Psychology - memory
STM and LTM
Capacity = a measure of how much can be held in memory (represented in terms of bits of info, such as
number of digits)
Coding = the way info is changed so that it can be stored as memory (info enters brain via senses, stored
in various forms such as visual codes (pictures), acoustic codes (sounds) or semantic codes (meaning of
the experience)
Duration = a measure of how long a memory lasts for before no longer available
Short term memory (STM) = memory for immediate events
Long term memory (LTM) = memory for events that happened in the past
Short term memory
● Memory for immediate events
● Measured in seconds and minutes (short durations)
● Disappear unless rehearsed
● Limited capacity of about 4 items or chunks
● Tends to be coded acoustically
● Sometimes referred to as working memory
Capacity (how much data can be held in the memory store):
● Limited capacity store
● Joseph (1880) - found average span for digits to be 9.3 items and 7.3 for letters
● Miller - came up with the magic 7 +/-2, found that span of immediate memory is about 7,
sometimes more or less (digit span to see the capacity of STM)
● Miller also found that if we chunk things together we can remember them more
Duration:
● STM doesn't last that long - has a short duration unless you repeat it over and over
● 18-30 seconds - Peterson & Peterson (1959)
● Used 24 students, each was tested over 8 trials, on each one they were given a consonant
syllable & a 3 digit number & asked to recall it after a certain number of seconds (a retention
interval - in which they had to count backwards from their 3 digit number)
● The experiment suggested that the STM had a very short duration of less than 18 seconds
Coding:
● Info that we store has to be ‘written’ in memory in some form
● Described as a code which is held in the form of sounds (acoustic) images (visual) or meaning
(semantic)
, ● Baddeley (1966) used word lists to test the effects of acoustic and semantic similarity on STM
and LTM
● Found that participants had trouble in remembering acoustically similar words in STM but had
little problem with semantically similar words
● Suggests that STM is largely encoded acoustically
Long term memory
● Memory for events that happened in the past
● Lasts from 2 mins for 100 years
● Has potentially unlimited duration and capacity
● Tends to be coded semantically
Capacity:
● Potentially infinite capacity
Duration:
● LTM potentially lasts forever
● Bahrick et al (1975) tested 400 people of various ages (17-74) on their memory of classmates
● A photo recognition test consisting of 50 photos, some from participants high school yearbook,
asked to list those who could remember of those graduating in their class
● Also tested with free recall
● Those who were tested within 15 years of graduating were about 90% accurate in identifying
faces, after 48 years it was about 70%
● Free recall was about 60% accurate after 15 years and 30% after 48 years
Coding:
● Baddeley (1966) used word lists to test the effects of acoustic and semantic similarity on STM
and LTM
● Found that participants did not have trouble in remembering acoustically similar words in LTM but
got muddled with semantically similar words
● Suggests that LTM is largely encoded semantically
Short term memory duration experiment *
Method:
● Class divided into pairs - one the investigator and the other one the participant (PPT)
● The participant has to remember the 3 letters from a table, e.g. XPR (nonsense trigram) whilst
counting back in 3’s from a specific number (e.g. 279) for a set period of time (e.g. 3, 6, 9, 12, 15
or 18 seconds)
● They then have to repeat the letters at the end of the time period
● After they have completed the sheet the participant and the investigator switch round
Independent variable (IV) = number of seconds - interval
Dependent variable (DV) = number of nonsense trigrams recalled
Conclusion:
● The % recall of nonsense trigrams decreases with time intervals until up to 12 seconds where it
increases at 15 and 18 seconds
, Discussion / evaluation:
Strengths:
1. Each interval was done 80 times, which gives the experiment good external validity
2. All carried out the same procedure - good external validity
Weaknesses:
1. Timings may not have been as accurate as they should be (can use machine to count down &
ping at 0)
2. Distraction - noise from other groups & hearing other nonsense trigrams
AO3 - STM
1. Point: The capacity of STM is not the same for everyone
Evidence: Jacobs found that recall (digit span) increased steadily with age, 8 years old could remember
an average of 6.6 digits but the average for 19 year olds was 8.6 digits
Explanation: This age increase might be due to changes in the brain capacity and / or to the development
of strategies such as chunking
Link: This suggests that the capacity of STM is not fixed and individual differences can play a role
2. Point: The size of the chunk affects how many chunks you are able to remember
Evidence: Simon found that people who had a shorter memory span for larger chunks, such as 8-word
phrases, than smaller chunks, such as one syllable words
Link: Therefore this supports the view that STM has a limited capacity and refines our understanding
AO3 - LTM
1. Point: LTM may not be exclusively semantic
Evidence: Frost (1972) showed that long term recall was related to visual as well as semantic categories
Explanation: LTM appears to be semantic but it is not always and it can vary according to circumstances
Link: Therefore, this limits the Baddeley’s method in explaining the long term memory
The multi-store model of memory
Multi-store model = an explanation of memory based on three separate memory stores and how info is
transferred between them
Sensory register = info in senses (info collected by eyes, ears…), the info is retained for a very short
period by the sensory registers and we are only able to hold accurate images of sensory info momentarily
(less than half a second). The capacity of the sensory memory is very large (e.g. cells on the retina) and
the method for coding depends on the sense organ involved (e.g. visual for eyes)
● Provides us with an analogy of how memory works
● Not exact copies, just models
