make a decision?
• Subtract time to perform A from time to perform B
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Sternberg Task
• Problem with Donder Subtractive tasks
– there could be an interaction between
A and B such that the reflex might not
be the same with the decision as when
it is alone
• Sternberg invented an additive task
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Sternberg Task (cont.)
• Subjects shown a list of letters ranging from 1
letter to 6 letters, then shown a single letter
as a memory probe.
• They were to respond as quickly as possible
indicating if the letter was in the list or not
• Reaction time was recorded
• Two important variables were involved
– The number of letters in each list
– The location of the letter in the memory probe – in
the beginning, middle, or end
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Sternberg Task (cont.)
• Three possible results:
– STM is searched in a parallel fashion – if true
then length of list or location should have no effect
– STM searched in a serial fashion, we search until
we find the letter – both length and position
important
– All of STM is searched and then we make a
decision, a serial exhaustive search – length
would have an effect location in the list would have
no effect
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Results of Sternberg Task
• Results:
– 1 letter list - 37.9 ms
– 2 letter list – 75.8 ms
– Each additional letter increased reaction time by
37.9 ms
– Location of the letter in the list or if the letter not in
the list had no effect
• Conclusions: we scan all of STM before
making a decision
• Many limitations found to this research, but it
led to major advances in cognitive sciences
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Coding information in STM
• Baddeley (1966) – information coded
acoustically or verbally
– Subjects asked to remember either a 5
word list or a 10 word list
– Remembering 5 word list STM; 10 word list
exceeds STM and is LTM
– In all lists, the words either sounded alike
(cat, hat, cat) had similar meanings (tiny,
small, little) or were unrelated
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Baddeley (1966)
• Results:
– 5 word list errors – most errors were made when
words sounded alike – house instead of mouse.
Fewer errors on lists with similar meaning or
unrelated
– 10 word list most errors with semantically similar
words – labor instead of work
• Conclusion: Similar sounding words confused
in STM because memory code was acoustic.
Semantically similar words confused in LTM
because memory code was using meaning
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Wickens (1972) – Release
from proactive interference
• Proactive interference occurring as a result of
semantic coding in STM
• 5 groups of subjects given 3 trials of lists of 3 words
each all from the same category
–
–
–
–
–
Group 1 – names of fruit
Group 2 – vegetable names
Group 3 – flower names
Group 4 - names of meats
Group 5 – names of different professions
• Then all groups given a 4 trial where all list contained
names of fruit
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Wickens (1972) – Release
from proactive interference
• Results:
–
–
–
–
1st trial all groups about 90% correct
2nd trial all groups about 50%
3rd trial all groups 35 – 45 %
4th trial professions 80%, meat 50%, flowers 47%,
vegetables 40% and fruit 32%
• Conclusion: Information was coded using
semantic information causing groups to
confuse current list with previous lists
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Visual coding in STM
• Mental rotation task of Shepard and colleagues
• Subjects shown 2 objects and asked if they were the
same or different in different orientations
• Interpretation people held the 1st figure in STM and
mentally rotated the 2nd to make a comparison
– Objects were either different or the same but rotated to a
different orientation
– Subjects took longer to answer when the object had been
rotated further 600, 900, 1200
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Working memory
• Developed as a result of STM memory
not being useful in explaining how short
term memory processes were used in
problem solving
• Also finding that some people with brain
damage can have impaired STM – a
digit span of only 2 items, but no deficits
in learning, comprehension, or memory
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Components of working
memory
• Executive control system – planning,
initiating, and integrating information – high
cognitive abilities
• Two subordinate systems:
– Articulatory or phonological loop – rehearses
verbal information – auditory and semantic coding
– Visual-spatial sketchpad – maintains images and
spatial representations – visual coding
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The working memory process
• Central executive gives subordinate systems
information to hold until it needs it again
• Example in textbook:
– (4 + 5)2
3+ (12/4)
Central executive does (4+5) 2 = 18 sends answer
to articulatory loop to remember while it calculates
3+(12/4) = 6
It then retrieves 18 to calculate 18/6 = 3
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Limited capacity of working
memory
• The subordinate systems have few
attentional resources; when they are involved
in a demanding task they must get resources
from central executive
• These resources are limited
• Creates the concept of dual tasks – two tasks
being performed at the same time
• The validity of working memory can be tested
using dual task methods
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Dual task studies
• Subjects given reasoning tasks of varying complexity
– performed by the central executive
• Then asked to perform different secondary tasks that
were similar in articulatory demands but whose
memory requirements differed
• It was found that the most complex reasoning tasks
were most effected by secondary tasks that required
the most memory resources
• As the articulatory loop took more resources from the
central executive, it found solving the complex
reasoning tasks more difficult
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Other supporting data for
working memory
• 8-arm maze
• Neuropsychological evidence
– Damage to areas of the left frontal lobe creates
deficits in verbal working memory
– Damage to areas of the left frontal lobe creates
deficits in spatial and visual working memory
– PET scans have shown that the Dorsolateral prefrontal cortex is most active when working memory
task are performed, same left and right distinction
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