Coding, Capacity and Duration

Duration = How long we can remember. Capacity = How much we can remember. Encoding = How we process and store this information. 

  • Peterson & Peterson: STM Duration
  • Procedure: 24 undergraduate students were asked to count backwards from a three-digit number after being told a trigram. The counting backwards prevented any mental rehearsal. They were then asked to recall the trigram.
  • Findings: As the retention interval increased the accuracy of recall decreased (as the time got longer the p’s were less accurate). Most people can recall info in their STM for 18 seconds
  • Evaluation: Artificial stimuli so lacked external validity.
  • Bahrick et al.: LTM Duration
  • Aim: To investigate the duration of long-term memory
  • Procedure: Asked 400 people to put names to faces from their high school yearbook with 70% accuracy 48 years after leaving school.
  • Evaluation: Had good external validity but the possible confounding variable of p’s looking at their yearbooks since then.
  • Findings: Infinite
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Coding, Capacity and Duration Pt.2

  • Jacobs: STM Capacity (digit span)
  • Aim: To investigate the capacity of short-term memory
  • Procedure: P’s were asked to recall numbers in order in increasing length. Continued until the recall was inaccurate.
  • Findings: Found the average STM capacity to be 7 letters, 9 digits.
  • Evaluation: Poor control due to being an early study but has been replicated since suggesting it is reliable.
  • Miller: Increasing capacity of STM
  • A meta-analysis found that most people can recall 5 to 9 items. We can recall the same number of words as letters or numbers due to chunking. This is when items are grouped together to increase capacity.

Baddeley (1966) gave participants one of four-word lists to learn. The lists contained words that were either acoustically similar or dissimilar; semantically similar or dissimilar. Participants either recalled the list immediately, testing the coding of (STM) or after 20 minutes, testing the coding of (LTM). Participants did worse with acoustically similar words in STM, suggesting that information in STM is coded according to sound, as similar-sounding information conflicted with each other. For LTM, they did worse with semantically similar words, suggesting that information in LTM is coded according to meaning, as information with similar meanings conflicted with each other.

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Multi-store model of Memory: Atkinson and Shiffrin

Sensory register: Receives all the sensory information around us. Has an iconic and echoic register. Capacity is huge but has a short duration. By paying attention to some of the information in enters our STM. 

STM: If we ignore information it decays after around 20 seconds according to Peterson and Peterson. If we rehearse info it enters the LTM. Has a limited duration so maintenance rehearsal has to be used to keep info in STM. 

LTM: Information can be retrieved from the LTM. Information can be lost due to interference, decay or retrieval failure. 

Flashbulb memory: A vivid and detailed memory of an event that happened once and has not been rehearsed. These suggest a physiological process in encoding a memory. E.g. Traumatic events. 

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Multi-store model of Memory: AO3

  • Strength - Scans
  • PET and fMRI scans show us that different areas are active when participants use different types of memory. Suggests that STM and LTM stores are separate. 
  • Strength - Testable
  • Any good scientific model makes clear predictions that can be tested. 
  • The MSM makes clear predictions, such as greater rehearsal of information in STM should equal a better recall of those things once in LTM. 
  • Limitation - Reductionist
  • A complex behaviour has been oversimplified to fit into the model. 
  • Some more complex aspects have been lost, e.g. ignoring the role of emotion in memory. 
  • E.g. the model assumes all STM memories are the same but this is not the case. 
  • Evidence - Patient K.F had a very poor memory on a digit span test when the numbers were read to him, but when he could read the numbers himself his results were much better. This shows that his brain was processing visual and acoustic information separately. The MSM cannot explain this. 
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Types of LTM

Tulving (1985) believed that the MSM's view of LTM was too simplistic. 

Episodic memory: When personal events occurred. Time-stamped. Conscious recall. 

Semantic memory: Our knowledge of the world. Not time-stamped and do not require conscious recall. 

Procedural memory: How to do things. Automatic. Not time stamped. 

Cohen and Squire - Declarative and non-declarative memories. 

Declarative/explicit: Consciously recalled. 

Non-declarative/ implicit: Memories that cannot be explained, e.g. knowing how to walk. 

