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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. www.psychlotron.org.uk.

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duration stm ltm
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

www.psychlotron.org.uk

duration stm
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

www.psychlotron.org.uk

duration stm3
Duration - STM

% recall

www.psychlotron.org.uk

3 6 9 12 15 18

Length of delay (s)

duration stm4
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)

www.psychlotron.org.uk

duration stm5
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

www.psychlotron.org.uk

duration ltm
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

www.psychlotron.org.uk

duration ltm7

Picture recognition

Name recognition

Free recall

Duration - LTM

% recall

www.psychlotron.org.uk

Years since leaving High School

duration ltm8
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

www.psychlotron.org.uk

duration ltm9
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

www.psychlotron.org.uk

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