- Aim: To determine the capacity of short term memory using the digit span technique.
- Procedure: participants listened to then repeated numbers, starting with 1 digit then adding another each time they got the previous correct. If they got the sequence wrong they were permitted 1 more attempt. Once the participant went wrong again the last amount of digits they successfully recalled were recorded.
- Findings: all but 4 participants could successfully recall between 5 and 9 numbers, the 4 that did not fall into this category could recall 4 digits.
- Conclusion: this proves that the majority of people fit into the 7 (+ or – 2) theory, showing that the short term memory has a limited capacity.~
- Criticisms: Strength: sufficient amount of participants involved, validity. Mundane realism, the situation replicates something you would see in real life (e.g. remembering a phone number) Weakness: non laboratory experiment means the external variables may not have been considered or adequately controlled.
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- Aim: To distinguish between encoding in the long and short term memory.
- Procedure: Each candidate is given set of 10 cards with words on them: 4 sets – from acoustically similar to semantically dissimilar. Shown each card for 3 seconds. After all cards have been shown the candidate has to write the words down in order.
- Findings: In the first four attempts at recalling the word lists in order participants recalled more words on each successive trial. In the first trial, the worst performance was by participants who had been givne the acoustically similar list. After the 20 minute interval the worst performance was by participants who had been given the semantically similar list.
- Conclusion: This suggests that the short term memory is acoustically encoded and the long term memory is semantically encoded
- Criticisms: strength: The study is replicable and highly controlled weakness: Other studies have suggested otherwise, eg Brandimonte et al (1992) have theorised that the short term memory is visually coded.
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Peterson and Peterson 1959
- Aim: To measure the effect of inhibiting rehearsal on the duration of Short Term Memory (STM)
- Procedure: Participants hear a list of trigrams (three-letter nonsense words), and then have to count, aloud, backwards in threes for a certain time (the IV in this experiment). After the time has completed, participants are tested on their recall of the trigrams
- Findings: There was a marked negative correlation between the delay and the percentage of trigrams recalled by participants; a delay of three seconds produced a mean score of almost 80%, but for a delay of eighteen seconds, the score dropped to 6%.
- Conclusion: In the absence of rehearsal, STM's duration is very short.
- Criticisms: Strength: These results have replicability; they have been reproduced many times. Weakness: As Keppel & Underwood (1962) showed, the fact that Peterson & Peterson ran "practice" tests, it could be that some of these results were influenced by proactive interference. Remembering trigrams is not an every day occurrence, and so it is questionable how much ecological validity these findings have.
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- Aim: Investigate reliability of EWT
- Procedure: Opportunity sample of 45 US students were shown slides of a car accident involving a number of cars and asked to describe what happened as if they were eyewitnesses. They were then asked specific questions, including the question "About how fast were the cars goingg when they (hit/smashed/collided/bumped/contacted - the five conditions) each other?" A week after they saw the slides they were asked "Did you see any broken glass?". There was no broken glass shown in the slides.
- Findings: those who had been asked questions with more emotive phrasing ("smashed") were more likely to say that they had seen broken glass
- Conclusion: False memories may be introduced in eye witnesses by careless questioning.
- Criticisms: Strength: Shows that questioning technique for EWTs is extremely important, spurred research into this area, e.g. Geiselman (1985). Weakness: Lacks mundane realism: witnessing a real-life event may have more emotional impact. Demand characteristics may have resulted due to the artificality of the task, revealing the research hypothesis and modifying their responses to be consistent with it.
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Geiselman et al 1985
- Aim: Geiselman (1985) set out to investigate the effectiveness of the cognitive interview.
- Method: Participants viewed a film of a violent crime and, after 48 hours, were interviewed by a policeman using one of three methods: the cognitive interview; a standard interview used by the Los Angeles Police; or an interview using hypnosis. The number of facts accurately recalled and the number of errors made were recorded.
- Results: The average number of correctly recalled facts for the cognitive interview was 41.2, for hypnosis it was 38.0 and for the standard interview it was 29.4. There was no significant difference in the number of errors in each condition.
- Conclusion: The cognitive interview leads to better memory for events, with witnesses able to recall more relevant information compared with a traditional interview method.
- Criticisms: strength: external validity, relates to a situation in real life. weakness: may breach the debriefing and deception guidelines, (ensuring the participant leaves in the same state as they arrived)
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