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Types of LTM AO3

Support - Clinical evidence:

·       Patient K.F had widespread brain damage including bilateral hippocampal lesions causing memory impairment. He retained his general knowledge of the world but not any personal events causing episodic amnesia of his entire lifetime. This shows that semantic and episodic memory are two different processes.

Support - Real-life evaluation:

·       Psychologists can improve people's lives by targeting certain kinds of memory. Being able to distinguish between types of LTM allows specific treatments to be developed.

Limitation - Clive Wearing and Patient KC are case studies which are idiographic (detailed research on a few individuals) which makes it harder to generalise the findings to the wider population. This is somewhat balanced by Tulving’s work being nomothetic.

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Working memory model: Baddeley and Hitch

Criticized the MSM for suggesting that STM was a single store. Patient KF tells us so. The WMM focuses on short term memory only. Working memory = The part of the memory that is active at any one time. Used when you need to keep in mind and manipulate information. Phonological loop: Processes auditory information and preserves order. Has an inner voice and inner ear. Maintenance rehearsal happens because of the phonological loop. 

  • EVIDENCE: Baddeley - The word length effect. Participants could recall more words from a list of one-syllable words than polysyllabic words. When participants were given a rehearsal suppression task the word length effect disappeared because the phonological loop cannot rehearse short or long words.
  • This shows that the phonological loop has a role in STM capacity.

Visuo-spatial sketchpad: Visual information, used when planning a spatial task or a vision. Can cope with 3-4 objects at at time. 

  • EVIDENCE: Baddeley. Participants cannot perform two visual tasks at the same time but can perform one visual and one verbal task.
  • This supports the WMM by showing that there are separate stores for visual and auditory information. We can do two different types of tasks if they rely on different stores.
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Working memory model: Baddeley and Hitch Pt. 2

  • Episodic buffer
  • A temporary store of information that can cope with visual, spatial and verbal information.
  • A temporary record that keeps things in order.
  • Acts as a storage to the central executive with a capacity of around four chunks. 
  • EVIDENCE - Baddeley
  • Participants can recall a multiple word sentence much easier than the same no. of unrelated words.
  • The episodic buffer is holding the words in order whilst making sense of the information
  • Central executive
  • Organises resources to where they are needed most. Direct attention.
  • No storage just organises.
  • EVIDENCE - Braver et al.
  • Participants in an fMRI were given a task involving the central executive. The prefrontal activity showed activity. When the task became more difficult the activity increased. This shows that the WMM may have physical correlates in the brain.
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Working memory model: Baddeley and Hitch AO3


·       Highly influential and used by most cognitive psychologists instead of the MSM, so it is highly applicable, e.g. educational assessment.

·       More plausible than the MSM as it explains memory as an active process and not passive.


·       Is not a full theory as it ignores the LTM

·       The role played by the central executive remains unclear. Appears to be the most important part but also the one we know the least about.

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Explanations for forgetting - Retroactive Interfer

Interference: Forgetting is caused by two memories competing. We are unable to remember something because the memory is either being affected by a memory that we already have or by future learning.

A new memory interferes with an older one. E.g. learning Spanish vocab interferes with your already learned French vocab.

Underwood and Postman (1960) - Research support
Aim: To investigate how retroactive interference affects learning.
Method: Lab experiment with participants split into two groups. Both groups had to remember a list of paired words. The experimental group also had to learn another list of words where the second paired word if different. The control group were not given the second list. All participants were asked to recall the words on the first list.
Results: The recall of the control group was more accurate than that of the experimental group. Conclusion: This suggests that learning items in the second list interfered with participants’ ability to recall the list. This is an example of retroactive interference.

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Explanations for forgetting - Proactive Interferen

  • Proactive interference = An older memory interferes with a newer one. E.g. calling your boyfriend by your ex's name. 
  • Retrieval failure: Information that is stored in LTM needs to be accessed. If we do not have the correct cues to help us to find the memory that is stored in LTM then we are unable to retrieve it.
  • Encoding specificity principle: Information can be triggered by a cue that is present at the time the memory was formed (encoding) and also when we are trying to recall it (retrieval).
  • Cues can be context-dependent or state-dependent: 
  • Context-dependent - Something external that acts as a cue. E.g. smell. 
  • State-dependent - Something internal that affects them when forming a new memory. 
  • Context-dependent – GODDON AND BADDELEY (1975) Aim: To test whether external context affects the recall of information
  • Method: Divers learned a list of words either underwater or on land and then were asked to recall the words either underwater or on land
  • 4 conditions: 1: Learn underwater and recall on land 2: Learn underwater and recall underwater 3: Learn on land and recall on land 4: Learn on land and recall underwater
  • Results: Recall was lower when the learning context and retrieval context did not match
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Retrieval Failure AO3

