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Key Studies
Memory
Memory: what you
need to know
• The multi-store model of memory: sensory register,
short-term memory and long-term memory.
• Features of each store: coding, capacity and duration.
• Types of long-term memory: episodic, semantic,
procedural.
• The working memory model: central executive,
phonological loop, visuo-spatial sketchpad and episodic
buffer. Features of the model: coding and capacity.
• Explanations for forgetting: proactive and retroactive
interference and retrieval failure due to
• absence of cues.
• Factors affecting the accuracy of eyewitness
testimony: misleading information, including leading
• questions and post-event discussion; anxiety.
• Improving the accuracy of eyewitness testimony,
including the use of the cognitive interview.
Key Term
Meaning
Encoding/Coding
Changing the format of
information for use in memory
Capacity
The amount of information
that can be held in memory
Duration
The length of time
information remains in
memory
Sensory register
A store of sensory
information that lasts no
more than a few seconds
Displacement/displaced
Information that was being
held is pushed out by new
information that enters our
memory
What is memory?
The term memory can refer to the process in which
we retain information and knowledge. You may think
that this is one process but in fact it is split in to 3
basic processes.
The first process is called Encoding. This is where
a sensory input (e.g. sounds or images) are
transformed for it to be registered in memory.
Sound, vision and meaning are all encoded
differently.
The second process is Storage. This simply is
holding information until it is required.
The third stage is the process of Retrieval. This is
where we locate and use the information we have
stored so we are consciously aware of it.
Short Term Memory (STM) and Long Term Memory
(LTM)
Psychologists believe that Short Term Memory and
Long Term Memory differ in the amount of
information that can be stored, encoded and the
duration the information can be held.
Short Term Memory (STM) is a system for
information that you are currently thinking of.
Information that is stored here is done so only on a
temporary basis.
Encoding in STM: Psychologists believe that
information in STM is mainly encoded acoustically
(sound).
Capacity of STM: The capacity (how much of
something can be held) is limited in STM. Only a small
amount of information can be held. This can be
demonstrated through studies using Serial Digit Span
techniques.
Table of differences between STM and LTM:
ENCODING
STM
LTM
CAPACITY
DURATION
Atkinson and Shiffrin’s
Multi-Store Model of
Memory
Sensory Memory
Iconic register: ‘Icon’ is another word for image or
picture. The iconic register therefore refers to our
memory for visual information.
Sperling (1960): Iconic Register
Atkinson and Shiffrin based their assumptions about iconic memory on the
findings of previous research. In particular, that of Sperling.
In his experiment, Sperling very briefly displayed to his Ps visual arrays
containing three rows of letters:
M
N
J
C
N
X
K
V
F
L
B
P
He found that Ps could only recall four or five letters from the 50
millisecond arrays, but reported being aware of more letters that they
could not report. Sperling assumed that, because visual information was
only available for a very short time, it faded in memory before Ps could
recall it. Sperling conducted a further experiment to investigate this,
using what he called a partial report procedure. He trained Ps to recognise
3 tones – high, medium and low. The high tone was related to the top row
of letters, the middle to the middle row of letters and the low to the
bottom row of letters. Sperling instructed Ps to learn which tone matched
with which row of letters. One Ps had learnt this, Sperling once again
presented Ps with a series of digits for 50 milliseconds each. This time
along with a tone, cueing Ps to a particular row. He found that Ps recalled
on average 75% of the letters in the cued rows, a much better % than the
whole array.
Sperling concluded that Ps performance improved because a row contained
fewer items than the whole display, therefore there was less decay of
information from memory before Ps had to recall it.
Recall was not 100% however, Sperling saw this as evidence that not only
does the iconic register have a very limited capacity but that information
decays and is lost very rapidly.
Echoic register: the sensory register for auditory information.
Darwen et al. (1972) suggest that the length of time
information is stored in echoic memory is about 3 seconds.
Darwen et al. (1972)
Ps were presented with spoken recordings of letter and
number lists. The lists were presented over headphones so
that it seemed that one list came from the left and one list
came from the right and a third from behind.
After hearing the lists, Ps were given a cue to recall one of
the three lists. The length of time from the presentation
to the cue varied from 0 – 4 seconds. The cue should have
made the task easier as then Ps only had to recall a
particular list from a particular direction.
