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Research on Coding and Capacity

Research on Coding

  • Once info's in the system it's stored in different formats depending on the memory store
  • Converting one to another is called coding - Baddeley (1966) gave different lists of words to 4 groups of ppts to remember
  • Group 1: acoustically similar, group 2: acoustically dissimilar, group 3: sematically simialr, group 4: semantically dissimilar
  • Ppts were hown original words and asked to recall themin the correct order - recalling immeadiately after (STM) they tended to do worse with acoustically similar words, when tested after 20mins (LTM) they did worse on sematically similar words

Research on Capacity

  • Jacobs (1887) developed a technique to measure digit span - the researcher gives a number of digitsthat the ppt must recall in the correct order - they then increase the number of digits until the ppt gets an incorrect order
  • Found that the mean span for digits was 9.3 items - letters was 7.3
  • Miller (1956) made observations of everyday practice e.g. he noted that things come in 7s - suggests that the span of STM is 7 items (+ or - 2) - Miller also nted that people can recall 5 words as well as recalling 5 letters, this is done through chunking (grouping things together)
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Research on Coding and Capacity - Evaluation

Artificial Stimuli

  • Baddeley's study used artificial stimuli rather than meaningful material - means we have to be cautious about generalising these findings to different kinds of memory tasks - suggests findings have limited application

Lacking Validity

  • Jacob'sstudy was conducted a long time ago - early research in psychology often lacked adequate control e.g. some pts may have been distracted whilst being tested not performing to their best ability
  • Could mean results aren't valid as there were confounding variables not controlled - results have been supported by other studues improving validity though

Not so Many Chunks

  • Limitation of Miller's research is that he may have overestimated the capacity of STM
  • Cowan (2001) reviewed other research and found the capacity was only about 4 chunks - suggests that the lower end of Miller's estimate is more appropriate than 7 items
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Research on Duration

  • Duration of STM
  • Peterson and Peterson (1959) tested 24 undergraduates - each student took part in 8 trials - on each trial they were given a consonant syllable (trigram) to remember and was also given a 3-digit number
  • Students were asked to count backwards from the 3-digit number until told to stop - this was to prevent rehearsal of the trigram - on each trial they were told to stop after different amounts of time: 3,6,9,12,15 or 18secs (retention interval)
  • Findings suggest that STM has a very short duration unless we rehearse something
  • Duration of LTM
  • Bahrick (1975) studied 392 ppts from Ohio aged 17-74 - high school yearbooks obtained from ppts or the school
  • Recall tested by: Photo-recognition and free recall where ppts recalled all names of their graduating class
  • Ppts tested within 15yrs of graduation were 90% accurate w/ photo recognition - after 48yrs  recall declined to 70% for photo recognition - free recall was worse: 60% after 15yrs and 30% after 48yrs
  • Evaluation - Meaningless stimuli for STM
  • Trying to remember consonant syllables doesn't reflect real-life memory activities - lacking external validity to a extent because we sometimes remember meaningless things like phone numbers
  • Evaluation - Higher external validity
  • Bahrick's study used real-life meaningful memories - confounding variables aren't controlled though which could be a problem
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Multi-Store Model

Sensory Register

  • Sights, sounds, smells etc go into sensory register - not one store but many (1 for each of the 5 senses)
  • 2 main stores are iconic memory (visual info is coded visually) and echoic memory (auditory info coded acoustically) 
  • Material in sensory register lasts for less than half a second - the sensory registers have high capacity each storing data - very litle of what goes into sensory register goes into memory system - key process is attention


  • Can only contain a certain number of things before forgetting takes place - capacity between 7+/-2 - info coded acoustically and lasts about 30secs unless rehearsed
  • Maintenance rehearsal occurs when we repeat our material - constant repetition will pass from STM to LTM


  • It's capacity is believed to be unlimited and can last for many years - LTM is coded semantically
  • When we want to recal a mmory it has to be retrieved and transferred back to STM - no memories directly recalled from LTM
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Multi-Store Model Evaluation

