Transcript Duration – STM & LTM

Duration – STM & LTM
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Peterson & Peterson (1959) – STM
Bahrick et al (1975) – LTM
These are key studies so make sure you
learn APFCC
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Clearly, LTM can store information for a
much longer time than LTM
Some researchers have tried to measure
their durations exactly:
Duration – STM
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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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Peterson & Peterson (1959)
PPs presented with ‘trigrams’ (CVC
nonsense syllables) and asked to recall
them (accurately & in order)
3
6
9
12
15
Length of delay (s)
18
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% recall
Duration - STM
Duration - STM
Recall declined steadily with time
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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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Duration - STM
The experiment lacked realism
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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
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We cannot tell if the info decayed (as the
Petersons claim) or was displaced by the task
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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
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Free recall
Recognition of photos
Name recognition & photo matching
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Duration - LTM
Duration - LTM
% recall
Picture
recognition
Free
recall
Years since leaving High School
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Name
recognition
Duration - LTM
Recall was remarkably high
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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
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Free recall becomes more difficult over time,
but recognition does not diminish much
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Duration - LTM
Ecological validity was high
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The study used a naturally occurring form of
info so avoided the artificiality often present in
memory studies
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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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The type of info used was very specific