Duration – STM & LTMDuration – STM & LTM

Clearly, LTM can store information for a Clearly, LTM can store information for a much longer time than LTMmuch longer time than LTM

Some researchers have tried to measure Some researchers have tried to measure their durations exactly:their durations exactly: Peterson & Peterson (1959) – STMPeterson & Peterson (1959) – STM Bahrick et al (1975) – LTMBahrick et al (1975) – LTM

These are key studies so make sure you These are key studies so make sure you learn APFCClearn APFCC

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Duration – STMDuration – STM

Peterson & Peterson (1959)Peterson & Peterson (1959)PPs presented with ‘trigrams’ (CVC PPs presented with ‘trigrams’ (CVC nonsense syllables) and asked to recall nonsense syllables) and asked to recall them (accurately & in order)them (accurately & in order) Between exposure & recall there was a delay Between exposure & recall there was a delay

in which they did an interference taskin which they did an interference task The length of the delay was varied The length of the delay was varied

Results obtained by plotting recall against Results obtained by plotting recall against length of delaylength of delay

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Duration - STMDuration - STM

3 6 9 12 15 18

% r

ecal

l

Length of delay (s)

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Duration - STMDuration - STM

Recall declined steadily with timeRecall declined steadily with time After 3s 80% correctAfter 3s 80% correct After 6s less than 50%After 6s less than 50% After 18s less than 10%After 18s less than 10%

Information is lost rapidly from STM, which Information is lost rapidly from STM, which seems to have a duration of about 20s if seems to have a duration of about 20s if nothing is done to maintain the info (i.e. nothing is done to maintain the info (i.e. rehearsal)rehearsal)

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Duration - STMDuration - STM

The experiment lacked realismThe experiment lacked realism Nonsense trigrams were used to eliminate the Nonsense trigrams were used to eliminate the

effect of meaningfulnesseffect of meaningfulness However, this is unlike the info that people However, this is unlike the info that people

typically deal withtypically deal with

The use of interference task is a problemThe use of interference task is a problem We cannot tell if the info decayed (as the We cannot tell if the info decayed (as the

Petersons claim) or was displaced by the taskPetersons claim) or was displaced by the task

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Duration - LTMDuration - LTM

Bahrick et al (1975)Bahrick et al (1975)

Test of VLTM using naturalistic materialsTest of VLTM using naturalistic materials

392 US PPs who had left high school 1-48 392 US PPs who had left high school 1-48 years previously tested for recall of years previously tested for recall of classmatesclassmates Free recallFree recall Recognition of photosRecognition of photos Name recognition & photo matchingName recognition & photo matching

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Duration - LTMDuration - LTM%

rec

all

Years since leaving High School

Picture recognition

Name recognition

Free recall

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Duration - LTMDuration - LTM

Recall was remarkably highRecall was remarkably high 80% accuracy for name recognition at 48yrs80% accuracy for name recognition at 48yrs 30% accuracy for free recall at 30yrs30% accuracy for free recall at 30yrs

Supports the idea that LTM can store Supports the idea that LTM can store some types of info for very long timesome types of info for very long time Free recall becomes more difficult over time, Free recall becomes more difficult over time,

but recognition does not diminish muchbut recognition does not diminish much

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Duration - LTMDuration - LTM

Ecological validity was highEcological validity was high The study used a naturally occurring form of The study used a naturally occurring form of

info so avoided the artificiality often present in info so avoided the artificiality often present in memory studiesmemory studies

The type of info used was very specificThe type of info used was very specific Classmates may have high emotional Classmates may have high emotional

significance, and there is usually great significance, and there is usually great opportunity for rehearsalopportunity for rehearsal

Conclusions not generalisable to other types Conclusions not generalisable to other types of informationof information

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