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Cognitive psychology
Cognitive psychology
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2.1 Models of memory
Recently, Schachter et al. (2000) added another LTM store – the perceptual
representation system (PRS), which is related to perceptual priming, i.e. the
increased likelihood of recognising something when you have recently seen
something similar.
After studying this section you should be able to:
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describe the multi-store model of memory, including the concepts of
encoding, capacity and duration
give strengths and weaknesses of the multi-store model
describe the working memory model and give strengths and weaknesses of
this memory model
describe the levels of processing approach and give strengths and
weaknesses of this approach model.
LEARNING
SUMMARY
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An empirical study is a
study (such as an
experiment or an
interview) where data
has been collected
through direct
observation or
experience.
U1
U2
Memory is the process
by which we encode,
store and retrieve
information. It includes
sensory memory, shortterm memory and longterm memory.
Atkinson and Shriffrin (1968) proposed the multi-store model of memory. The
model identifies three stores (see diagram below) and explains how information
is transferred between these stores. Information enters sensory memory (SM). If
attention is paid to the information, it is transferred to short-term memory (STM)
where it is stored briefly. Verbal rehearsal maintains information in STM.
Continued rehearsal creates long-term memories (LTM). Material may be
retrieved from LTM via STM for recall or further processing.
An example of a stimulus
used in Sperling’s study:
7 I V F
X L 5 3
B 4 W 7
MULTI-STORE MODEL
The multi-store model of
memory aims to describe
the structure of memory
and explain how
information is transferred
from STM to LTM.
rehearsal
sensory
memory
attention
short-term
memory
transfer
long-term
memory
retrieval
A familiar example of
sensory memory is when
you still ‘hear’
information 1 or 2
seconds after it was first
heard. The information is
very briefly held in
sensory memory. This
explains why sometimes,
when you say ‘Pardon?’,
you are simultaneously
aware of what was said.
People have poor recall
of events from childhood
(called infantile amnesia)
but particularly good
recall for events from
adolescence and early
adulthood (reminiscence
bump) and also for
events from the last few
years (recency effect).
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retrieval
In these studies of
memory, what kind of
LTM memory is being
tested – semantic,
procedural or episodic?
How does this affect the
ecological validity of the
findings?
The structure of memory
1. Sensory memory (SM) – The sensory form of a stimulus remains unaltered in
the mind for a brief time. This could be an auditory or visual trace. It is rapidly
lost through spontaneous decay (i.e. the physical trace disappears).
2. Short-term memory (STM) – Information receives minimal processing. It is
relatively limited in capacity (it holds about seven items) and rapidly decays
unless it is maintained through rehearsal. It may be held in a visual or auditory
form (code), though it is mainly the latter.
3. Long-term memory (LTM) – Relatively permanent storage that has unlimited
capacity. Different kinds of long-term memory have been identified:
• Procedural memory – knowing how. Our knowledge of how to do things,
and skills such as riding a bicycle.
• Declarative memory – knowing that. Memory for specific information or
facts, which is subdivided into semantic or episodic memory.
Research evidence related to the MSM
The evidence for separate memory stores comes from empirical studies of
duration, capacity and encoding. Evidence also comes from the serial position
effect, case studies of brain damage, brain scans and understanding of forgetting.
1. Duration
Duration refers to how long a memory lasts in storage. Short-term memories last
a short time – between 15 and 30 seconds, if not rehearsed. Long-term
memories may last forever.
The multi-store model (MSM)
AQA A
AQA B
Semantic memory – storage for language, other cognitive concepts and
general knowledge. It is well organised, usually is not forgotten, and does
not disappear in cases of amnesia. It is this kind of memory that is tested in
experimental work.
Episodic memory (also called autobiographical memory) – memory for
personal events and people, i.e. the episodes of your life. Episodic memory
is reconstructed as an evolving process of a person’s history. A person’s
episodic memory may not be reliable because of memory distortions.
Miller suggested that the
magic number 7±2
might explain why things
so often come in sevens
– like seven days in the
week or seven wonders
of the world.
Think of your postcode.
How many bits of
information are there in
it? How many chunks of
information are there?
Phone numbers are also
presented in chunks, for
example, 0181 654 3462.
• Sensory memory (SM) – Sperling (1960) presented a display (like the one on
the left) to trained participants for 50 milliseconds. After the display was
presented, participants were told to report the whole array or just one row. In
the whole array condition, they typically recalled 4 out of 12 items (about
33% recall). In the one row condition participants could recall 3 out of 4 items
(75% recall), suggesting information decays quickly after presentation.
• Short-term memory (STM) – Peterson and Peterson (1959) studied the recall
of trigrams (i.e. consonant triplets of letters that had no meaning). If
participants had to wait three seconds before recalling the trigram they could
remember 80%. But if they had to wait 18 seconds, recall was reduced to
10%. (Participants did an interference task – counting backwards – between
presentation and recall to prevent rehearsal).
• Long-term memory (LTM) – Bahrick et al. (1975) demonstrated the existence
of very-long-term-memories (VLTM). Nearly 400 adults of various ages were
shown photographs from their high school yearbooks, and were asked to
identify individuals. Even after 34 years, ex-students were still able to name
90% of their classmates. This shows that people have accurate VLTMs.