Strength: Application

  • Considering context could help to improve memory recall in certain situations.
  • E.g. you may revise in a quiet place so that it replicates the quiet context of the exam hall in which you will have to retrieve this information.
  • Knowledge of context has also been used to help improve the accuracy of eye witness testimony accounts.
  • Huge amounts of supporting evidence from lab studies

Limitation: Real-life application

  • In real-life context is unlikely to make that much difference to how much information is remembered, e.g. you may learn information in a classroom and then have to recall the information in the different context of an exam hall but this is unlikely to affect your ability to remember the material you have learned.
  • Baddley says that it is difficult to find two contexts that are different enough to affect learning.
  • This may be because it is sufficient simply to imagine the context.
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Eyewitness Testimony: Misleading information

Wells et al reported 40 cases in the US where people convicted due to EWT now cleared after DNA evidence. 5 of these people were awaiting execution.
Leading question: Any question that directs the respondent towards a particular answer. 

Factor 1: Misleading Information: Loftus and Palmer Leading Q's study
Aim: Investigate effect of leading questions of participants’ estimates of speed when recalling a witnessed motor accident.
·       45 American students formed an opportunity sample. 7 films of traffic accidents presented in a random order to each group. After watching the film participants were asked to describe what had happened. Then asked about how fast were the cars going when they (smashed/collided/bumped/hit/contacted) each other?
Findings: The estimated speed was affected by the verb used. The verb implied information about the speed, which systematically affected the participants’ memory of the accident.

Conclusion: The verb conveyed an impression of the speed the car was travelling and this altered the p’s perceptions. Eyewitness testimony might be biased by the way questions are asked after a crime is committed.

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Misleading information: Post-event discussion

Post-event discussion = When there are multiple witnesses to a crime and these co-witnesses discuss the crime with each other

Fiona Gabbert (2003)
Aim: To find out if post-event discussion between witnesses can lead to distortions in original memory
Method: Pairs watched the same crime filmed from different POVs and had different knowledge about the crime. They then discussed what they saw before individually completing a test of recall.
Results: 71% of p’s mistakenly recalled aspects of the event that they did not see themselves in the video but had picked up in discussion with their partners.
In a control group with no misinformation, 0% mistakenly recalled information.
Conclusion: This could be due to conformity or source monitoring problems = the witness can recall information about the event but they cannot recall where it came from

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Misleading information AO3

+ Realistic material used (film footage of a car accident)
- Artificial situation: ps knew they had to pay attention – wouldn't happen in real life and would be less stressful. This matters because it was a lab experiment and Ps knew their responses would not really matter. Foster et al. carried out a study in which p’s believed they had witnessed a real robbery and that their responses would influence the trial. Their responses were more accurate than Loftus’ p’s despite the misinformation

Strength – Huge impact on legal system – courts are now more aware of how unreliable EWT can be and effect of post-event information 

EWT research relies on artificial tasks that take place in a safe environment with no consequences. This is very different to real life so studies can lack external validity.
Foster et al. (1994) argue that the consequences of making a mistake in real-life are far greater for the actual witness of a crime rather than a p in a research study. In real-life, therefore, witnesses are more likely to take their responsibility seriously and try harder to give an accurate record as possible. This difference in motivation may mean that EWT studies do not reflect the way p’s behave in real life and as such overestimate the influence of misleading information.