Darwen et al. found that as the time between presentation
and cue increased, the recall performance of Ps decreased.
After a 3 second delay Ps performed no better than they
would have without cues.
Further testing showed that performance did not
significantly improve when Ps were cued to recall letter or
digit lists.
Capacity of STM
Jacobs (1887): Capacity of STM
Jacobs read allowed a list of either letters or
numbers, with one syllable (‘w’ and ‘7’ were excluded).
The lists increased until participants could recall
them only 50% of the time. A wide age range was
used in his sample.
Jacobs found that STM capacity for digits was 9,
whereas letters was 7.
The conclusion was that STM has a limited capacity
of 5-9 digit and that numbers were easier to recall
than letters.
Criticisms show that practice can affect information
recall and also newer research shows people have
differing abilities associated with their attention
levels.
Capacity of STM – Miller (1956):
‘Chunking’
George Miller (1956) made observations of everyday
practice. For example, he noted that things come in
sevens (7 notes on the musical scale, 7 days of the week
etc.). This suggests that the span of the STM is about 7
items 9plus or minus 2). However, Miller also noted that
people can recall 5 words as well as recall 5 letters.
They do this by chunking – grouping sets of letters or
digits together into units or chunks.
Limitations of Miller:
Cowan (2001) who reviewed other research and concluded that the
capacity of STM was only about 4 chunks.
Simon (1974) found memory span as measured in chunks depends on the
amount of information contained in the chunk. He investigated the
ability of Ps to recall one-syllable, two-syllable and three-syllable words
and two-word and eight-word phrases. He found that larger chunks
resulted in reduced memory span, so that Ps accurately recalled fewer
larger chunks (e.g. eight-word phrases) and more smaller chunks (e.g.
two-word phrases).
Duration of STM
The duration of STM is short - less than 30 seconds.
This is best evidenced by Peterson and Peterson (1959)
who used nonsense trigrams (3 letters with no meaning,
i.e. WQT). Ps were instructed to read the trigrams and
then straight after had to count backwards in 3’s from a
large number (e.g. 375). They counted for a specific time
period. The participants had specific times in which to
recall the trigrams ranging from 3 seconds to 18 seconds.
(The counting was done to stop the retention of the
trigrams.)
The findings showed that 90% of trigrams were recalled
after a 3 second interval and only 6% after an 18 second
interval proving that the duration of STM is a matter of
seconds.
One criticism of Peterson and Peterson’s study is that
the stimulus for memory was artificial. Trying to
remember consonant syllables does not reflect real-life
memory activities, so we might say that this study lacks
external validity.
Craig and Tulving (1973) stated it is not the amount of rehearsal time
in STM that determines long-term retention, rather, it is how the
information is rehearsed. They suggested that there are two types of
rehearsal – maintenance rehearsal, which is when a person continually
repeats the information and elaborative rehearsal – which is where
the information is transformed in to something meaningful. They
stated that only elaborative rehearsal allows information to transfer
in to LTM, for example, you will remember a phone number that is
similar to another phone number you know – you will attach meaning to
it by linking it to the previous phone number.
Sebrechts et al. (1989)
Demonstrated the idea that duration of STM depends on a
number of factors. In addition to rehearsal, we can extend
duration by our intention to recall the information later.
They tested recall for sets of three familiar English nouns.
In the condition where Ps were not expecting to be asked to
remember the words, correct recall fell to 1% after only
about 4 seconds.
Encoding in STM and LTM: Most psychologists
believe that information is encoded semantically
(meaning) in LTM and acoustically (by sound) in
STM.
Baddeley (1966) illustrated this in a study which involved lists of
words. List A had acoustically similar words (cat, mat, sad, sat).
List B had acoustically dissimilar words such as (pit, day, cow).
List C had semantically similar words such as (big, huge, tall). List
D had semantically dissimilar words such as (hot, safe, foul).
After they were given the list they had a 20 minute retention
interval where they performed another task.
This ensured that recall would have to come from LTM.
The list C (semantically similar) was the least well remembered
(55%).
This seems to suggest there was semantic confusion and this
leads to the idea that LTM information is encoded
semantically.
