Short-term and Working Memory

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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 3s 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 Brown-Peterson

• 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 Brown-Peterson 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

• Donders reaction time studies 1880s
• Subtractive tasks
• A - a simple reflex see light-push button
• B decision reflex see blue light- push
  button see red light dont 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 (45) 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
  pre-frontal cortex is most active when working
  memory task are performed, same left and right
  distinction