2. Capacity
Capacity refers to how much can be held in a memory store. STM has a very
small capacity, whereas LTM is potentially unlimited.
• STM – Miller (1956) suggested that the span of STM is limited, not by the bits
of information, but by the chunks; people can remember the same number of
10-letter words as 5-letter ones. The number of chunks that can be remembered
is 7±2 (i.e. between 5 and 9). However, Simon (1974) found that there is a limit
beyond which, chunk size does have an effect: participants had a shorter
memory span for larger chunks (e.g. 8-word phrases) than for smaller chunks.
Chunking relies on LTM in order to determine meaningfulness. Bower and
Springston (1970) showed that participants recalled meaningful chunks (e.g. FBI
PHD TWA) better than they recalled meaningless chunks (e.g. FB IPH DWT A).
Recent research (Cowan et al., 2001) suggests that STM may actually be
limited to 4, rather than 7, chunks.
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Cognitive psychology
Cognitive psychology
• LTM – Merkle (1988) estimated (using the number of synapses) that LTM may
have a capacity of between one thousand and one million gigabytes.
3. Encoding
Encoding describes the form or code used to store data in memory. This may
be based on the sound of the information (an acoustic code), the way
the information appears (a visual code) or may be in terms of meaning (a
semantic code).
STM tends to be stored acoustically, whereas LTM is more semantic.
Some examples of the
word lists used by
Baddeley:
Acoustically similar:
cap, cab, can, mad
Acoustically dissimilar:
pit, few, cod
Semantically similar:
great, large, broad
Semantically dissimilar:
good, huge, hot
• Conrad (1964) found that participants made mistakes when recalling words
that sounded similar (acoustic similarity), when recall was immediate (i.e.
when testing STM).
• Baddeley (1966) investigated both STM and LTM by giving participants lists
of words that were acoustically similar or dissimilar, or semantically similar
or dissimilar.
It is not reasonable to
generalise from a sample
of one person. But, other
studies have also supported
the importance of the
hippocampus. For example,
Baddeley (1990) described
the same symptoms in a
man, Clive Wearing, whose
hippocampus was
damaged by infection.
In an experiment testing STM, he found that participants who were given
words that were acoustically similar recalled about 55% of the words,
compared to 75% recall in the other three conditions. In the experiment
testing LTM, it was found that participants given words that were semantically
similar again recalled about 55% of the words compared to 75% recall in the
other three conditions.
4. Serial position effect
Are the first words that are heard recalled best (primacy effect)? Or are the
words that are heard most recently recalled best (recency effect)?
Maguire et al. (2000) used MRI scans to show that taxi drivers in London, who
use their memory in their work, have larger hippocampi than non-taxi drivers.
Beardsley et al. (1997) showed that the pre-frontal cortex of the brain was active
when participants were involved in an STM task.
The hippocampus is a
small structure found
deep inside the brain.
There is one in each
hemisphere of the
forebrain.
Glanzer and Cunitz (1966) asked participants to recall word lists. If this was done
immediately, there was both a primacy effect and a recency effect (early and later
words were better recalled) due to STM and LTM effects. If there was a delay of
10 seconds or more, there was only a primacy effect – LTM alone was affected.
3 6 2 9 8 5 1 4 7 3
Above is a string of digits.
Cover up all the digits
except the first four and
say the digits, then shut
your eyes and recall them.
Were you right? Now try it
with five digits. Keep going
until you don’t get them
right. This is called the ‘digit
span technique’ and is a
way to assess the capacity
of a person’s short-term
memory.
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Hippocampi in the brain
Primacy is due to the fact that the first items are more likely to have entered
LTM. Recency occurs because the last items on the list are still in STM.
5. Brain damage
Brain injury to specific areas can affect STM. Shallice and Warrington (1970)
studied K.F., who experienced memory losses after a motorbike accident. He
performed poorly on STM tasks (e.g. digit span) but his LTM was intact.
Brain injury may also affect LTM. In anterograde amnesia, permanent memories
remain intact but sufferers cannot remember any new information for more than
the normal STM span. This is probably because transfer from STM to LTM is lost.
This case study suggests that the hippocampus may function as a memory
‘gateway’ through which new memories pass before being permanently stored
in LTM.
6. Brain scans
A more recent method of studying brain activity is the use of brain scans (see
page 114). CAT (computerised axial tomography), MRI (magnetic resonance
imaging) and PET (positron emission tomography) scans all produce images of
the brain in action.
These findings suggest that in STM, information tends to be acoustically coded
(and that is why acoustically similar words were muddled up) and in LTM,
information tends to be semantically coded (and that is why words with
similar meanings tended to be muddled up).
Other research has found that STM does not always use an acoustic code. This
depends on whether verbal rehearsal is prevented and/or whether recall is
tested in an acoustic manner. For example, Brandimonte et al. (1992) found
that participants used visual encoding in STM if they were given pictures to
remember (a visual task). Verbal rehearsal was prevented (they had to say
‘la la la’) and they were asked to recall the items by drawing them (a visual
recall task).