The support for this comes from cognitive sense. In everyday life
we can remember the meaning of things but not the words. An
example would be a TV programme, you can remember what
happened (semantic) but not the exact words (acoustic).
Baddely also repeated this experiment but instead of leaving a 20
minute interval he asked Ps to recall immediately after seeing
them. He noted that Ps tended to perform less well on the list
with acoustically similar words. He therefore concluded that
STM encodes acoustically.
Conrad (1964) – encoding in STM as acoustic
Showed Ps a random sequence of consonants, projected very rapidly on
to a screen. Some Ps were shown consonants that were acoustically
similar, that is, they sounded similar when spoken (B, C, T, D,). Other Ps
were shown consonants that were acoustically dissimilar (R, E, J)
Immediately following the presentation, Ps were asked to write the
letters down in order that they were shown. Since this task was well
within the 5-9 capacity of STM it should have been relatively easy for
Ps. However, Conrad found that Ps frequently made errors of recall. Ps
found it more difficult to accurately recall sequences that sounded the
same compared with sequences that sounded different. Conrad
concluded that while the consonants had been presented visually, they
had been encoded acoustically by Ps in STM. It was this encoding that
caused difficulties in recalling letters that sounded similar.
Limitations of STM encoding acoustically:
Shulman (1970) presented Ps with a series of word pairs and required them to indicate
as fast as possible if one of the two words (the ‘probe’ word) was identical to the
other, a homonym of the other (prey-pray) or a synonym of the other (leap-jump). He
found a similar performance for all three probe types, leading him to conclude that
semantic encoding is possible in STM as Ps had obviously had to understand the
meaning of the words in order to complete the task.
Capacity and Duration
of LTM
Capacity and Duration of LTM
The potential capacity of LTM is unlimited. This is because we know that our brains
are not full of information on everything. This is why there has been no limit placed
on it.
In LTM the duration lasts as long as you live. You will have memories that you have
from childhood that will last until you die. Information in LTM doesn’t have to be
rehearsed or repeated. For example you may not have ridden a bike for many years
but you can still do it.
Bahrick et al. (1975): Duration of LTM
Duration in LTM was demonstrated in a study by Bahrick et al (1975). They
gathered 400 participants aged 17-74 years and asked them to remember names of
classmates from high school (free recall task). They were also shown a list of names
and photos. They had to identify their ex-schoolmates (recognition task).
Those who left school within the previous 15 years recalled 90% of the names and
faces in the recognition task. Those who had left within the previous 48 years
recalled 80% of names and 70% of faces. These high percentages show we
remember names and faces for a very long time.
The amount of time information stays in LTM is also determined by how well the
information was learned in the first place.
Bahrick and Hall (1991)
Tested LTM for geometry and algebra. People who had only taken maths courses up
to secondary school level showed a steady decline in their recall accuracy over the
years. However, students who had gone on to take a higher level course in maths
showed greater levels of accurate recall as much as 55 years later.
See encoding in LTM and STM
page for evidence that LTM
encodes semantically
Strengths and
weaknesses of the MultiStore Model of Memory
Strengths:
One of the greatest strengths of Atkinson and Shiffrin’s
assertion that STM and LTM are different memory stores
comes from people that have suffered brain damage. The loss
of memory among such people is usually selective – that is, it
affects one type of memory but not another.
Shallice & Warrington (1970)
The case of KF
KF was a young man who sustained brain injuries after a
motor cycle accident. He had an impaired STM working
alongside a fully functioning LTM. He appeared to have an
intact LTM in that he was able to learn new information and
recall stored information. However, his STM had a much
reduced capacity so that he was only able to store a couple
of bits or chunks of information rather than the normal 5-9
chunks.
Drachman and Sahakian (1979)
Alzheimer’s disease is a serious disorder of the brain, and early symptoms include
severe memory impairment. Researchers have been interested in investigating
some of the specialised chemicals in the brain called neurotransmitters , which
are involved in brain processes. Patients with Alzheimer’s disease have been found
to have low levels of acetylcholine, compared to people without the disease. D & S
investigated this by administering to a group of Ps a drug that clocks the action of
acetylcholine in the brain . They then gave Ps tasks that tested either their LTM
or STM and compared their performance with Ps that had not had the chemical
blocked. They found that Ps that had had the chemical blocked performed at
normal levels for their STM but more poorly on the LTM tasks. This suggests that
STM and LTM work as separate stores involving different neurotransmitters.