  • Supporting Research Evidence - Baddeley found that we tend to mix up words that sound similar when we're using our STMs - we mix up words with similar meanings when using our LTMs
  • The study shows that coding in STM is acoustic and in LTM it's semantic - they're different and this supports the MSM's view that the 2 memory stores are seperate/independent
  • There is More Than One Type of STM - MSM states STM is a unitary store (only 1 type of STM)
  • Evidence from people suffering amnesia shows that this isn't true
  • Shallice and Warrington (1970) studied a patient with amnesia known as KF - KF's STM for digits was poor when they were read aloudto him. When he read them himself his recall was much better - further research shows there could be a store for non-verbal sounds e.g. noises
  • The unitary STM is a limitation because research shows that there are at least 2 processes - 1 for visual and 1 for auditory
  • There is More Than One Type of Rehearsal - According to the MSM what matters in rehearsal is the amount of it you do - the more you rehearse the more likely you are to transfer it into LTM
  • Craik and Watkins (1973) found that this prediction is wrong - what really matters is the type of rehearsal
  • They discovered 2 types of rehearsal - maintenance rehearsa is the one described in the MSM but this doesn't transfer info to LTM - that is the job of elaborative rehearsal
  • This occurs when you link the info to your existing knowledge
  • This is a big limitation of the MSM as it's another research finding that can't be explained by the model
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Types of LTM - Tulving

  • Episodic Memory
  • Refers to our ability to recall events - likened to a diary of daily happenings
  • These memories are much m ore complex than you'd think - you remeber when they happened (time-stamped) and your memory of a single event will include several elements e.g. people, places, objects and behaviours - all of these are interwoven to produce a single memory
  • You have to make a conscious effort to recall episodic memories
  • Semantic Memory
  • This store contains our knowledge of the world - includes facts, in the broadest sense - likened to a combination of an encyclopedia and a dictionary
  • Semantic memory contains meaning of words - your knowledg of an impressinve number of concepts
  • Semantic knowledge is less personal and more about facts we all share - they're not time-stamped
  • It contains an immense collection of material which is constantly being added to
  • Procedural Memory
  • Our memory for actions/skills
  • We can recall these memories without conscious awareness or a great deal of effort
  • These are the sorts of skills we might find hard to explain to someone else
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Types of LTM - Evaluation

  • Clinical Evidence - Case Studies of HM and Clive Wearing - episodic memory in both men was severely impaired as a consequence of amnesia, they had great difficulty recalling events that had happened in their pasts
  • Their semantic memories were relatively unaffected; they still understood meanings of words - their procedural memories were also intact; they both knew how to tie shoelaces, how to walk and speak. Wearing remembered how to play piano, read music and sing
  • This supports Tulving's theory of different types of LTM - one store can be damaged but the others can remained untouched
  • Neuroimaging Evidence - Evidence from brain scan studies that different types of memory are stored in different parts of the brain
  • Tulving et al (1994) got their ppts to perform memory tasks while their brains were scanned using a PET scanner
  • They found that episodic and semntic memories were both recalled from the prefrontal cortex - the left side for semantic, the right for episodic
  • Supports the view that there is a physical realoity to different types of LTM within the brain
  • Real-life Apllications - Belleville et al (2006) demonstrated that episodic memories could be improved in older people who had a mild cognitive impairment
  • The trained ppts performed better on a test of episodic memory after training than a control group
  • It enables specific treatments to be developed as episodic memory is the one most often affected by mild cognitive impairment
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Working Memory Model

  • WMM is an explanation of how one aspect of memory (STM) is organised and how it functions - concerned w/ the part of the mind active when we're temporarily storing and manipulating info
  • Central Executive - essentially an attentional process that monitors incoming data, makes decisions and allocates slave systems to tasks - The CE has a very limited processing capacity
  • There are three slave systems
  • Phonological Loop - deals with auditory info and preserve the order in which the info arrives
  • The PL is divided into: a) the phonological store, which stores he words you hear and b) the articulatory process, which allows maintenance rehearsal
  • Capacity of the loop is believed to be 2 seconds' worth of what you can say
  • Visuo-spatial Sketchpad - stores visual and/or spatial info when required
  • Has a limited capacity of about 3 or 4 objects
  • The VSS is divided into: a) the visual cache which stores visual data and b) the inner scribe which records the arrangement of objects in the visual field
  • Episodic Buffer - added to the model by Baddeley in 2000
  • It's a temporary store for info, integrating the visul, spatial and verbal info processed by other stores and maintaining a sense of time sequencing
  • It can be seen as the storage component of the CE and has a limited capacity of about 4 chunks
  • The EB links working memory w/ LTM and wider cogitive processes e.g. perception
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Working Memory Model - Evaluation

