Memory
Coding, Capacity + Duration of Memory
Short-Term Memory (STM): The limited-capacity memory store. Coding is
mainly acoustic (sounds), capacity is between 5 + 9 items on average,
duration is between about 18 + 30 seconds.
Long-Term Memory (LTM): The permanent memory store. Coding is mainly
semantic (meaning), it has unlimited capacity + can store memories for up to a
life time.
Memory
The process by which we retain information about events that have happened
in the past. A memory system has to be able to:
Acquire information (coding)
Store information (retaining)
Retrieve information (recovering)
Research on Coding
Coding is the format in which information is stored in the various memory
stores.
Baddeley (1966) gave different lists of words to 4 groups of participants to
remember:
Group 1 (acoustically similar): words sounded similar (e.g. cat, cab, can).
Group 2 (acoustically dissimilar): words sounded different (e.g. pit, few,
cow).
Group 3 (semantically similar): words with similar meanings (e.g. great,
large, big).
Group 4 (semantically dissimilar): words that all had different meanings
(e.g. good, huge, hot).
Participants were shown the original words + asked to recall them in the
correct order. When they had to recall the word list immediately after hearing it
,(STM recall), they did worse with acoustically similar words – suggests that
information is coded acoustically in STM.
If participants were asked to recall the word list after a time interval of 20 mins
(LTM recall), they did worse with semantically similar words – suggests that
information is coded semantically in LTM.
Evaluation – Artificial Stimuli
Baddeley’s study used artificial stimuli rather than meaningful material
(word lists had no personal meaning to participants) – low ecological
validity.
This means we should be cautious about generalising the findings to
different kinds of memory task.
E.g. when processing more meaningful information, people may use
semantic coding even for STM tasks.
This suggests that the findings from this study have limited application.
Research on Capacity
Capacity is the amount of information that can be held in a memory store.
Digit Span
Jacobs (1887) measured digit span.
He gave participants 4 digits + then asked them to recall the digits in the
correct order out loud.
If this was correct, Jacobs read out 5 digits + so on until the participants
couldn’t recall the order correctly.
This determined the individual’s digit span.
Jacobs found that the mean digit span across all participants was 9.3
items.
The mean span for letters was 7.3.
Evaluation – Lacking Validity
Jacobs’s study was conducted a long time ago.
Early research in psychology often lacked adequate control.
E.g. participants may have been distracted while being tested so they
didn’t perform as well as they might.
This would mean that the results might not be valid because there were
confounding variables that weren’t controlled.
, However, the results of this study have been confirmed in other research,
supporting its validity.
Span of Memory + Chunking
Miller (1956) made observations of everyday practice.
He noted that things come in 7s: 7 days of week, 7 deadly sins, etc.
This suggests that the span/capacity of STM is about 7 items (± 2).
However, Miller also noted that people can recall 5 words as well as they
can recall 5 letters.
They do this by chunking – grouping sets of digits/letters into units/chunks.
Evaluation – Not So Many Chunks
In Miller’s research he may have overestimated the capacity of STM.
E.g. Cowan (2001) reviewed other research + concluded that the capacity
of STM was only about 4 chunks.
This suggests that the lower end of Miller’s estimate (5 items) is more
appropriate than 7 items.
Research on Duration
Duration is the length of time information can be held in memory.
Duration of STM
Peterson + Peterson (1959) tested 24 students.
Each student took part in 8 trials.
On each trial the student was given a consonant syllable (a trigram, i.e.
YCG) to remember + was also given a 3-digit number.
The student was then asked to count backwards from that 3-digit number
until told to stop.
Counting backwards was to prevent any mental rehearsal of the trigram
(which would increase the student’s memory for the trigram).
On each trial they were told to stop after different retention intervals – 3, 6,
9, 12, 15, or 18 seconds.
Participants remembered 90% with a 3 second interval.
20% with a 9 second interval.
2% with an 18 second interval.
STM has a duration of less than 18 seconds – if verbal rehearsal is
prevented.
,Evaluation – Meaningless Stimuli in STM Study
In Peterson + Peterson’s study the stimulus material was artificial (lacks
ecological/ external validity).