Squire et al. (1993) found during brain scans that different parts of people’s brain
were activated for STM and LTM tasks, suggesting again that STM and LTM are
separate stores (hippocampus more active during LTM, prefrontal cortex more
active during STM).
Weaknesses:
The MSM has been accused of being overly simplistic – human
memory is extremely complex, and it is highly unlikely that
such a simple model could reflect this complexity.
Brown and Kulik (1977): ‘Flashbulb memory’
Flashbulb memory is a special type of remembering that
involves the insignificant details surrounding an emotional or
shocking event being imprinted on to long term memory
without rehearsal. For example, those involved in the
terrorist attacks in Paris will not have needed to rehearse
the finer details of the event in order to remember them,
they will be imprinted onto their long term memory
automatically.
Ruchkin et al. (1999)
Measured brain activity in Ps who were required to listen to a set of
words and pseudo-words. If people only process information
acoustically in STM, there should be no difference in brain activity
when processing words and pseudo-words. However, Ruchkin et al.
found that there were considerable difference in the recall of the two
types of word, which suggests that semantic information stored in
LTM was being used in this task.
Brandimonte et al. (1992)
Prevented acoustic coding in STM by asking Ps to learn a list of words
whilst reciting a meaningless chant (La, La, La). Found that Ps accuracy
of recall was not affected and concluded that STM can use visual
coding as opposed to acoustic and went so far as to say that visual
coding is actually more effective than acoustic.
Working Memory
Model
Strengths: the WMM has been extremely influential and most cognitive
psychologists now use the term working memory in preference to the term STM. It
is a much more plausible model than the MSM because it explains STM in terms of
both temporary storage and active processing. It also incorporates verbal rehearsal
as just one optional process within the articulatory loop, instead of being the sole
mode and means of transferring information to LTM, as suggested by Atkinson and
Shiffrin.
Baddely et al. (1998)
Presented evidence that the phonological loop plays a key role in the
development of reading and that the PL is not functioning properly in
some children with dyslexia. It is less important for adult readers but
still has an important role in helping to understand complex text.
Gathercole and Baddeley (1993)
Participants followed a spot of light with a pointer (tracker task). At
the same time half the participants had to describe the angles on a
letter ‘F’. This group found the task very hard as they were using the
visuo-spatial scratchpad for both tasks. The other group did a verbal
task along with the tracker task and had little difficulty performing
both tasks.
Explanations for
Forgetting
Retroactive Interference: Waugh and Norman (1965)
Presented Ps with a sequence of 16 digits, after which they were shown
one of the digits from the list (the ‘probe). Ps had to say which digit in
the sequence occurred just prior to the probe. The researchers found
that the fewer items there were following the probe in the original
sequence, the more likely Ps were to recall the preceding digit
correctly. This demonstrates retroactive interference. If the probe
occurred early in the sequence then the greater numbers of digits
following it increased the chances of interference. Likewise, if the
probe occurred towards the end of the sequence then there would be
fewer digits to cause interference.
Proactive Interference: Keppel and Underwood (1962)
Ps required to recall consonant trigrams after varying intervals, during
which they counted backwards in 3s. While forgetting was found to
increase with the interval, Keppel and Underwood noted that there was
little or no forgetting of trigrams from the start of the procedure.
They concluded that the earlier trigrams had entered into LTM and
were interfering with the memory for later trigrams.
Retrieval Failure
Tulving and Thompson (1973): Encoding-specificity principle
More likely to forget something when the context during the encoding
is absent when you try to retrieve it. For example, when you decide in
one room of the house you want something from another area of the
house, once you get to the next room in the house you have forgotten
what you went in there for. Tulving and Thompson would argue that this
is because in the next room, the cues that were there when you encoded
what you needed to remember are absent in a different room.
