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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 l.jpg
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

  • 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


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Duration - STM

% recall

www.psychlotron.org.uk

3 6 9 12 15 18

Length of delay (s)


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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


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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


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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


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Picture recognition

Name recognition

Free recall

Duration - LTM

% recall

www.psychlotron.org.uk

Years since leaving High School


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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


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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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