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Factors affecting EWT: Anxiety has a negative impa

  • Anxiety leads to increased arousal in the body which can stop us from paying attention to important cues, e.g. attacker’s face and therefore recall is worse
  • Weapon focus effect = If the crime is violent then heightened anxiety may focus attention on the central details of the attack, e.g. the weapon used, rather than other information such as the perpetrator’s face
  • Evidence – Johnson and Scott (1976)
  • Participants in a waiting room overheard a heated discussion in the room next door...
  • Condition 1: Man emerges holding ink-stained pen – low anxiety - 49% of participants accurately identified the man. Condition 2: Man emerges holding a blood-stained knife – high anxiety – 36% of participants accurately identified the man
  • Evaluation:  Lacks ecological validity – although the p’s were waiting in the reception area outside the lab, they may have anticipated that something was going to happen, and affect the accuracy of their judgements
  • Numerous ethical guidelines were broken - participants were deceived about the nature of the experiment and not protected from harm, the man holding the knife may have created extreme feelings of anxiety.
  • o   The participants may have left the experiment feeling stressed and anxious, especially if they or someone they knew had been involved in knife crime.
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Factors affecting EWT: Anxiety has a positive impa

Anxiety: positive effect on recall
·       The stress of witnessing a crime creates anxiety
·       The flight-or-fight response is triggered which increases our alertness and improves our memory for the event because we were more aware of cues in the situation

Evidence – Yuille & Cutshall (1986)
·       25 customers in a gun shop in Vancouver witnessed the owner of a shop shoot and kill a thief
·       They all gave statements to the police
·       13 of these original witnesses were interviewed 5 months later by YnC. The original statements were compared with the interviews for accuracy
·       Participants were also asked to rate how stressful they found the event, on a scale of 1-7. 

We can account for these contradictory findings with the Yerkes-Dodson law. This states that when arousal is concerned, there is an optimum level at which performance will be best, but below or above this it will be worse.

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Factors affecting EWT: Anxiety AO3

Anxiety or surprise? Limitation

  • Johnson and Scott’s study on weapon focus may test surprise rather than anxiety. The reason participants focus on the weapon may be because they are surprised at what they see rather than scared.
  • Pickel placed unusual items in a hairdressing salon video (where scissors would be not unusual and low anxiety) some of the other items included a handgun and a raw chicken. EW accuracy was significantly poorer in the high not-unusualness conditions.
  • This suggests that the weapon focus effect is due to surprise rather than anxiety/threat and tells us that anxiety may not have an impact on EWT.

Ethics - Limitation

  • Creating anxiety in participants is very risky.
  • It may subject people to psychological harm for the purpose of research.
  • This is why real-life studies are so beneficial – as the researchers are interviewing people who have already witnessed a real-life event.
  • This does question the need for recreating an event of anxiety.
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Cognitive interview

Based on two principles: 

  • Organisation: Because our memories are like a network of connected events, they rely on triggering one element of a memory in order to activate the rest.
  • Encoding specificity principleMemories are cue-dependent: they use state and context cues present during the original encoding. Recall will be easier if the cues present at encoding can be present at recall. So interviewers should try and reinstate the context in which the memory was encoded.

CI uses four techniques:

  • Reinstate thecontext – helps the interviewee go back in their mind to the context in which they encoded the memory.
  • Change of narrative order – changing the order in which events are recalled can be very beneficial as it ensures that details are not skipped and gaps can be filled.
  • Change perspective – You are asked to describe the incident from the perspective of other people who were present at the time.
  • Report everything – you are required to report back any information about the event that you can remember, even if it does not seem to have a bearing on the crime.
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Variations of the Cognitive Interview

Children - Modified cognitive interview:

  • Holliday (2003) developed a modified CI for use with children. This removes the ‘change of perspective’ element as children are less able to imagine another person’s perspective.
  • Vekampt and Ginet interviewed 229 children and found the MCI to be better than both the standard police interview and the cognitive interview.

The elderly:

  • Mello and Fischer showed a video crime to young witnesses and old witnesses.
  • Ps were then interviewed using either the standard police interview or the CI.
  • The CI produced better recall for all p’s but the improvement was greater for the old participants.
  • Mello and Fisher concluded that the emphasis on ‘report everything’ meant older Ps were encouraged to overcome the negative stereotype about older people’s memories.
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AO3 of cognitive interview


-        Fisher et al. found that witnesses reported greater detail in their accounts of crimes when American detectives had been trained to use the technique.

-        The technique is more structured than the standard technique and seems appropriate for crime-related interviews to be very though in order to gather the detail required for a useful testimony


-        Koehnken et al. (1999) found that witnesses recalled more incorrect information when interviewed with the CI compared to the standard interview technique, perhaps because more detailed recall increases the chances of making mistakes

The interview is far more time-consuming than the standard interview. 

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