Marian and Fausey (1986)
Context-dependent forgetting – relevant environmental cues are
absent during recall
Found that memory for a story was better if the language in which it
was presented and the language that was used to test memory were
the same. Ps in their study were residents of Chile who were fluent
in their native language (Spanish) and English. They were required to
listen to four academic type stories, two of them spoken in Spanish,
two of them spoken in English. Shortly afterwards they were asked
to recall features of each story and answer in the same language as
the question. Half the questions matched the language of the story
(e.g. English story – English questions) and half did not (English story
– Spanish questions). M & F found that Ps who heard the story and
questions in the same language had greater accuracy of recall than
those who had heard the story and questions in different languages.
This demonstrated encoding specificity, as memory is better when
there is a match between context during encoding and retrieval – the
language used provided a retrieval cue for the recall of story details.
Peters and McGee (1982)
State-dependent forgetting - relevant physiological or psychological
cues that were present when encoding are absent during recall
Gave half their Ps a low nicotine content cigarette before learning a
list of nouns. Ps who were in the same state the next day (having
smoked or not smoked a cigarette) performed better on a recognition
task than those who were in a different state. Peters and McGee
concluded that the arousal caused by the cigarette had helped cause a
physiological context, creating a state-dependent effect.
Eye-Witness
Testimony
Misleading Information
Research tells us that one of the
main factors affecting the
accuracy of memory for an event
seems to be what happens after
the event has taken place.
Misinformation after an event
can introduce serious errors into
eyewitnesses’ recall of the
event. Loftus (1992) calls this
‘misinformation acceptance’,
where people accept misleading
information after an event and
absorb it into their memory for
the actual event.
Loftus and Palmer (1974): Leading Questions
A leading question is one that by its content or format has the
answer embedded within it. This has been found to influence the
eye witness account of an event.
This was studied by Loftus and Palmer. The procedures involved
45 students being shown 7 films of different traffic accidents.
After each film the participants were given a questionnaire
which asked them to describe the accident and then answer a
series of specific questions about it. There was one critical
question: “About how fast were the cars going when they hit
each other?”. One group of participants was given this question.
The other four groups were given the verbs ‘smashed’, ‘collided’,
‘bumped’ or ‘contacted’ in place of the word ‘hit’.
The mean speed estimate was calculated for each group, as
shown in the table. The group given the word ‘smashed’ estimated
a higher speed than the other groups (about 41mph). The group
given the word ‘contacted’ estimated the lowest speed (about
32mph).
Loftus and Palmer concluded that the form of question can have a
significant effect on a witness’s answer. In other words, leading
questions can affect the accuracy of memory. Such leading
questions are an example of what psychologists call post-event
information – information given after the event which may alter
memory. It is possible that such post-event information causes
the information to be altered before it is stored so that memory
is permanently affected. A second possible explanation is that
the form of the question actually alters the participant’s
memory representation of the accident, which leads them to
produce a higher or lower estimate.
Loftus and Zanni (1975): Leading Questions
Showed Ps brief film clips of a car accident and then
asked a series of questions. Half the Ps were asked if
they had seen ‘a’ broken headlight, the other half were
asked if they had seen ‘the’ broken headlight. Although
there was no broken headlight in the film, 17% of
people asked about ‘the’ broken headlight reported
seeing one as opposed to only 7% reporting seeing on in
the ‘a’ broken headlight group.
Using ‘the’ had implanted the idea that there was
indeed broken glass, leading some Ps to change their
recall accordingly.
Gabbert et al. (2003): Post Event Discussion
Studied Ps in pairs. Each P watched the same video of
a crime being committed, but filmed from different
points of view. This meant that each P could see
elements in the event that others could not. For
example, only one P could see the title of a book being
carried by a young woman.
Both Ps then discussed what they had seen before,
individually completing a test of recall.
Gabbert et al. found that 71% of the Ps mistakenly
recalled aspects of the event that they did not see in
the video but had picked up in the discussion.
Gabbert concluded that witnesses often go along with
each other, either to win social approval or because
they believe the other witnesses are right and they
are wrong.
Effects of Anxiety on
EWT
Deffenbacher (1983) was one of the first to investigate links between
stress and EWT. He found that as we become moderately
stressed/anxious, performance in EWT improves. As we hit the peak of
stress our levels of accuracy drop because we feel fatigued.
