MEMORY
Features of each store:
SHORT TERM MEMORY (STM) – the limited-capacity
memory store. Coding is mainly acoustic, capacity is
between 5 and 9 items on average, duration is
between 18 and 30 seconds
LONG TERM MEMORY (LTM) – the permanent memory store. Coding is mainly
semantic, it has unlimited capacity and can store memories for up to a
lifetime
CODING – how information is processed. In sensory register, iconic memory
coded visually, and echoic memory coded acoustically. In STM, information
coded acoustically. In LTM, information coded semantically
CAPACITY – how much information can be stored. In sensory register, very
high capacity. In STM, magic number 72. In LTM, unlimited capacity
DURATION – the amount of time information stays in the memory store for. In
sensory register, less than half a second. In STM, 30 seconds unless
rehearsed. In LTM, potentially permanently
Capacity of STM – Miller (1956):
PROCEDURE – Miller noted that things tend to come in
sevens, eg. 7 days of the week, 7 deadly sins, 7 notes on a
musical scale etc. which suggests that the span/capacity
of the STM is 72. He also noted that people can recall 5
words as well as they can recall 5 letters, which they do by
chunking (grouping sets of digits or letters into units or
chunks)
EVALUATION - he may have overestimated the capacity of the STM.
Cowan (2001) concluded that the capacity of the STM was four chunks, so the
lower end of Miller’s estimate (five items) may be more accurate
, Coding of STM/LTM – Baddeley (1966):
PRODECURE – Baddeley gave four groups of participants
different lists of words to remember (acoustically similar,
acoustically dissimilar, semantically similar, semantically
dissimilar). They were shown the original words and asked to
recall them in the correct order. When they had to do this
recall task immediately (STM recall) they did worse with
acoustically similar words, suggesting that information is
coded acoustically in the STM. When they had to do this
recall task after 20 minutes (LTM recall) they did worse with semantically
similar words, suggesting that information is coded semantically in the LTM
EVALUATION – used artificial stimuli rather than meaningful material, so
findings cannot be generalised to different memory tasks (findings have
limited application)
Duration of STM – Peterson & Peterson (1959):
PROCEDURE – They tested 24 undergraduate students, each of whom took
part in eight trials (tests). The student was given a trigram to remember as
well as a three-digit number, which they were asked to count backwards from
until told to stop. This counting backwards was to prevent mental rehearsal
which would increase the memory. On each trial they were told to stop after a
different amount of time (3, 6, 9, 12, 15 or 18 seconds). This is called the
retention interval. The percentage of correct responses decreased as the
retention interval increased, suggesting that the STM has very short duration
unless we rehearse verbally.
EVALUATION – the stimulus material was artificial and meaningless so does
not reflect real-life memory activities (low external validity)
Duration of LTM – Bahrick et al. (1975):
PROCEDURE – studied 392 American participants aged 17-74
and tested recall in various ways using their high school
yearbooks. (1) photo-recognition test using 50 photos, some
2
Features of each store:
SHORT TERM MEMORY (STM) – the limited-capacity
memory store. Coding is mainly acoustic, capacity is
between 5 and 9 items on average, duration is
between 18 and 30 seconds
LONG TERM MEMORY (LTM) – the permanent memory store. Coding is mainly
semantic, it has unlimited capacity and can store memories for up to a
lifetime
CODING – how information is processed. In sensory register, iconic memory
coded visually, and echoic memory coded acoustically. In STM, information
coded acoustically. In LTM, information coded semantically
CAPACITY – how much information can be stored. In sensory register, very
high capacity. In STM, magic number 72. In LTM, unlimited capacity
DURATION – the amount of time information stays in the memory store for. In
sensory register, less than half a second. In STM, 30 seconds unless
rehearsed. In LTM, potentially permanently
Capacity of STM – Miller (1956):
PROCEDURE – Miller noted that things tend to come in
sevens, eg. 7 days of the week, 7 deadly sins, 7 notes on a
musical scale etc. which suggests that the span/capacity
of the STM is 72. He also noted that people can recall 5
words as well as they can recall 5 letters, which they do by
chunking (grouping sets of digits or letters into units or
chunks)
EVALUATION - he may have overestimated the capacity of the STM.
Cowan (2001) concluded that the capacity of the STM was four chunks, so the
lower end of Miller’s estimate (five items) may be more accurate
, Coding of STM/LTM – Baddeley (1966):
PRODECURE – Baddeley gave four groups of participants
different lists of words to remember (acoustically similar,
acoustically dissimilar, semantically similar, semantically
dissimilar). They were shown the original words and asked to
recall them in the correct order. When they had to do this
recall task immediately (STM recall) they did worse with
acoustically similar words, suggesting that information is
coded acoustically in the STM. When they had to do this
recall task after 20 minutes (LTM recall) they did worse with semantically
similar words, suggesting that information is coded semantically in the LTM
EVALUATION – used artificial stimuli rather than meaningful material, so
findings cannot be generalised to different memory tasks (findings have
limited application)
Duration of STM – Peterson & Peterson (1959):
PROCEDURE – They tested 24 undergraduate students, each of whom took
part in eight trials (tests). The student was given a trigram to remember as
well as a three-digit number, which they were asked to count backwards from
until told to stop. This counting backwards was to prevent mental rehearsal
which would increase the memory. On each trial they were told to stop after a
different amount of time (3, 6, 9, 12, 15 or 18 seconds). This is called the
retention interval. The percentage of correct responses decreased as the
retention interval increased, suggesting that the STM has very short duration
unless we rehearse verbally.
EVALUATION – the stimulus material was artificial and meaningless so does
not reflect real-life memory activities (low external validity)
Duration of LTM – Bahrick et al. (1975):
PROCEDURE – studied 392 American participants aged 17-74
and tested recall in various ways using their high school
yearbooks. (1) photo-recognition test using 50 photos, some
2