Trying to memorise trigrams doesn’t reflect most real-life memory activities
where what we’re trying to remember is meaningful.
However, we do sometimes try to remember fairly meaningless things, i.e.
phone numbers, so the study is not totally irrelevant.
It also lacks population validity as student participants are more intelligent
+ younger than average.
Duration of LTM
Bahrick et al. (1975) studied 400 participants aged between 17 + 74. High
school yearbooks were obtained from the participants or their schools. Recall
was tested by:
1) Photo-recognition test consisting of 50 photos from the
participant’s high school yearbook.
2) Free recall test – participants recalled all the names of their
graduating class.
15 years after graduation, photo recognition was 90% accurate. After 48
years, recall declined to about 70% for photo recognition.
Free recall was poorer than recognition – after 15 years this was about
60% accurate, dropping to 30% after 48 years.
This shows that LTM can last a very long time.
Evaluation – Higher External Validity
Bahrick et al.’s study has high external validity.
Real-life meaningful memories were studied.
When studies on LTM have been conducted with meaningless pictures to
be remembered, recall rates were lower.
However, confounding variables are not controlled – e.g. participants may
have looked at their yearbook photos + rehearsed their memory over the
years.
The Multi-Store Model of Memory
, The Multi-Store Model (MSM)
Atkinson + Shiffrin’s (1968, 1971) multi-store model describes how
information flows through the memory system, how information is
remembered + how it’s forgotten. Information flows through the stores in a
linear way.
The model suggests that memory is made up of 3 stores linked by processing:
Sensory Register
A stimulus from the environment; e.g. sights, sounds, smells etc. will pass into
the sensory registers. This part of memory stores for each of our 5 senses.
The two main stores are:
Iconic memory (vision) – visual information is coded visually.
Echoic memory (hearing) – sound/auditory information is coded
acoustically.
The sensory register is not under cognitive control + is the first storage system
for incoming information – information received is raw + unprocessed
The sensory register has a large capacity (millions of receptors) however the
duration of storage is only very brief (less than half a second) – unless given
focused attention which will cause it move to the STM.
Short-Term Memory (STM)
Coding, Capacity + Duration of Memory
Short-Term Memory (STM): The limited-capacity memory store. Coding is
mainly acoustic (sounds), capacity is between 5 + 9 items on average,
duration is between about 18 + 30 seconds.
Long-Term Memory (LTM): The permanent memory store. Coding is mainly
semantic (meaning), it has unlimited capacity + can store memories for up to a
life time.
Memory
The process by which we retain information about events that have happened
in the past. A memory system has to be able to:
Acquire information (coding)
Store information (retaining)
Retrieve information (recovering)
Research on Coding
Coding is the format in which information is stored in the various memory
stores.
Baddeley (1966) gave different lists of words to 4 groups of participants to
remember:
Group 1 (acoustically similar): words sounded similar (e.g. cat, cab, can).
Group 2 (acoustically dissimilar): words sounded different (e.g. pit, few,
cow).
Group 3 (semantically similar): words with similar meanings (e.g. great,
large, big).
Group 4 (semantically dissimilar): words that all had different meanings
(e.g. good, huge, hot).
Participants were shown the original words + asked to recall them in the
correct order. When they had to recall the word list immediately after hearing it
,(STM recall), they did worse with acoustically similar words – suggests that
information is coded acoustically in STM.
If participants were asked to recall the word list after a time interval of 20 mins
(LTM recall), they did worse with semantically similar words – suggests that
information is coded semantically in LTM.
Evaluation – Artificial Stimuli
Baddeley’s study used artificial stimuli rather than meaningful material
(word lists had no personal meaning to participants) – low ecological
validity.
This means we should be cautious about generalising the findings to
different kinds of memory task.
E.g. when processing more meaningful information, people may use
semantic coding even for STM tasks.
This suggests that the findings from this study have limited application.
Research on Capacity
Capacity is the amount of information that can be held in a memory store.
Digit Span
Jacobs (1887) measured digit span.
He gave participants 4 digits + then asked them to recall the digits in the
correct order out loud.
If this was correct, Jacobs read out 5 digits + so on until the participants
couldn’t recall the order correctly.