  • Clinical Evidence
  • KF who had suffered brain damage - KF had poor STM ability for verbal info but could process visual info normally presented visually i.e. he had difficulty w/ sounds but could recall letters and digits
  • This suggests that his phonolgical loop had been damaged but not his other areas of memory
  • Supports existence of a seperate visual and acoustic store - brain damaged patients may not be reliable though as it concerns unique cases w/ those who've had a traumatic experience
  • Dual Task Performance
  • Baddeley et al (1975) showed that ppts had more difficulty doing 2 visual tasks (tracking a light and describing the letter F) than doing both a visual and a verbal task at the same time
  • This increased dificulty is because both visual tasks compete forthe same slave system but there is no competition when doing a verbal and visual task simultaneously
  • This means there must be a seperate slave system (VSS) that processes visual input, independent from phonolgical loop; able to work together
  • Lack of Clarity Over The Central Executive
  • Baddeley said the CE is the most important aspect but the least understood of working memory
  • The CE needs to be more clearly specified than just being simply 'attention'
  • This means that the WMM hasn't been fully explained - limitation
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Explanations for Forgetting - Interference

  • Some forgetting takes place due to interference - occurs when 2 pieces of info conflict w/ each other resulting in forgetting 1 or both or in some distortion of memory
  • Interference mainly as an explanation for forgetting in LTM - once info has reached LTM it's more or less permanent - any forgetting is most likely because we can't access the memory
  • Proactive Interference - occurs when an older memory interferes w/ a newer 1
  • Retroactive Interference - occurs when a newer memory interferes w/ an older 1
  • Effects of Similarity
  • McGeoch and McDonald (1931) studied retroactive interference by changing the amount of similarity between 2 sets of material
  • Ppts had to learn a list of 10 words until they could remember them 100% accurately
  • They then learned a new list - there were 6 groups of ppts who had to learn different types of lists
  • 1) synonyms (words w/ same meaning as originals)
  • 2) antonyms (words w/ opposite meanings to originals)
  • 3) words unrelated to originals
  • 4) nonsense syllables
  • 5) 3-digit numbers
  • 6) no new list - these ppts just rested
  • When ppts recaled original list of words their perfomrance depended on nature of second list
  • Synonyms had the worst recall - shows interference is strongest when memories are similar
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Explanations for Forgetting - Interference Evaluat

  • Evidence From Lab Studies
  • 1000s of lab experiments have been carried out into the explanation of forgetting e.g. McGeoch and McDonald
  • Most of these studies show that both types of interference are very likely to be common ways we forget info from LTM
  • This is a strength because lab experiements control the effects of irrelevant influences and thus giving us confidence that interference is a valid explanation for at least some forgetting
  • Artificial Materials
  • There is a much greater chance that interference will be demonstrated in the lab than in real-life situations, for 1 good reason
  • Stimulus material used in most studies is a list of words - the task is to learn these words - learning words is more realistic than consonant syllables but this is stil a distance from what we remember in everyday life
  • This is a limitation as artificial tasks make interference more likely in the lab - may not be as likely in everyday situations
  • Real-life Studies
  • Baddeley and Hitch (1977) asked rugby players to remember the names of the teams the had played in the season, week-by-week
  • Most players had missed games, for some their last game was 2-3 weeks ago or more
  • Results showed that accurate recall didn't depend on how long ago the matches took place but the number of games they had played in the meantime - a player's recal of a team from 3 weeks ago was better if they'd played no matches since then
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Explanations for Forgetting - Retrieval Failure

  • The reason people forget may be due to insufficient cues - when info is placed in memory, associated cues are stored at the same time  - If cues aren't available at the time of recall it make it appear as though you've forgotten but infact it is just retrieval failure
  • Encoding Specificity Principle - Tulving (1983) reviewed research into retriecal failure and discovered a consistent pattern to the findings - summarised this pattern as the encoding specificity principle
  • ESP states that if a cue is to help us recall info it has to be present at encoding and at retrieval - if the cues available at encoding and retrieval are different there will be some forgetting
  • Some cues are linked to the material to be remembered in a meaningful way - other cues are also encoded at the time of learning but not in a meaningful way
  • Context-Dependent Forgetting - Godden and Baddeley (1975) carried out a study of deep-sea divers working underwater
  • The divers learned a list of words either underwater or on land and then recalled them either underwater or on land - 4 conditions (land and land, land and underwater, underwater and land, underwater and underwater)
  • Accurate recall was 40% lower in the non-matching conditions - external cues available at learning were different from the ones at recall - led to retrieval failure
  • State-Dependent Forgetting - Carter and Cassaday(1998) gave anti-histamine drugs to their ppts which made them slightly drowsy (creates an internal physiological state different from normal state of awake and alive)
  • Ppts had to learn a list of words and passages and recall the info - 4 conditions (learn on drug and recall on it, learn on it and recall not on it, learn not on it and recall on it, learn not on it and recall not on it)
  • When cues were absent there is more forgetting - conditions where there was mismatch recall was worse
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Explanations for Forgetting - Retrieval Failure Ev