The serial position effect
refers to whether the
position of words in a list
affects the likelihood
of recall.
What are some of the
weaknesses with using
evidence from braindamaged individuals?
Examples include Korsakoff’s syndrome, which is due to severe alcohol poisoning,
and the case study of H.M. (Milner, 1959). H.M. had an operation to remove
both hippocampi from his brain to alleviate his severe epilepsy. H.M.’s personality
and intellect remained intact, but his memory was affected. He suffered extensive
anterograde amnesia, so he had no memory for events after the operation. His
memory for events prior to the operation was reasonable, but not as good as it
had been. He could still talk and recall all the skills he knew previously (semantic
memory) but his memory did not incorporate new experiences. For many years
he reported that his age was 27 and that the year was 1953. After a while he
realised this was absurd and tried guessing. In other words, he tried to
‘reconstruct’ memories. He watched the news every night yet he had no recall
for major events. He happily re-read magazines with no loss of interest. He
couldn’t memorise lists of words or recall faces of people he met.
7. Forgetting
Explanations for forgetting are different for STM and LTM. See pages 39–42.
The scientific method
revolves around theorytesting. Scientists produce
theories to explain events
in the world. In order to
test the validity of such
theories, research is
conducted. A ‘good’ theory
should be easy to test, i.e.
experiments can be
designed to test the
specific predictions of
the theory.
Evaluation of the MSM
Strengths
• The distinction between STM and LTM is well-supported by research
evidence (see pages 25-27).
• The MSM has encouraged psychologists to conduct empirical research to
test the model, which has increased our understanding of memory.
• The MSM has encouraged other psychologists to provide alternative
explanations of memory.
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Cognitive psychology
The MSM is no longer
regarded as an adequate
representation of memory
processes. However,
historically, it is an
important theory.
Cognitive psychology
Weaknesses
• The model is over-simplified – Research has since shown that there are more
than three memory stores and more than two processes involved (see
evidence on page 30).
• More memory stores – As we have already seen, LTM is divided into several
different stores (procedural, declarative, episodic and semantic). The working
memory model (see page 29) identifies subdivisions within STM.
• Processes – The levels of processing approach (see page 32) suggests that
lasting memories are created through elaborative processing, rather than
simply verbal or maintenance rehearsal, as suggested by the MSM.
• STM and LTM are not as separate as the MSM suggests. For example,
chunking requires that LTM is accessed in order to establish the meaning of
the chunks.
• The MSM presents a passive view of memory and cannot account for active
processes such as reconstruction, that is, when memories are altered because
of expectations (see accuracy of eyewitness testimony on page 35).
• Validity – The research studies have tended to concern only semantic memory
and, therefore, the results and the MSM may be relevant only to this kind of
memory rather than explaining, for example, memory for riding a bicycle or
memory for events in the past.
The working memory (WM) model
AQA A
AQA B
U1
U2
Baddeley and Hitch (1974) suggested that short-term memory should be subdivided. They used the phrase ‘working memory’ instead of short-term memory
to reflect their view that this is the area of memory that is active when you are
working on information. Working memory consists of the following parts:
sensory input
(from world around us)
visuo–spatial
sketchpad
central executive
(visual &
spatial info.)
phonological
loop
(acoustic &
verbal info.)
Progress check
1 Identify six distinguishing features of the MSM.
2 STM and LTM differ in terms of duration. Name one study that
illustrates this.
3 List the six ways that STM can be distinguished from LTM.
4 Outline two weaknesses with the research evidence for the MSM.
episodic buffer
visual
store
long-term memory
acoustic
store
4 E.g. Only one kind of memory is usually tested (semantic); Experiments may use artificial stimuli; In studies of
brain damage we cannot be sure of the cause of observed behaviours; Case studies cannot be generalised.
3 Capacity; Encoding; Serial position effect; Brain damage; Brain scans; Forgetting.
2 E.g. Peterson and Peterson; Sperling; Bahrick et al.
1 E.g. SM; Attention; STM; Rehearsal; LTM; Based on stores and processes.
The working memory model
The structure of working memory
1. Central executive – This component of working memory is modality-free (i.e.
not visual or auditory). It is roughly the same as attention (the concentration
of mental effort on sensory or mental events). The central executive allocates
resources to other components.
2. Visuo-spatial sketchpad (or scratchpad) – This part is used to hold visual
memories, such as people’s faces.
The phonological store
allows an individual to
rehearse information
acoustically.
3. Phonological loop – This deals with verbal material and preserves the order of
information. Information passes round and round in a loop as it is rehearsed.
The phonological loop consists of…
• a phonological store, which allows an individual to rehearse information
acoustically – a kind of inner ear
• an articulatory process, which is used for words that are heard or seen – a
kind of inner voice.
4. Episodic buffer – This has recently been added by Baddeley (2000) because
there was nowhere for information that is both visual and acoustic to be
stored. The episodic buffer integrates information from the central
executive, the visuo-spatial sketchpad and the phonological loop. It has a
limited capacity.
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