STM and LTM
Capacity = a measure of how much can be held in memory (represented in terms of bits of info, such as
number of digits)
Coding = the way info is changed so that it can be stored as memory (info enters brain via senses, stored
in various forms such as visual codes (pictures), acoustic codes (sounds) or semantic codes (meaning of
the experience)
Duration = a measure of how long a memory lasts for before no longer available
Short term memory (STM) = memory for immediate events
Long term memory (LTM) = memory for events that happened in the past
Short term memory
● Memory for immediate events
● Measured in seconds and minutes (short durations)
● Disappear unless rehearsed
● Limited capacity of about 4 items or chunks
● Tends to be coded acoustically
● Sometimes referred to as working memory
Capacity (how much data can be held in the memory store):
● Limited capacity store
● Joseph (1880) - found average span for digits to be 9.3 items and 7.3 for letters
● Miller - came up with the magic 7 +/-2, found that span of immediate memory is about 7,
sometimes more or less (digit span to see the capacity of STM)
● Miller also found that if we chunk things together we can remember them more
Duration:
● STM doesn't last that long - has a short duration unless you repeat it over and over
● 18-30 seconds - Peterson & Peterson (1959)
● Used 24 students, each was tested over 8 trials, on each one they were given a consonant
syllable & a 3 digit number & asked to recall it after a certain number of seconds (a retention
interval - in which they had to count backwards from their 3 digit number)
● The experiment suggested that the STM had a very short duration of less than 18 seconds
Coding:
● Info that we store has to be ‘written’ in memory in some form
● Described as a code which is held in the form of sounds (acoustic) images (visual) or meaning
(semantic)
, ● Baddeley (1966) used word lists to test the effects of acoustic and semantic similarity on STM
and LTM
● Found that participants had trouble in remembering acoustically similar words in STM but had
little problem with semantically similar words
● Suggests that STM is largely encoded acoustically
Long term memory
● Memory for events that happened in the past
● Lasts from 2 mins for 100 years
● Has potentially unlimited duration and capacity
● Tends to be coded semantically
Capacity:
● Potentially infinite capacity
Duration:
● LTM potentially lasts forever
● Bahrick et al (1975) tested 400 people of various ages (17-74) on their memory of classmates
● A photo recognition test consisting of 50 photos, some from participants high school yearbook,
asked to list those who could remember of those graduating in their class
● Also tested with free recall
● Those who were tested within 15 years of graduating were about 90% accurate in identifying
faces, after 48 years it was about 70%
● Free recall was about 60% accurate after 15 years and 30% after 48 years
Coding:
● Baddeley (1966) used word lists to test the effects of acoustic and semantic similarity on STM
and LTM
● Found that participants did not have trouble in remembering acoustically similar words in LTM but
got muddled with semantically similar words
● Suggests that LTM is largely encoded semantically
Short term memory duration experiment *
Method:
● Class divided into pairs - one the investigator and the other one the participant (PPT)
● The participant has to remember the 3 letters from a table, e.g. XPR (nonsense trigram) whilst
counting back in 3’s from a specific number (e.g. 279) for a set period of time (e.g. 3, 6, 9, 12, 15
or 18 seconds)
● They then have to repeat the letters at the end of the time period
● After they have completed the sheet the participant and the investigator switch round
Independent variable (IV) = number of seconds - interval
Dependent variable (DV) = number of nonsense trigrams recalled
Conclusion:
● The % recall of nonsense trigrams decreases with time intervals until up to 12 seconds where it
increases at 15 and 18 seconds
, Discussion / evaluation:
Strengths:
1. Each interval was done 80 times, which gives the experiment good external validity
2. All carried out the same procedure - good external validity
Weaknesses:
1. Timings may not have been as accurate as they should be (can use machine to count down &
ping at 0)
2. Distraction - noise from other groups & hearing other nonsense trigrams
AO3 - STM
1. Point: The capacity of STM is not the same for everyone
Evidence: Jacobs found that recall (digit span) increased steadily with age, 8 years old could remember
an average of 6.6 digits but the average for 19 year olds was 8.6 digits
Explanation: This age increase might be due to changes in the brain capacity and / or to the development
of strategies such as chunking
Link: This suggests that the capacity of STM is not fixed and individual differences can play a role
2. Point: The size of the chunk affects how many chunks you are able to remember
Evidence: Simon found that people who had a shorter memory span for larger chunks, such as 8-word
phrases, than smaller chunks, such as one syllable words
Link: Therefore this supports the view that STM has a limited capacity and refines our understanding
AO3 - LTM
1. Point: LTM may not be exclusively semantic
Evidence: Frost (1972) showed that long term recall was related to visual as well as semantic categories
Explanation: LTM appears to be semantic but it is not always and it can vary according to circumstances
Link: Therefore, this limits the Baddeley’s method in explaining the long term memory
The multi-store model of memory
Multi-store model = an explanation of memory based on three separate memory stores and how info is
transferred between them
Sensory register = info in senses (info collected by eyes, ears…), the info is retained for a very short
period by the sensory registers and we are only able to hold accurate images of sensory info momentarily
(less than half a second). The capacity of the sensory memory is very large (e.g. cells on the retina) and
the method for coding depends on the sense organ involved (e.g. visual for eyes)
● Provides us with an analogy of how memory works
● Not exact copies, just models