  • Supporting Evidence
  • Studies by Godden and Baddeley and Carter and Cassaday are 2 examples of supporting evidence
  • Eysenck (2010) argues that retrieval failure is the main reason for forgetting in LTM
  • Strength because supporting evidence increases validity, especially when evidence shows it happens in real-life situations and not jut in the lab
  • Questioning Context Effects
  • Baddeley (1977) argues that context effects are actually not very strong, especially in real life
  • Different contexts have to very different before an effect is seen e.g. learning on land and recalling underwater
  • This is a limitation as it means that te real-life applications of retrieval failure due to contextual cues don't actually explain much forgetting
  • Recall vs. Recognition  
  • Godden and Baddeley (1980) replicated their underwater experiment but used a recognition test instead of recall - ppts had to say whether they recognised a word read to them from the list instead of retrieving it for themselves
  • When recognition was tested therewas no context-dependent efect, performance was the same in all 4 conditions
  • Limitation of cntext effects as it means that the presence or absence of cues only affects memory when you test it in a certain way
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Factors Affecting EWT - Misleading Info

Leading Questions

  • Loftus and Palmer (1974) arranged for ppts to watch film clips of car accidents and then gave them questions about the accident - in the critical question (a leading q) ppts were asked to describe how fast cars were travelling
  • This is a leading question because the verb 'hit' suggests the sped the car was going - 5 groups of ppts all given different verbs: hit, contacted, bumped, collided and smashed
  • Mean estimated speed was calculated for each group - 'contacted' got 31.8mph whereas 'smashed' got 40.5mph - leading question biased the ew recall of the event

Why do leading Qs affect EWT?

  • Response-bias explanation suggests that the wording of the question has no real effect on pts memories but influences how they decide to answer - 'smashed' encourages a faster speed than 'bumped'
  • Loftus and Palmer (1974) conducted a 2nd experiment that supported the substitution explanation - the wording of a leading Q actually changes ppts memory of the clip
  • Ppts who heard 'smashed' were later more likely to report seeing broken glass (there wasn't any) than those who heard 'hit'
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Factors Affecting EWT - Misleading Info

Post-event Discussion

  • When co-witnesses to a crime discuss it with each other their EWTs become contaminated - they combine (mis)info from other witnesses with their own memories
  • Gabbert and colleagues (2003) studied ppts in pairs - each ppt watched a video of the same crime but filmed from different points of view
  • Each ppt could see elements others couldn't - both ppts then discussed what they'd seen before individually completing a test of recall
  • Researchers found that 71% of ppts mistakenly recalled aspects of the event that they hadn't seen in the video but had picked up from discussion
  • The corresponding figure in a control group, where there was no discussion, was 0%
  • Gabbert et al concluded that witnesses often go along with each other, ether to win social approval or because they believe the other witnesses are right - this is called memory conformity
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Factors Affecting EWT - Misleading Info Evaluation

  • Useful Real-life Applications
  • Research into misleadng info has important practical uses in the real world - where consequences of inaccurate EWT can be very serious
  • Loftus (1975) believes that leading questions can have such a distorting effect on memory that police officers need to be careful about how they phrase questions when interviewing eyewitnesses
  • Research into EWT is 1 area in which psychologists believe they can make an important positive difference to the lives of real people - by improving the legal system and how it works
  • The Tasks are Artificial
  •  A real limitation of Loftus and Palmer's study is that their ppts watched film clips of car accidents - a very different experience from witnessing a real accident (clips lack stress of a real accident)
  • This is a limitation because studies that use artificial tasks may tell us very little about how leading Qs affect EWT in real accidentsand crimes
  • Individual Differences
  • Evidence that older people are less accurate than older people when giving EWTs - Anastasi and Rhodes (2006) found that people in ages groups 18-25 and 35-45 were more accurate than those 55-78
  • All age groups more accurate when identifying people of their own age (ow age bias)
  • Research studies often use younger people as the target to identify and this may mean that some age groups appear less accurate - this isn't true
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Factors Affecting EWT - Anxiety

