Duration

1
Duration STM LTM

• Clearly, LTM can store information for a much
  longer time than LTM
• Some researchers have tried to measure their
  durations exactly
• Peterson Peterson (1959) STM
• Bahrick et al (1975) LTM
• These are key studies so make sure you learn
  APFCC

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2
Duration STM

• Peterson Peterson (1959)
• PPs presented with trigrams (CVC nonsense
  syllables) and asked to recall them (accurately
  in order)
• Between exposure recall there was a delay in
  which they did an interference task
• The length of the delay was varied
• Results obtained by plotting recall against
  length of delay

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3
Duration - STM
recall
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3 6 9 12 15 18
Length of delay (s)
4
Duration - STM

• Recall declined steadily with time
• After 3s 80 correct
• After 6s less than 50
• After 18s less than 10
• Information is lost rapidly from STM, which seems
  to have a duration of about 20s if nothing is
  done to maintain the info (i.e. rehearsal)

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5
Duration - STM

• The experiment lacked realism
• Nonsense trigrams were used to eliminate the
  effect of meaningfulness
• However, this is unlike the info that people
  typically deal with
• The use of interference task is a problem
• We cannot tell if the info decayed (as the
  Petersons claim) or was displaced by the task

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6
Duration - LTM

• Bahrick et al (1975)
• Test of VLTM using naturalistic materials
• 392 US PPs who had left high school 1-48 years
  previously tested for recall of classmates
• Free recall
• Recognition of photos
• Name recognition photo matching

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7
Duration - LTM
recall
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Years since leaving High School
8
Duration - LTM

• Recall was remarkably high
• 80 accuracy for name recognition at 48yrs
• 30 accuracy for free recall at 30yrs
• Supports the idea that LTM can store some types
  of info for very long time
• Free recall becomes more difficult over time, but
  recognition does not diminish much

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9
Duration - LTM

• Ecological validity was high
• The study used a naturally occurring form of info
  so avoided the artificiality often present in
  memory studies
• The type of info used was very specific
• Classmates may have high emotional significance,
  and there is usually great opportunity for
  rehearsal
• Conclusions not generalisable to other types of
  information

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