Loftus (1979): The Weapon Effect
Ps asked to sit outside a lab where they thought they were hearing
genuine exchanges between people inside the laboratory. In one
condition, they heard an amicable discussion about an equipment
failure. A man with greasy hands came out of the lab holding a pen.
In the other condition they heard a hostile discussion, followed by
the sound of breaking glass and overturned furniture. A man then
emerged from the laboratory holding a knife covered in blood.
Following these events, Ps were given 50 photos and asked to
identify the man that had come out of the laboratory. It was found
that Ps that had witnessed the peaceful scene were more accurate
in recognising the man than people who had witnessed the more
violent scene. Loftus believed that the anxiety caused by seeing the
blood-stained knife narrowed the focus of attention for the witness
and took attention away from the face of the man.
From this, Loftus coined the phrase ‘The Weapon Effect’ – the
eyewitness will pay particular attention to the weapon that a
perpetrator uses during a crime, resulting in other aspects of the
scene going unobserved.
Criticisms of Loftus:
Yuille and Cutshall (1986)
Interview 13 witnesses to an actual crime (not one
that was laboratory based as all of Loftus’ had been)
some four months after the event. The researchers
found that recall was very accurate, despite the
inclusion of leading questions in the interview. This
suggests that both misleading information and
anxiety might not have the same impact on real-life
witnesses as it does in laboratory-based studies.
Christianson and Hubinette (1993)
Carried out a survey among 110 people who had
witnessed between them 22 genuine bank robberies.
Some of those people had been threatened by the
robbers during the event while others hadn’t. They
found that those that had been directly threatened
by the robbers during the robbery (so would have
felt the most anxiety) actually had more detailed
recall than those that hadn’t been threatened. This
finding suggests that in real incidents involving high
levels of stress, memory can be accurate, detailed
and long-lasting.
Cognitive Interview
Fisher and Geiselman reviewed memory literature
– people remember things better if they are
provided with retrieval cues. They then
developed the cognitive interview, this technique
has 4 components:
1. Report everything (report every single detail
of the event).
2. Context reinstatement – recreate the internal
and external environment ie what mood were you
in? what was the weather like?
3. Changing the order - try alternative ways
through timeline of incident as it is productive to
vary the different ‘routes’ into an individual’s
memory.
4. Changing the perspective - imagining how it
would appear from another witnesses’ point of
view .
Evidence Supporting the
effectiveness of the
Cognitive Interview
Kohnken et al conducted a meta-analysis of 53 studies
and found on average a 34% increase in amount of
correct information generated in CI.
Milne and Bull (2002) Found that when they used a
combination of “report everything” and “mental
reinstatement”, participants’ recall was significantly
higher. This suggests the CI is relatively effective in
increasing recall.
Stein and Memon (2006) compared normal interviewing
technique and CI in Brazil. CI increased the amount of
correct information obtained and the richness (detail)
of information.
Weaknesses of the
Cognitive Interview
Kebbell et al. (1999) carried out a survey of police
officers in the UK and found that there was quite
widespread use of the CI. However, while officers
generally found it useful, they expressed some concern
about the amount of incorrect recall generated and the
amount of time it took to carry out. In practice, it
seemed that the officers were using the RE and CR
instructions, but rarely using the CP and RO
instructions.
Geiselman et al (1985) found that the cognitive
interview compared favourable against a standard
interview. The cognitive interview has since been
improved and now includes an attempt to build a greater
rapport between the witness and interviewer. This is
called the enhanced cognitive interview. However this
means that it is difficult to evaluate the effectiveness
of the cognitive interview as the use of the enhanced
cognitive interview introduces a ‘lack of control’. It is
difficult to draw conclusions about the effectiveness of
the interview when some interviewers have better
social skills than others and are therefore able to
generate a better rapport with witnesses. This raises
questions about the validity of research into the
enhanced cognitive interview. Research into the
cognitive interview has obvious ‘practical applications’
This research can help the police to aid the recall of
witnesses. In practice however many police forces
report that they only use ‘recall everything’ and
‘context reinstatement’ in police interviews as they
believe the ‘change perspective’ and ‘reverse order’
techniques confuses witnesses.