  • Anxiety has a negative effect on recall - Johnson and Scott (1976) researched the effects weapons (which cause anxiety) have on EWT
  • Led ppts to believe they were taking part in a lab study - while seated in waiting room ppts heard an argument in room next door
  • 'Low anxiety' condition - a man walked through waiting room carrying a pen w/ grease on his hands
  • 'High anxiety' condition - there was the sound of breaking glass and there a man walked through with a paper knife covered in blood
  • Ppts later picked out the man from a set of 50 photos - 49% of ppts who had seen man carrying a pen were able to identify him - the figure for the 'high anxiety' condition was 33%
  • The tunnel theory of memory argues that the witness' attention narrows to focus on weapon because it's a source of anxiety
  • Anxiety has a positive effect on recall - Yuille and Cutshall (1986) studied a real-life shooting in a gun shop in Vancouver - the shop owner shot a thief dead - 13/21 witnesses took part in the study
  • Interviews held 4-5 months after the event and these were compared w/ original police interviews - accuracy determined by the number of of details reported - witnesses also asked how stressed they felt on a 7 point scale and found out if they had any emotional problems since the event
  • Witnesses very accurate in accounts, little change over the 5 months - some details less accurate e.g. colours - pts reporting highest levels of stress were the most accurate - 88% compared to 75%
  • Explaining Contradictory Findings - Yerkes-Dodson Law - lower levels of anxiety, lower recall, very high levels of anxiety, low recall (inverted U)
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Factors Affecting EWT - Anxiety Evaluation

  • Weapon Focus Effect may not be Relevant
  • Johnson and Scott may have tested suprise rather than anxiety - reason ppts focused on weapon was because it suprised them
  • Pickel (1998) conducted an experiment using scissors, a handgun, a wallet or a raw chicken as the handheld items in a hairdressing salon video (scissors low anxiety)
  • EW accuracy was significantly poorer in the unusual conditions (chicken and handgun)
  • Suggests weapon focus effect is due to unusualness rather than anxiety/threat - tells us nothing specific about the effects of anxiety on EWT
  • Field Studies Sometimes Lack Control
  • Researchers usually interview real-life EW sometime after the event - all sorts will have happened in this time that researchers have no control over
  • This is a limitation of field research as it's possible that these extraneous variables may be responsible for the accuracy of recall
  • Effects of anxiety may be overwhelmed by these factors and impossible to assess by the time the ppt is interviewed
  • There Are Ethical Issues
  • Creating anxiety in ppts is risky - it may subject them to psychological harm purely for the purposes of research
  • This is why real-life studies are so beneficial - psychologists interview those involved as a witness in real-life
  • This issue doesn't challenge findings of studies like Johnson and Scott but questions the need for such research
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Improving the Accuracy of EWT - Cognitive Intervie

  • Fisher and Geiselman (1992) argues that EWT could be improved if police used better techniques when interviewing witnesses

1) Report Everything - witnesses are encouraged to include every single detail of the event even if it may seem irrelevant or the witness doesn't feel confident about it

2) Reinstate the Context - witnesses should return to original crime seen 'in their mind' and imagine the environment and their emotions. This links to context-dependent forgetting

3) Reverse the Order - events should be recalled in a diffrent chronological order to the original sequence. This prevents people reporting their expectations of how the event must've happened rather than the actual events. Also prevents dishonesty.

4) Change Perspective - witnesses should recall the incident from other people's perseptives. This is done to disrupt the effect of expectations and schema on recall. The schema you have for a particular setting generates expectations of hat would've happened and it's the schema that's recalled instead

  • Fisher et al (1987) developed some additional elements to focus on the social dynamics of the interaction - the enhanced CI also includes ideas such as reducing EW anxiety, minimising distractions, getting the witness to speak slowly and asking open ended questions 
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Improving the Accuracy of EWT - Cognitive Intervie

The CI is Time-Consuming

  • Police may be reluctant to use the CI because it takes a lot more tie than the standard police interview
  • The CI also requires special training and many frces haven't been able to provide this for more than a few hours
  • It is unlikely that the 'proper' version of the CI is being used - may explain why police haven't been that impresed by it

Some Elements May Be More Valuable Than Others

  • Milne and Bull (2002) found that each individual element was equally valuable - each technique used singly produced more info than the standard police interview
  • Milne and Bull found that using a combination of 'report everything' and 'reinstate the context' produced better reacall than any other condition
  • Confirmed police's suspicions that some asects of the CI aremore useful than others
  • This is a strength as it suggests that at least 2 elements should be used to improve police interviewing

Support for the Effectiveness of the ECI

  • The ECI may offer special benefits - a meta-analysis by Kohnken et al (1999) combined data from 50 studies - the ECI consistently provided more correct info than the standard interview used by police
  • Strength as studies like this indicate that there are real practical benefits to thepolice of using the ECI
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