This determined the individual’s digit span.
Jacobs found that the mean digit span across all participants was 9.3
items.
The mean span for letters was 7.3.
Evaluation – Lacking Validity
Jacobs’s study was conducted a long time ago.
Early research in psychology often lacked adequate control.
E.g. participants may have been distracted while being tested so they
didn’t perform as well as they might.
This would mean that the results might not be valid because there were
confounding variables that weren’t controlled.
, However, the results of this study have been confirmed in other research,
supporting its validity.
Span of Memory + Chunking
Miller (1956) made observations of everyday practice.
He noted that things come in 7s: 7 days of week, 7 deadly sins, etc.
This suggests that the span/capacity of STM is about 7 items (± 2).
However, Miller also noted that people can recall 5 words as well as they
can recall 5 letters.
They do this by chunking – grouping sets of digits/letters into units/chunks.
Evaluation – Not So Many Chunks
In Miller’s research he may have overestimated the capacity of STM.
E.g. Cowan (2001) reviewed other research + concluded that the capacity
of STM was only about 4 chunks.
This suggests that the lower end of Miller’s estimate (5 items) is more
appropriate than 7 items.
Research on Duration
Duration is the length of time information can be held in memory.
Duration of STM
Peterson + Peterson (1959) tested 24 students.
Each student took part in 8 trials.
On each trial the student was given a consonant syllable (a trigram, i.e.
YCG) to remember + was also given a 3-digit number.
The student was then asked to count backwards from that 3-digit number
until told to stop.
Counting backwards was to prevent any mental rehearsal of the trigram
(which would increase the student’s memory for the trigram).
On each trial they were told to stop after different retention intervals – 3, 6,
9, 12, 15, or 18 seconds.
Participants remembered 90% with a 3 second interval.
20% with a 9 second interval.
2% with an 18 second interval.
STM has a duration of less than 18 seconds – if verbal rehearsal is
prevented.
,Evaluation – Meaningless Stimuli in STM Study
In Peterson + Peterson’s study the stimulus material was artificial (lacks
ecological/ external validity).
Trying to memorise trigrams doesn’t reflect most real-life memory activities
where what we’re trying to remember is meaningful.
However, we do sometimes try to remember fairly meaningless things, i.e.
phone numbers, so the study is not totally irrelevant.
It also lacks population validity as student participants are more intelligent
+ younger than average.
Duration of LTM
Bahrick et al. (1975) studied 400 participants aged between 17 + 74. High
school yearbooks were obtained from the participants or their schools. Recall
was tested by:
1) Photo-recognition test consisting of 50 photos from the
participant’s high school yearbook.
2) Free recall test – participants recalled all the names of their
graduating class.
15 years after graduation, photo recognition was 90% accurate. After 48
years, recall declined to about 70% for photo recognition.
Free recall was poorer than recognition – after 15 years this was about
60% accurate, dropping to 30% after 48 years.
This shows that LTM can last a very long time.
Evaluation – Higher External Validity
Bahrick et al.’s study has high external validity.
Real-life meaningful memories were studied.
When studies on LTM have been conducted with meaningless pictures to
be remembered, recall rates were lower.
However, confounding variables are not controlled – e.g. participants may
have looked at their yearbook photos + rehearsed their memory over the
years.
The Multi-Store Model of Memory
, The Multi-Store Model (MSM)
Atkinson + Shiffrin’s (1968, 1971) multi-store model describes how
information flows through the memory system, how information is
remembered + how it’s forgotten. Information flows through the stores in a
linear way.
The model suggests that memory is made up of 3 stores linked by processing:
Sensory Register
A stimulus from the environment; e.g. sights, sounds, smells etc. will pass into
the sensory registers. This part of memory stores for each of our 5 senses.
The two main stores are:
Iconic memory (vision) – visual information is coded visually.
Echoic memory (hearing) – sound/auditory information is coded
acoustically.
The sensory register is not under cognitive control + is the first storage system
for incoming information – information received is raw + unprocessed
The sensory register has a large capacity (millions of receptors) however the
duration of storage is only very brief (less than half a second) – unless given
focused attention which will cause it move to the STM.
Short-Term Memory (STM)
